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LM35 IC Temperature Controller Circuit with Push Button

Last Updated on February 23, 2024 by Swagatam 238 Comments

In this post I have explained a simple yet very accurate temperature controller circuit using IC LM35, featuring an automatic cut off with a push button latch.

Table of Contents
  • Circuit Diagram
  • How the Circuit Works
  • How to Setup and Test
  • Troubleshooting
  • Parts List

LM35 is a precision temperature sensor IC, which can be effectively used for detecting temperature differences accurately. For more details regarding this IC you can refer to this article.

Circuit Diagram

warning message: electricity is dangerous, proceed with caution
LM35 IC Temperature Controller Circuit with Push Button
NOTE: PLEASE CONNECT A 1uF/25V CAPACITOR ACROSS THE BASE/EMITTER OF THE BC557 TRANSISTOR, WHICH IS MISTAKENLY NOT SHOWN IN THE DIAGRAM.

How the Circuit Works

The IC1 741 is configured as a comparator circuit.

Its pin#3 which is its non-inverting input pin, is attached with the output of the heat sensor IC2 LM35.

The inverting input pin#2 of IC1 is configured with a preset P1, which is used for setting the reference voltage at pin#2.

Whenever pin#3 voltage exceeds pin#2 voltage, the IC1 output at pin#6 turn high.

Conversely, as long as pin#3 voltage remains below pin#2 voltage, the output pin#6 of IC1 remains at 0V, or logic low.

At normal room temperature the LM35 output will be low which will keep the pin#3 potential of the 741 lower than its pin#2 reference.

Therefore, when the push button is pressed, the IC741 momentarily activates sending a 0V (low) to the base of BC557 which now conducts so that the whole circuit now gets latched even if the push button is released, and stays powdered through the BC557.

In this situation the relay switches ON and its contacts shift to the N/O points. Since the heater is wired with the supply through the N/O contacts of the relay, it is also switched ON.

The heater temperature now starts rising. Since the IC2 LM35 is attached with the heater, the LM35 also starts heating up which causes its output voltage at pin#3 of IC 741 to rise proportionately.

When the LM35 output voltage at pin#3 of IC1 741 reaches a point where it exceeds its pin#2 potential, the output of IC 741 instantly reverts and goes high.

As soon as the output of IC 741 goes high, it inhibits the negative or 0V supply to the base of BC557. Due to this the BC557 turns off.

As BC557 turns OFF, it breaks the latch so that the 12V supply to the circuit is cut off, the whole circuit along with the relay is turned off.

This also turns OFF the heater and the circuit returns to its previous original condition.

How to Setup and Test

Assemble the circuit as shown in the above diagram. Initially, do not connect any heater with the relay contacts.

Keep the P1 slider fully at the positive level or fully towards R2.

Switch ON the 12V DC to the circuit.

Push and release the SW1 switch momentarily. This should instantly cause the circuit and the relay to switch ON and get latched. Both the LEDs must illuminate.

Next, using a soldering iron heat the LM35 to the desired level. Monitor the temperature with an accurate thermometer, make sure it does not exceed 100° Celsius.

Once the desired temperature is reached, slowly adjust the P1 preset until the IC1 output turns high causing the latch to break and turn OFF the relay. This is indicated by the LEDs which are now turned OFF.

Repeat the above procedure a few times to confirm the results.

The circuit is now set and ready to work with an actual heater attached with the relay contacts.

Troubleshooting

If somehow the circuit does not work, please implement the following improvements in the circuit.

Please connect a 1uF/25V capacitor across the base/emitter of the BC557 transistor. This will ensure that the circuit does not start by itself during power switch ON, rather initiates only when the push-button is pressed.

Please remove R2 (10k resistor) and replace it with a jumper. This will ensure that when initially the slider of the preset is held at the positive side, the op amp output delivers a low logic without fail.

Also, connect a 1uF/25V across pin#3 of the IC and ground, this is optional.

After finishing the above operations, please follow the steps explained under "How to Setup and Test."

Parts List

  • All Resistors are 1/4 watt 5% CFR
  • 1k, 4.7k = 1 each
  • 10k = 2
  • 4.7k preset = 1
  • Semiconductors
  • IC 741, IC LM35 = 1 each
  • Transistor BC557 = 1
  • LEDs 20mA, 5mm = 2
  • Relay 12V 10 amp = 1

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About Swagatam

I am an electronics engineer with over 15 years of hands-on experience. I am passionate about inventing, designing electronic circuits and PCBs, and helping hobbyists bring their projects to life. That is why I founded homemade-circuits.com, a website where I share innovative circuit ideas and tutorials. Have a circuit related question? Leave a comment.... I guarantee a reply!

Previous Post: « Flashlight Circuit with Long Backup and High Efficiency
Next Post: Adjustable Voltage Regulator Circuit using LM324 IC with Over Current Protection »

Reader Interactions

Comments

  1. Neeraj says

    August 13, 2024 at 11:42 am

    sir please look at the link !

    Reply
    • Swagatam says

      August 13, 2024 at 1:27 pm

      Neeraj,
      The circuit diagram for MP4560 is easily available online.
      Let me know what more information you need about this device?

      For further discussion, please post your comment under the following article:

      https://www.homemade-circuits.com/ic-mp1584-datasheet-and-circuit-diagram/

      Reply
  2. Neeraj says

    July 14, 2024 at 10:50 am

    Hello sir how are you I hope you doing fine ! here I am again for something sorry! can we do something with the push button function and replace it with touch module ?

    Reply
    • Swagatam says

      July 14, 2024 at 5:23 pm

      Hello Neeraj, I am good, thank you!
      Did you connect any capacitor at the base of the BC546 transistor?
      If not just try touching the base of the BC546 transistor with your finger and check whether that works or not.
      If capacitor is present, remove it from the base of BC546 and connect it between base/emitter of the BD140. After this touch the base of the BC546 and check the response.

      Reply
      • Neeraj says

        July 14, 2024 at 5:45 pm

        actually bc546 doesn’t have any capacitor at the base and I am asking for enabling touch module so I can do the push button function! without even touching bd140 with the twizzer ! understood?

        Reply
        • Swagatam says

          July 14, 2024 at 6:43 pm

          If you touch the base BC546 it should work as a touch switch without push button, i hope you understood now.
          If you use TTP223 it will become unnecessarily complicated.

          Reply
          • Neeraj says

            July 16, 2024 at 2:49 pm

            yeah sir the base of bc546 worked but the real issue is can we make capacitive touch function? because the circuit will be behind 5mm thick plastic sheet and this bc546 can’t make it happen ! I know ttp223 will be problematic but can’t we find another way to make it possible?

            Reply
            • Swagatam says

              July 16, 2024 at 5:50 pm

              Another way is to use two or three BC546 BJTs and connect them in Darlington form and then connect first transistor base with a wire whose end can be terminated with a large plate. If you bring your hand close too this plate then the circuit will be triggered,
              But the problem is, this type of circuit can also get triggered by external RF interference and RF noise.

              Reply
              • Neeraj says

                July 16, 2024 at 6:51 pm

                can we connect bc546 base with the ttp223 ? or with the copper plate ! ?

                Reply
                • Swagatam says

                  July 17, 2024 at 8:22 am

                  First confirm the TTPP223 capacitive touch distance with an LED, whether it works as per your your specifications or not, then we can configure it with the BC546. Copper plate will get triggered with other external RF disturbances, so it is not good.

                  Reply
                  • Neeraj says

                    July 17, 2024 at 11:06 am

                    yeah sir it worked i have tested it with some distance!

                    Reply
                    • Swagatam says

                      July 17, 2024 at 11:23 am

                      Neeraj, please provide more information regarding how you tested the module?

                  • Neeraj says

                    July 17, 2024 at 9:23 pm

                    last time i tested this circuit which you have provided me long ago !

                    " rel="ugc">comment image

                    with this ttp223 was able to work with my conditions also with 5mm thick plastic sheet!

                    Reply
                    • Swagatam says

                      July 18, 2024 at 8:12 am

                      Ok, then you can connect the 1N4148 end which is shown as “to BC557 base” to the base of BD140.

                  • Neeraj says

                    July 18, 2024 at 5:13 pm

                    but it’s too complex! can’t we make it more straight and simple?

                    Reply
                    • Swagatam says

                      July 18, 2024 at 5:19 pm

                      It is the most basic configuration, and all the parts included in it are necessary.

                    • Swagatam says

                      July 18, 2024 at 10:07 pm

                      Actually the BC547 can be removed and the ttp223 output can be directly connected with the base of BC546 transistor through a 10k resistor…

                    • Neeraj says

                      July 27, 2024 at 3:21 pm

                      sir now we are getting 5.4 v in the input of the ttp223 and still the circuit is not getting started because in the i/o pinout the voltage ttp223 is producing only 0.22v and this cause us ! if I use mannual option and monitor voltage at base of the bc546 then I got around 0.75 to 0.77v ! you have suggested me to connect 10k resistor at the i/o pin to base of the transistor if we monitor voltage at the i/o pin above the resistor we got 0.4v ! we need to trigger the bc546 then we need 0.7 v atleast! am I right?

                    • Swagatam says

                      July 28, 2024 at 7:50 am

                      Neeraj, Please disconnect the 10k from the I/O of the TTP and check the voltage directly between the I/O and GND. The voltage here should be around 0V in normal condition, and should turn 5V momentarily when you touch the TTP touch-pad.
                      If you are not getting 5V after touching the touch-pad that means your TTP has some problems, then you must diagnose the TTP separately.
                      Yes 0.7V is required to switch ON any BJT.

                  • Neeraj says

                    July 19, 2024 at 9:20 pm

                    but how we can use simply with 10k resistor?

                    Reply
                    • Swagatam says

                      July 20, 2024 at 8:48 am

                      Sorry i did not understand your question…where do you want to connect the 10k?

                  • Neeraj says

                    July 20, 2024 at 9:38 am

                    in simple terms can’t we reduce the input voltage for ttp223 to 3~5v and then directly connect it’s i/o pin to the base of bc546. it will be less complicated and also we can use power resistor to reduce voltage just like we did with our ic lm358 ! ????

                    Reply
                    • Swagatam says

                      July 20, 2024 at 10:17 am

                      That’s exactly what I suggested in my earlier reply.
                      You can connect the TTP223 output directly with the base of BC546 through a 10k resistor.
                      The +5V can be extracted directly from the opamp supply pin by replacing the IC zener diode with a 5V zener diode.

                  • Neeraj says

                    July 20, 2024 at 10:29 am

                    so can you show me the modifications on the diagram ? because of the diagram I can understand it easily please 🥺

                    Reply
                    • Swagatam says

                      July 20, 2024 at 1:07 pm

                      You can try the following modified heater controller design with touch switch…..both the zener diodes are now 5v zener diodes:
                      " rel="ugc">comment image

                    • Swagatam says

                      July 20, 2024 at 1:09 pm

                      The ground side 1k resistor at the BC546 base must be replaced with a 4.7k resistor….

                  • Neeraj says

                    July 24, 2024 at 1:16 pm

                    I have followed this circuit diagram!

                    " rel="ugc">comment image

                    Reply
                    • Swagatam says

                      July 24, 2024 at 1:30 pm

                      You can modify it in the following manner:
                      " rel="ugc">comment image
                      If it has problems, try replacing the 1k associated with the 5V zener with 4.7k or 10k.

                  • Neeraj says

                    July 28, 2024 at 11:45 am

                    yeah sir I removed the 10k resistor and then I checked voltage in gnd and i/o this whole ttp223 workes on 3v or 2.7 v and I got 2.5 v at the i/o pin should I connected this i/o directly to the bc546 base ??

                    Reply
                    • Swagatam says

                      July 28, 2024 at 1:19 pm

                      Since we already have a 10k resistor in series with the VCC pin of the TTP, so it may be fine to connect the I/O output of TTP directly with the BC546, however I would still recommend using a 1k in series between th I/O and BC546 base.
                      Please check the results and let me know.

              • Neeraj says

                July 24, 2024 at 12:36 pm

                sir it didn’t worked! I have replaced 12v both zener to 5v and connected 4.7k ohm to the bc546 but still the ttp223 is not working if I touch bd140 manually and then ttp223 while the circuit is on the ttp223 module will be illustrated for some seconds and also whole circuit is not working as it was working with 12v zener there’s no voltage at the pin 2 and 3 of the ic and if I touch bd140 manually the circuit will on and then I remove my twizzer circuit will turned off !

                Reply
                • Swagatam says

                  July 24, 2024 at 1:06 pm

                  Neeraj, Please do only the following modifications, without changing anything else:
                  For the opamp circuit, replace both the 5V zener diodes with 12V zeners, and supply the TTP223 with a separate 4.7k/4.7V zener diode across its VCC pin, as done in the original diagram:
                  " rel="ugc">comment image

                  Reply
                  • Neeraj says

                    July 27, 2024 at 12:31 pm

                    sir it doesn’t work at all even after replacing 1k and 4.7k and 10k the results were same as Before sir I have a little doubt if I push manually bd140 the circuit works and if I touch ttp223 is also works and led blinks whenever I touch it ! i checked the voltage across vcc and gnd pin of the ttp233 we got 5.4 v after the circuit was not before thats means if we wanna to operate this touch module as a push button then we have to make any changes so that we can get voltage to this module before we start the whole circuit! understood? can we connect the zener of this ttp223 directly to the input of the circuit? at the emitter of the bd140? as my assumption this will provide ttp223 5v and this ttp223 can start circuit! !

                    Reply
                    • Swagatam says

                      July 27, 2024 at 1:18 pm

                      Neeraj, You are absolutely right, I completely missed that point.
                      Yes the TTP223 module’s Vcc must be supplied directly from the 48V DC input so that its output can provide the triggering voltage to the BC546 base.
                      So, in the following diagram, please disconnect the TTP223 1k from the 12V zener diode. Then replace the 1k with 10k and connect it with the +48V supply, make sure the 5V zener remains connect across the Vcc and ground of the TTP223:
                      " rel="ugc">comment image

                  • Neeraj says

                    July 29, 2024 at 9:12 am

                    sir it worked 🎉🎉🎉🎉🎉 after implantation of the 1k with the series of the i/o it worked seamlessly now I am testing it with every condition if I face any issues during testing I will tell you ! thanks sir 👍

                    Reply
                    • Swagatam says

                      July 29, 2024 at 9:22 am

                      That’s great Neeraj,
                      Let me know if you have any further problems with the circuit…

                    • Neeraj says

                      April 14, 2025 at 10:43 am

                      sir as you can see above of this comment this is the circuit we were working on last year and now I am getting issues with the touch module !!!!! I’m waiting for your comments please help me

                    • Swagatam says

                      April 14, 2025 at 11:47 am

                      Neeraj,
                      I have answered you under the TTP223 article, please discuss under that article.
                      Please post the exact image which you are discussing. Right click on the image and click “copy image address” and paste it in your comment…

                    • Neeraj says

                      April 14, 2025 at 12:34 pm

                      this one sir

                    • Swagatam says

                      April 14, 2025 at 5:05 pm

                      Ok, please disconnect the TTP223 and check it separately, connect an LED with resistor across its output and check its response to touching..

                  • Neeraj says

                    April 10, 2025 at 6:12 pm

                    hello sir I know it’s been a long time since we talked I hope your are good and healthy i just wanna ask you a thing that! last time we fixed the all issues with the ttp223 but now if I install new one onto the circuit the whole story completely changes ! don’t know how I have tried several ttp223 but still all the responses were same the toggle function of the ttp223 couldn’t proform well it’s stays on whenever I touch it it’s bed how could I fix it ? i/o have 1k to the bc546 ! but still it’s not working at it should have to be !

                    Reply
                    • Swagatam says

                      April 11, 2025 at 9:42 am

                      Hello Neeraj,
                      Let us discuss the matter under the following article, please post your question here:
                      https://www.homemade-circuits.com/ttp223-capacitive-touch-module-explained/

  3. Neeraj says

    April 25, 2024 at 3:46 pm

    Finally it worked both leds was working at 6v Max and I also connected 5v dc motor after replacing the leds motor also working super efficiently now I understood the whole work of the opamps thanks sir ji. Now what should we do next ?

    Reply
    • Swagatam says

      April 25, 2024 at 5:34 pm

      That’s good Neeraj,
      Now build the following circuit and test the push button action:
      " rel="ugc">comment image

      Reply
      • Neeraj says

        April 26, 2024 at 5:19 pm

        Congratulations sir we have made it 🎇
        Everything is fine and working super efficiently and I have understood the function of the opamps so it is getting easy for me and I have also tested the latch function which is working so nicely now what’s the next step ?

        Reply
        • Swagatam says

          April 27, 2024 at 8:27 am

          That’s great Neeraj,
          Now you can attach the LM35 at pin#2 of the opamp and check the results, as per the following diagram:
          " rel="ugc">comment image
          As you know, now if the LM35 voltage at pin#2 of the IC exceeds pin#3 voltage set by the preset, the opamp output will go LOW and the latch will break.
          Suppose if you want the trip point to be at 80 degrees Celsius and if suppose at this temperature the LM35 output is 0.6V, then the preset voltage at pin#3 of the IC must slightly lower than this, maybe at 0.5V.
          So when the LM35 output at pin#2 reaches 0.6V it will higher than pin#3 0.5V and the output of the opamp will go LOW breaking the latch and switching off the circuit.
          We will use the relay afterwards once the above step is completed.

          Reply
          • Neeraj says

            April 30, 2024 at 1:13 pm

            Sir I don’t know why all the time I am getting faulty lm35 i have bought them from different different retailers but still I got the faulty lm35 why ! I have also bought it from Amazon!

            Reply
            • Swagatam says

              April 30, 2024 at 2:25 pm

              Neeraj, how are you testing it?
              First connect the LM35 Vcc/gnd to +12V and -12V of a DC supply
              Then heat the IC slowly.
              Across output and gnd of the IC you should see voltage steadily rising from 0.1V to 0.7V.
              Use the mV range of your meter or 2V range

              Reply
              • Neeraj says

                April 30, 2024 at 2:39 pm

                I have tried same concept but I have found every ic is faulty! Some shows me fluctuating voltage and some shows me 0v also after heating up !

                Reply
                • Swagatam says

                  April 30, 2024 at 5:36 pm

                  Ok, In that case you can try a 10k NTC instead….

                  Reply
                  • Neeraj says

                    April 30, 2024 at 5:43 pm

                    But for 10k ntc we have to change the whole circuitry?

                    Reply
                    • Swagatam says

                      April 30, 2024 at 6:25 pm

                      You can use the same circuit.
                      " rel="ugc">comment image
                      At pin#2 replace the upper 1k with your NTC.
                      Again at pin2, replace the lower 1k with 10k.

                    • Neeraj says

                      April 30, 2024 at 7:04 pm

                      But what about the accuracy? And if I got a good lm35 then I will continue with it because I think it have a higher accuracy and for now I will use ntc for testing purpose! !!!!?

                    • Swagatam says

                      April 30, 2024 at 7:29 pm

                      Yes, LM35 will have better accuracy.
                      For the time being you can try an NTC, by modifying the previous circuit, as described by me.

                    • Neeraj says

                      May 2, 2024 at 11:30 am

                      Sir it worked! now what’s The next step relay ? The input is 24v now so I think there will be no problem for the ic !

                    • Swagatam says

                      May 2, 2024 at 1:22 pm

                      Neeraj,
                      Now connect a 24V relay coil directly across the supply terminals of the circuit (on the left side).

                      Remember to connect a 1n4007 diode across the relay coil. Cathode will go to positive side of the coil and the anode to the negative side of the coil.

                      Make sure you are using LM358 opamp for 24V operation. IC 741 will burn at 24V.

                    • Neeraj says

                      May 3, 2024 at 3:40 pm

                      Sir relay worked but sometimes it’s a bit slow to off but now how can I use it for 48v heater ? Because now the input voltage is 48v and 8~7 amps ! How can we modify circuit in order to make it workable on 48v ! And also please suggest me which relay should I use for 48v contact rating ! ?

                    • Swagatam says

                      May 3, 2024 at 5:42 pm

                      Neeraj, The slow switch OFF is due to the 10uF capacitor, you can reduce it to 1uF.
                      Connect the heater and the 48V supply with the 24V relay contacts as shown in the first article diagram.
                      Use a buck converter to step down 48V to 24V for supplying the emitter side of the BC557.
                      You can use a 48V 15 amp relay or any similar which suits your requirement.

                    • Neeraj says

                      May 3, 2024 at 6:42 pm

                      But I don’t wanna use any buck convertor is there any way to implant something which can reduce the voltage for lm358?

                    • Swagatam says

                      May 3, 2024 at 6:59 pm

                      If you use any linear regulator, it will become very hot.

  4. Neeraj says

    April 24, 2024 at 10:39 pm

    Got an update after remaking all the circuit again I got the right things but still the leds didn’t light up! I checked the pin2 I got 6v and when the preset was little downward I got 4v or some in pin3 so thats means I got 0v at the output after turning preset I got 10.4v at the output but at the first led I only got 1.5v and at the second I got full 10.4v but the second one didn’t light up ! For now I got this results I will buy new lm358 tomorrow so let’s see what will gonna happen!

    Reply
    • Swagatam says

      April 25, 2024 at 8:22 am

      If the LED is not illuminating, then the LEDs could be faulty.
      You can change the LEDs, or simply check the output with a meter.
      Also make sure the preset is of good quality.
      Try buying all the parts from amazon or ebay.

      Reply
  5. Neeraj says

    April 24, 2024 at 5:41 pm

    Sir here’s the explanation of the method which have worked for me : I have connected vcc to the 5v and ground to the ground and connected both pin2 and pin3 to the ground to see the voltage at the pin1 which is output and at the pin1 I got 0v so thats means ic is fine and now I connected the pin3 to the vcc and now I can see the voltage at the output is 5v now if we reverse it means now pin2 is connected to the vcc and pin3 to the ground now I got 0v at the output at the pin1

    Is this method is right?

    Reply
    • Swagatam says

      April 24, 2024 at 6:15 pm

      You must test it with a preset as shown in my previous diagram, otherwise we cannot proceed with any related circuit.

      Reply
  6. Neeraj says

    April 24, 2024 at 5:26 pm

    But my opamp worked with other methods! The same method I have mentioned in this link ! They have mentioned some voltage follower mode and other methods also and i found that useful please look at it

    Reply
    • Swagatam says

      April 24, 2024 at 5:38 pm

      Neeraj, it should work in the basic comparator circuit in my previous link, without that we cannot proceed.

      It is the foundation circuit for any opamp or a comparator IC.

      Please try to learn how an opamp comparator works.

      https://www.homemade-circuits.com/how-to-use-ic-741-as-comparator/

      Reply
  7. Neeraj says

    April 24, 2024 at 3:04 pm

    Sir I this comment is vanished this is the link of the article which I have found for opamp testing without testing circuit use http circuitdigest.com/comment/28421#comment-28421

    Reply
    • Swagatam says

      April 24, 2024 at 5:08 pm

      Hi Neeraj,
      If your opamp does not work with the following circuit then your IC is 100% faulty or your are doing something seriously wrong.
      The following circuit is a simple comparator circuit and any opamp should work with this circuit.
      If your opamp does not work in this circuit then I am afraid I cannot help you any further with any opamp related project.

      " rel="ugc">comment image

      Reply
  8. Neeraj says

    April 18, 2024 at 11:33 am

    Sir I have bought 10 (741ic’s) and I am also using another tester circuit for this ic’s because I don’t have trust on this ic that’s why I bought 10 of them lets see which one will work I will update you all the ic’s is from texes instrument! I will update you as soon as I got any update

    Reply
    • Swagatam says

      April 18, 2024 at 11:54 am

      That’s good, Neeraj.

      Please try the following setup first to confirm your ICs (as explained previously), make sure to use an IC socket for the iC so that you can change the ICs quickly. Also, build the circuit by soldering and not on breadboard.
      " rel="ugc">comment image
      Use 5V to 12V DC as the supply, not above that.

      Reply
      • Neeraj says

        April 20, 2024 at 8:49 pm

        Sir I am done with the 741ic I have bought 15 of them and not even a single one worked 😭 not even a single one I am done with it. I have doubts in building my circuit but after so many trys i am sure that my circuit connection is super fine but not the ic I have tried another circuitry for ic testing but still answer was the same the ic’s were faulty as always. Can we use another opamp ? Like lm358 because it’s more versatile and I have seen so many articles using same lm358ic if yeah then please suggest me tester for for the lm358 ic 🙏

        Reply
        • Swagatam says

          April 21, 2024 at 8:31 am

          Hi Neeraj,
          Yes, if your 741 ICs are not working with the following basic setup then your ICs are definitely faulty:
          " rel="ugc">comment image
          For IC LM358, the pin3 and pin2 connections will be the same.
          For pin#6, replace it with pin#1 of Lm358
          And for pin#7, replace it with Pin#8 of Lm358

          Reply
          • Neeraj says

            April 21, 2024 at 9:32 am

            Sir lm358 have 2 opamps so it will be much better because if one opamps is faulty then I can work with the second one isn’t that !?

            Reply
            • Swagatam says

              April 21, 2024 at 10:08 am

              Neeraj,
              please confirm with one opamp first using pin3, pin2 and pin1 of the IC. Make sure to connect supply pins also, pin8 (+Vcc) pin4 (Ground)

              Reply
  9. Neeraj says

    April 14, 2024 at 3:15 pm

    Sir can you please make a video on this circuit because whatever I do i fail all the time I am desperate right now please make a video on this circuit and how do you make it I wanna see it where is i am wrong because now I do everything right but at the end the results are same as before ? it’s my humble request to you please make a video on this circuit and also show me how to make it from scratch on your YouTube channel please because I have done previously so much works with circuits but this one is so simple but frustrating please make a video it’s my humble request and tomorrow is my birthday if this circuit won’t work tomorrow then I can’t celebrate my birthday happily !

    Reply
    • Swagatam says

      April 14, 2024 at 4:52 pm

      Neeraj, a video is not required for such a simple operation. You are not not reading the steps and not discussing the results that’s why you are not able to solve it.
      You have already confirmed that when you press the push button the 741 latches and the LED turns on, right?
      Next, you just have to set the preset mid-way and touch the pin2 to positive for a second then remove, this should break the latch and revert the circuit to its original position, with LED switched off.

      " rel="ugc">comment image

      Reply
      • Neeraj says

        April 14, 2024 at 5:30 pm

        Yeah but today I was frustrated and i remade the circuit again but now the new circuit is not even functional for the push to on and the 741ic is not latching I have checked the all the connection but every connection was good but still didn’t got the result! Why ? Sometimes it’s works and sometimes it’s don’t why ? I am using all new components but still unable to make it happen why!

        Reply
        • Swagatam says

          April 14, 2024 at 5:39 pm

          Please build it by soldering on a strip-board and then it should work. If you try it on breadboard it can be difficult to get the correct results. Use an IC socket when you build it on a strip board.

          " rel="ugc">comment image

          Reply
          • Neeraj says

            April 14, 2024 at 5:48 pm

            Sir I know the breadboard is not good that’s why I am using zero pcb which you have suggested me right now how can I upload pictures of our circuit on the comment section if I can then I will show you

            Reply
            • Swagatam says

              April 14, 2024 at 6:55 pm

              Have you used an IC socket?
              I can only suggest the steps and explain the functioning of the steps, beyond this i cannot do anything.
              So a picture will not help.
              The best way to troubleshoot is to understand the circuit working in a step wise manner, which I have already explained to you.
              When pin2 voltage becomes higher than pin3, the output pin6 becomes 0V and vice versa.

              Reply
  10. Neeraj says

    February 22, 2024 at 6:12 pm

    Sir I was working on this circuit which is shown in the article and with lm385 and the voltage is 24v but the real thing is that the push button function is not working at all and when I connect this circuit to the power it’s directly went on and also it’s can’t even sensing the temperature and also the second led is not working at all

    I followed the whole stages as described in the article

    And still the circuit is not working also checked all the connection and everything is fine but still !

    Reply
    • Swagatam says

      February 22, 2024 at 6:42 pm

      Neeraj, the circuit is obvious and straightforward and will surely work, however it can be successfully completed only by proper understanding and proper setting up procedures. Tomorrow I will update the above article with the full step by step set up and troubleshooting procedures…please read it, understand it and go ahead accordingly…

      Reply
    • Swagatam says

      February 23, 2024 at 9:24 am

      Neeraj,
      I have added the necessary details in the article under “troubleshooting”.
      Please follow the steps and test the circuit without a relay and with 12V supply first. Check the LED response at the output of the opamp.

      Reply
      • Neeraj says

        February 25, 2024 at 2:42 pm

        Sir I did everything for the trouble shooting but nothing worked now I got both LEDs on but the issue is same as before there is no push button function is working and no temperature sensor at all after giving it power it’s went automatically on that’s all I also connected 1uf capacitor at pin3 of the IC to the ground! Also I am using UA741CN IC! -_-

        Reply
        • Swagatam says

          February 25, 2024 at 6:17 pm

          Hi Neeraj,

          Please note that 741 might burn if supply voltage is above 15V.

          Try the following basic setup without relay, without LM35, and with 12V and first confirm the push button action:

          " rel="ugc">comment image

          Reply
          • Neeraj says

            February 26, 2024 at 8:24 pm

            Hey sir it’s working perfectly with 12.3v what’s the next steps!

            Reply
            • Swagatam says

              February 26, 2024 at 10:20 pm

              Neeraj,
              Now first check and confirm the working of the LM35 ic separately.
              Connect its vcc pin to 12v, gnd pin to gnd and connect a voltmeter across it’s out pin and gnd….heat it slowly with soldering iron upto 70 degrees and check the voltage output, if the voltage increases proportionately, then your lm35 is OK, now you can connect it with opamp pin3 as shown in the previous diagram…and check the circuit as explained in the above article, make sure lm35 is cooled down before initiating the testing procedures.

              Reply
              • Neeraj says

                March 21, 2024 at 3:58 pm

                sorry sir I know it’s been a whole month actually my grandmother was died and on the next week my grandfather also so I couldn’t test those lm35 but I have returned from the village so I tested the lm35 and heated it and connected multimeter’s ground to the lm35 ground and positive to the output pin of the lm35 but I got confused the voltage is increasing after heating it up but it’s too fluctuates ! the voltage at the output pin and gnd of the ic fluctuates so much that’s why I didn’t get the accurate results! what should I do now !

                Reply
                • Swagatam says

                  March 21, 2024 at 7:44 pm

                  Hi Neeraj,
                  Please refer to youtube videos, you can find some good videos which shows how to test Lm35 IC. The output should rise slowly as long as the temperature rises, and as soon as the heat source is removed the output voltage should start dropping towards.
                  The range of the meter should be set to 2V or 1.5V.
                  The meter reading will fluctuate as the temperature is connected or removed.
                  Make sure you do not exceed the temperature above 100 degrees C.

                  Reply
                  • Neeraj says

                    March 24, 2024 at 8:00 pm

                    sir I tried everything after testing push button function I connected the lm35 to the pin3 of the 741ic and heated it but nothing happened with the preset was turned up fully and the input voltage was 12v ! I bought 3 lm35 ic’s but got the same result! either the store owner is crock or my luck is faulty ! I don’t know ?

                    Reply
                    • Swagatam says

                      March 25, 2024 at 8:17 am

                      Neeraj,
                      It will work only if you do it with proper understanding.
                      LM35 must be connected to pin#2 of the new circuit which is suggested, not pin#3
                      The idea is simple, after pressing the push button the red LED will illuminate.
                      After this when Lm35 is heated it will create a rising voltage at pin#2.
                      As soon as the pin#2 voltage rises above the pin#3 voltage (as per the preset setting) the latch will break and the red LED will shut off, the transistors will shut off.
                      It is a simple circuit and should work immediately without much efforts.
                      " rel="ugc">comment image

                    • Neeraj says

                      April 6, 2024 at 10:11 am

                      Sorry sir but suggest me other temperature ic because I have tried 4 lm35 and nothing happened i have checked all the circuit again and again and did not found any miscommunication but still lm35 is not working as it should have to be suggested me another ic so I can complete our remaining work and after that if I visit outer market from the town then I will buy the good quality lm35 but for now suggest me other temperature ic! Please

                    • Swagatam says

                      April 6, 2024 at 1:49 pm

                      Neeraj, if your LM35 output is not increasing from around 100mV to 700mV in response to temperatures from 30 degrees C to 100 degrees C, that means your IC is not good. If it does, then your circuit will definitely work.
                      Unfortunately there are no other equivalent type temperature sensing ICs which are commonly available in the market.
                      I would still recommend checking the LM35 separately and see whether the output increases from 100mV to 700mV or not…there are many youtube videos you can refer to.

                    • Neeraj says

                      April 12, 2024 at 8:49 pm

                      Sir can you suggest me how to check the 741ic because after getting right lm35 the circuit isn’t working! I have taken every step carefully all the time but still unable to make it ☹️☹️? this is so bad it’s shameful for me because I can’t even make this simple circuit!

                    • Swagatam says

                      April 13, 2024 at 8:09 am

                      Hi Neeraj,
                      In the the following circuit, suppose you set the preset so that voltage at pin#3 of the IC is 0.5V. Now, when you heat the Lm35 if its output voltage at pin#2 of the IC exceeds the 0.5V then the output pin#6 will turn from 12v to 0V, turning off the transistors and breaking the latch.
                      Before the above operations you must press the push button to latch the IC 741 so that pin#6 is at 12V.
                      " rel="ugc">comment image
                      So basically when pin#3 voltage is higher than pin#2, then the output is high or at +DC supply level.
                      If the voltage at pin#3 goes below pin#2 voltage, then the output voltage at pin#6 becomes low or 0V.
                      Conversely, when pin#2 voltage is higher than pin#3, then the output is low or 0V.
                      If the voltage at pin#2 goes below pin#3 voltage then the output voltage at pin#6 becomes high or +DC supply level.
                      More can be found here:
                      https://www.homemade-circuits.com/how-to-use-ic-741-as-comparator/

  11. Neeraj says

    February 20, 2024 at 6:13 pm

    Sir I have a one general question one of my friend asked me this question if I have 1 wire and I have 2 different loads first is 48v 360w with 7.5amps and second one is the 24v 360w with 15amps so can you tell me at which load this wire will heater up much faster ? At 48v or 24v ? Because the power is same but the amps is so different I am so confused ?

    Reply
    • Swagatam says

      February 20, 2024 at 7:09 pm

      Hello Neeraj,
      24V heater will burn if used with 48V, so it cannot be used. It will heat fast and burn or get damaged after some use.

      Reply
      • Neeraj says

        February 20, 2024 at 7:26 pm

        It’s not about heater it’s about wire just simple copper wire

        Reply
        • Swagatam says

          February 20, 2024 at 7:45 pm

          OK, sorry I misread your question. The wire will heat up more with the 24v load because it will pull more current than the 48v load.

          Reply
          • Neeraj says

            February 20, 2024 at 7:55 pm

            So power doesn’t matter

            Reply
            • Swagatam says

              February 20, 2024 at 10:21 pm

              Power does matter, and it’s the current in the power which does the damage, so it’s the current which needs to be considered.

              Reply
          • Neeraj says

            February 20, 2024 at 8:14 pm

            And 48v is much more safer then 24v in terms of everything!

            Reply
            • Swagatam says

              February 20, 2024 at 10:23 pm

              If all the relevant parameters are rated at 48V then 48V is better than 24 V in terms of power efficiency.

              Reply
  12. Neeraj says

    February 19, 2024 at 11:43 am

    Hey have a one Little doubt can I use this circuit with 48v ?

    Reply
    • Swagatam says

      February 19, 2024 at 1:34 pm

      You can use with modifications.

      Reply
      • Neeraj says

        February 19, 2024 at 2:26 pm

        Which type of modification any suggestions?

        Reply
      • Neeraj says

        February 19, 2024 at 6:42 pm

        Sorry I am so needy but as we can assume 24v takes almost 15a in order to achieve 360w but on the other hand 48v needs only 7.5a for 360w and it won’t give much strain on the wire !

        Reply
        • Swagatam says

          February 19, 2024 at 6:53 pm

          You will need a 48v coil relay for this, to avoid a regulator circuit, I hope that is OK with you.

          Reply
          • Neeraj says

            February 19, 2024 at 7:51 pm

            So if I wanna switch from 24 to 48 then just change the relay ?

            Reply
            • Swagatam says

              February 19, 2024 at 8:32 pm

              A few more modifications will be required, I will update the drawing tomorrow.

              Reply
              • Neeraj says

                February 20, 2024 at 12:00 pm

                Which type of modification sir any suggestions!

                Reply
                • Swagatam says

                  February 20, 2024 at 12:13 pm

                  You can try the following circuit:

                  " rel="ugc">comment image

                  Reply
                  • Neeraj says

                    May 3, 2024 at 7:18 pm

                    Remember this one ! You have made this for me it’s a 48v version! And this circuit need a little modifications! Please look at this ! And also we are now using lm358 so check it if you can make some modifications on it ! !!!!

                    Reply
                    • Swagatam says

                      May 4, 2024 at 8:46 am

                      Ok, you can try the following modified design which will work with 48V supply, relay and heater.

                      " rel="ugc">comment image

                    • Neeraj says

                      May 4, 2024 at 9:22 am

                      😊 I will update you soon but I have a doubt is there any need for the capacitor?

                    • Swagatam says

                      May 4, 2024 at 9:28 am

                      The capacitor at the BC546 base is not needed. I have replaced it with a 1k resistor, which is more effective.
                      However, if your relay chatters while switching OFF, you can add a 10uF capacitor parallel to the 1k at the base of the BC546.

                    • Neeraj says

                      May 5, 2024 at 11:49 am

                      So here’s the issue the latch is not working with bd140 ! And ic is getting 12v and if I connect one wire of the thermistor to the positive line then at the pin 2 I got 24v and more and at the pin3 i only got some 12~15v and If I connect thermistors wire to the 12v input of the ic then it works ! But still the latch is not working I have seen 46~48v at the base point of the bd140 but if I push the button then the push to on function is not even working! So it’s not latching nor its functioning like push button!

                    • Swagatam says

                      May 5, 2024 at 12:47 pm

                      Neeraj, please try the following setup first to confirm latching. I have removed the relay here, we can connect the relay once the latching confirmed:

                      " rel="ugc">comment image

                    • Neeraj says

                      May 9, 2024 at 12:53 pm

                      Sir latch didn’t worked circuit is not even getting started! And when I touched and hold the emitter and collector of the bd140 then I got voltage on the circuit! Also I am using 55c12 zener which produce 12v at 0.5w ! Is this gonna make issue?

                    • Swagatam says

                      May 9, 2024 at 3:02 pm

                      Neeraj, in the following circuit which you are testing, the latch will work only when the pin#3 voltage is initially adjusted to be higher than pin#2 voltage.
                      So keep the push button pressed and check the voltage at piin#3 and pin#2. Make sure pin#3 is slightly higher than pin#2.
                      " rel="ugc">comment image

                    • Neeraj says

                      May 9, 2024 at 3:54 pm

                      It is i have checked it the pin3 voltage is higher then pin2 but still the latch is not working! Diodes are not the issue?

                    • Swagatam says

                      May 9, 2024 at 4:30 pm

                      When you press the push button does the LED light up?

                    • Neeraj says

                      May 9, 2024 at 5:18 pm

                      Nope but as I said you earlier i have to hold the bd140 and if I checked the voltage across leds terminal I got 11v or some ! But the led didn’t light up at any situation!

                    • Swagatam says

                      May 9, 2024 at 5:21 pm

                      If the LED is not lighting up that means the IC pin#8 is not getting 12V supply, please check all these basic steps. Without power the IC will not work, the transistors will not work, the LED will not light up the latch will not work…

                    • Neeraj says

                      May 10, 2024 at 9:17 am

                      Sir can I have a testing circuit for the latch function testing? Because for now I have checked all the connection and components! But still the circuit is not latching! !

                    • Swagatam says

                      May 10, 2024 at 11:01 am

                      Neeraj,
                      the test setup is the same which I gave you earlier, without the relay, using two zener diodes.
                      Please follow the steps which I suggested earlier, check pin#8 voltage of the IC, check why the LED is not illuminating.

                    • Neeraj says

                      May 11, 2024 at 12:55 pm

                      Sir now the led illuminated but now the issue is the push button function is not working bd140 is getting on when it connected to the input with even touching and thermistor is also working and same as before latch is not working like if I heat thermistor then the led will turned off and after the thermistor is cooled the led and whole circuit will turn on automatically! Latch function is not working and can you tell me I have connected bd140’s collector pin to the input and the base is pin3 and at pin1 is a emitter is connected to the circuit! Is this correct?

                    • Swagatam says

                      May 11, 2024 at 1:20 pm

                      Neeraj, you can refer to the following diagram for the BD140 connection details:
                      " rel="ugc">comment image

                    • Neeraj says

                      May 11, 2024 at 3:08 pm

                      Congratulations 🎉 sir we have made another successful circuit it worked last time the main cause was led and now I have changed it and now the circuit is working as it needed thanks sir for all of this ☺️ now what’s the next step?

                    • Swagatam says

                      May 11, 2024 at 4:50 pm

                      That’s good news Neeraj, now you can connect the 48v relay coil with a parallel diode, as shown in our earlier diagram, and check the results by heating the thermistor with a soldering iron. Make sure to adjust the preset correctly.

                    • Neeraj says

                      May 11, 2024 at 8:03 pm

                      Do I also have to add the extra diode and 10k resistor which we have added for testing circuit?

                    • Swagatam says

                      May 11, 2024 at 9:52 pm

                      Yes, for 48v operation it should be exactly as shown in the following image, the dotted lines will go to the relay coil

                      " rel="ugc">comment image

                      Don’t forget to add a diode across the relay coil….

                    • Neeraj says

                      May 18, 2024 at 7:58 pm

                      Sir I have a question I have tried your lm2576 ic article and i tried the circuit which can be used for 40 to step down 5v or so but as I can see now it worked on 48v too but the real issue is that when I connected this lm2576 fixed voltage circuit to the relay i saw that at the input of this circuit I got 48v and it was dropping and I didn’t even on the circuit of the temperature control circuitry and when I did the input was fine but I didn’t got anything at the output then I got confused then I tried with 12v temperature control circuitry and the same thing happened! If I use this lm2576 circuit directly with the SMPS and the load is 5v dc motor it worked super efficiently! But then I did it with temperature control circuitry I didn’t got anything! Why ?I am using lm2576 5v fixed ic ! And a standard circuit which I have found on the datasheet of this ic ! Sorry I have written down too lengthy 😅

                    • Swagatam says

                      May 19, 2024 at 8:05 am

                      Hello Neeraj,
                      The maximum tolerable input voltage of LM2576 is 40V, so you must not exceed this limit at any cost.
                      Please provide the schematic link in which you are trying to use the LM2576.

                    • Neeraj says

                      May 19, 2024 at 8:44 am

                      " rel="ugc">comment image

                      This is the circuit

                    • Swagatam says

                      May 19, 2024 at 9:21 am

                      Not this, the temperature controller circuit in which you are integrating the LM2576…

                    • Neeraj says

                      May 19, 2024 at 9:36 am

                      " rel="ugc">comment image

                      This one

                    • Swagatam says

                      May 19, 2024 at 11:33 am

                      Is the above circuit operating normally as per our previous discussion, did you connect the relay and check?

                    • Neeraj says

                      May 19, 2024 at 1:07 pm

                      Yeah I checked it the circuit is working super nicely 🙂 with relay !

                    • Swagatam says

                      May 19, 2024 at 1:13 pm

                      Ok, but you cannot connect the LM2576 with 48V, you can use LM2576HV instead.

                    • Neeraj says

                      May 24, 2024 at 3:53 pm

                      Sir I have bought lm2576hv 5v fixed and as I said earlier as soon as I turn on the temperature control circuitry the lm2576 blasts and the whole step down circuit stopped working it’s my second time 😭 but the small results can’t we use power resistor as we used for our temperature control circuitry to step down 48v to 12v or so ! Because all I need is a 5v Motor to be turn on with my heater at the output of the temperature control circuitry! Please sir do something!!!!!!

                    • Swagatam says

                      May 24, 2024 at 5:27 pm

                      Hi Neeraj,
                      Resistor can be used to drop 48V to 5V but the resistor might dissipate a lot of heat.
                      Please provide the AMPERE specifications of your motor, I will try to calculate the resistor value.

                    • Neeraj says

                      May 24, 2024 at 6:31 pm

                      The motor I am using is used in dvd so I don’t think it will take more than 2 amps !?

                    • Swagatam says

                      May 24, 2024 at 7:06 pm

                      You can use Ohms law to calculate the resistor value;

                      R = (V_supply – V_motor) / I_motor = 48 – 5 / 2 = 22 Ohms
                      Power = R x I^2 = 22 x 2 x 2 = 88 watts.

                      Resistor will waste around 100 watts of power.

                    • Neeraj says

                      May 24, 2024 at 7:44 pm

                      Alright so we can’t do that ? But idk how the lm2576hv is getting blasted everytime! This is how I connect the step down circuit to the temperature control circuitry positive input of the stepdown goes to the relays NO connection just like the heater and the nagative goes just like -48v directly is this ok I know it is but why ! And now how could we make something which can work!

                    • Swagatam says

                      May 25, 2024 at 8:18 am

                      Neeraj, the LM2576HV is a adjustable buck converter. Did you make it as per the instructions given in this article or its original datasheet?:
                      https://www.homemade-circuits.com/0-to-50-v-adjustable-switching-power-supply-circuit-using-ic-lm2576/
                      If yes, then your IC may be duplicate type and not original.
                      I think you should buy the assembled board from amazon, and then check its response.

                    • Neeraj says

                      May 31, 2024 at 3:04 pm

                      Sir can you tell me which step down module is better for my needs ! mp4560dn module or XL7015 module ?
                      Which one should I choose?

                    • Swagatam says

                      May 31, 2024 at 3:16 pm

                      Hi Neeraj,
                      The mp4560dn looks perfect for your application since it can supply 2A current as required by your motor…just make sure to buy a readymade preassembled tested module.

                    • Neeraj says

                      June 4, 2024 at 10:06 am

                      Sir how are you? I have a question can we use igbt or bjt instead of relays because I couldn’t find out any single relay which can work on 48v 360w or maximum 400w load I got one 48v coil voltage relay but after some use the relay melted a bit and I don’t consider it good for long term if there is any way to use igbt in this circuit the it might help us ! ? Reply me as soon as possible because I am going Market today if you suggest me a igbt then I will buy it now !

                    • Swagatam says

                      June 4, 2024 at 11:46 am

                      Hi Neeraj,
                      If your load is a 48V DC load then you can use a MOSFET or an IGBT.

                    • Neeraj says

                      June 4, 2024 at 11:49 am

                      So which MOSFET or igbt should I use and buy ? And how can I implant it in our circuit?

                    • Swagatam says

                      June 4, 2024 at 12:02 pm

                      What is the ampere rating of your 48V heater?

                    • Neeraj says

                      June 4, 2024 at 12:06 pm

                      Not more then 8A it’s a maximum ampere

                    • Swagatam says

                      June 4, 2024 at 12:15 pm

                      Actually MOSFETs can be unpredictable devices and might get damaged without any clues….so I would recommend using a BJT instead.
                      You can try a TIP35 BJT it will work perfectly for your 48V 8A load

                    • Neeraj says

                      June 4, 2024 at 12:34 pm

                      What about igbt ?

                    • Swagatam says

                      June 4, 2024 at 12:51 pm

                      IGBTs are good you can use any 100V 20 amp IGBT

                    • Neeraj says

                      June 4, 2024 at 12:53 pm

                      So which one will not require heat sink igbt or bjt ??

                    • Swagatam says

                      June 4, 2024 at 2:01 pm

                      Both will require heatsink

                    • Neeraj says

                      June 4, 2024 at 2:44 pm

                      Alright 👌 but as per my opinion the igbt will be better then bjt ! ?

                    • Swagatam says

                      June 4, 2024 at 5:03 pm

                      Yes an IGBT is always better than a BJT.

                    • Neeraj says

                      June 4, 2024 at 5:30 pm

                      So how can we implant it to the circuit and which igbt should I use for the operation

                    • Swagatam says

                      June 4, 2024 at 7:44 pm

                      Any IGBT rated at 100V and over 20 amps will do the job….Once you buy the part let me know I will show you how to integrate it with the circuit…

                    • Neeraj says

                      June 5, 2024 at 10:41 am

                      MBR20100CT ? Can this igbt will work ?

                    • Swagatam says

                      June 5, 2024 at 10:49 am

                      That’s a Schottky Diode, not an IGBT

                    • Neeraj says

                      June 5, 2024 at 11:00 am

                      I have searched the internet but all I see is 1200v or 600v igbt ! Can you suggest me something?

                    • Swagatam says

                      June 5, 2024 at 11:08 am

                      Yes, IGBTs are mostly rated with high voltage, in that case you can try a 1000V IGBT such as FGA50N100BNTD

                    • Neeraj says

                      June 6, 2024 at 12:08 pm

                      Sir this igbt that you have suggested me is not available on the market so I bought this one it’s a H20R1203 igbt it’s a 1200v 20a igbt can this igbt will work for us ?

                    • Swagatam says

                      June 6, 2024 at 12:29 pm

                      Hi Neeraj, It should work according to me. You can try the following configuration:

                      " rel="ugc">comment image

                    • Neeraj says

                      June 6, 2024 at 10:59 pm

                      Sir I know I am so demanding guy but can I use irf540 MOSFET for this circuit because it’s have 100v and 33a rating ! Because currently I have irf540 MOSFET!

                    • Swagatam says

                      June 7, 2024 at 8:00 am

                      Yes, you can use IRF540 MOSFET also, connection will be exactly similar to the IGBT diagram shown previously.

                    • Neeraj says

                      June 7, 2024 at 10:26 am

                      MOSFETs drain will go to the positive line of the circuit and source will go to the negative line and gate will be that same ??

                    • Swagatam says

                      June 7, 2024 at 11:20 am

                      The drain will go to the positive through the heater load, not directly.
                      Source to ground
                      Gate to the 12V zener cathode.
                      Please refer to the previous IGBT diagram, the connections are identical, just replace collector with drain, emitter with source, and gate with gate.
                      " rel="ugc">comment image

                    • Neeraj says

                      June 11, 2024 at 11:52 am

                      Good morning sir 🌄 I have bought mp4560dn module 5v output but I ma confused at the input of this module because what is the meaning of the EN at the vin+ input ? Because when I connected + input and – input the module didn’t worked at the output I didn’t get anything! now should I have to connect EN instead of +input and -input ? I am confused! I am sharing the link of the module

                    • Swagatam says

                      June 11, 2024 at 1:28 pm

                      Good Morning Neeraj,
                      Yes EN is the enable input.
                      Pulling this pin below the specified threshold shuts the chip down.
                      Pulling it up above the specified threshold or leaving it floating enables the chip.
                      Please read this datasheet pinout details carefully, everything is explained in this datasheet:
                      https://www.farnell.com/datasheets/3161503.pdf

                    • Neeraj says

                      June 18, 2024 at 12:28 pm

                      Sir irf540n MOSFET is getting so hot within seconds at the load of 48v 7.5A ! Is there any other MOSFET is available which is suitable for our circuit?

                    • Swagatam says

                      June 18, 2024 at 1:20 pm

                      Hi Neeraj, you can try the following MOSFET.
                      https://www.homemade-circuits.com/high-current-mosfet-irfp2907-for-wind/

                    • Neeraj says

                      June 18, 2024 at 2:29 pm

                      Sir I have doubt can’t we use the same tip36c for heater because I think it’s more worthy then anything else! Because I couldn’t feel heat on it at the input! Can I use it also for output?

                    • Swagatam says

                      June 18, 2024 at 2:49 pm

                      Neeraj, I had suggested you TIP35 in the beginning, but you said that you wanted to use a MOSFET.
                      Anyway, yes you can use the transistor TIP35 for operating the heater, not TIP36 because it is PNP.
                      For base resistor you can use 100 ohms 1 watt

                    • Neeraj says

                      June 18, 2024 at 2:54 pm

                      Alright tip35c with 100ohm 1watt ?

                    • Swagatam says

                      June 18, 2024 at 5:17 pm

                      Yes, TIP35c with 100 ohm 1 watt base resistor.

                    • Neeraj says

                      June 23, 2024 at 1:21 pm

                      Sorry sir for the late my exam was on going btw I have bought tip35c with 100ohm 1watt resistor and now i am a bit confused about the connection 😕!

                    • Swagatam says

                      June 23, 2024 at 2:15 pm

                      No problem Neeraj,
                      The TIP35 connection will be exactly identical as the IGBT connections which I had shown you earlier, just make sure to add the 100 ohm in series with its base.

                    • Neeraj says

                      June 23, 2024 at 3:07 pm

                      Sir tip36c is unsuccessful it’s touch 100°c within seconds I can’t work on it !

                    • Swagatam says

                      June 23, 2024 at 4:11 pm

                      Neeraj, are you referring to TIP35 or TIP36? I think tip36 is on the input side and tip35 is supposed to be on the output side with the heater…so which transistor are you referring to?

                    • Neeraj says

                      June 23, 2024 at 4:44 pm

                      Oh sorry it’s tip35c !

                    • Neeraj says

                      June 23, 2024 at 6:46 pm

                      Well I am using tiny thin wire at emitter of this transistor does it can cause this issue? -_- because this tip35c should have to handle that much current without any hassle!

                    • Swagatam says

                      June 23, 2024 at 8:43 pm

                      It should be thick wire otherwise the wire will not hold 8 amps and melt…The wire should be 2mm thick…

                    • Neeraj says

                      June 23, 2024 at 6:48 pm

                      90% of the circuit is completed but the rest 10% is taking everything 😕

                    • Neeraj says

                      June 23, 2024 at 8:05 pm

                      Sir after changing the emitters wire to the thik one it’s doesn’t made any difference still tip35c is heating Maddy!

                    • Swagatam says

                      June 23, 2024 at 8:49 pm

                      Then I think a relay is the only option left, because all transistors will heatup. You will need a heatsink for all types of transistor.

                      Or you can try configuring the tip35 like a Darlington pair with 2n2222 and see how it works…this should allow to reduce the heat on the transistor.

                    • Neeraj says

                      June 24, 2024 at 9:20 am

                      Alright leave transistors now we only gonna work on relays but relay also have some issues like it’s chaters also maker noises when it is going on off stat and the pins also makes some sparks ! And finding 48v coil voltage relay in the market is very tough 😕 also 30v 10a DC load relay heats alot and sometimes melted also I have one 48v coil voltage relay with 28v 10a DC load this relay worked but the same issues gave me pain ! So now which type of relay should I need ! And what will be the coil voltage? And my load current is not that much it’s stay between 7.5 to 6A !

                    • Swagatam says

                      June 24, 2024 at 12:05 pm

                      You can do one thing, take two 24V relays and put their coils in series, and contacts in parallel, this will solve all the related issues instantly.

                      To solve the chattering problem, simply add a 220uF/100V capacitor parallel to the relay coil (end to end across the series coils).

                      Don’t forget to put the 1N4007 freewheeling diode also across the relay coil…

                      For the relays you can use OEN make 24V relays such as these:
                      " rel="ugc">comment image

                    • Neeraj says

                      June 24, 2024 at 12:07 pm

                      So these relays are not available in 48v version?

                    • Swagatam says

                      June 24, 2024 at 12:58 pm

                      It may be available but not everywhere, because there’s less demand for 48V relays compared to 12V and 24V. So 24V may be more easily available.

                    • Neeraj says

                      June 24, 2024 at 1:17 pm

                      Couldn’t I use 2 normal 24v relays which have 5 pins in series?? It will be more easier then this relay! And also easily available to the market! What’s your thoughts?

                    • Swagatam says

                      June 24, 2024 at 1:29 pm

                      The OEN relay is also an ordinary relay with 5 pins, but its quality is very good…you can use any other 24V relay 5-pin if you want.

                    • Neeraj says

                      June 24, 2024 at 3:26 pm

                      So right now I have 2, 24v 15A relay they are generic and now how can I make connections! Can you show me with an image ? Because words are confusing me !

                    • Swagatam says

                      June 24, 2024 at 6:20 pm

                      You have to wire the relays in the following manner:
                      " rel="ugc">comment image

                    • Neeraj says

                      June 24, 2024 at 9:29 pm

                      Spotted a mistake in the diagram the heaters positive input should have to be connected to the emitter of the bd140 not at the collector of the transistor! Because bd140s emitter to collector continues current carrying capacity is not enough am I right?

                    • Swagatam says

                      June 25, 2024 at 8:13 am

                      You are absolutely right, here’s the corrected diagram:
                      " rel="ugc">comment image

                    • Neeraj says

                      June 25, 2024 at 7:33 pm

                      https://drive.google.com/file/d/1n_2OIa8tTKsc0tjydMkqcVWJUpoSFKe7/vie w

                      Remove the dash between view and link will be available

                      I have contacted oen relay dealer he told me there is one relay which can help me so can you check the datasheet! 1 form C and 1 form A which one should I consider both have 24v and 48v versions

                    • Swagatam says

                      June 26, 2024 at 8:20 am

                      The google drive link must be in the shared mode so that others can open it. Right now it is not in the shared mode so it is not giving me the access.

                    • Neeraj says

                      June 25, 2024 at 9:13 pm

                      Can I use OEN 26 RELAY 1 form A or 1 form C ? You can see it’s datasheet by searching oen 26 relay ! Please check the datasheet and tell me which one is better for me because these relay comes in both 48v and 24v version this also have 12A and 16A current carrying capacity oen dealer suggested me this relay ! Please check

                    • Swagatam says

                      June 26, 2024 at 8:28 am

                      You can use the 48V 12 A or 16 A both should work, because your heater load is 8A.

                    • Neeraj says

                      June 26, 2024 at 8:54 am

                      But sir in this pdf you can see 1 form A relay is with 4 pins and it have 16a load rating and another 1 form C have 5 pins and 12a rating both have 28v dc load voltage which one should I choose?

                    • Swagatam says

                      June 26, 2024 at 9:55 am

                      I think 28V DC load specification will not work because your heater load is rated at 48V.

                    • Neeraj says

                      June 26, 2024 at 8:56 am

                      And 1formA have no NC pin should I go for it ?

                    • Swagatam says

                      June 26, 2024 at 9:55 am

                      without NC is fine, but 28V DC load restriction is not OK…

                    • Neeraj says

                      June 26, 2024 at 10:00 am

                      But every relay have the same dc voltage 28v max load rating and have difference between current and i remember when you said that voltage doesn’t matter much the current carrying capacity matters ! And power !

                    • Swagatam says

                      June 26, 2024 at 12:13 pm

                      It is my assumption, I may be wrong, so it is better to confirm with the OEN dealer.

                    • Neeraj says

                      June 27, 2024 at 9:21 am

                      Sir I got an idea the relay will take time to deliver to my residence until then can we work with irf540n MOSFET? Because last time i used this MOSFET in our circuit it worked but since it’s got heated we decided to change it with tip35c but this transistor heated so faster then ever faster then MOSFET so in my opinion can we use 2 irf540n MOSFETs ? In this circuit I think they will heat less then ever? What’s you thought on this please tell me !

                    • Swagatam says

                      June 27, 2024 at 11:32 am

                      Hi Neeraj,
                      You can try two MOSFETs in parallel, it will be cooler compared to a single MOSFET.
                      Make sure to connect the positive side terminal of the heater directly with the +48V DC input.

                    • Neeraj says

                      June 28, 2024 at 9:41 am

                      Sir we made it we made it possible it worked after all this month’s we made it possible I have used 2 irf540n MOSFET in parallel and it worked and believe me the MOSFET heated so less that I can hold it with my bere finger it worked i have tested it with full load but I have seen a bit difference one MOSFET heated a bit higher then the other is that gonna make any issue?

                    • Swagatam says

                      June 28, 2024 at 11:31 am

                      Thanks Neeraj, glad it is working now using MOSFETs.
                      If one MOSFET heats up little more then it will proportionately start introducing higher resistance to the load current, so that the other MOSFET is forced to handle this extra current, so now the previous MOSFET starts cooling and the new MOSFET starts heating up…this current exchange will continue and the heat will be thus uniformly shared across the two MOSFETs.
                      So it won’t have any serious issues.
                      This is just the opposite to BJTs, because MOSFETs have negative temperature coefficient, meaning as it heats up, the current passage through it is reduced proportionately.
                      Still, if you are not sure, you can simply mount the two MOSFETs over a single common heatsink, very close to each other.

                    • Neeraj says

                      June 30, 2024 at 9:52 am

                      The accuracy of the thermistor is not good because sometimes circuit off at 80°c of the water temperature and on the next time it’s cut off at 77 or 75 ! I have sets preset and i didn’t touched it again but this type of accuracy is not good enough! Should I use lm35 because I can calculate voltage to temperature easily in lm35 but also most of the temperature ic I get were faulty!

                    • Swagatam says

                      June 30, 2024 at 10:12 am

                      Sure, You can try LM35 sensor in place of the NTC thermistor. Buy it from amazon or any other reputed online source.

                    • Neeraj says

                      June 26, 2024 at 10:54 am

                      Like this calculation – 28v x 12a = 336w dc load capacity? And 28v x 16a = 448w and our needs is 48v x 7.5a = 360w I think both relay can work without any hassle! ?

                    • Swagatam says

                      June 26, 2024 at 12:14 pm

                      You can check the relay practically, and verify if it works or not.

                    • Neeraj says

                      June 24, 2024 at 1:25 pm

                      And I think using 2 relay in series won’t increase there current load capacity! ?

                    • Swagatam says

                      June 24, 2024 at 1:30 pm

                      using 2 relay coils in series with parallel contacts will decrease coil current, and increase contact current capacity.

                    • Swagatam says

                      June 7, 2024 at 11:23 am

                      ….actually " rel="ugc">this circuit was designed for a relay operation by the input BD140 transistor…now since you are connecting the 8 amp load directly with the BD140 supply, this transistor will not work, it will burn.
                      You must replace the BD140 with TIP36.

                    • Neeraj says

                      June 7, 2024 at 6:20 pm

                      What about MJE2955T instead of tip36? Can I use it ??

                    • Swagatam says

                      June 7, 2024 at 7:27 pm

                      It is rated at 10 amps only, it won’t take the load….tip36 is rated at 25 amps

                    • Neeraj says

                      June 7, 2024 at 7:46 pm

                      Yeah but the load is also 48v 8.5A !

                    • Swagatam says

                      June 8, 2024 at 8:28 am

                      You can try it and see if it works or not.

                • Swagatam says

                  February 20, 2024 at 12:47 pm

                  I forgot to show a push-button between the collector/emitter of BD140, please insert a push button in that position.

                  Reply
                  • Neeraj says

                    February 20, 2024 at 1:55 pm

                    Okay sir

                    Reply
                  • Neeraj says

                    February 20, 2024 at 1:57 pm

                    And I can use lm358 IC instead of lm741

                    Reply
                    • Swagatam says

                      February 20, 2024 at 3:06 pm

                      Yes 1/2 LM358 can be used, IC 741 will also work nicely.

                  • Neeraj says

                    February 20, 2024 at 2:04 pm

                    It’s accuracy is same as this previous circuit?

                    Reply
                    • Swagatam says

                      February 20, 2024 at 3:07 pm

                      It is the same circuit as earlier except the voltage range which is 48V now.

                    • Swagatam says

                      February 20, 2024 at 3:19 pm

                      Also please make sure to connect a 12V zener diode between pin3 of the IC and the ground line, to ensure that pin3 voltage never exceeds the pin7 voltage of the IC.

  13. Neeraj says

    February 11, 2024 at 2:05 pm

    Thats great but it’s with much more parts and I have a question does this circuit can work with 24v 15a 360w ? Directly? And how there is no transistor to operate the relay and can I connect 24v input directly?

    Reply
    • Swagatam says

      February 11, 2024 at 2:54 pm

      Yes, you can use 24V directly with a 24V relay, but then the opamp will need to be from the IC LM358.
      The relay is operated by the BC557 output itself.

      Reply
      • Neeraj says

        February 11, 2024 at 3:09 pm

        Yeah but 24v relay is not available widely in the Market! So if I need 12v relay to be used then I have to add 7812 in the input of the circuit?

        Sorry but I couldn’t understand the “opamp will need to be from the IC LM358”

        Reply
        • Swagatam says

          February 11, 2024 at 3:16 pm

          You can use the circuit as shown with 12V supply and 7812 IC but then the 7812 will heat up a lot.
          If you use 24V DC and 24V relay then the opamp should be from LM358.
          There are two opamps inside LM358, use any one of them.

          Reply
          • Neeraj says

            February 11, 2024 at 3:22 pm

            What about the connection of the lm358 ? And I have heard that this lm358 is more versatile then the lm741. Please confirm about its connections

            Reply
            • Swagatam says

              February 11, 2024 at 6:07 pm

              Pin3, pin2 and pin4 will be as it is. No change required.
              Replace pin7 with pin8.
              Replace pin6 with pin1.
              Yes, LM358 is more efficient than IC 741.

              Reply

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