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Transformerless Power Supply

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ajanogi

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Hello Everyone

I need a power supply without transformer (12V 3W)(Vin:220V AC 50Hz, Vout: 9-15VDC). My circuit should be small size. I was searching about that design for a while. I tried LNK306 but it is not very good in my opinion. I couldn't get a quality voltage level with it.

Also i tried some of big capacitor and resistor circuits. But with that u have to use big capacitors and they are expensive and huge size. So i need some help about that.

Is anyone know anything about with this circuit? Please help me, thanks..
 

most of the simple designs of transformerless powersupplies contains a ceramic capacitor 105, 450v in series with phase line of 220v of ac mains and a high value resistor in series or in parallel to capacitor mostly greater than 100k ohms, and after that to reduce/clip the amplitude 2 zener diodes are connected in series in such a way that their kathods are joined together and the series combination is then connected in parallel between phase and neutral lines. suppose if you are using 15v zener diodes you will get 15v peak to peak signal at the output that can be passed through bridge rectifier to get smooth 30v dc. for high power simply use high power components.

see the following images to get the idea:


 

Thank u guys for your response. I want to ask u, have u tried this schematics before? And may i use this for 3Watt circuit?
 

ajanogi said:
Thank u guys for your response. I want to ask u, have u tried this schematics before? And may i use this for 3Watt circuit?
Click to expand...
12V 3W --> 250mA

At low voltage output, that power source deliver ~60mA per microfarad (C1) --> you need at least C1 = 3.9 uF x 400V poliester --> it isn't a small cap.

Take a measure of the real max current what sink your circuit and then choose C1.
 

I afraid of this :(

well i use 4.7uF 400V capacitor (Don't know poliester or not). It s ok for me. Not so huge. 250mA is good. But there is a question, may i should (phase-neutral-ground) short-circuit gnd with neutral? And also same question for analog gnd with digital gnd?.
 

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