Both cap and resistor perform the same function in current limit. The cap
can eliminate the power loss though but for flash application this power
loss is not significant moneywise. Limits the current at 10mA max will
significant increase the charging time, my calculation is 100mA max at start
up which is more practical.
C.H.Ling
----- Original Message -----
From: "W Shumaker" <om4t@xxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Sunday, September 28, 2003 10:43 PM
Subject: Re: [OM] T-32 AC power options - an actual on-topic post
> Resistors will dissipate power, how about a charge pump type circuit,
> where a capacitor and rectifiers deliver the power. This will give an
> equivalent resistance without dissipating power. Something on the order
> of R = 1/(C*60Hz). So 200V/10mA = 20K ohms => C = 0.8uF capacitor.
> This will limit current to 10mA at 200V drop. If more power is needed,
> a larger cap is needed, which will become impractical if it gets too
> large since high voltage caps are large. (or else a higher frequency
> will be needed). The problem with resistive current limit is the low
> current at the rated voltage. Next step, dc-dc converter that will provide
> some current an voltage regulation.
>
> Wayne
>
> At 08:16 PM 9/27/2003, you wrote:
> >If you put a 10mA fuse in series, I believe it will burn immediately, the
> >initial charging current is much higher than that and may keep for a few
> >seconds. If you want to use other transformers and limit the current you
can
> >add a power resistor in series, a good value may be around 2K ohms 20W.
> >
> >C.H.Ling
> >
> >----- Original Message -----
> >From: "Piers Hemy" <piers@xxxxxxxx>
> >
> >> Noted, good point!
> >>
> >> The label actually* says "Output DC 200V 10mA", so how about we add
"and a
> >> 10mA fuse" to "with a bridge rectifier"?
> <snip>
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