Em 13/9/2011 07:56, Forrest Christian escreveu:
> I was looking at the capacitive power supplies, but it looks like the=20
> required capacitors for those are rather large, and probably not surface=
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> mount.   Of course, I may have missed some schematic somewhere which=20
> uses smaller sized/valued caps for this... but the general one needs big=
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> ugly capacitors.  Plus, it seems these are very line voltage sensitive,=20
> which means I get to burn off some more heat in a voltage regulator (aka=
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> resistor and/or zener, or a linear regulator).   Or I can spend money on=
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> a switcher which isn't in the budget.


For 10mA @ 220V @ 60Hz (Brazil), you would need a 120nF x 400V
capacitor, not that bad. Double the capacitance because probably you
will use half-cycle rectification to be able to have a "ground"
reference (neutral).

For 50Hz it is slightly larger, but perhaps you won't need 10mA.

The capacitive power supply is not critical, and you will probably use a
Zener as a primary "coarse" voltage regulator followed by a 78Lxx.

A 150nF x 450V SMD capacitor is available in 1812 package (4.5mm x 3.2mm
x 2.0mm).


Best regards,

Isaac

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