RC step down

Nov 07, 2008 2 Replies

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cell 17 years ago

Hi, everyone,

I have seen several circuits from a book to step down 220V AC to 12V DC using only resistor, capacitors, diodes, and a 12V Zener diode.

220V---Parallel RC---R---Bridge---Zener and smoothing caps---Gnd

Load is connected to the 12V from the Zener and Gnd is from the bridge negative pin

I am curious about why the portion "Parallel RC---R" can be used.

For RC parallel components, R=750k C=0.1u (400V)

For another resistor, R=22

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miso 17 years ago

Since this provides no isolation, there are no survivors of this design to give you the schematic.

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Mook Johnson 17 years ago

The R is there to discharge the C when the item is unpluged.

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