alan smith wrote:
> I've used a PIC PWM to generate a analog out (RC filter on the
> output) but its always been at the rails of the processor..ie...3.3V
>
> So now I'm required to generate a 0-10V, so I'm thinking just an
> opamp for this with a gain of 3, with the rails of the opamp at least
> 12V (but I have 24V so it will probably be that)..but they need 500mA
> drive.
>
> So...looking for an opamp that will give me 500mA drive, or is it
> better to use a transistor to drive that much current?

If you filter the signal first and then amplify it, you essentially make a
linear regulator.  500mA out at 10V from a 24V supply is going to dissipate
7W.  That's more than even a big transistor can dissipate without some sort
of heat sinking.

A better answer could be to have the PIC PWM drive switches at the full 0
and 24 volt power rails.  Now you essentially have a switching power supply
produce the 0-10V output from the 24V input.  It will dissipate far less if
done right.  If you're driving something mechanical, like a motor or
solenoid, then this is all you need.  Other things might require some
filtering, like a series choke, possibly followed by a capacitor.  It will
depend on the requirements of your load, which you didn't mention.


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