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Topic: PWM to 1V out supplying at least 200 mA (Read 5353 times) previous topic - next topic

dhenry

Nice schematic by dc42 - it graphically reproduced what I described ealirer - sorry that it confused some poster.

The output voltage on the emitter will be the same as the input voltage on the opamp's non-inverting pin.

Howerev, it is not without potential issues:

1) You want a base resistor to save-guard the opamp. It also helps with stability should you use a mosfet there.

2) For opamps that cannot swing with 07v of the negative rail (gnd in this case), you want to use a darlington or a diode to pad the Vbe. More diodes to pad the Vbe more. This will linit the max positive swing, however.

3) As is, the output current is determined by the input voltage + load resistance. To the extent that the load has non-linear v-i characteristics, you can float the load to the collector or introduce a sampling resistor - this type of circuit is often used in a current loop trnasmission.

Hope it helps.

Grumpy_Mike

@dhenry
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1) You want a base resistor to save-guard the opamp. It also helps with stability should you use a mosfet there.

Wrong on both counts.

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Hope it helps.

I have yet to see  thread where you do help.
Your advise is flaky at best, I suggest you finish learning about the subject before offering advice here.

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