Olin, thanks for that explanation.

I would have never thought of that.

But I see how it could work.


Mark Skeels
Engineer
Competition Electronics, Inc.
TEL: 815-874-8001
FAX: 815-874-8181
www.competitionelectronics.com

On 9/15/2010 12:12 PM, Olin Lathrop wrote:
> Mark E. Skeels wrote:
>> I suppose you will now tell me.....
> I'm not Dave, but:
>
>>      * It's really simple
> At your power levels (150W if I remember right), it's a bit more than
> "simple".  That's 1.4A back to a 110V power line.
>
> For low powers and simple, you can dump your power onto a cap, which you
> then discharge thru a diode during the falling half of the positive half =
of
> the power sine until it goes below some threshold voltage.  The cap is bi=
g
> enough to that it doesn't build up too much voltage during the time it's =
not
> being discharged to the power line.  The dumping the power onto the cap p=
art
> is just a boost converter, except that its feedback regulates the input
> current or voltage instead of the output current or voltage.  The cap jus=
t
> builds up voltage according to Volts =3D Sqrt(2 * Joules/Farads) until th=
e
> next dump to the power line.
>
> At 150W however, you probably need to wake up and do it right, even if po=
wer
> factor regulations don't force it.  You still dump power to a cap the sam=
e
> as before, but now you've got a reverse PFC circuit maintaining the cap w=
ith
> about 200V and dumping current onto the power line in little pulses
> proportional to the instantaneous power line voltage.  This is simpler th=
an
> a real inverter, since the power line is there and you can consider it a
> voltage source.  This is basically a "electronic load" circuit meant to
> handle more than trivial amounts of power.
>
>>      * any real/qualified EE should be able to do this
> Well, um, actually yes.
>
>>      * I am morally obligated to do this
> Not really.  The decision whether to do this or just dissipate the power
> depends on a lot of things, mostly economic considerations you haven't to=
ld
> us about.  However, heat sinks, fans, and the extra space to put them
> someplace, weight to ship them, etc, aren't cheap.  I don't know the deta=
ils
> of your sitation (and don't care, you're problem, you figure it out), but=
 it
> may well be cheaper to handle the power by dumping it back onto the power
> line than to deal with 150W of heat.  Compare the cost of a few FETs, cap=
s,
> inductors, and a dsPIC to that of a heat sink and fan, not to mention
> reliability costs which inevitably happen when things get hot.
>
>
> ********************************************************************
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> (978) 742-9014.  Gold level PIC consultants since 2000.
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