Voltage Stabilized Transformerless Power Supply

The post explains how an ordinary capacitive power supply may be transformed into a surge free voltage stabilized or variable voltage transformerless power supply applicable for almost all standard electronic loads and circuits. The idea was requested by Mr. Chandan Maity.

Technical Specifications

If you remember, I communicated you sometime before with comments at your blog.

The Transformerless circuits are really good and I tested couple of those and running 20W, 30W LED.Now, I am trying to add some  controller, FAN and LED all together , hence, I need a dual supply.

The rough specification is:

Current rating 300 mAP1= 3.3-5V 300mA ( for controller etc)P2=  12-40V (or higher range), 300mA (for LED)
I thought to use your 2nd circuit as mentionedhttps://homemade-circuits.com/2012/08/high-current-transformerless-power.html

But, I am not able to freeze the way how to get 3.3V without using extra capacitor. 1. Can, a second circuit may be placed from the output of first one? 2. Or, a second TRIAC, bridge to be placed in parallel with first one, after capacitor to get 3.3-5V

I shall be glad if you kindly help.


The Design

The function of  the various components used across the various stages of the above shown voltage controlled transformerless power supply circuit may be understood from the following points:

The mains voltage is rectified by the four 1N4007 diodes and filtered by the 10uF/400V capacitor.

The output across the 10uF/400V now reaches around 330V which is the peak rectified voltage achieved from the mains.

The voltage divider network configured at the base of the TIP122 makes sure that this voltage is reduced to the expected level or as required across the power supply output.

If a 12V is required the 10K pot may be set to achieve this across the emitter/ground of the TIP122.

The 220uF/50V capacitor ensures that during switch ON the base is rendered a momentary zero voltage in order to keep it switched OFF and safe from the initial surge in-rush.

The inductor further ensures that during the switch ON period the coil offers a high resistance and stops any inrush current to get inside the circuit, preventing a possible damage to the circuit.

For achieving a 5V or any other attached stepped down voltage, a voltage regulator such as the shown 7805 IC may be used for achieving the same.

Circuit Diagram

Need Help? Please send your queries through Comments for quick replies!


Chandan Maity said…
Thanks a lot.
Some questions:
1. Can I use MOSFET like P4NC60 in place of TIP122?
2. Can I use zener at base of transistor to get more fixed stabilization?

3. If I want to get another channel of 30-40V, can I use same circuit (Transistor+choke) in parallel with different configuration ? In this case, I am intending to use the Capacitor bank and rectifier as common for both.
Chandan Maity said…
Other questions:
1. 100uF/225V, may be little less for 310V, should I increase to 450V?
2. 1K+10K in series may be dangerous. When the Pot will be at less than 1K, high current may burn the port.
3. Will it be better suggestion to use feedback from output as you have indicated at 2nd circuit of https://homemade-circuits.com/2012/08/high-current-transformerless-power.html ??

Swagatam said…
1) using a BJT would be more favorable due to its less complex charcteritics.

2) yes zener diode can be used instead of the pot for clamping the output to the zener voltage.

3) for getting two 30/40 outputs the existing transistor output may be simply bifurcated into two through individual diodes (1N4007)
Swagatam said…
1) actually it should have been a 10uF/400V, it's wrongly shown as 100uF/225V in the diagram.

2) NO, the 1K will take care and prevent the pot from burning, however the 1K may become hot and therefore higher wattage could be tried.

3) this is a different concept, feedback is not relevant here.
1 can i use tip 127 in place it is PNP transistor...if yes plz guide me how to connect it
2.d circuit looks like a simple smps .
..if set at 5v, can i charge a cellphone with d circuit?.... thanks sir
Swagatam said…
PNP will need many changes to be done, so TIP122 must be followed
Swagatam said…
the circuit will give a lethal shock if touched in switched ON condition, so not recommended for cellphone charging or similar applications
Naresh Jain said…
sir I want constant current circuit for led tube light,
say 60 to 70 volt output with constant current 300 to 500 mA
Swagatam said…
Naresh, you must go for an SMPS circuit, it'll be safer.
Naresh Jain said…
sir have you any suitable smps circuit for my requirment
Swagatam said…
Naresh, you can try the following :


modify the output winding and the zener diode as per your requirement
Gentle Soul said…
Sir, what I want to ask is different from this article.
I made an astable multivibrator usin resistors{R1 to R4} and capacitors {C1 and C2} with two NPN 547 transistors and two LED. But it does not vibrates, its only the LED that was blinking what should I do sir?
Hoping to hear from you soon
Swagatam said…
If the LED is blinking it means it's oscillating or vibrating.
can tip122 directly connected to 7805 without 100turn,1mm wire on any ferrit ?
Swagatam said…
yes you can remove the coil but with a reduced safety....
jeelani said…
sir my name is mohiud ,i accidently came across ur site ,i am impressed by ur ckts and quick helpful replies in the blog,i have a query that example ,according to transformerless power supplies if we connect a transformer primary winding which is 400 ohms as a load the output is dropped upto 18 v according to the mains caps and i experimented with that and no component is heating or warming as i connected for a week,i assume with this trick the power supplies might have long life .normally we use zenner diodes but due to high fluctuations it may get burnt and disturb the whole ckt. i want a power supply which should run continiously,it shoud bear high power and have cut off for the main appliance and no component should get heat ...please suggest and advice me ,thanks for ur wonderful cooperation with all of us
Swagatam said…
Thanks Mohuid, you are correct that would work, but the transformer must be compact and small
Kalyan Appana said…
Sir i am connecting above circuit as it is but the power supply is given to the circuit input side 2uf/400v capacitor is burned .
1.)what is the watage of the 1M resister i am given 1M /1watt.
please help me.
Kalyan Appana said…
Sir i am connecting the above as it is but ofter given the power supply 2uf/400v capcitor is burned.
1.)what is the wattage of the 1M resister i am given 1M/1watt.
please help me.
haranath said…
Dear Swagatam Majumdar,
I have tried the circuit.. But as soon as I connected to 230V,AC, 2MF cap at input was burnt. There was smoke. What would have gone wrong? I have used both 1M and 1K with 1WATT rating. I have not used ferrite. Please suggest what to do
Swagatam said…
Kalyan, it means your 2uF capacitor is of bad quality and is faulty...even under short circuit condition this capacitor should not burn....make sure it's 400v rated and not 250V.

1M can be 1/4 watt also/...1 watt is even better.
Swagatam said…
Please refer to the above comment for the solution.
jeelani said…
the capacitor might b reversely connected,check polarity
Swagatam said…
it's supposed to be non-polar cap...so polarity is not relevant.
jeelani said…
oh yes u r right,it is before the bridge,i did not seen the ckt,i thought the cap was after the bridge
jeelani said…
dear maju can u suggest me a home entertainment projector with features as led light with long life,high lumens,3d support,approx 200''projection,wifi,usb,hdmi,tv ports,etc
jeelani said…
i googled a lot i found in egate and luxcine but i am afraid that can i get spares and the standard,pls help me out in hybrid laser led proj,,,,,,.lacks all features and the price is also too much
Swagatam said…
I am sorry I have little idea about all these gadgets, however I'll investigate and let you know if I find something interesting.
emmantrop said…
Good day.
please sir I need your help and sugestion. Sir, I Need a transformerless power supply that can handle up to 300v AC input, and I want it to power a 12v dc relay. And via the common and normally open terminal of the relay I will pass an AC input to power mine SMPS which is mine main power supply that will power my circuit. However, the main function of the transformerless power supply is to trigger the relay once AC input voltage is above 240V and this will enable it to protect my SMPS from burning due to high voltage but the transformerless power supply and its components will be harm.

Or can I archieve this from the above circuit? if yes, How?

Thanks and waiting for your amicable reply.
Swagatam said…
emmantrop, I don't think that's required because SMPS units are all rated to work safely upto 265V...and normally mains AC never reach above this value
emmantrop said…
Hello sir, apart from securing my SMPS there are some other devices I will like to protect However, there was a time our mains supply developed fault and the voltage we got was up 275 - 300v and as a result of that almost all the electronics devices that were connected to main got burnt and spoiled.

Finally, if u have an idea or solution for any transformerless over-voltage (voltage surge) protection circuit. please share with me. Thanks
Swagatam said…
Hello emmantrop, you can try the last circuit from this article:

emmantrop said…
ok thanks for your quick respond, I will try it.
PranavGC said…
Swagatam ji, i am using DG (automatic) when current goes off, the DG is configured to give 750Watts of power through a Breaker if i try to run above the wattage it would trip, the problem is that when i don't use 750 watts also it trips, when a Set-top-box (dish TV) adopter or a cell phone charge is in ON position... is it because of surge ... is there a circuit to over come this problem.. guide me pls
Swagatam said…
Pranav, the problem is with the breaker, if it's rated to handle 750 watt then it should not trip due to fractional surge issues, you should change it and check the response.
Hello sir,
Can i use this circuit for a 12V/10Amp max power supply for a project am working on.
Or do you have another suggestion?
You do an amazing job by the way.
Greets from Belgium.
Hello sir,
Can i use this circuit as a 12V/10Amp max power supply for a project i work on?
Or do you have another suggestion?
You do an amazing job by the way!
Greets from Belgium.
Swagatam said…
Thanks Malik, although not recommended, you can try it by replacing the capacitor with a 200uF/400V :)
and the BJT with a IRF450 mosfet
sir!I have a question regarding the above design.Have you allready determined the output current?if yes,pls tell me how and which part is responsible for that.Or I have to add on the output still Current Limiter Circuit.
Thanks a lot.
Swagatam said…
The 2uF/400V capacitor value determines the input current which is around 100mA
Dheeraj said…
What is the role of transistor TIP122 in this circuit?
what is output current?
Swag said…
it's configured as an emitter follower, therefore the emitter voltage will follow the base voltage and can be set by adjusting the base voltage, the output current will depend on the power supply input current
Nanigopal mahata said…
hello swagatam sir, I have tried to make a 12 volt 2amp power supply from 230 main, i have used three 475k 400v ac cap in parallel with a 10Mohm 1watt bleeder resistance, and make a rectifier with 1N5408 , and i get the output 140 v dc .... can i use a 12 volt zener here. is it safe ? if possible make a suitable circut diagram with this component.
Swag said…
Hello Nanigopal,

you can use 12V 2watt zener diode, for stabilizing the output however three 475 will give you around 220mA current, not 2 amp.

you can refer to the following article for more info


use 10 ohm 1 watt for R2

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