Re: Feedback for low frequency PWM regulator

JMini wrote:

On 7/7/2008 2:22:24 PM, "HarryD" wrote:

"nospam" <nospam@xxxxxxxxxxxxxx> wrote in message
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"HarryD" <harryd@xxxxxxxxxxxxx> wrote:


"JMini" <j.minihane@xxxxxxxxxxxxxxxx> wrote in message
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I'm building a PWM regulator for an incandescent bulb. Some of thos was

Cut lots of bad ideas!

Cut another bad idea.

He needs to regulate the power in a resistive load. The required PWM duty
cycle is inversely proportional to the square of the supply voltage. You
don't square anything with an RC network.

You could get a square law by making the PWM on time inversely
proportional
to the supply voltage *and* the PWM period proportional to the supply
voltage but there are simpler solutions.
--

He needs to regulate luminous intensity, controlling power may be one way.
A better way may be controlling current thru the lamp. VFF is a simple
current control. We need a plot of lamp current and power vises luminous
intensity. I'm betting on current being the more linear and best to
control intensity. Where is Don Klipstein when you need him? Sorry if this
is a rehash.

Cheers,
Harry



Luminous intensity is fine if the flashlight will only be operating in a
constant ambient luminosity level, however it almost definitely won't.
I don't why you're making it so hard on your self..
Simply place a photo detector diode in the path of the light and use
that as a feed back to the PWM circuit..
the circuit can be operating on a low voltage fixed regulator ..
etc..


--
http://webpages.charter.net/jamie_5";

.

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