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Smart Electronics

Transformer-less Power Supply Circuits

I have received a few emails asking for a transformer-less power supply. Here is such a supply. This supply uses no heavy step down transformer and has an extremely low parts count. The circuit can be built very small and can supply small currents for small projects. The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents. 


Parts:


C1 : 10.39uF 250V Capacitor

C2 : 1220uF 25V Electrolytic Capacitor

D1 : 11N4741 11V Zener Diode

BR1 : 11 Amp 200V Bridge Rectifier

MISC : 1Line Cord, Board, Wire, Case 


Also Read 3 phase transformer description


Notes:


  1. The value of C1 can be increased to increase the amount of current the circuit can supply. With the values shown, the circuit can supply up to about 15mA. Remember to increase the size of C2 also. 
  2. A different value can be used for D1 to increase or decrease the voltage as needed. 
  3. Please note that this circuit is not isolated from 120VAC. Because of this, the circuit must be treated with caution and enclosed at all times. Do not work on the circuit (or any other circuits attached to it) when it is plugged in. 
  4. You may want to add a resistor in series with C1 to limit current if the circuit is plugged in and the mains is at its full voltage. 
  5. If you are running the circuit from 220VAC, then use a capacitor rated at greater than 400V for C1. 
  6. If you want isolation from the AC line, you can connect up a small isolation transformer at the inputs of the circuit. Small 600ohm:600ohm audio transformers work nicely.