[sdiy] VCO Cap Switch

harry harrybissell at prodigy.net
Thu Jun 6 05:23:24 CEST 2002


IMHO the LM311 does need a pull-up resistor... it is an open collector
output, capable of wire-or operation.  You may set the emitter of the output
transistor to any voltage you like, most other comparators pull down to the
negative rail (like the LM393).

H^) harry

Ian Fritz wrote:

> At 10:00 PM 6/4/2002, Scott Bernardi wrote:
> >The datasheet shows the LM319 spec'd at 36v max, same as a LM311.
>
> True. But I found that to get full output swing I had to use a rather small
> (750R - 1k) pullup resistor. In my TRI oscillators this caused the chip to
> run quite hot, so I reduced the PS voltages. Tracking was then much
> improved. For a SAW oscillator this isn't a big issue.
>
> >The LM311 needs
> >a pullup resistor also, doesn't it?
>
> Not that I can see.
>
> Another issue with the 319 is that there aren't any good application
> schematics. I must say, I really don't know the proper way to connect the
> ground pins. I just hooked them to the - supply, but this actually violates
> one of the max ratings. May be this is why I had trouble with heating.
>
> >I used the second comparator in the LM319 for the pulse output (sawtooth
> >on one
> >input and PWM input on the other).
>
> A good plan.
>
>   Ian

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