Transformer less AC to DC power supply circuit using dropping capacitor

Production of low voltage DC power supply from AC power is the most important problem faced by many electronics developers and hobbyists. The straight forward technique is the use of a step down transformer to reduce the 230 V or 110V AC to a preferred level of low voltage AC. But i-St@r comes with the most appropriate method to create a low cost power supply by avoiding the use of bulky transformer.Yes, you can construct power supply for your development without a transformer. This circuit is so simple and it uses a voltage dropping capacitor in series with the phase line. Transformer less power supply is also called as capacitor power supply. It can generate 5V, 6V, 12V 150mA from 230V or 110V AC by using appropriate zener diodes. See the design below.

Circuit diagram

Transformer+less+AC+to+DC+power+supply+circuit+using+dropping+capacitor Transformer less AC to DC power supply circuit using dropping capacitor

Components required

  1. Resistors (470kΩ, 1W; 100Ω)
  2. Capacitors (2.2µF, 400V, X rated; 1000µF, 50V)
  3. Bridge rectifier (1N4007 diodes x 4)
  4. Zener diode (6.2V, 1W)
  5. LED (Optional)
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Working of Transformer less capacitor power supply

  • This transformer less power supply circuit is also named as capacitor power supply since it uses a special type of AC capacitor in series with the main power line.
  • A common capacitor will not do the work because the mains spikes will generate holes in the dielectric and the capacitor will be cracked by passing of current from the mains through the capacitor.
  • X rated capacitor suitable for the use in AC mains is vital for reducing AC voltage.
  • A X rated dropping capacitor is intended for 250V, 400V, 600V AC. Higher voltage versions are also obtainable. The dropping capacitor is non polarized so that it can be connected any way in the circuit.
  • The 470kΩ resistor is a bleeder resistor that removes the stored current from the capacitor when the circuit is unplugged. It avoid the possibility of electric shock.
  • Reduced AC voltage is rectifiered by bridge rectifier circuit. We have already discussed about bridge rectifiers. Then the ripples are removed by the 1000µF capacitor.
  • This circuit provides 24 volts at 160 mA current at the output. This 24 volt DC can be regulated to necessary output voltage using an appropriate 1 watt or above zener diode.
  • Here we are using 6.2V zener. You can use any type of zener diode in order to get the required output voltage.

Design

Reactance of the capacitor,
Transformer+less+AC+to+DC+power+supply+circuit+using+dropping+capacitor+design+1 Transformer less AC to DC power supply circuit using dropping capacitorwhere f is the supply frequency and C is the capacitance.
If the supply frequency is 50Hz, then reactance of 2.2µF X rated capacitor is given by,
Transformer+less+AC+to+DC+power+supply+circuit+using+dropping+capacitor+design+2 Transformer less AC to DC power supply circuit using dropping capacitor
So output current,
Transformer+less+AC+to+DC+power+supply+circuit+using+dropping+capacitor+design+3 Transformer less AC to DC power supply circuit using dropping capacitor
You can design your own supply if you need high current rating other than 159mA by choosing different capacitor values.

Pin outs of Capacitor, Diode, Zener diode etc

Remember:

Do not touch at any points in the circuit because some points are at mains potential. Keep away from touching the points around the dropping capacitor to prevent electric shock, even after switching off the mains. Great care should be taken to construct the circuit since there is no isolation between mains and our circuit. Adequate spacing must be given between the components.
Related Power supply circuits:

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22 thoughts on “Transformer less AC to DC power supply circuit using dropping capacitor

  1. How we get 24v since the out voltage of the bridge = Vrms X 0.9 = 115 (230/2) X 0.9 = 103.5 is that related to filter capacitor how we calculate the 24v , regards

  2. how can we say that there will b 24 volts in output after rectification
    can u please briefly explain it sir…
    i’ll b very thankful to you if u will clear my concepts about the transformerless power supply circuit…

  3. I come from a lifelong background of software development, but this hardware stuff is all mostly a mystery to me. However, this looks like just what I need! I am trying to miniaturize my atmega328P device, but the power supply has been a difficulty. Now my question – Can this circuit be modified to:

    1) Take in 110vac 60hz USA standard power
    2) Output 12vdc at somewhere around 1 amp

    Thanks in advance. This is a great site and I will look around for more inspiration.

    • 1) You may use the same circuit for 110vac 60hz USA standard power for < 159 ma
      2) Using capacitor power supply for 1 ampere output is improper, use SMPS instead

  4. In the above circuit one diode 1N4007 is need to be put in output side otherwise the LED will be keep glowing if battery is charged due to reverse current. one more thing 6.2 volt diode will give very less charging current and it may also not match the all 6v battery charging voltage so i think better to put 9.1V/1watt zener.
    Tested by me and i got this reverse current problem and successfully rectified.
    Thanks.

    • Hi Ashutosh,
      Above circuit is a Power Supply Circuit only. If you are using it as a Battery charger you have to connect the Diode as you said.

      • Dear sir,
        please tell me i have Li-ion 3.7volt 2.2Ah battery with PCB/PCM circuitry.
        now i am trying to charge this battery using your this Transformer less power supply.
        I had check power supply output is 3.3volt & 138mA is it ok for Li-ion battery or any other constant voltage circuit or protection circuit is required plz replay im waiting

  5. i have made this circuit and join two white led series and same another two string in parallel to first one

    but the problem is after a some hour of working all the led cant’t glow and burn out so what’s the matter in this

    also can i use 474k poly cap instead of 2.2

    is there need to connect in series with led string or not

    just i doesn’t wont to add the indicater led so i have removed from this so is this happen due to this or not

  6. need betweed to turn 120 ac to dc transformerless this will be used for roach killing trap. copper flats 1/8 spacing.
    know to keep 1hand in pocket when working on this type unit. thanks richard

  7. When I try this circuit, It always burnt the 100R resister, and also LED is not glowing even once. I triple checked the circuit; but nothing wrong found with soldering or components,where the things gone wrong? What should I do? Pls help.

    2.2uf 400v ceramic cap
    470k 1w
    IN4007 *4
    1000uf 35v
    6.2v 1w zener
    100R
    1kR
    LED

  8. What value of capacitor needed for 6V supply??? I want to remove Zenner diode due to place constraint.

  9. hi
    sir i m working on that circuit,and i got 213V dc after bridge rectifier.when i connect capacitor 1000uf/35v and resistor 100k so that it will warm very quickly because of that zener (6.2,1w) also got damaged.
    component i used.
    2uf 250v X-rated cap
    IN4007 *4
    1000uf 35v
    6.2v 1w zener
    100R
    1kR

  10. Great Work

    i Made this circuit but unfortunately in my area i cant find out 2.2 mf 400v capacitor but i got 474K capacitor circuit works fine
    its out put voltage around 6.75 and current is 15 mA
    but i need to glow 12.no 5 mm white led with parallel connection on good brightness (around 20 mA) and this circuit deliver around 15mA Current what to do increase the current

    this whole circuit i want to fit in a wall clock

    also i have 223j 400v capacitor so is it useful in this circuit

  11. using this way of conversion is depending on power loss ; still you need the transformers to step down the voltage without power loss ; the good of the transformers that while step down the voltage the current is stepped up ;
    there is another way that act like transformer known as the buck and boast converters

  12. You have mentioned that it provides 160 m Amp. Also mentioned that 100 Ohm should be 1 watt rated. But when 160 milli Amp flows through 100Ohm, its power dissipation will bw 0.16*.16*100=0.0256*100=2.56 watt. Hence will 1 watt rated 100Ohm work or will it get burnt at this rated current? If we are to have 1 watt rating then current will have to be limited to around 64 milli Amp.

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