I'm trying to fix an AC-DC line regulator that I have build and doesn't work as expected.
I'm trying to convert AC 220V mains to DC 5V 10mA without a transformer. To do this I'm using an 1uF 250VAC Polypropylene Film cap like in the schematics bellow, followed by a voltage regulator with TL431.
When I simulate the circuit in Proteus, I get 5V at output with/without C3.
In real circuit with C3 I get 5V output (not sure how noisy though; no oscilloscope), but if I remove C3 I get 2.5V, which clearly indicates that the shunt regulator TL431 oscillates.
I tried putting a 22p cap between the cathode pin and ref of TL431 (pin 1-2), but no dice.I have also tried removing D4.
WARNING: - The output of this circuit is not "isolated"from AC mains and should be treated as being at mains potential at all times. [RM]
Failure of C1 or reversal of Vac connections or other conditions will result in mains live (Phase) voltage appearing at output.
C1 MUST be an "X rated" capacitor designed and certified for use on 230 VAC AC mains by its manufacturer.