On Fri, 01 Apr 2011 21:08 -0400, "Herbert Graf" wrote:

>=20
> As you can see there's a whole spectrum of "stuff" coming out of this
> thing. The base switching freq seems to be around 50Khz, I kinda
> expected that given the size of the wall wart, but why the spread
> spectrum stuff?
>=20
> Is this for PFC? Is it to reduce EMI or something like that? Anybody
> ever design a switching power supply that outputted something like this?
>=20
> I want to dim these beasties, my initial thought was that the wart
> outputted DC and I could use a simple 555 circuit to dim it, now it
> looks like I might have to do things another way.

Hi Herbert,

I'm guessing that the frequency changes 120 times per second. Since the
load is basically resistive, they don't need to do PFC. So the frequency
changes because the circuit is simple.

I wonder how well a simple triac-type lamp dimming circuit would work at
50KHz and ~12 volts? RCA used SCR's at 15KHz in televisions and that
worked well. Losses at 12 volts would be substantial, but not crazy.

Cheerful regards,

Bob

--=20
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