TransformerLess Low Cost DC Power Supply : Resistive & Capacitive

TransformerLess Low Cost DC Power Supply : Resistive & Capacitive

One on the major part of our electronics products is the DC Power Supply that converts mains AC voltage to a lower DC voltage. Usually we use a step down transformer to reduce mains AC voltage to desired low voltage AC and then convert it to DC or we use Switched Mode Power Supplies. But in both cases cost is very high and it takes considerable amount of space. Another Low Cost alternative for Transformer and Switcher based power supply is Transformer Less Power Supply. There are basically two types of Transformer Less Power Supplies.

  • Capacitive
  • Resistive

The main difference between them is, in resistive transformer less power supply excess energy is dropped as heat across a voltage dropping resistor while in capacitor power supplies voltage is dropped across a voltage dropping capacitor so there is no energy loss or heat dissipation.

 Capacitive TransformerLess or Capacitor Power Supply

In Capacitor Power Supplies we use a Voltage Dropping Capacitor in series with the phase line. An ordinary capacitor should not be used in these applications because Mains Spikes may create holes in dielectric of ordinary capacitors and the capacitor will fail to work. This may destroy the device by rushing current from the mains. Thus we use X Rated Capacitor with required voltage is used for this task. X Rated Capacitors rated for 250, 400, 600 V AC and higher are available. Reactance of the voltage dropping capacitor should be greater than the load resistance to keep constant current through the load.

Reactance of Capacitor, X = 1/2ΠfC


Where f is the frequency and C is the Capacitance. Thus a 0.22μF capacitor has reactance of 14.4KΩ on mains frequency (50Hz). The approximate value of maximum current can be find out by dividing mains voltage by reactance of the capacitor (since load resistance is small).

I = V/X

I = 230 V / 14. 4 = 15.9 mA

Thus a 0.22μF capacitor can supply a maximum current about 15mA.

Circuit Diagram

Capacitive Transformer Less Power Supply - Circuit Diagram

Capacitive Transformer Less Power Supply – Circuit Diagram

As shown 1A fuse may be used to avoid damages due to short circuit and a MOV (Metal Oxide Varistor) also may be connected as shown above to avoid problems due to voltage transients. The resistor R1 is used to limit the high current that may occur during power on. Capacitor C1 225K (2.2μF) is used as the Voltage Dropping Capacitor. A Bleeder resistor is connected parallel to it for discharging the capacitor when the supply is switched off. Diodes D1 – D4 is wired as Bridge Rectifier and the capacitor C2 is used to filter the pulsating DC. Zener Diode is used to regulate the filtered DC or you can use IC Voltage Regulator for better results. Resistor R3 is used to limit the current through the Zener Diode.

The following table shows the maximum current and open circuit voltage of some commonly used capacitors.

CapacitorVoltageCurrent
104K48 mA
334K1022 mA
474K1225 mA
684K18V100 mA
105K24V40 mA
225K24V100mA

Advantages

  • Significantly smaller in size and lesser in weight than transformer power supplies.
  • Lesser in Cost when compared to Transformer or Switcher based power supplies.
  • Capacitor Power Supply is more efficient than Resistive Transformer Less Power Supply.

Disadvantages

  • Higher Cost when compared to a Resistive Power Supply.
  • No isolation from AC mains which introduces many safety issues.

Resistive TransformerLess Power Supply

Resistive Transformer Less Power Supply is similar to Capacitor Power Supply except that instead of Reactance it uses resistance to limit current. Thus here excess energy is dissipated as heat across the Voltage Dropping Resistor.

Circuit Diagram

Resistive Transformer Less Power Supply Circuit Diagram

Resistive Transformer Less Power Supply Circuit Diagram

Care should be taken while selecting Voltage Dropping Resistor since the excess power is dissipated across it. Calculate power by multiplying Voltage and Current. P = VI 

It is better to use a resistor of double the rated power.

Advantages

  • Significantly small size and less weight than transformer based power supplies.
  • Lesser Cost than Transformer or Switcher based power supplies.
  • Lesser Cost than Capacitor Power Supply.

Disadvantages

  • No isolation from AC Mains which introduces many safety issues.
  • Resistive Power supplies are less efficient as the excess energy is losted in the form of heat across the Voltage Dropping Resistor.

Caution

Don’t Try this circuit if you don’t have much experience with electronics. Care should be taken while testing or using this circuit. Don’t touch at any points of the circuit since some points of this circuit is at Mains Potential. After constructing and testing enclose the circuit in a metal casing without touching PCB and metal-case. The metal case should be properly earthed to avoid shock hazards. 

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Comments (69)

  • Mouhab Abdel Hadi

    1. What do you mean by “table shows the maximum current and open circuit voltage of some commonly used capacitors”??
    Did you mean the design value for the circuit above or what?
    2. how to calculate the value of R2 and R1?

    February 7, 2013 at 10:21 am
  • Ligo George

    R1 is used to limit inrush current during startup leave it 100 ohms……..

    R2 is used to discharge the capacitor to avoid the risk of electric shock…

    The table shows the open circuit voltage and maximum current can drawn by using some capacitors…

    February 7, 2013 at 3:37 pm
  • Colin55

    How can a 225 capacitor be 1w????

    March 7, 2013 at 5:20 am
  • Colin55

    The 10k resistor on the front-end will dissipate more than 5 watts.

    March 7, 2013 at 5:22 am
  • Ligo George

    It is an X – Rated capacitor …….

    March 7, 2013 at 5:57 am
  • Ligo George

    There is no 10K resistors..

    March 7, 2013 at 5:58 am
  • Paul John Aranas

    what kind of capacitor to be used for the output of 3000ma of current ? thanks for this circuit..

    March 7, 2013 at 12:32 pm
  • Ligo George

    Thank you for pointing some of the errors.

    March 7, 2013 at 5:05 pm
  • Ligo George

    For 3A, use a transformer power supply,…….. transformer less power supply is not suitable for high current applications………

    March 7, 2013 at 5:10 pm
  • Paul John Aranas

    for 1500 ah what capacitor should i use?

    March 12, 2013 at 1:12 pm
  • Paul John Aranas

    is this circuit can produce 1500 mah? what capacitor should i used.. please help thanks in advance

    March 15, 2013 at 9:19 am
  • Ligo George

    mah,……. ??…. Ah is the rating of battery,,…. for producing 1.5A it is better to use transformer power supply… transformer less power supplies are suitable only for producing low currents..

    March 15, 2013 at 9:42 pm
  • Colin Mitchell

    R2 in the resistive power supply is not needed. It serves NO purpose.

    April 21, 2013 at 7:07 pm
  • aleeee

    how can we make variable

    Resistive TransformerLess Power Supply maximum output voltage 20volts??/

    July 30, 2013 at 2:58 pm
  • Ligo George

    In my opinion ..Transformer less power supplies are not suitable for variable applications.. It is better to use transformer… or make a variable smps power supply..

    July 30, 2013 at 6:22 pm
  • Udhaya Raj

    Bro the R1 resistor is getting Burnout , so instead of 100ohms can i use 2nos of 100ohms in parallel
    is it a correct procedure…..

    November 30, 2013 at 2:29 pm
  • Ligo George

    Increase the wattage of the resistor…
    or use two 220 ohm resistors in parallel..

    November 30, 2013 at 7:23 pm
  • Vishal suthar

    Sir is it better than transformer or SMPS ?

    December 5, 2013 at 3:06 pm
  • Vishal suthar

    I want to use 230 vac to 12v dc

    December 5, 2013 at 3:07 pm
  • Ligo George

    No .. never

    December 5, 2013 at 7:42 pm
  • Feroz60

    Are these values ok to AC 110V?

    December 9, 2013 at 8:29 am
  • Chu

    Should I use 3w or 5w resistors for R1 and R3? Both R1 and R3 with 1W are getting burnout, they are too hot …

    January 4, 2014 at 8:40 am
  • Simba

    Hey, nice work! Here is my question. My circuit has a micro (PIC16F505), a BTA06-600CW Triac and a few other components. I need this PS to supply at least 40mA. What’s your suggestion? My plan is to use the micro to switch my Triac.

    January 9, 2014 at 4:04 am
  • Ligo George

    If so..Increase the wattage.. It will depend on the current consumption of your load..

    January 12, 2014 at 5:27 pm
  • Ligo George

    Read the application note of Microchip :
    http://ww1.microchip.com/downloads/en/appnotes/00954a.pdf

    January 12, 2014 at 5:52 pm
  • Charles

    I find this interesting but I still have a question. What is the maximum voltage from a transformerless circuit and why is it limited to the voltage?

    January 15, 2014 at 9:51 am
  • Ligo George

    Maximum output voltage will be the maximum input mains voltage..

    January 19, 2014 at 7:38 pm
  • Peter

    the answer to the first part of the question is very handy but you still haven’t said why it is restricted to voltage. thanks

    January 20, 2014 at 2:15 am
  • Ligo George

    I don’t understand your question?? What limit??

    January 23, 2014 at 9:41 am
  • Simba

    Thanx! I got it to work. It dropped a great deal of the output voltage but this micro also works at lower supply voltages.

    January 24, 2014 at 10:52 pm
  • hossein

    hi

    please can help me.
    whats Mov in circuit diagrams???
    and when i use first diagram R1 resistor warm up and Burned after 10 Seconds
    what should i do??

    February 18, 2014 at 2:53 am
  • Nirvana

    Can i use a ceiling-fan capacitor (Metal film) of same rating instead of x-rated capacitor??

    Can I use x-rated capacitor in ceiling-fan??

    April 26, 2014 at 11:47 pm
  • John Lam

    Transformerless power supply is designed for a specific application that consume small current from a few mA to a few tenths mA. Current capacity is pre-determined by either the dropping C1 in capacitive or R1 in resistive. The available current capacity will distribute among the zener diode, LED and the load.

    Some of the power ratings of components in both capacitive and resistive circuits are too low.

    In the capacitive circuit, C1 is labelled 225k 400V; 225k means 2,200,000 picofarad or 2.2 microfarad. That means current available is roughly 150mA.

    Power dissipated by R1 = I^2 * R = 2.25W. If 1W rating as indicated is used, it certainly will blow in a minute. Use 5W will be safe.

    The same is true for R3. In a transformer power supply, R3 is needed to limit the current flowing through the zener diode. In these two circuits, the current has been limited already, R3 is not necessary. Otherwise, maximum power dissipated by R3 is close to that of R1. Then a 5W rating resistor should be used as well. My suggestion is to get rid of R3.

    As for the zener diode, there is no power rating for it. Suppose no load is connected, about 5mA will pass through the LED, the remainder around 145mA will flow through the zener that would dissipate a power of VI = (5.1)(145mA) =0.74W. Most zener diodes are rated 1/4W to 1W. Higher ratings is a bit hard to find and probably more expensive. Use a 1W rating should be fine.

    In a custom-designed circuit, the load current is known, so all the components can be adjusted to provide the required load current, and low rating components like 1/8W to 1/2W could be used.

    The resistive circuit supplies 110mA current. Power of R1 = I^2 * R = 24.2W. You decide the proper rating of R1 yourself. As mentioned, both circuits are for supplied current ranging from a few mA to a few tenths mA. For example, if supplied current is 23mA, R1 will be 10k ohms, then power dissipated by R1 is 1W only.

    R2 is redundant, if you want it to stay in the circuit, use a 2W rating.

    For the zener diode, P = VI = 5.1 * 0.11 = 0.561W. If you can’t find a 1W zener, use a 0.5W one, and make sure the load is connected before plug-in to mains.

    MOV stands for metal oxide varistor which is a voltage sensitive element that will shunt current to protect the circuit when line voltage surge above the rated voltage.

    August 26, 2014 at 11:00 am
  • John Lam

    Current passing through R1 and R3 is independent of load current. It is determined by majorly by C1 in capacitive, or by R1 in resistive. The load current only affects the current passing through the zener diode that takes up whatever left over from the LED and the load.
    The current that a transformerless power supply can supply is determined by design by changing the values of components. Once the appropriate values are decided, the supplied current stays the same regardless of load. Simply speaking, in the capacitive circuit, roughly 150mA will flow through R1 and R3 once plug in.
    In fact, R3, and R2 in resistive circuit are redundant. They are necessary only in transformer power supply to limit the current passing through the zener diode as theorectically the transformer power supply can suppy an infinite amount of current without load.
    I’ve just provided some information to hossein above. You may want to read those.

    August 26, 2014 at 11:45 am
  • Madhura

    what is the MOV item number? i mean how can i ask from the shop?if we take capacitor,it has a number like 10uf 16v.then how can i ask MOV?

    December 5, 2014 at 3:07 pm
  • Ligo George

    Eg : MOV 10D471

    December 8, 2014 at 4:22 pm
  • BEE

    hello all,what if i want a high current battery charger of say 40A. What modifications can be done

    January 10, 2015 at 11:59 pm
  • Ligo George

    I don’t think you can get 40A with this.

    January 15, 2015 at 7:26 am
  • keepg0

    What stops one from using multiple x rated capacitors to generate a higher current? Are there issues with heat in other parts of the circuit across resistors that make it impractical for higher current applications? Could the output be regulated properly instead of with a zener?

    February 18, 2015 at 2:30 am
  • Ligo George

    Yes, you can use multiple x rated capacitors…
    You may also use other regulators like 7805 etc.

    February 23, 2015 at 4:11 pm
  • sasi

    Hai Ligo George

    I am unable to understand the X rated capacitor…?

    what is X-rated capacitor…

    Where do I get it…

    is it available in the online shoping like Digi key…

    Can u pls mention any online portal where I can buy X-rated capacitor…..
    is there any industrial name for X-rated capacitors….like disk capacitor.,Electrolytic,Ceramic Capacitors,Polyester – Box Capcitors, Polyester – Myler Capacitors
    which capacitor should I buy……
    I stay in india….

    March 12, 2015 at 11:37 am
  • Ligo George

    It is a class of non polar capacitors… https://electrosome.com/x-and-y-rated-capacitors/
    It will be available in all local electronics shops….
    Just tell the value of capacitor instead of “X Rated” ..

    March 17, 2015 at 4:52 pm
  • Nirmala Ranawat

    Hi,

    How do i know output voltage of x-rated capacitor. I need a supply of 5v, 40-50mA. Using 105K will give me 40mA but output voltage will be 24V, and i will have to drop rest of it across a resistance which will cause power wastage. How do i find out X rated cap with output voltage suitable to my application.

    June 7, 2015 at 6:15 pm
  • Maulik D

    Thank you Ligo George…,

    I have done this project, getting sufficient voltage, but it is not 5V DC, its 12V DC so by using 7805 i achieved 5V DC.

    Only one problem i have that is of heating from the resisters of 100R 5W, both resister got heated very high.

    Any solution of this overheating of resistor?

    i have also attached an images of supply and marked that two resistors.

    And one another question is that can i use SMD components for the same value?

    July 1, 2015 at 12:51 pm
  • Ligo George

    Try increasing the resistance values.

    July 1, 2015 at 7:36 pm
  • Maulik D

    ok i will do that and what about the SMD component?, Can i use it? special for capacitors, as u recommended X rated capacitor.

    July 2, 2015 at 10:29 am
  • Maulik D

    hello Liho,

    i am waiting for your answer, please suggest as soon possible from your side.

    July 6, 2015 at 12:43 pm
  • Maulik D

    Hello Ligo i am waiting

    July 7, 2015 at 6:05 pm
  • Ligo George

    The size of capacitor increases as per your current requirement. I haven’t yet used smd component for this.

    July 18, 2015 at 10:55 am
  • Maulik D

    ok, Thanks for your reply

    July 18, 2015 at 1:17 pm
  • Ram V

    Is it possible to get 130mA by this circuit, What Will Happen If i give 230V DC as input to this circuit?

    August 7, 2015 at 5:18 pm
  • Ram V

    Is it possible to get 130mA by this circuit, What Will Happen If i give 230V DC as input to this circuit?

    August 9, 2015 at 7:07 pm
  • Ligo George

    It will work only with AC.

    August 14, 2015 at 9:42 pm
  • Gion

    How can I get 60V DC 300ma on output?

    October 26, 2015 at 3:44 pm
  • tiago pereira

    i need a transformerless: 6V at 120VAC and 12V at 220VAC! Is possible?

    December 8, 2015 at 3:51 am
  • Ligo George

    It will be possible, but you need to do some R & D on it.

    December 19, 2015 at 3:48 pm
  • tiago pereira

    do you have someone circuit?

    December 20, 2015 at 5:10 am
  • tiago pereira

    have someone circuit schematic?

    December 20, 2015 at 6:37 am
  • Ligo George

    Sorry, presently I don’t have.

    December 30, 2015 at 8:31 am
  • Rakib

    Hi, I want 12volt 5watt load , how to calculate this curcite.

    February 27, 2016 at 11:04 pm
  • Ligo George

    I don’t think it will be easy to achieve. You need very big capacitors for that. Better go for a SMPS power supply.

    March 19, 2016 at 10:38 am
  • majid313

    hi Ligo George
    are you make and test this circuit?

    November 14, 2016 at 1:58 pm
  • Ligo George November 27, 2016 at 2:35 pm
  • Ajay Kamat

    What is mov and what should be its value.
    Can i use this with my 8051 microcontroler with rtc.

    December 5, 2016 at 9:04 pm
  • Ligo George

    MOV is for spike protection. You may use 275V MOV.
    You can use for 8051 microcontroller with proper filters.

    December 7, 2016 at 11:35 am
  • Huzaifa Nur

    Sir , What if I want to increase the current upto 18 apms?

    February 15, 2017 at 8:16 pm
  • Chandrika Chandu

    can we use 2 zener and 2 normal diodes instead of 4 normal diodes in bridge circuit

    September 6, 2017 at 9:04 pm
  • Ilya Ilba

    I don’t understan how the (maximum?) open circuit voltage figure is obtained. For example, for 225K, it’s 24V
    100mA. I undersntan how we get 100mA (although in theory it should be 158mA, isn’t it? but in reality it might be 100mA). But what is the limiting factor for the voltage?

    November 29, 2017 at 1:38 am
  • Punit Patel

    Could you please assist with a 230v 15 amps to a 60v 57 amps transformer less circuit or its components

    March 2, 2019 at 6:22 am

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