micro Ampere power supply

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aalbaschar

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Hi!

I'm working on designing a touch button using pico power AVR microcontroller.
upon detecting a touch, the system should activate an AC appliance. For that i will use a triac.
The whole circuit should consume no more than 1 mA at 2V.

Now I'm searching for the best way to power this circuit from the AC mains without using a bulky power supply and with lowest possible cost.

Do anyone have some suggestions?

Thanx for help
Baschar
 

Try capacitor coupling to the mains. The reactance of the cap(s) can be used to drop the voltage. You can omit C3 (on the neutral wire) in the image if you don't need isolation. Realize though, that the voltage will vary with the load And that line harmonics are coupled though the caps easily.


 

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Thank you very much bobmcbride !
I think that is exactly what I was looking for
 

Word of warning, the capacitors MUST be of the correct types because if the one connected to the live mains was to fail short circuit, it would destroy a lot of components and give some one a lethal shock. :-(
Frank
 
Thanx for the warning!

I'll use ceramic capacitors with 500V Dc rated voltage.
 

You'll want a zener clamp on the output or input of the bridge to prevent huge voltages under very light load.
 
I use X or Y rated coupling caps depending on the situation.
 

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