Old 06-02-2011, 12:38 PM #33
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Default Re: LM317 based driver for 1W 445

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Originally Posted by Cyparagon View Post
I have little/no experience with PWM, but are you sure about that much capacitance across the diode? At a higher modulation rate the cap will absorb the pulses and you'll just get a wiggling output rather than a pulsing output.
Depends on how fast you pulse it and how much current you are driving. I would suggest using a scope to find a good value where you don't have a lot of overshoot but still good capacitance.


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Old 06-02-2011, 01:14 PM #34
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Default Re: LM317 based driver for 1W 445

Well, 47uF fails the PWM supply as "pulses" also if they are just 100Hz or few more.

If you want a fast pulsed system, place only a 10nF cap, in parallel to the LD.

Also, wires shorts as possible, and with decent section, and a "fast" diode in antiparallel with the LD (an 1N4148 must be enough, but if you want to be super-paranoid, use a Schottky diode).

And again, place a BIG capacitor (2200uF or similar) BEFORE the regulator, in parallel with the 100nF one (this take care of a bit of the current needs), or also better, an LC group.
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