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3 Simple DC Motor Speed Controller Circuits Explained

3 Simple DC Motor Speed Controller Circuits Explained

3 easy to build speed controller circuits for DC motors are presented here, one using Mosfet IRF540, second using IC 555 and the third concept with IC 556 featuring torque processing.

Design#1: Mosfet based DC Motor Speed Controller

A very cool and easy DC motor speed controller circuit could be build using a just a single mosfet, a resistor, and a pot, as shown below:

DC motor speed control with single mosfet with common drain mode

Using a BJT Emitter Follower

motor speed control using BJT emitter follower circuit

As can be seen the mosfet is rigged as a source follower or a common drain mode, to learn more about this configuration you may refer to this post, which discusses a BJT version, nevertheless the working principle remains the same.

In the above DC motor controller design, the pot adjustment creates a varying potential difference across the gate of the mosfet, and the source pin of the mosfet simply follows the value of this potential difference and adjusts the voltage across the motor accordingly.

It implies that the source will be always 4 or 5V lagging behind the gate voltage and vary up/down with this difference, presenting a varying voltage between 2V and 7V across the motor.

When the gate voltage is around 7V, the source pin will supply the minimum 2V to the motor causing a very slow spin on the motor, and 7V will be available across the source pin when the pot adjustment generates the full 12V across the gate of the mosfet.

Here we can clearly see that the mosfet source pin seems to be "following" the gate and hence the name source follower.

This happens because the difference between the gate and the source pin of the mosfet must be always around 5V, in order to enable the mosfet to conduct optimally.

Anyway, the above configuration helps to enforce a smooth speed control on the motor, and the design could be built quite cheaply.

A BJT could be also used in place of the mosfet, and in fact a BJT would produce a higher control range of about 1V to 12V across the motor.

Video Demo

When it comes to controlling motor speed uniformly and efficiently, a PWM based controller becomes the ideal option, here we will learn more, regarding a simple circuit to implement this operation.

Design#2: PWM DC Motor Control with IC 555

The design of a simple motor speed controller using PWM may be understood as follows:
Initially when the circuit is powered, the trigger pin is in a logic low position since the capacitor C1 is not charged.

The above conditions initiates the oscillation cycle, making the output change to a logic high.
A high output now forces the capacitor to charge via D2.

On reaching a voltage level that's 2/3 of the supply, pin #6 which is the threshold of the IC triggers.
The moment pin #6 triggers, pin #3 and pin #7 reverts to logic low.

With pin #3 at low, C1 yet again begins discharging via D1, and when the voltage across C1 falls below the level that's 1/3 of the supply voltage, pin #3 and pin #7 again become high, causing the cycle to follow and go on repeating.

It is interesting to note that, C1 has two discretely set paths for the process of charging and discharging via the diodes D1, D2 and through the resistance arms set by the pot respectively.

It means the sum of the resistances encountered by C1 while charging and discharging remains the same no matter how the pot is set, therefore the wavelength of the out put pulse always remains the same.

However, since the charging or the discharging time periods depends upon the resistance value encountered in their paths, the pot discretely sets the these time periods as per the its adjustments.

Since the charge and discharge time periods is directly connected with the output duty cycle, it varies according to the adjustment of the pot, giving form to the intended varying PWM pulses at the output.

The average result of the mark/space ratio gives rise to the PWM output which in turn controls the DC speed of the motor.

The PWM pulses are fed to the gate of a mosfet which reacts and controls the connected motor current in response to the setting of the pot.

The current level through the motor decides it speed and thus implements the controlling effect via the pot.

The frequency of the output from the IC may be calculated with the formula:

F = 1.44(VR1*C1)

The mosfet can be selected as per the requirement or the load current.

The circuit diagram of the proposed DC motor speed controller can be seen below:

IC 555 potentiometer based DC motor speed controller


practical DC motor speed controller prototype image

Video Testing Proof:

In the above video clip we can see how the IC 555 based design is used for controlling speed of a DC motor. As you may witness, although the bulb works perfectly in response to the PWMs and varies its intensity from minimum glow to maximum low, the motor does not.

The motor initially does not respond to the narrow PWMs, rather starts with a jerk after the PWMs are adjusted to significantly higher pulse widths.

This does not mean the circuit has problems, it is because the DC motor armature is held between a pair of magnets tightly. To initiate a start the armature has to jump its rotation across the two poles of the magnet which cannot happen with a slow and gentle movement. It has to initiate with a thrust.

That's exactly why the motor initially requires a higher adjustments for the PWM and once the rotation is initiated the armature gains some kinetic energy and now achieving slower speed becomes feasible through narrower PWMs.

However still, getting the rotation to a barely moving slow status can be impossible because of the same reason as explained above.

I tried my best to improve the response and achieve a slowest possible PWM control by making a few modifications in the first diagram as shown below:

modified pwm DC motor control circuit

Having said this, the motor could show a better control at the slower levels if the motor is attached or strapped with a load through gears or pulley system.

This may happen because the load will act as a damper and help to provide a controlled movement during the slower speed adjustments.

Design#3: Using IC 556 for Enhanced Speed Control

Varying a DC motor velocity may appear to be not so difficult and you may find plenty of circuits for it.

However these circuits do not guarantee consistent torque levels at lower motor speeds, making the functioning quite inefficient.

Moreover at very low speeds due to insufficient torque, the motor tends to stall.

Another serious drawback is that, there’s no motor reversal feature included with these circuits.

The proposed circuit is completely free from the above shortcomings and is able to generate and sustain high torque levels even at lowest possible speeds.

Circuit Operation

Before we discuss the proposed PWM motor controller circuit, we would also want to learn the simpler alternative which is not so efficient. Nonetheless, it may be considered reasonably good as long as the load over the motor is not high, and as long as the speed is not reduced to minimum levels.

The figure shows how a single 556 IC can be employed for controlling speed of a connected motor, we won’t go into the details, the only notable drawback of this configuration is that the torque is directly proportional to the speed of the motor.

Coming back to the proposed high torque speed controller circuit design, here we have used two 555 ICs instead of one or rather a single IC 556 that contains two 555 ICs in one package.

Circuit Diagram

PWM Motor Speed Controller Circuit Using IC556

Main Features

Briefly the proposed DC motor controller includes the following interesting features:

Speed can be varied continuously right from zero to maximum, without stalling.

The torque is never affected by the speed levels and remains constant even at minimum speed levels.

The motor rotation can be flipped or reversed within a fraction of second.

The speed is variable in both the directions of the motor rotation.

The two 555 ICs are assigned with two separate functions. One sections is configures as an astable multivibrator generating 100 Hz square wave clocks which is fed to the preceding 555 section inside the package.

The above frequency is responsible for determining the frequency of the PWM.

The transistor BC 557 is used as a constant current source which keeps the adjoining capacitor at its collector arm charged.

This develops a saw-tooth voltage across the above capacitor, which is compared inside the 556 IC with the sample voltage applied externally over over the shown pin-out.

The sample voltage applies externally can be derived from a simple 0-12V variable voltage power supply circuit.

This varying voltage applied to the 556 IC is used to vary the PWM of the pulses at the output and which eventually is used for the speed regulation of the connected motor.

The switch S1 is used to instantly reverse the motor direction whenever required.

Parts List

  • R1, R2, R6 = 1K,
  • R3 = 150K,
  • R4, R5 = 150 Ohms,
  • R7, R8, R9, R10 = 470 Ohms,
  • C1 = 0.1uF,
  • C2, C3 = 0.01uF,
  • C4 = 1uF/25VT1,
  • T2 = TIP122,
  • T3, T4 = TIP127
  • T5 = BC557,
  • T6, T7 = BC547,
  • D1---D4 = 1N5408,
  • Z1 = 4V7 400mW
  • IC1 = 556,
  • S1 = SPDT toggle switch

The above circuit was inspired from the following motor driver circuit which was published long back in elecktor electronic India magazine.

Controlling Motor Torque using IC 555

using 2 IC 555 for achieving outstanding speed control on DC motors

The first motor control diagram can be much simplified by using a DPDT switch for the motor reversal operation, and by using an emitter follower transistor for the speed control implementation, as shown below:

Motor Speed Controller Circuit Using DPDT Switches

About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

199 thoughts on “3 Simple DC Motor Speed Controller Circuits Explained”

  1. Hello Swagatam,
    I am trying to control a 12V high torque geared dc motor. It spins a disc with couple of kilogram load and required to run at constant torque in 10%-100% duty cycle. I would be using a mobile app to set the motor speed which would be translated by an Arduino into a PWM value to the controller. Therefore your design #3 looks very interesting from constant torque perspective, however since we need to be able to set the speed remotely, is it possible in anyway to replace the mechanical POT with something digital (digital pot?).

    I have used commercially available controller with pot and it has worked perfectly with my requirement while the ones that were interfaced digitally with the arduino through PWM would loose troque at lower PWM duty cycle.

      • Thanks for your very swift reply Swagatam. Could you please let me know if the POT in design#3 can be simply replaced with a digital pot? Are there any voltage/current issues that we need to be aware off? Would there be any impact on the torque behavior? I have already ordered for X9C104 digipots (to experiment replacing the analogue pot in the commercial controller). Could I use it to replace the pot in your circuit?

        PS: I am not much of a hardware guy. 🙁


    • Just a another follow up question. Is it possible to redesign that circuit in such a way that we can do away with the pot?


          • If the Arduino allows PWM adjustment through a push button, then the output can be directly integrated with a MOSFET for the required motor control. Do you have this kind of programming for the Arduino?

            • Good Morning Swagatam,
              I am not using push buttons. Currently i am getting the motor speed setting from the mobile app and mapping that to an appropriate pwm value (which ranges from 0-255) and writing it to the pwm pin on the arduino. This pin in turn is connected to the pwm pin off the dc driver from robokits that i mentioned in my earlier post. The only issue i have with that dc driver is that it looses torque at low speeds otherwise it’s all good for my requirements.

            • Good Morning Sunil,

              I meant to say if you are able to control the Arduino by some external means, push button was just an example. So in that case no need of any driver, the varying PWMs can be directly integrated with any MOSFET for getting the required motor control. As far as torque is concerned it will go down proportionately as the PWM become narrower, due to the reduction in the average current.

            • Hi Swagatam,
              Got your point on the push button! Regarding loss of torque at low speeds, isn’t your design #3 meant to overcome this exact issue…i.e lose of torque?
              On another note I have used the controller in the below given link and there isn’t any perceptible loss of torque even when the motor is run very slow for eg, 12V 10 rpm motor run at 2rpm still has very good torque. Any idea how is this achieved?


              In summary my requirement is for a controller that retains torque at low speeds, but does not use a pot and can be interfaced and controlled with arduino.

              PS: The portal isn’t giving an option to reply to your last message (may be it has reached its maximum nesting?). So sorry the messages may look out of sequence in the conversation thread.

            • Hi Sunil,
              I have practically tried the single IC 555 version and the two IC 555 version, and I found the latter having substantially more torque than the single IC version. It was a long time ago and I did not check the waveform then, so can’t explain the exact reason. However technically it is clear that the output power to the motor will be directly proportional to the fed PWM level. Unless there’s some kind of automatic compensation involved the torque cannot increase.

              Yes the comments have a limitation on the maximum number of threads, it’s fine to open a new thread in that case.

            • Good Morning Swagatam,
              Got it! Thank you!
              I have sent you a mail on homemadecircuits @ gmail.com.


  2. Good morning Swagatam Ji.
    I am Sakthivel from tuticorin. I want help some handy happed friends to run their try cycles using 500watts universal motor with 24 volt 12Ah battery, for which I need dc motor speed controller circuit ( with IC 555 as a Pulse Width Modulator with reference to your _https://www.brighthubengineering.com/diy-electronics-devices/123681-how-to-make-a-dc-motor-speed-controller-circuit-using-two-555-ics/ )
    The above said motor may take normal load current about 21amps and at beak may be 44amps for 10 seconds.
    Can you please put a suitable circuit diagram with Parts List and with its values? Post in your homemade-circuits.com. Also please mention where I have to use Pot meter in the circuit, either in R2 or R4 or somewhere else, because I am diploma mechanical engineer hence I not well versed in electrical and electronic circuit.
    My whatsapp no: +91 9092733451
    I hope you may post it.
    Thank you very much.

  3. Swagatam Ji,
    I am really very much thankful to you for your technical support in building circuits .

    Yesterday , I tried with another motor . When I rotated pot from 0 to full , it was amazing experience! I was so happy and thankful to you for your contribution.
    Motor was running smoothly , and responding very well to pot rotation.

    Earlier when I was doing experiment with smaller motor , it was taking 0.70 amp , when I stopped motor shaft by hand multimeter was showing 0.03 amp . As soon as I release the motor shaft amp reading was 0.70 amp. I was surprised. I thought there must be a inbuilt sensing mechanism in MOSFET . So I asked to you.
    Actually multimeter connection was loose and all that happened.
    Once again when I conducted same experiment I found it was taking 1.5 amp when stopped and 0.70 when running.

    Now, I am running a 650 watt universal motor at 220 volt ac , using a full bridge rectifiers.
    At motor terminals volt is 100 volt dc and current value is 1.00 amp when motor is in running condition. When not running volt is 330 and zero amps.
    In this condition is it true that motor is using only 100×1.0 = 100 watts only!
    Thanks you Swagatam Ji

    • You are welcome Devendra ji, I am glad you could understand and solve the issue successfully.

      yes, if the voltage is 100V across the load, and current is 1 amp, then the effective consumption will be approximately 100 watts.

  4. bro i need a circuit of h bridge that can handle 24v and upto 20amp current . that can control the direction as well as pwm by pins. i realy needs. i have made a circuit but its goes off when about 10amp current flows. 🙁

    • Abubakar, you can try increasing the transistor rating and check the response. You can try the concept explained in the above article and replace the BJTs with appropriately rated mosfets to handle 20 amp

    • Hi Swagatam Ji,

      I have to run a 650 watt universal motor, at lower speed .
      I am using MOSFET FQPF 4N60 , 555 IC as driver , at 12 v Dc.
      10 watt LED is showing very good dimming effect at output.
      When I connected 12 volt wiper motor (50 rpm)at output , MOSFET become too much hot within 15 sec time , and motor was running at 4rpm. Pot was at 80% setting.

      Mosfet was running very well in 12 v 2amp SMPS power supply.
      Motor is running very well at 12 volt and taking only 1 amp.

      Would you suggest me how to solve problem-

      1.Mosfet heating
      2.To get full rpm of motor.

      Why not getting trouble in bulb but in motor.

      Devendar Jakhar

      • Hello Devendar ji,

        did you make the circuit exactly as per the 3rd design in the above article? And did you connect the diode and the capacitor across the motor as suggested in the design? By the way your mosfet rating is not appropriate for the application, because it is rated at 600V, 2.5 amps, please try IRF540 instead and see the response!

        For getting full RPM you may have to try the last diagram, using two IC 555, or you can simply try the first design also….

        • Thanks for reply.
          Actually I have to run a universal motor from mains 220 volt. I can’t use traic based controller because of insufficient torque at lower rpm. I think PWM based controller can provide sufficient torque at lower rpm.
          Would you please help to modify ready made controller as shown in ‘Prototype’ just above video.

          Motor watt 650, 220 volt , Rpm 12000 (1400 at output shaft after gearbox)

          Can I use in 4007 for ac to dc conversion, for MOSFET and capacitor based power supply to operate circuit .
          Full load current may be up to 5 amp.


          • If it is a DC motor then your existing circuit is correct, but the mosfet is still not correct, because 2.5 amp is not sufficient for your motor, so make sure to use a mosfet which is rated at minimum 10 amps, which should hopefully solve your problem. You can try IRF840 for the mosfet.

            for making the bridge you must use a 6A4 diodes, 1N4007 will quickly burn.

            • Good morning Swagatam Ji.
              I used K1794 MOSFET for small motor.
              Working well .

              Motor is 12 volt 1 amp.
              At 65 volt dc input motor rpm is 0 to 60.

              While at 12 volt dc rpm is only 0 to 5.
              How to get full rpm (60) at 12 volt.

              When we rotate potentiometer –
              What we change frequency or width of pulse of Gate

              Volt or amperes at Drain -Source .

              When motor is running at full (60) rpm
              pot is at 100% , if I stop motor shaft by hand ,
              Drain -Source amps will increase or decrease or will be constant ?

              Thanks a lot !

            • Good morning Devendra ji, If you are using the last circuit, then the motor should operate from 0 to full range without issues. Here, we only change the PWM, which decides the ON time and OFF time of the motor very rapidly. If the ON time is high motor rotates fast, and vice versa. At full supply voltage at pin#5 of IC2 the PWMs are maximum wide which allows the motor ON time to be almost permanent, as the voltage at pin#5 is lowered the ON time decreases and OFF time increases and motor average speed also proportionately decreases.

              If you try to stop the motor by hand, the drain current will increase and may damage the mosfet, unless the input current is lower than the mosfet current specification.

            • *motor has low torque and a lever is connected with shaft ,and can be stalled easily by hand at full (60) rpm*
              Just add this…

  5. Will there b any problem to my motor if the voltage is 180vdc and i rotate the pot to max 220v. I want to know ur opinion about the 3 circuit u have including the above and the 1 with 2 ic and the 1 wid a 200 turn coil. Which 1 of those will suit my need to control my motor if i use them for a lathe machine. 2motor 1.5hp and 1 thats 2hp. All of them 180vdc. Which circuit will suit if reduce to low speed and the torque will not b sacrifice

    • You can restrict the pot highest position to 180V. You can do this adding a fixed resistor in series with either D1, or D2 with some trial and error and determine a value which precisely gives 180 V at the output. The output could be checked by connecting a 40 watt bulb instead of the motor.

      To set the resistor with one of the diodes the pot should be first moved to one of its extreme ends which produces the max voltage across the bulb, after this the fixed resistor could be added as mentioned above, until the max output is dropped to 180V

  6. Regarding the circuit above can i use a 110v lamp dimmer to replace vr1. Also the other circuit that uses a coil l1 200 turn of 0.6 magnet wire what is the diameter of the iron core to b used. Or can i replace it also with the lamp dimmer and omit the 220k pot

    • In the above design VR1 is a potentiometer and is a part of the IC 555 circuit, it has no relation to a 110V mains supply, only the motor can be associated with a specified DC high voltage.

      I guess you may be referring to some other post.

  7. I’ve made this circuit successfully and it controls the speed of motors and brightness of LEDs.
    But I am disappointed with its performance. The difference between the highest and lowest speed limited by this controller is very less. It’s very hard to notice the difference of speed when the POT is lowest and highest. I only noticed difference when plugged a high power 12V LED.
    How can I increase the motor speed range with this circuit. I believe one or two components can be altered to increase the difference between highest and lowest speed. I am guessing either C1 or VR1 should be of a different value to do this. Could you please advise? I believe, I am looking for a change in the circuit which will increase the difference between duty cycles of the astable multivibrator output.

    • If an LED is working with the circuit, that means the circuit is generating the PWMs correctly. The motor could be having troubles due to low current from the source or due to high frequency.

      If the problem is due to higher frequency, you can try changing the value of C1 to 1uF and see whether that helps or not.

      VR1 is for altering the PWMs and is correctly configured, so it need not be changed

  8. hey guys i am trying to put together something a little different i need to control 12v dc but i need to have and adjustable soft start(start at 30% or 50% ect.) possibly adjustable freq and adjustable max speed with amp draw of about 20 amps is this something feasible

  9. Where do I connect the negative supply from the motor? The motor is 48Volt dc. I assume I connect it to the negative rial off the circuit.

  10. Hey People. I want to use the circuit to dim 6x100w 36v dc LED chips. what mosfet must i use and what diode do i need. the power supply 12v dc to dc 36v convertor

    • you can use IRF540 on a large heatsink, diode won’t be required since LED is not an inductive load.

      feed the 12V to the IC circuit and 36V to the LED. The motor should be replaced with the LeDs….

      • Hey swag
        Can I drive 4 IRF540 mosfet on pin 7 of the 555 pwm. I have 4 side on the LED bar that I want to dim

        the Front will have 6 x 100w LEDs
        Back, left and right will only have 3 x 300w LEDs

        • hey Gysie, that means the total wattage of the LED is 1500watts, can you specify the voltage rating of the respective LeDs, this will allow us to calculate whether IRF540 could be suitable or not….

          • hey swag.
            one led is 100w at 32-36 volt I will be running a max of 9 Led on one dimmer. And a max of 6 on the other dimmer. what about connecting the leds in series?

            Kind Regards

            • Hi Gysie, yes you can connect them in series and limit the current requirement to 3 amps, however from where do you intend to get the voltage source for driving these LEDs, is it from mains 220V directly? and how do you plan to control current for these LEDs? please specify these parameters, it will help me to suggest the most appropriate configuration.

          • [20:57, 9/9/2017] +27 63 773 1688: Hi Swag,

            These led are going to be use on a harvester operating at 12vdc.
            I am planning to use the dc-to-dc with the following spec
            Input voltage:12V-60V
            Input Current:Maximum input current of 15A
            Output voltage:12V -80V continuously adjustable
            Output current:maximum output current of 10A ( adjustable )
            Output power:the effective power P = input voltage V * 10A
            Conversion efficiency:up to 95% ( input voltage, current; output voltage and current impact of conversion efficiency )
            Short circuit protection:Fuse

            The harvester needs 6 LED in front I was thinking of connecting them in parallel.

            then 3 LEDS on the left side, 3 on the right side and 3 on the back.

            I have no problem building multiple dimmer, if you can only help me out with the right amount of led bulbs per mosfet and what mosfet. I can really afford burning out bulbs, it takes about 3 months to get them where…

            Model Type: High Power Integrated Chip lamp Beads
            Chip size: 24MIL*44MIL
            Forward Voltage: 30-36V
            Forward current: 100w(3000mA)
            Luminous Flux: 90-120LM/W
            Color-rendering index: 60-85
            Beam Angle: 120 degrees
            Working Temperature: -20 centigrade to 60 centigrade
            Color Temperature: Warm White: 3000-3200K
            White: 6000-6500K
            Lamp Body Material : Pure Copper Bracket
            Life Span: 100,000 Hours
            [20:57, 9/9/2017] +27 63 773 1688: dan brand hulle
            [21:14, 9/9/2017] +27 63 773 1688: Hi Swag,

            What mosfet do I need to be able to dim 3 of these LeDs connected in parallel at 36vdc?

            These led are going to be use on a harvester operating at 12vdc.
            I am planning on using dc-to-dc converters with the following specs:

            Input voltage:12V-60V
            Input Current:Maximum input current of 15A
            Output voltage:12V -80V continuously adjustable
            Output current:maximum output current of 10A ( adjustable )
            Output power:the effective power P = input voltage V * 10A
            Conversion efficiency:up to 95% ( input voltage, current; output voltage and current impact of conversion efficiency )
            Short circuit protection:Fuse

            The harvester needs 6 LED in front I was thinking of connecting them in parallel.

            then 3 LEDS on the left side, 3 on the right side and 3 on the back.

            Model Type: High Power Integrated Chip lamp Beads
            Chip size: 24MIL*44MIL
            Forward Voltage: 30-36V
            Forward current: 100w(3000mA)
            Luminous Flux: 90-120LM/W
            Color-rendering index: 60-85
            Beam Angle: 120 degrees
            Working Temperature: -20 centigrade to 60 centigrade
            Color Temperature: Warm White: 3000-3200K
            White: 6000-6500K
            Lamp Body Material : Pure Copper Bracket
            Life Span: 100,000 Hours

            Kind Regards

            And thanks a lot for all you help.

            • Hi Gysie, I’ll explain briefly how to quickly calculate the mosfet ratings for your specific LEDs. If we take the example of IRF540, its max current handling capacity (with optimal heatsinking) is around 25 amps, and voltage is 100V.

              The voltage looks definitely well above the specifications of your LeDs and the input supply level, so we can ignore this parameter. and concentrate on the current specs. You just have yo ensure that if the LeDs are connected in parallel with this mosfet the total current (sum) of the LEDs must not exceed the 25 amp limit. If it does then you can simply add another IRF540 in parallel with the existing one, which will instantly raise the capacity of the system to 50 amps, and so on.

              In this way you can yourself adjust and optimize the mosfets with the LeDs in order get the prefect match across the selected dimmers.

              I hope this will help you to understand and optimize your design

          • Hi Swag.
            I only have this last question. Connecting IRF540 in parallel like?

            Gate-to-gate to pin7(DIS) on the 555 pwm ciruit

            Kind Regards
            thanks for your time in helping me

            • Thanks Gysie, yes you can connect drain with drain, source with source and for the gates connect their resistor ends in parallel.

  11. Hi sir, is putting a freewheel diode across mosfet necessary as flyback from motor can damage mosfet, and what can I do if I don't have a freewheel diode, can I use make freewheel using 1N4007 and 1n4148 in combination if yes then how?

    • Hi Abhishek, the value of the diode will depend on the motor current, if it is a low current type motor not above 3 amps, then a 1N4007 can be used…..combination of parallel diodes may not work correctly.

      however today all mosfets have built in freewheeling diodes.

    • Hi Abhishek, it will be difficult for me to troubleshoot a fault in your circuit without practically checking it…the above design is a fully tested and confirmed design, and it is a standard PWM circuit so it cannot be wrong.

      you can do one thing, connect an LED across pin#7 and ground, and check its brightness in response to the pot adjustment, if it varies then your IC 555 section is good

    • OK, then connect an LED from pin#3 to ground with a 1K resistor in series…and check the illumination by adjusting the pot….

    • Hi sir swagatam, bravo, I modified circuit as same shown above and it's perfectly working, now speed is also controllable, thanks for your guidance. New question, I had not added 1N4007 to irf540, so now should I add it and it's not operating 12vdc 775 motor general purpose pcb drill motor, it's 15w. I'm using two 9v battery.

    • That's great Aabhishek, however your previous circuit is also correct and should have worked…investigate why it did not work.

      it is better to add the 1N4007 diode for ensuring 100% safety to the mosfet.

      9V PP3 can be used only for very low current applications, motors will never work with these batts, you should use a bigger battery or many AAA 1.5V cells together

    • Hi sir, through 9v small motors are perfectly working but the 12v 775 motor (15w)not even move. All other motors are perfectly working. Should I use 12v 7.6ah lead acid battery, are you sure 7.6ah lead acid battery will not burn the circuit or ic

    • Hi Abhishek, even a small motor will quickly drain your 9V battery, so it is not recommended for motors.

      you can use 7.5AH batt, it will not harm the motor as long the voltage is correctly matched.

  12. Well done sir, but how can I use MOSFETs IRFP064 to drive a 100V, 10A DC motor on the above circuit, thanks

  13. Hey swagatam , can I use this circuit to power a 3V or 6V DC motor that I will use to drive a small remote controlled(wired) toy?

  14. sir——–i have 35 v load needs 3.3 A current—-around 120 w—–i am providing 12 v dc separately to 555——-

    ——my doubts are

    1——- should i connect 35-0 v dc directly to motor +ve terminal and neutral wire to other side as shown——figure

    2—–approx weight size of heatsink for 200 watts for mosfet

    3—–i have 10 k pot will that be ok

    4———-1 kohm of ??? watts resistor should be connected wiper of pot and 3 pin —prevent pot from burning———–i have a doubt

    5—-1 peice mosfet like irf 540——sufficient for how max watts

    ————-thank you——————

    • Rahul

      1) yes you can do that, but first test with a lamp of the same specs for confirming the actions.

      2) heatsink will need to be optimized with practical experimentation.

      3) yes will do!

      4) pin#2 has high resistance so that may not be required but you can add it, there's no harm

      5) more than 200 watts if heatsink is adequate

    • sir————-thank you a lot————-irf 540—datasheet shows 150 w at 25 celcius temperature———–but in real life almost it is impossible—-to maintain 25c so—-i have to keep 2 irf 540 in parallel——–now there i have some problem—–i tried earlier also with other voltage regulators could not make them parallel—-hogging issue 1 regulator taking more load than other—–

    • Rahul, Just attach the mosfets over a single common heatsink without mica isolator…..this will ensure there's no hogging issue, and by the way mosfets behave oppositely to BJTs as far current hogging is concerned so anyway this cannot be a problem.

  15. hi sir,

    i want to make a wireless system to control 2dc motors.

    2 dc motors180v,1.9amp. this ,motor is connected to a AC source.1 bluetooth is connected to a computer as signal sender & 1 as receiver at motor side,i need a motor driver circuit and ac to dc converter circuit also

    • Hi Lidya, you will require a PWM transmission for this, I have not investigated how to send PWM through bluetooth, so I will have to do some research first before commenting….I'll try to upadte it soon

    • Hi Sir ,
      Thank you for the information & the immediate response.

      I think,this was the mistake i made in explanation.

      The transmitter bluetooth just send the data from the computer (how much the user want to controll) to the receiving side.
      At the receiving side we receives the data from receiver bluetooth & send to ANy microcontroller(i would like to use PIC). This Microcontroller makes the PWM signal for the motor.

      My doubt is,

      1.how can i connect this specified motor (180V,1.9A,1/3 Hp DC Motor)with the controlling signal?(in microcontroller side we using 5V,)

      2.how to convert AC for 180v,19A DC Motor.

    • Thanks Lidiya, got it now.

      you can use the mosfet/motor driver configuration that's shown in the article above and integrate it with your available 5V PWM.

      But mofet might not trigger correctly with a 5V source so you can try replacing the mosfet with a BJT MJE13005.

      converting the 220V AC to 180V DC could be difficult. A possible solution could be through an appropriately wound coil over a laminated iron core which would drop the 220V AC to 180V AC, which could be further rectified with a bridge diode for the final DC

  16. I have a DC motor (77 V and 1.5 A). I want to control speed of 3 such motors simultaneously by PWM. Can you please suggest which IC driver to be used for the same?

    I have a microcontroller board (robokits.co.in/control-boards/rhino-robot-control-board/rhino-robot-control-board-avr-based-with-quick-c-compiler) too which has 5 A motor driver on it but output voltage is 12 Volts. An IC which is compatible with this board would be most welcome.

  17. Using same the circuit with triac it can run AC motor….but how???
    How many triac are required?
    What changes are required in the circuit?
    Which triac I can use any specific for high voltages?

    • connect the gate (left lead) of the triac with the 555 output pin through a 1K resistor

      connect the right side lead with the negative of the circuit.

      connect the the center lead with one of the wires of the load….connect mains with the other wire of the load and the negative of the circuit.

  18. Hai, I bought one motor and one 12v 2amp dc adapter. when I connected the new motor directly to the adapter, the motor is 2 seconds spinning, 2 seconds stopped, spinning, stopped,contiues.. Then I tried with another similar motor (Removed the motor from pcb drill machine,Rating:12-18V, 30watts) with the same adapter, the motor is spinning good. Then I connected both the motors in parallel with the same adapter. Then both motors are spinning good. so can u able to find the reason why the new motor is not spinning continuesly when I connected it separately with the adapter?
    And is there any way to find the rating of a motor? Bcoz nothing is mentioned or labled on the new motor. Its plain.

    • Hai, may be it's due to some improper connection inside the motor or the adapter…because if both the motors are running together then they would do the same individually too.

      Connect an ammeter in series with the motor wire and you can get the amp consumption on the meter while its running.

  19. Thanks
    Your circuit diagram is ok. I added 7812 for 12v for circuit section. 24v for motor. The mosfet I used is 50n06.

    At present I don't have a 470mfd or more value with voltage rating greater than 25vdc to try parallel with motor.I will try once I get it.

    My problems started after I connecting the 470mfd to drain and source. But I need it to avoid buzzing sound at low speed.

    Anyway once again I connected 470mfd to drain and source. I removed led parallel with motor and connected to mosfet gate and ground. Now the led brightnes varies with motor speed. So visual indication issue solved…..! ( Without the 470mfd, led brightness–parallel with motor –varies with motor speed…….! ).

    But motor still rotates at speed more than I want even if 100k pot at its minimum setting. I hope I can solve this by adding a fixed resistor at the middile pin of 100k pot. Not yet tried, will try later..

    I am sharing this post here for helping other readers.

    • OK, thanks very much for updating the info!

      you can also monitor the PWM rate at the mosfet gate with a meter for assessing the proceedings correctly.

    • Hi Swagatham
      At last I found an answer for my 470md related problem from your one another circuit.


      Please read the 2nd paragraph above the circuit diagram starting " However only the average DC voltage is finally fed to the cell phone due to the presence of the 10uF……."

      I suspect, my 470mfd did the same roll of the 10mfd in this circuit. So I cannot attain very slow speed after I connected the 470mfd accross the drain and source.

      Without the 470mfd, I can control speed of motor + and brightness of an LED with 2.2K series resistor across the motor from 0% to 100%……!

    • Thanks Anil, yes that could be the issue, the 470uF might not be allowing the motor to switch OFF completely during the OFF periods of the mosfet. You can try decreasing the 470uF to 22uF which might help to control the noise level of the motor as well as allow complete control of the motor speed.

  20. Hi Swagatham
    I assembled this circuit to control the speed of a 24vdc, 1ampere, 15000rpm motor(mixer motor from an automatic coffee vending machine). It is working perfectly. But at very low speed, the motor does not rotate. It makes only a humming sound.
    When I control the 100k pot, the LED parallel to motor also works from 0 to full brightnes.
    Then I connected 470md capacitor to drain and source. Now I noticed the LED always stay at full intensity. Stil I can control the speed. But now POT at lower side the motor rotates at slow speed, say 10% or 20% duty cycle.
    I need to modify the circuit with that 470mfd and 0 to 100% duty cycle. What changes should I make..?

    • Hi Anil,

      the circuit is actually providing 0 to 100% PWM output but your motor is not responding at lower PWMs due to lack of torque, you can try connecting the capacitor right across the motor leads and see if that helps, because I cannot see any other possible modification for rectifying this issue in the circuit.

  21. Dear sir thanks for your good response , because I use other mosfet for 220 v 5,ampere dc motor but the out put voltage controled from 145 v to 220 v . But my requirement is 0v to 220 v variable… So plz guide me I m waiting plz sir

  22. Thanks swagatam for your good response , I changed mosfet but found not working . Accrording to me that I apply only 220 v dc to only mosfet not connect ground and positive through resistor same as traic to 555 power supply . Sir is I am correct or not ? Dc motor is 1.5 hp. 5ampere . Sir plz send me circuit or guide me with special thanks

    • which mosfet did you use? the ground connections (symbols) shown in the diagram all needs to be connected together (made common)….in other words the 220V (-) needs to be connected with your 555 IC's 12V (-)…..I hope you have use a 12V DC supply separately for powering the 555 circuit,

  23. Dear sir I use this circuit and found wonderful working …nut now today I have a treadmill 220v dc motor so please guide me that this circuit will work properly or not if yes then changing will be required ? Wating your good response with thanks

    • Dear Mohammad,

      you will only have to change the mosfet and use everything as given in the diagram, you can try FQP6N70 if your motor current is within 5 amp

  24. hi, swagatam bro my teacher gave me your circuit as my semester project, but he add some more thing like mathematical modeling and transfer function of this pwm circuit. will you help me to find out these…please

  25. R/Sir,
    In my design I used 220v dc by using 35 A bridge to power Field supply of the motor.@ I used 6A4 bridge to power Armature supply.But when I am connecting the said cct. one 6A4 get shorted.Then I changed the supply bridge to armature and vice versa.till one diode is shorted.The motor is 1.5 hp @ rating 8amp. named dc shunt. So sir please give suggestion to work this motor. Anothr thing is I was used another cct. having 2n5269 in its output.I used bridge for field. and 40 volt dc for armature. the ccct. works nomally.but actually operation is on 220v.this is the total information about this project.since last month I am following your site. which is very nice @ halpful to all. Mostelywhen I am reading the reply from your site it looks like we are siting in front of you @ you are giving explanation of the project.
    lot of thanks.@ wating for the reply.

    • Mukund, I do not have much experience with motors that are designed with two winding, I'll have to study more and only then I would able to suggest you correctly whether your implementation is correct or not.

      I'll try to do it soon, once I finish other pending assignments.

      keep in touch until then….

    • R/Sir,
      After long time I am making contact.Sir If there is any Idea about controlling the pwm motor with field and Armature with 220volt supply? hopping to be excused. Waitin for your plesant reply.

  26. R/Sir,
    I am willing to control 2hp dc motor.having field 220volt @ armature is 200volt.which cct. is suitable to control the motor by armature supply variation.These motors are used in printing industry. I hope that you will give me a proper guidance.

    • Mukund, if it's a DC motor then you can try the circuit that's presented in the above article, it's a PWM circuit and well suited for controlling DC motor speeds

  27. Hi swagatam.
    I'm trying to use this circuit to control speed on my radiator fans in my truck
    (dual fans, 15 amps each, wired in parallel) based on temperature.
    the temp sensor is fastened to ground with one wire out

    what I came up with was to put the sensor between the 555 GND so as to vary the gnd supply to the 555 based on temp. I know this is not the ideal way but is all I could come up with.

    Also wondering about mosfets, I have a couple that are rated at 30vdc and 70 amps
    so by all means one of these should do the job right?
    …just find it hard to believe that one of these could power such large fans..
    any help will b greatly appreciated, thank you.

    • Hi Henry,

      your idea regarding using the sensor with pin1 of the IC is technically incorrect and inapplicable, so that won't be feasible.

      However pin#5 can be targeted for delivering the purpose by using BJTs, mosfets won't be effective, if possible I'll try to figure out the design….

      I would be interested to know about the output from the sensor at the peak temperature (at the desired cut of threshold)

  28. Hi swagatham,
    Thank u so much, now the circuit is working perfect, I have two more doubt.
    1.) Can I use a common (parallely connected )potentiometer for two circuit ( as I'm using this for a robot car, there will be two motor left and right both working by different but speed should be maintained same)
    2.)I want to switch frequently so If I use the switch on after the MOSFET while the circuit is on continuously I'll control the motor through the output, is that cause any damage to circuit?

    • Thanks Swarajit, I am glad to know it's serving the purpose.

      1) you can use a dual pot for implementing a simultaneous operation of the two circuit's PWMs, in sync

      2) you can use a DPDT switch in series with the motors, it won't do any harm to the circuit functioning.

  29. Hi swagatham,
    I tryed this circuit in bread board,I'm using 12v, 7 amp motor 2nos connected parallel so the load is 14 amps. It is not working when I tune the pot in one place motor start running in full speed and after that not working. I do no where I made mistake please guide me.
    IRF540N is the MOSFET
    Waiting for your reply…

    Swarajit Alakananda

    • Hi Swarajit, first confirm whether your 555 is working correctly or not.

      remove the mosfet and the motor from the circuit and connect an LED with a 1K resistor across pin#7 and ground of the IC….now adjust the pot around and see if the LED alters its intensity from zero to max and back….if this is not happening then you could assume something to be not correct in your circuit.

    • Hi swagatham,
      Yes as u said something to be wrong in the circuit. Do u have any breef images or vedio to guide, because it will be help me better…

    • Now my circuit is OK swagatham, the problem is I can't feel much difference in the motor speed

      If i use a high amps MOSFET for low amps motor will that be an issue …..
      I'm using IRF 540N, For a 7 amps motor..

  30. Thanks so much Daan,

    I think the above 555 circuit can be used without any issues for your application and it's a good and a reliable option to begin with.

    The mosfet parameter is not relevant to the circuit, that means any mosfet with any voltage/current specs can be used with the shown circuit.

    I have not yet researched on the concept of a resonant HHO generator but I think it's an interesting topic to investigate on, and I will surely look into it and try to post an pertinent article. Thanks and do keep in touch!

  31. Hey Swagatam, I am an engineering student trying to build a pwm to control a 24v 750w motor. This will be used to power a 250lb vehicle with a driver weight of 150lb. I am a mechanical person and am new to circuitry. I can't seem to view your schematic that is supposed to be with this article. But do you think it will work with my application? I plan on using a potentiometer in order to control the speed of the vehicle. Thanks in advance

    • Hi James, yes definitely the above shown design can be used for your application.

      Just make sure the FET is rated to handle 50V 1000 watt, and the 555 IC is supplied with a stepped down 12V through a 7812 IC regulator.

  32. What would happen if this was used on an AC motor? Power all the control ckt with the proper DC voltage, but put the FET in series with an AC motor.

  33. Dear sir,
    I am a mechanical guy,currently working on an electric vehicle and i want to control the speed of my motor using pedal . i am not getting a controller for my motor please help me to build my own i''ll be highly thankful
    Motor Specifications are 36volt,43ampsand 1.5hp brushed dc motor

  34. Dear Sir,

    I am a beginner.

    Can I use the above circuit for my treadmill with 180V 6A 4200 RPM DC Motor. I would like to use the mill only for normal walking of about 30 to 45 minutes in normal speed.

    Can I reduce the RPM to my desired speed (only for walking with speed of 4 to 6 KM/hour) using the above circuit. If I use the POT, what would be the changes in the RPM when the POT gets in to its maximum and minimum positions. If I can use the above circuit, pl suggest me the appropriate MOFSET for the above load.

    I went through all your reply and it is interesting and valuable. I really appreciate your patience and commitment.

    Sir, my thanks to you in advance

    Shine K P

    • Thank you dear Shine!

      yes, according to me you can use the above circuit for your said application.
      The maximum achievable speed is near 95% and the minimum is near 5% so it's pretty efficient with its control spces.

      You can use IRF840 as the mosfet.

    • Dear Sir,

      Sorry for bothering you…..

      I tried this circuit but in between got stuck because, I am not finding any way to bring 12V dc to IC 555 as my rectified DC is 180V, which I am using for motor, in the board. I believe, I cannot connect LM7812 directly to this volt. Can you please help me on this?

      Thanks & regards,
      Shine K P

    • Dear Shine you can use any standard 220V to 12V AC/DC SMPS power supply for this….you can get it in the local market,

      even your phone charger will work for the time being.

    • Dear Sir,

      Thank you for your mail…

      Sir, then I have to connect Ground of 180V DC supply to Drain pin of MOFSET. Am I right sir?

      Shine K P

    • Dear shine,

      the drain will connect with the (-) of the motor, please see the diagram above.
      The (-) of the 180V will become common with the (-) of the 12V supply…..the motor (+) will connect with the (+) of the 180V supply

    • Dear Sir,

      I tried this

      1)Motor didn't run when the power on
      2)When I turned the POT, it started running but immediately 555 got burned and MOFSET as well LM7812 also got hot.
      3)Even though the smoke was comming from 555 motor was running.
      4)I checked the circuit and found no short circuit.

      Sir, what could be cause for this? Can you pl advise me…..

      Thanks & Regards,
      Shine K P

    • Dear Shine,

      I recommended using a separate 12V AC/DC adapter for powering the IC stage…not a 7812 IC so please build it again and power it as suggested.

      also connect a 6amp rectifier diode right across the motor coil in order to safeguard the fet from motor back emfs.,

    • Dear Sir,

      I didn't get 12V AC/DC Adapter but got 15V AC/DC from my nearest shop. That is the reason, I used 7812 to get the regulated 12V DC to IC.

      1)Should I use 12 AC/Dc adapter and remove 7812?

      2)Sir, I joined both -ves (180 and 12) and grounded wherever it is mentioned in the circuit, even to source of MOFSET. Hope it is correct.

      3)Offcourse, I can connect protector diode and will try again.

      Thanks & Regards,
      Shine K P

    • Dear shine,

      yes, 7812 with 15V input is perfectly fine, and making the negatives common along with the fet source is also perfect….I think attaching the diodes across the motor should solve the problem.

    • Dear Sir,

      I connected the 6A4 diode across the motor, now IC and 7812 are okay but MOFSET is getting hot. I think, the MOFSET got damaged while it got heated last time.Now motor is running in its full speed. No control on POT and MOFSET is getting hot also.I put heat sink for MOFSET and 7812. I noticed, even without inserting 555, motor is running in its full speed.I checked the POT and it is working fine. Let me change the MOFSET. I would require your hep sir….sorry for bothering you.

      Shine K P

    • Dear Shine, if without IC the motor is running that surely indicates a faulty mosfet…try using two mosfets in parallel for ensuring better safety to the mosfet and reducing heat dissipation

    • Dear Sir,

      Thank you….noted your suggestion. Let me try this also. Can you please advise me on below

      1)PIN 7 of 555 will be connected to GATES of two MOSFETs seperatly. Do I need to need to add 10k again? ie Do i need to add 10k before each GATE?

      2)DRAIN of two MOSFETs will be joined together and connected to -ve of motor

      3)SOURCE of two MOSFETs will be grounded.

      Am I right sir?

      Shine K P

    • Dear Shine, the 10k need not be repeated, pin7 needs to be connected with each mosfet gates via separate 22 ohm resistors.

      next, drains will join together and connect with the motor negative, sources will join together and connect with the ground

    • Dear Sir,
      I tried with two MOSFET and connected 22 ohms resistor also. It was working fine.When I applied the load (I started walking), the motor was about to stop but when I increased the POT , motor started running for my desirable speed for walking but suddenly MOSFET got burned. There was some noise from motor while in low RPM. 6A4 diode is already connected across motor coil.

      Can you please advise?

      Shine K P

    • Dear Shine, that's perfect, the IRf840 are rated to handle 500V at 8amps so it shouldn't be a problem…there could be two possibilities either your motor is drawing over 16 amps when loaded or the mosfets are not original.

      you can try connecting two more (4 total) mosfets in parallel in an identical fashion as explained previously and check the response

  35. hi,
    what power supply and mosfet should i use for a 180 to 220vdc motor, as well as adisplay in the circuit to show the motor rpm

    • An IRF840 mosfet could be tried, power supply should be DC and as per the maximum rating of the motor….for RPM you'll have to procure a ready made RPM meter and integrate it with the motor.

  36. Hi, that's completely rubbish…if the motor is specified to run at 12V it can be safely connected with any 12V supply (regardless of the amp rating of the supply).

    shunt resistor may be required for protecting the power supply (SMPS) from the back emf that may be generated by the motor…. so its the power supply that may need protection with a shunt, not the motor.

    The above may be true only with big heavy duty motors only….not in your case.

    • Thanks for the clarification… so the shop man cheated me by giving a damaged motor itseems :-(… Now am having a 12v, 0.28A DC motor. I like to use this motor in ur above circuit. so Could u tell me that wat mosfet i can use for this??

    • mosfet may not be necessary, you can use a TIP122 in its place and connect the motor as indicated (across collector and positive)

  37. Hai, I bought one 12v dc motor. I connected it directly to the 12v adapter. Then the motor is running in a pulse mode. Means like clocks seconds needle moving. running, stopped, running, stoped. like that. When i asked abt this to the shop man, he told that the motor got damaged due to directly connected to the 12v power supply, a 12v motor should not directly connected to a 12v power supply, It should connected through shunt (resistor). But he dont know what resistor have to put.
    Could u tell me, is that correct which he told?? and wat resistor i have to connect between the motor and the power supply if I want to connect the motor directly to the 12v power supply?
    Now I bought another motor which is rated 12v ,0.28A. I like to connect this motor to ur above circuit. so still do I need a Shunt (resistor)?? and wat value, rated mosfet I can use for ur above circuit?

  38. Is this circuit 0 to 100% duty cycle? I want the frequency to be constant 60 Hz. How would I do that?
    Using this formula? F = 1.44(VR1*C1)
    Based on your circuit you put 100k for vr1 and 0.1u for c1. Frequency will be 0.0144 hz?

  39. the pot control is for speed control, it has no relation with current….use a 2amp fixed current power-supply for getting the required current restriction.

  40. In the diagram no resistor is indicated, but you can use 100ohms with the gates, will be OK.
    4amp will not give you 15amp….you will need a 15amp supply for that.

  41. Connect the mosfet leads in parallel, use separate resistors for the gates.

    And do not short circuit the positive with drain, this will instantly blow off the mosfets.

  42. Thank you for you speedy response. I would have commented earlier but i was waiting for an email telling me you responded. (never came) could you please verify for me the value of R4. i believe that should be 2k ohms.

    also one other thing, From what i gather, adjusting pot at pin 5 will control the duty cycle, but could you please explain how i would go about adjusting the frequency should i need to. I have built your other PWM circuit and it worked great. (using one 555ic)

    I remember a time back when i was in air force tech school when i could of done all this with my eyes closed. they were very thourough. its amazing to me how only in a few years i could forget so much!

    • My replies here are supposed to reach the commentor in their email IDs, you should find these discussions in your email inbox, according to me.

      Although the frequency has no relevance to the motor speeds, it can be controlled by varying R1 or the 180k resistor value.

      I am sure the discussions here will help you to restore all you had learned back:)

  43. So much SWAG! 🙂

    Im trying to build a PWM controller for a dc motor that runs a fluid pump. I know it would need 0-100% control, but I also think that your constant torque circuit would be better. (since i need to deliver exact amounts of fluid) However the constant torque circuit you provided shows a bi-directional motor and I could not follow your text instructions for making it single direction. I would like to be able to adjust frequency, and pulse width. Circuit will a regulated 8v from the batterypack/power supply. Can you maybe point me to a good instructions page to build for this? (motor "on time" will be determined by a lookup table using a micro processor, but thats a whole nother issue)

    • Thanks JC,

      Please refer to the following diagram, you can try this design:


      Connect your motor across the drain and positive of the circuit…please ignore the bridge rectifier it's not meant for us.

      The shown PNP transistor is BC557 and not BC547 as wrongly given in the diagram.

      The pot at pin5 of IC2 can be used for controlling the speed,

      The mosfet can be replaced by a power transistor, if desired. In this case use ordinary 555 IC, and not 7555.

  44. for zero to 100% speed control you will have to make the following circuit, the above circuit will not provide 100% control:


  45. The power supply rating should have a voltage rating exactly matching to the load……current is immaterial, but should be higher than the load, if it's lower, the voltage will drop.

    The mosfet can be anything…just needs to be rated at least twice to the load rating, if it's higher no issues, but preferably shouldn't be lower.

  46. HI,
    You may misunderstand me… You know my motor have 18k rpm in no load and about 5k rpm when connected to 4v 3 amp battery and about 10k rpm on 6v 4.5ah battery.

    For got about my stupid TDA7274 circuit. its giving me about 700-900 rpm to me which is not any value and its not giving me any airflow that can I feel from 12" far.
    So I want to through the Circuit to the dustbin as its useless and the IC is getting about too many hotter, you can feel that it can cook your rise in 10 minutes. So I am pretty sure the circuit will not last long and it can be make any damage as its hotting up.

    Now I want your help, I hope you seen my motor and which fan I connected (s10.postimg.org/7da0t1c6h/2013_07_16_02_25_04.jpg)

    Please give me any circuit that can drive my motor with this fan (load) at 2-4 k rpm. I found that my motor is stable on this RPM but it getting hot if I it go to more that 5k rpm.

    Please don't leave me alone here. want your help,

    Awaiting to hear from you.


  47. The same circuit can be used for your application too. Just make sure the IC circuit gets around 12V supply derived from the 90V supply.

    The motor can be connected with the 90V supply directly in the manner shown in the diagram.

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