Simple transformerless power supply

Posted by Ilias-Man On Wednesday, February 1, 2012 14 comments
This is a low current transformerless power supply for small applications. The capacitor C1 reduces the high volt AC. D1-D4 rectifies AC to DC and C2 reduces ripples. R1 discharge stored energy in C1 to avoid electric shock when power is off. R2 limits inrush current. The Zener diode is used to get regulated DC output.

 -The Zener value can be changed to get other output voltages.

If you don't have a zener diode use normal diodes in series for exemple 3 diodes in series give 1.8v-2.2v depending on the load current.

- The value of the capacitor determines the maximum output current, now let's calculat'it it's easy...: 

  1. First we calculate the impedance of the circuit (C1 and R2): Zc+R2 = (1/(2*pi*F*c))+R2 = (1/(314*0.0000022))+100 = 1547Ω. 
  2.  Second we calculate the voltage across C1 and R2: V-Vz-Vd = 230-12-1.4 =216V. (( V (main AC) Vz (Zener voltage) Vd (voltage drop across diode brige 1.4v) )).
  3. Third the max current: 216/1547 = 140 mA.

Use the same calculations for other values.

Ask if you have any questions.


Rah said...

Sir Please Tell me about efficiency of the above main circuit.

& please describe the efficiency calculation & also the power factor & ripples calculation... Thanks.

Bilal Tahir said...

how to determine current capability of a capacitor?
i mean i wanted to use a series capacitance for high power circuit.
i have a 220v ac supply at 50 Hz. and need to lower ac voltage to 160 v ac current required at 160v is 5 A approx
can i use a capacitor for this much power.
should i use parallel capacitors of small values to get this much current?


Vaibhav Shinde said...

Can we use this power supply for 4.6 W audio amplifier with CD6283CS IC??

zain-ul-abidin Zain said...

i want 100 watt at output what value of capacitor i would introduce in circuit(x rated as well as electrolytic means filter capacitor)

asaad un said...

hi sir i want 94 volt dc supply how i make ?? i want circuit design

Bhasi stingfly said...

I like the way you explained and the most important thing i liked is replacement of zener diode its great

Christian Medina said...

why you divide for 1547 when ur looking for current max?

Aaron Nobel said...

It is very informative post.

James Hozy said...

Thanks for sharing this great information it is very helpful but I have a problem please help me, can you please give me a formula for calculating the voltage output of this circuit with the capacitor voltage and resistor ratings as the parameters. I would like to say a special thank to you in advance.

Unknown said...

Please note the circuit has high voltages. It is not for inexperience hobbyists.

Ravindra Dasanayaka said...


Ravindra Dasanayaka said...


nightex said...

Why zener is without resistor? It looks like short circuit?

Tanvir Fakir said...

Hello sir I my. Capacitive ckt i have used 474 and 105 cap to get ouptput current of 120mA .and after that bride ckt i have used zende diode which 47v 5W bcoz my load is 5 watt..and after that iIhave connnetced 100V 47uF cap..vutbresult i am getting is zener diode increase very high temperature .so what will be the best possible solution

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