Re: Feedback for low frequency PWM regulator

"JMini" <j.minihane@xxxxxxxxxxxxxxxx> wrote:

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.

I'm all ears. I'm really looking for all input here.
If someone has simple solution to keep the RMS voltage constant into a
resistive load using PWM while the input voltage drops, I'd love to hear
them. I showed you mine, now you show me yours. TIA, guys.

For less that $1 you can get a PIC in SO8 (and smaller) which has built in
5v regulator, built in voltage reference, built in oscillator, 10 bit ADC,
10 bit PWM generator, and enough processing power to measure the supply
voltage, calculate and apply the required PWM duty at several hundred Hz
(and still have 4 pins left over).

If you can't do software the lamp filament *is* a thermistor providing
direct feedback of what you are actually trying to control (the filament
temperature). You can connect the lamp as one leg of a wheatstone bridge
and make a bistable circuit controlling the MOSFET from a comparator which
flips off when the filament resistance exceeds a value set by the rest of
the bridge resistors. A second comparator can make a timer to flip the
bistable on again after a fixed dead time or an oscillator which flips the
bistable on at constant frequency.

Both are one chip (+ maybe something to drive the MOSFET hard) solutions.


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