WARNING: Don’t touch any part of the circuit when the circuit is running (connected to the powerline), this circuit is not isolated from mains supply.
This is transformerless power supply circuit. This circuit is used to generate fixed voltage power supply capable of supplying 35mA. This circuit uses 4 diodes in a bridge that is consist of 2 zener diodes and 2 ordinary diodes. It is not useful if this circuit uses 4 zener diodes. Using 18v zeners and 2 ordinary diodes will gives output voltage of be 17v4. Here is the circuit:
The left zener provides 18v limit, When the incoming voltage is positive at the top. the left power-diode produces a drop of 0.6v. This allows the right zener to pass current with the voltage available to it is just 18v. The output of the right zener is 17v4. other half-cycle is same with first cycle.
The X2 capacitor is used to limit the current (7mA for each 100n when in full-wave). The 10R used as safety-fuse resistor. This circuit will only deliver 35mA before the output drops, although Theoretically the circuit will supply 70mA. The project being powered with this circuit must be totally enclosed in a box with no outputs because it can kill the user due to the “live” nature of the negative rail of this circuit.
