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Transformer less power supply.

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Jammy

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Dear Friends,
I had made a small project which energize the relay according to the logic…
But for powering this CMOS IC I want a transformer less power supply which can power this circuit and it can reliably run the relay…
The requirement is :
———————————
Voltage : 12volt
Current : 100ma
———————————-

The resistance of the relay is 200 ohms and power supply is 12 volt…
 
Transformerless power supplies are very dangerous and quite impractical.

TRANSFORMERLESS POWER SUPPLY
This clever design uses 4 diodes in a bridge to produce a fixed voltage power supply capable of supplying 35mA.
All diodes (every type of diode) are zener diodes. They all break down at a particular voltage. The fact is, a power diode breaks down at 100v or 400v and its zener characteristic is not useful.
But if we put 2 zener diodes in a bridge with two ordinary power diodes, the bridge will break-down at the voltage of the zener. This is what we have done. If we use 18v zeners, the output will be 17v4.
When the incoming voltage is positive at the top, the left zener provides 18v limit (and the other zener produces a drop of 0.6v) This allows the right zener to pass current just like a normal diode. The output is 17v4. The same with the other half-cycle.
The current is limited by the value of the X2 capacitors and this is 7mA for each 100n when in full-wave (as per this circuit). We have 1u capacitance. Theoretically the circuit will supply 70mA but we found it will only deliver 35mA before the output drops. The capacitors should comply with X1 or X2 class. The 10R is a safety-fuse resistor.
The problem with this power supply is the "live" nature of the negative rail. When the power supply is connected as shown, the negative rail is 0.7v above neutral. If the mains is reversed, the negative rail is 340v (peak) above neutral and this will kill you as the current will flow through the diode and be lethal. You need to touch the negative rail (or the positive rail) and any earthed device such as a toaster to get killed. The only solution is the project being powered must be totally enclosed in a box with no outputs.

**broken link removed**
 
Last edited:
Thanks colin55 for suggestions .... I was not knowing that it will be dangerous...
So do You have any alternative solutions to accomplish this project....
 
Use a plug pack ---- wall wort - power supply - anything that has a transformer so you get isolation from the mains.
 
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