PWM Control IC Problem (SG3525)

Where are you seeing sawtooths? Pin 13?

--- sam | Sci.Electronics.Repair FAQ:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

snipped-for-privacy@ece.drexel.edu wrote in news:16ea6110-be19-4a21-aecc- snipped-for-privacy@e39g2000hsf.googlegroups.com:

That is my question. Why do you have output A and output B (pin 11 and 14) grounded?

Also, pin 13 is VC in for the transistor collectors. Why do you have this connected as an output?

.html

Yes the sawtooth is on pin 13. Pin 13 is being used as an output and pins 11 and 14 are grounded because the chip is being used in single- ended supply mode (see

alphamnemonic wrote in news: snipped-for-privacy@i18g2000prn.googlegroups.com:

I'd avoid the funky setup you have. In my opinion I'd connect pin 13 and 15 together and use either output A or B.

I'm not sure what Q4 is doing, I've never seen it used this way, but you must know more than me since you designed this elaborte circuit.

Keep us posted at what you do to resolve the problem.

snipped-for-privacy@i18g2000prn.googlegroups.com:

ror

It's not my design. I am trying to repair a commercial unit. I will keep you posted.

innews: snipped-for-privacy@i18g2000prn.googlegroups.com:

First, I've never scoped pin 13 so don't know for sure what should be there.

But, my guess is that one of the 3 transistors is not behaving properly.and you're seeing one of the caps charging.

--- sam | Sci.Electronics.Repair FAQ:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

Steve wrote in news:Xns9AD0CDEF8F97Fnobodynobodycom@216.196.97.136:

@i18g2000prn.googlegroups.com:

I have been looking at the circuit and the datasheet.

I'm willing to bet the schematic is drawn wrong. It doesn't make any sense to have pin 13 driving the base of a transistor.

EPAIR/

=EF=BF=BD =EF=BF=BD | Mirror

in the

The schematic is drawn correctly. This mode of operation is described on p.6 of the datasheet (link is given in my post from July 3). I removed the board and re-soldered R1 and R2, and the supply is now working properly again. A rather boring fix, but if it works long term I won't complain... If anyone else is having trouble with this supply, I can send you waveforms captured with FlukeView from the working unit. Thanks for the suggestions everyone.

alphamnemonic wrote in news: snipped-for-privacy@y38g2000hsy.googlegroups.com:

I'd like to see them. Do you have them in a format you can easily email?

snipped-for-privacy@y38g2000hsy.googlegroups.com:

g/R

orm

Hide quoted text -

Yes: .rtf

alphamnemonic wrote in news: snipped-for-privacy@d45g2000hsc.googlegroups.com:

I phrased that incorrectly.

I meant can you post them on here for downloading or on a site?

Thanks

snipped-for-privacy@d45g2000hsc.googlegroups.com:

=BD

k F

I don't have a website, but I will post them here if you tell me how.

This isn't a binary newsgroup, and you can't post pictures through Google Groups.

Sign up for a free photo hosting service and post the link to the pictures.

The pics are up at

alphamnemonic wrote in news: snipped-for-privacy@z6g2000pre.googlegroups.com:

Those are interesting waveforms.

Nothing I would have expected if I was working on this or I didn't have a known working unit for comparision.