In this post I have explained how to make a simple variable power supply circuit using transistor 2N3055 and some other passive components. It includes variable voltage and variable current feature, fully adjustable.
Main Specifications
1) Adjustable from 0-30V, 0-60V, and 0-100V, and 500mA to 10 Amp as per user preference
2) Short Circuit Protected when mounted on proper heatsink
3) Ripple free, with less than 1Vpp
4) Output is Stabilized and filtered DC
5) Short circuit LED indicator
6) Overload Protected
Introduction
A power supply circuit that does not include the features of a variable voltage and current control can by no means be considered truly versatile.
A variable workbench power supply circuit I have explained in this article is not only specified with a continuously variable voltage control but is also equipped with the feature of overload or continuously variable current control.
Circuit Diagram
How it Works
A keen look at this 2N3055 based variable voltage current power supply circuit using transistor 2N3055 reveals that it’s actually only an ordinary stabilized power supply circuit, however it yet still provides you with the proposed features very efficiently.The voltage variations are made by using the preset P2, through a feedback configuration employing the components D1, R7, T2 and P2.
The inclusion of D1 makes it sure that the voltage can be lowered right down to 0.6 volts, which happens to be the forward voltage drop of the diode.
If any other specific minimum value is required then the diode can be replaced by zener diode having the required specified value.
Therefore in this variable power supply circuit using 2N3055 transistor, the transformer being a 0 – 40 V, the output becomes variable right from 0.6 to 40 volts maximum, that’s very handy indeed.
For implementing the current control feature, T3 along with P1, R5 and R4 are involved.
The value of R4 is specifically becomes responsible for defining the maximum allowable output current.
P1 is set to choose the maximum range within the value that’s marked or identified by the resistor R4.
PCB Design
Parts List
- R1 = 1K, 5 watt wire wound
- R2 = 120 Ohms,
- R3 = 330 Ohms,
- R4 = to be calculated using Ohms law.
- R5 = 1K5,
- R6 = 5K6,
- R7 = 56 Ohms,
- R8 = 2K2, P1,P2 = 2k5 presets
- T1 = 2N3055,
- T2, T3 = BC547B,
- D1 = 1N4007,
- D2, D3, D4, D5 = 1N5402,
- C1, C2 = 1000uF/50V,
- Tr1 = 0 – 40 Volts, 3 Amp
2N3055 Pinout Details
If you have any doubts regarding this variable voltage and current power supply circuit using transistor 2N3055 circuit please do not hesitate to ask then through the comments below.
Original Transistor Power Supply Diagram:
The above design was inspired from the following circuit which was designed and presented in the elektor electronics magazine by the elektor engineers:
Simplified Variable Power Supply Design using 2N3055 and 2N2222 Transistors
The above designs were assessed and simplified with more effective results by Mr. Nuno. The revised and simplified design can be viewed in the following diagram:
The design features an over-current shut down with LED indication.
Video clip of the tested prototype:
For PCB Design and other Related Data, you can Download the following ZIP File:
PCB Design for the above Circuit
Another Similar Power Supply Design as Referred by Mr. William C. Colvin is presented below for the viewer assessment:
2N3055 Wide Range Variable Voltage Regulator
The key highlights of the circuit are: wide range output: 0.1 to 50 volts excellent load regulation: 0.005% between 0 and 1 amp, decent line regulation: 0.01%, reduced output disturbance: superior to 250 microvolts.
The broad output selection is implemented with thehelp of the integrated circuit CA 3130, that is able to work even with a zero volt input/output differential. In addition, higher extension of the output range becomes feasible through the inclusion of T4 between the IC and the series pass transistor.
The high gain as a result acquired enables a superior level of regulation, and the T1/T2 Darlington pair offers a adequately large current boosting. T3 works like an output current controller.
When P1 is rotated totally anti-clockwise, T3 restricts at 0.6 amps. The limiting circuit becomes inactive when P2 is moved completely clockwise. The regulator circuit specifically operates in the following manner.
The IC CA 3130 analyzes the output voltage given to the non-inverting input with respect to a reference voltage at the inverting input.
The output voltage of the regulator is reduced with a potential divider to protect against damage to the IC.
The reference voltage is determined by P2, which needs to be a top-notch part, since any kind of noise upon its slider arm will probably be transferred to the regulator output terminals.
A additional IC, HFA3046 , offsets the reference voltage intended for temperature variations. The IC is made up of 4 transistors applied as diodes or zener and another transistor for cutting down the output impedance of the reference circuit.
The reference IC furthermore provides a stepped down supply voltage for powering CA 3130. This feature necessitates the use of each ICs in the regulator stage; if IC1 is removed can result in the break down of IC2. Each of the transistors shown in the diagram must be rated with a breakdown voltage of a minimum of 55 volts.
High Current Variable Power Supply
In this high current linear power supply circuit, we have used a 2N5686 transistor instead of 2N3055, so that the circuit is able to deliver a minimum of 10 amp current, and the preset P3 could be used to adjust a current range of 10 amp.
The power supply itself is pretty straightforward to construct. An IC LM329 provides a steady reference voltage of 6.9 V.
P4 is a potentiometer, and this pot is utilized to determine the output voltage using a preset potential divider P2-P4-R2. The power stage of the circuit is made up of IC1 and T1, which operate like an operational amplifier when it comes to positive voltages (negative voltages are not relevant here, obviously).
This non-inverting amplifier is built using an combo of op amp, P1, R5, and R6. This indicates that the voltage at P4's wiper is proportionate to the voltage across the output terminals.
P1 is a potentiometer that controls the peak output voltage, while P2 is used for setting the minimum output voltage from the power supply.
Preset P3 is used for setting up the maximum current limit of the output.
R11 converts the output current to a voltage to accomplish this. When this voltage (controlled by P3) is large enough to turn on T2, the circuit's voltage regulation is superseded by current regulation through IC1's strobe input. The maximum current that can be adjusted is from 0.8 A to 10 A, depending on how the controls are adjusted.
When the output of the power supply are short-circuited, the current must not increase above 25 A to prevent T1 from being damaged and due to over dissipation. The circuit setting up is not complicated. To begin, adjust P4 to highest possible resistance and wait about a minute until Z1 and IC1 reach their typical working temperatures. Next, adjust P1 to get a 25 V output voltage.
Finally, tweak P2 to provide a 250 mV output voltage by setting P4 to lowest resistance. The lowest output voltage of 250 mV was selected on purpose to guarantee that the individual parts always are able to work with a linear region of their characteristics. There are a couple of things to remember here: the earth lines must be routed exactly as shown in the schematic, and T1 must be installed on a 1.5 K/ W heat sink.
Questions & Answers
use the scan that is below first scan it is cleaned up better I used photo paper which allows scraping ink from pathways after printing with laser printer because i erased text from image there seems to be artifacts of it still showing up in traces so it still needs to be examined before final transfer to pcb.
Thanks very much mike, it is nicely done, I hope the readers will find it very helpful…
also filled Scan2025-02-20_233920.pdf
Thanks very much Mike, I extracted the image from the pdf, here it is:
i am trying to send image again dont see it and trying again
The above image is not clear, but your pdf image is very good, so I have extracted it and processed it as below:
I hope converting the pdf file to zip file is good enough smaller” I did have to take a sharp object to my toner transfer sheet printed out pcb and open up pathways before transfer to pcb which is much easier than cutting copper this is the same pcb layout as the one seen in article minus text writings on it and added copper where possible using it maybe will do more amps ?.
Yes, the pdf version is smaller and without any issues, i could quickly convert it into a jpeg image.
Thanks very much for the kind efforts, much appreciated.
I am working on the next design and i do not understand why the voltage drop is so much more a 600-ma load bring it to 7-8 volt drop compared to not loaded a 3 volt drop from impute compared to output. a variable workbench power supply and I duplicated the pcb used as a example with much thicker traces similar to first circuit trying to improve it.I have went thru all comments trying to learn all that I can about the large voltage drop and I must say I still don’t understand it or what to do next i have used a jumper for r-5/and r-6 based on comments. I am thinking about doing the idea not explained very well about a Darlington configuration and maybe see what exactly is how to do it if you think that is the solution if there no way to fix the circuit i would like to know but I am trying to learn why its doing that I guess that’s the real point here is learning how things work I don’t understand what’s wrong with it or if that’s normal for this circuit using that pcb design?? thank you for a response ahead of time and I hope you can spare time for me even though i haven’t been to school and don’t know some simple obvious thing about this circuit i am trying to figure this out on my own i don’t want to waste your valuable time anything would be sincerely appreciated I will share the pcb if its ok to i don’t know, it is filled copper and looks different but seems like it isn’t intended to be shared so I think I would need permission ?? also may be flawed ? but does seem to work? 20 vin and 12v out under 600 mA load. no load 17v out from 20vin. should I abandon or try something to improve it I can’t figure it out.
The output voltage will drop if the pass transistor is not able to supply the required amount of current to the load.
Yes, Darlington is the key to this problem, which will help boost the current for the load and solve the voltage drop issue.
You can try a TIP142, which is a Darlington BJT, and check the response.
Sure, you can upload the PCB, i will check it out. If possible please reduce the size of the image to a smaller scale before uploading…
Thank you very much for your detailed analysis.
top side mr nuno build with silkscreen provided and as toner transfer method used with slight changes of components orientation’s the tracks are the schematic exactly q-4 belongs in q-5 position and q-5 replaces it then is spun 180 degrees also spin q-1 180 degrees
Thanks so much for providing the detailed pictures of your prototype. I hope the all the other readers will find these very helpful.
one more
here is another pic cant seem to do more than 1 at a time
i have said mv and mean mA in my post you probably knew that but there it is sorry for any confusion.
Ok, no problem…noted!
hello i am posting some info about the mr nuno version circuit having done the build using the toner transfer method and using the plans provided thanks for that it works nicely as exactly shown in schematic but there is changes to do first before soldering transistors in place as for using silkscreen layout on the board. 1 switch q5 with q4 then turn q-5 the same direction as q-4. 2 turn q-1 around facing away from 3055. 3 beware that the pads for 3055 are arranged c/e/b when facing component ,you likely will need to move it to a heatsink regardless off board a large one, if you use a large adjustment range like 10v difference from input and output no more than 700mv as built by me using same parts as described in schematic cheap parts as a matter of fact except for 3055 i used a 2sc5200 on a 10cm+8cm+15mm heatsink probably twice the size needed but was handy i experienced a 2.6v drop compared to input v that’s better than other designs i have built. the led will start to light up after encountering under voltage. when that happens i have found that 1 extra turn of the 5 k pot what i had gets a clean noiseless output back on track so that is a nice feature, if you have a scope make sure to probe the collector of q-1 or q-3 to see the limit you want to know about on these things when stretching it 10–11 v i used the board as thru hole mounting plenty of room for it. so without mods its doing 700mv no problems and at 10-11v difference from input tried 1.2 amps and it got hot quickly q-1 q-3 so maybe better parts ? will do better. so i hope this is useful for someone and thanks for the whole package on this design. thankyou
Hi, thanks for the update, much appreciated.
However a picture upload could have been even more helpful.
Since this design is a linear regulator circuit, the device will get hotter as the input/output difference is increased.
Nevertheless, thanks very much for your detailed explanation.
thank you for the responce i will use schemtic i did the toner transfer method and did not want to just power up without checking for mistakes first i am a hobbyist and am learning on my own and what i can pickup from others.
Sure, no problem! I understand! Let me know if you have any further doubts.
thanks not so in advance oops/ another question how do i subscribe i see no page to join doesnt just allow password email?
Once your comment is replied by me and approved, you will get an email notification along with a “Subscribe” link, when you click on that link you will be automatically subscribed for all the future comment reply notifications.
i am building the nuno vertion and i would like to know if the silk screen is accurate depiction of componant placement or is the schematic acurate and thus requires complete difrent placement and oreintations of transistors q-4-5-1
The component placement is not critical, so you can place it as per your convenience. I would recommend the schematic placement so that you can align the prototype with the schematic design, which can make the testing and troubleshooting easier.
Dear Sir, Thanks for your prompt response. Could you please guide me to configure the TL431 (R1,R2,R3) as the voltage input in the given circuit is 30V, and my transformer Output is 60V @ 10A.
Hello Imsa, please use 4.7k 1 watt for the R2 resistor. No other changes would be required.
For 10 A current you may have to use a 0.033 ohm 2 watt for R20.
Thank you very much for the sound plans where you sent me to build a power supply – what is interesting for me is the power supply 1.5 -30 volz 10 Amber adjustable as a rule, I would like to thank you in advance
You are most welcome IOANNIS!
Sir,
Can I connect 4(four) Nos.3055 in your circuit above? I like to charge 4Nos 12V 60AH batteries and also use it as a Lab power supply.
Can I use 10K for (P1,P2) ? if so, any changes/replacements in circuit required?
Thanks in anticipation.
Hi Imsa, adding 4nos of 2N3055 to the above circuit may not be a good idea, instead I would recommend you trying the following circuit:
Let me know if you have any further questions….
Thank you very much indeed for your express reply. However, I like to have 58-60V output. with 10Amp. How do I go about it ? Can you please advise?
OK, in that case you can try the second design from the following article. You can change to mosfet to any 100V mosfet. Remember not to connect the filter capacitor at the input side, instead connect it at the output side, this will help the mosfet to dissipate proportionately less heat.
https://www.homemade-circuits.com/0-300v-variable-voltage-current/
How to adjust the current from 0-10A in order to make it a Variable Voltage, Current Power Supply ?
You can replace R2 with multiple calculated resistors and use a rotary switch to select one of these resistors for the desired current control.
Sir, I like to have – Adjustable Voltage from 0-60V, and Variable Current from 0-10 Amp. (without using rotary switch) similar to your first circuit above.
I have a Transformer rated at 60V 10A.
Can you help ?
OK, you can try the following circuit, you can increase the input upto 60 V by appropriately adjusting the circuit:
https://www.homemade-circuits.com/universal-variable-power-supply-circuit/
I am having 19.5v 4.5amp Sony LED tv power supply unit I want 0 to 18v&0 to 4.5amp power supply unit using single fet transistor
You will require an SMPS for that, and unfortunately I do not have an SMPS circuit with a variable current feature.
Dear Swagatam,
I also need to make ~150V AC-DC linear voltage regulators. Its current capacity need to be higher than 200 mA. I am not familiar with a transistor based voltage regulators, but I think that I need a transistor based regulator to build a high voltage (~150V) regulated power supply. Can you comment how I can get 150V 200mA voltage regulator? Which components can I change from your 2N3055 based regulator?
Thank you,
Chang
Hi Chang,
I would recommend you to try the SECOND LAST circuit from the following article:
https://www.homemade-circuits.com/0-300v-variable-voltage-current/
However, remember, since this is a linear regulator the transistor might heat up a lot as the difference between input and output voltage increases.
Dear Swagatam,
I am still studying regulated high voltage power supply.
My wanted output voltage can be 100~125V. If I changed a transistor from 2N3055 to MJ15001, do you think I can get 125V output?
I am designing an instrument, which is very sensitive to electrical noise. I might use 2n3055 based regulator for 100V output power supply.
Can you tell me which method(transistor based regulator or MOSFET based regulator) produce lower noise for 100~125V output power supply ?
Thank you,
Chang
Hi Chang,
Yes the main pass transistor can be changed to MJ15001 for handling 125V output.
I think noise can be removed by adding a 100uF capacitor across base/ground of the mains transistor, as done in the following circuit:
The capacitor C1 will reduce noise drastically and make the output noise free.
Dear Swagatam,
I found another transistor 2n3773, Vcb of which is 160V. Do you think that 2n3773 is more safe than MJ150001?
I planned to modify the circuit, designed by Nuno Figueiredo.
Current limit will be 0.2A, so R5 will be 3 ohm.
I will remove Q4 BC547 transistor.
Since the unregulated voltage will be around 130 V,
-2N3055 will be replaced by 2N3773 or MJ150001.
-The two diodes will be replaced by 1N4007.
-R1 will be 1Watt 33kOhm.
-RV1 will be 2Watt 20kOhm potentiometer.
-C1 will be 100uF 200V.
-C2 will be 1000uF 200V.
Do I need to modify more the circuits of Nuno Figueiredo?
Thank you,
Chang
Hi Chang,
Since yur maximum operating voltage is 130V so both the transistors will work and both will be safe.
I think Q1 and Q2 will also need to replaced with a higher voltage transistor. You can replace it with maybe a 2N3501
The remaining specifications look fine to me.
Dear Swagatam,
I designed a 120V, 0.2A power supply using 2N3773, 2N3501, and I confirmed that the 120V power supply is working. Now I have to make a low noise 200V, ~0.3A power supply at the other my project. When I checked your website, I found three options. Can you recommend which option will be best for the low noise 200V, ~0.3A power supply?
1.Variable Voltage, Current Power Supply Circuit Using Transistor 2N3055 , after modifying power transistor (https://www.homemade-circuits.com/how-to-make-versatile-variable-voltage/)
2.0-300V Adjustable MOSFET Transformerless Power Supply Circuit (https://www.homemade-circuits.com/0-300v-variable-voltage-current/)
3.600 V DC Voltage Regulator Circuit Module (https://www.homemade-circuits.com/600-v-dc-voltage-regulator-circuit-module/)
Thank you,
Chang
Thank you Chang,
I think the 0-300V design looks perfectly suitable for your application.
However, to make it safer for the MOSFET, you can add an input current limiting capacitor to this design, as shown in the following diagram:
Dear Swagatam,
When I looked at the 0-300V design, the maximum current is 100mA. Do you know How I can increase the current to 300mA? Thank you,
Chang
Hi Chang,
You can replace the 3.3 ohm R2 resistor with a 1.8 ohm resistor, this will enable to to get the required 300 mA current output.
The formula is:
R2 = 0.6 / Max output Current
Hello,
I want to make low-noise and fixed output linear regulated power supplies.
The current output can be 100mA or higher than 100mA, and the fixed output will be 9V or 12.8V.
When I looked at the ripple noise level of commercial low noise power supply is about 1mVrms.
Can you comment which device (2N3055 based regulator ,or LM317 based regulator ) can produce lower noise power supply?
Thank you,
Chang
Hi,
The LM317 will produce lower noise, especially when the appropriately rated capacitors are connected across its input and output terminals.
Dear Swagatam,
Thank you for your reply. I have a following question about the low noise linear power supply. If I use a second regulator (like low-noise TPS7A47 LDO regulator) after the LM317 regulator, do you think that the noise level will decrease more?
If the second regulator works, can you recommend other low noise regulators?
Thank you,
Chang
Hi Chang,
Yes, since the TPS7A47 is an ultra-low noise regulator it will reduce the noise to a great extent. However if you are using TPS7A47 then what is the need of LM317 regulator? The LM317 can be avoided completely according to me. I will try to investigate more such regulators and let you know, if possible.
Dear Swagatam,
I have never made linear voltage regulator. However, when I read about LDO voltage regulator online, inputs of LDO regulators are usually batteries or kind of “regulated” voltage. The datasheet of TPS7a47 also suggest that the TPS7a47 can be used for post dc-dc converter regulation. I feel that the input of TPS7a47 should be regulated voltage not be un-regulated voltage if it works best. If I am wrong, let me know.
Thank you,
Chang
Thanks for the clarification Chang! I agree with you. The LDO must be fed from a regulated DC supply, therefore using a LM317 based input makes sense.
Dear Swagatam,
I tested linear voltage regulators, using LM317 with LT3045 and LM337 with LT3094. I am happy with my setup although I need further test to reduce some noises including EMI. I think that both LT3045 and TPS7a47 have low noise voltage outputs. I chose LT3045 since the range of its voltage and current is smaller than TPS7a47’s, so its noise level will also be smaller than TPS7a47’s.
Thank you,
Chang
Thank you so much Chang, for updating the valuable information. Appreciate it!
I’m a recently retired software engineer trying to teach myself electronics. I have no trouble understanding the amperage control part of this circuit. I’m still trying to understand the voltage control side of things. Can someone recommend some reading that will help me understand how that part works? Thanks.
I will try to explain you. The transistor T1 is configured as an emitter follower, which means that its collector voltage will be always equal to it base voltage minus 0.6V. Now, the base voltage of T1 is controlled by T2, so at any given instant, depending on the setting of P2, the T2 will try to cut off the base voltage of T1. For example, if suppose P2 is adjusted such that once the collector voltage of T1 reaches 9V, T2 is switched ON. This means that at 9V T2 will switch ON. When T2 switches ON at 9V, T1 base will be cut off at 9V. Now, since T1 base is cut off it will turn off and its collector voltage will begin dropping below 9V. When this happens T2 will again switch ON, and this will allow T1 to switch ON again, and the voltage at its collector will again try to reach above 9V, which will yet again cause T2 to switch ON….and this cycle will keep repeating ensuring that the collector voltage of T1 is constantly held at 9V, so the output will be at 9V. In this way P2 can be adjusted for getting other constant output voltage values. And this is how the output voltage control works.
Thank you very much for your time. I will implement this as soon as I wrap up my current project. I have a lot to learn.
No problem! All the best to you!
Dear sir,
Please sir, for the modified design by Nuno Figueiredo. If the transformer is 2A, will be circuit output current be 2A when R5 is 0.3 ohms?
Thank you sir for your response.
Hi Godfrey,
Yes roughly it will be around 2 amp output
Dear sir,
Please sir, I have a 230v/5 winding secondary voltages 2A transformer.
I have got 24.8v from one winding and 18.3v from another winding on the secondary.
I connected them in series and got 43.9v
Please sir, can I use the 43.9v from the series connection on the modified design by Nuno Figueiredo?
2. Do the values of the components: capacitors, resistors, diodes etc in the circuit need to be modified to suit the 43.9v?
3. What would be the output current of the circuit at 0 – 40V using the 2A 43.9v transformer?
Thank you sir
Hi Godfrey,
Yes you can connect the 43.9V to the circuit designed by Nuno Figueiredo. Just make sure the capacitor voltage rating are around 100V. Rest everything can be as is.
The output current will depend on the value of R5, but the maximum will not exceed 2 amps.
Okay sir, thank you very much.
Please sir, help me with these points concerning the circuit.
1. Will the R5 = 0.27ohms output 2A max current? Or how do I determine the value from Ohm’s law that will output almost 2A max current?
2. What is the wattage of R5 and other resistors?
3. IN4001 is not handy, can I replace with IN4007?
4. Is the LED for Power ON indication or for Over-current shut down indication
5. 2K5 pot is not handy, can I use 5k or 2k pot?
Thank you sir for your response.
Hi Godfrey, here are the answers.
1) When the output current exceeds 2 amps, a potential difference of around 0.6V must develop across R5. For this to happen R5 can be selected by using the following formula:
R5 = 0.6 / 2 = 0.3 ohms.
2) wattage = 0.6 x 2 = 1.2 watts, all other resistors can be 1/4 watt
3) 1N4007 can be used.
4) LED is for over current indication.
5) 5K pot will work
Dear sir,
I have successfully built the circuit, and it’s working. Thank you very much sir.
Am using it to power 12v Yamaha keyboard, though I have observed that the 2N3055 is very hot even with the heat sink I have used. Am afraid if it will burn when I use for some hours.
Please sir, can it be replaced by another transistor or any way to handle the heating effect?
2. Where can I include an LED for Power ON indication in the circuit?
Hi Godfrey,
Glad you could build it successfully.
The transistor heat is directly proportional to the difference in the input and the output voltage. For example if the input is 12V and the output is set at 9V then the heat on the transistor will be relatively less, but if the output is reduced to 6V, the heat will increase proportionately, and if the output is further reduced to 3V the heat will increase even further. So as the input/output difference increases the heat on the transistor increases proportionately. Make sure the input supply is not too large compared to the set output voltage.
You can replace the transistor with TIP35 if required.
You can put an LED across the output terminals of the power supply.
Okay Sir, thank you very much. I have confirmed it by reducing the input AC supply from the transformer, and the heat was less.
Please sir, is there a circuit for variable Ac supply from 24V transformer?
So as to vary the input AC supply from 0- 24V.
Thanks Godfrey, Glad you could solve it.
For controlling a 0-24V AC you can probably try using a triac dimmer circuit. You can try the first circuit from this article:
220V Light Dimmer and Ceiling fan Regulator Circuit
You can replace the lamp wires with the primary 220V wires of the transformer.
Hi Swagatam;
I have the transformer 24 Volts 100 VA(maybe around 4 Amps). I need a voltage and current adjustable circuit to my transformer. I think it is possible to charge a 60 amps battery thru this my transformer. I need your recommendation and suggestion about most convenient of adjustable volts and currents circuit. Lots of thanks
Hi Suat, According to me, the best option is using an LM338 IC for making the required variable power supply. You can use a large heatsink on it and easily charge a 60 Ah battery at 4 amp rate from the transformer.
Hi again;
Sorry, You mean any one of the above circuits replaced by LM338 or I may use the circuit that I had seen with the following parts LM317, 2N3055 and BD139 I will change the LM317 to LM338. Thanks.
No problem Suat, The above circuits do not use LM338, they use 2N3055 transistors. You just need a basic LM338 variable power supply circuit without any 2N3055 transistor, and use the IC directly to get the variable output at 5 amp current output with full short circuit protection. You can refer to the first circuit presented in the following article as an example:
https://www.homemade-circuits.com/ic-lm338-application-circuits-explained/
Regarding the 2N3055 based variable voltage current power supply circuit, are C1 and C2 only used for filtering? I would like to remove the transformer and rectification, and then feed the circuit with a fixed 40VDC that I have available. Should I also remove C1 and C2, and their connections to ground since filtering is no longer needed?
Thanks for this and all the other circuits and instruction you have made available to us hobbyists!
The capacitors C1, C2 do some additional work also other than filtering an AC.They eliminate noise and other invisible high frequency disturbances or spikes.
If your supply input is already a filtered DC, then C1 can be perhaps removed, but C2 should not be removed as it makes sure that the switched output from T1 is perfectly stable and without any interference.
Hello sir,
I Want to vary DC Output from 4 volts to 300 Volts, also want to vary Output Current 4 miliAmp to 300 miliAmp, please can you help me to suggest me any circuit
Hello Vinod, one method of implementing would be use a light dimmer circuit, and feed its output to the circuit shown in the following article:
0-300V Adjustable MOSFET Transformerless Power Supply Circuit
So you will have three pentameters to adjust. One from the light dimmer which will determine the maximum range as per the load connected to the MOSFET circuit.
The MOSFET voltage control pot, which will further provide the final voltage adjustment to the load.
The current adjustment pot which will decide the max current output. The current adjustment might not be too accurate unless fixed resistors are employed instead of a pot control.
Hi Sir Swag. hope you are fine. I use a 220V Triac based dimmer to decrease and increase the output AC of a 220 to 30V, 2A Transformer. Is there a way other than dimmer, except wire resistor to do that? I should add that all of the diagrams I have seen in your very interesting and informative site are DC circuits as know better. May I hope to have your reply Sir?
Regards
Veronika
Hi Veronika, using a triac dimmer with the 220V side of the transformer is probably best way to control the secondary side voltage. There’s no other easier way to do this.
Glad you found all the diagrams useful…
Hi dear Sir Swagatam. Thank you very much for your response, good man.
Bye
You are welcome Veronika!
Thanks so much sir. But am a bit confused. I meant maximum output current of 0.2A. If 3ohms should be the resistor and 0.6v is used in the calculation. Is it because of the minimum out put voltage of 0.6v necessited by the diode used. If not, is there any other criterion used to arrive at 0.6v used in your calculation. For me I calculated directly using the transformer specifications.
Hi Moses, the transistor T3 is responsible for cutting off the output when max current is detected. To trigger T3 at the max current a 0.6V must develop across R4….therefore 0.6 V is used as the reference value.
Ok sir now I understand. But sir please, 0.6v is it a rating of the T3 transistor as part of its data sheet information or that of diode. I am asking this in case of using a different transistor for the same purpose. God bless you.
It is the optimal voltage required across base/emitter of all silicon BJTs for switching ON fully. So except Darlington transistors, all BJts will have the same requirement of 0.6 V threshold across their base/emitter for full switch ON.
Ok thanks sir. Am grateful
You are welcome Moses!
Please sir, considering the first circuit above which has transformer rating as 3A, 40V, should we use R4 = 200 ohms in order to obtain maximum of 0.2A (I.e.200mA) using ohm’s law as you pointed out. If so what of the Wattage of the resulting R4 or should we use any of 1/2, 1/4 , …. as desired.
Moses, for 200 mA output current, R4 will be = 0.6/0.2 = 3 Ohm
wattage will be 0.6 x 0.2 = 0.12 watts