Feedback for low frequency PWM regulator - sci.electronics.design

Message from discussion Feedback for low frequency PWM regulator

JMini

View profile

More options Jul 6, 6:23 pm

Newsgroups: sci.electronics.design

From: "JMini" <j.minih...@minihane.tzo.com>

Date: Sun, 06 Jul 2008 13:23:49 GMT

Local: Sun, Jul 6 2008 6:23 pm

Subject: Re: Feedback for low frequency PWM regulator

  Reply to author
  |
  Forward
  | Print
  | View thread
  | Show original
  | Report this message
  | Find messages by this author
  

On 7/4/2008 7:13:09 PM, John Popelish wrote:

> JMini wrote:

>> OK. I've uploaded a quick drawing to imageshack. PLEASE forgive the hand
>> drawing. I'm awful at getting this stuff into schematic software.
>> http://img386.imageshack.us/img386/9920/pwmschemajx8.jpg

> I'm not so sure about the error amplifier part, but I see
> why you are using an RMS converter, so you are controlling
> the "effective" voltage to the lamp. I take it you are
> after constant brightness. Of course, you could also
> measure the lamp light output so you compensate for it aging
> (and for the initial tolerance).

> Are you very cramped for space, or is there some other good
> reason you don't want to average the voltage of the pulses
> with an inductor, so you can eliminate the RMS converter?
> Having the inductor would lower the current ripple from the
> power source and also the losses in the switch.

I am extremely cramped for space. the RMS converter is an 8-MSOP package. The
inductor would be HUGE. This regulator will carry about 10-11 amps RMS. I'm
also looking at keeping the frequency rather low to avoid a ton of switching
noise an reduce the phantoms that pop up when using high frequency PWM in
close proximity to other sentitive bits. I don't imagine 40+ kHz 10 Amps RMS
would play bery nicely just millimeters away from my RMS converter.

Reply to author Forward