design question

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Dear AVRFreaks,

Please see .jpg attached.

The OPAMP's Open Drain output is controlling the base of a NPN BJT. Because of the OPAMP's Open Drain output Saturation
Voltage, I would like to ask your opinion if this is a critical design ???

OPAMP datasheet:
https://www.fairchildsemi.com/ds...

Thank you in advance.

Attachment(s): 

Michael.

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Err, it's a comparator, not an opamp. The output is open collector. I don't think there is an issue in the comparator's output turning off the transistor.

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Dear Kartman,

Thanks for your reply.

Just wanted a second opinion.

Thanks a lot friend !!!

Michael.

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Well the output saturation voltage of the comparator is between 160mV (good) and 700mV (bad, may keep the transistor on). I would sleep a lot better with a diode in series between the pull up resistor and the base and maybe a 100K to ground from the base.

But I'm a bit paranoid... :-)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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I don't see the need for R207...

Ross McKenzie ValuSoft Melbourne Australia

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That's true Ross.

Michael.

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A bit of hysteresis on the comparator might avoid oscillations as would some rf bypassing on the inputs.