alphamnemonic wrote in
:

On Jul 7, 6:09Â*pm, Steve wrote:
Steve wrote
innews:Xns9AD0CDEF8F97Fnobodynobodycom@21
6.196.97.136:

alphamnemonic wrote in
news:ba29f199-331f-48c1-ab96-28c3a81d42d8

@i18g2000prn.googlegroups.com:







On Jul 2, 6:20�pm, Steve wrote:
wrote in news:16ea6110-be19-4a21-aecc-
:

On Jul 2, 3:35 pm, alphamnemonic wrote:
Hi Everybody

This chip normally puts out square pulses. In the power supply
I am working on (http://www.laserfaq.org/sam/150rcsch.pdf) it
is putting out a sawtooth wave. I am testing it in 'standby
mode', in which Q4 is off and R33 is in control of the duty
cycle. Replacing the IC1 has no effect. Does anyone have any
ideas?

Where are you seeing sawtooths? �Pin 13?

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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?- Hide quoted text -

- Show quoted text -

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
http://www.datasheetcatalog.org/data...G3525AN.pdfp.6
for an example of this configuration). I can see why you find that
strange--I did too!

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.

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.- Hide quoted
text
-

- Show quoted text -

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.


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