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Wish to use open drain comparaotr to turn PNP on, so don't need pull up resistor?

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treez

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Hello,

I wish to use the open drain version of this comparator......(MCP65)

http://ww1.microchip.com/downloads/en/DeviceDoc/22269B.pdf

I do not want to use a pull up resistor at the output though....because all i want to do is get this comparator to turn a PNP transistor on when its output goes low.

Do you think this kind of operation is possible with this comparator?
 

Tahmid

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You should still use a pull up resistor to turn the transistor off and to ensure that it stays off. I have had bad experiences with PNP transistors turning on and staying on with floating base.

Hope this helps.
Tahmid.
 

FvM

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You didn't tell how the comparator output is connected to comparator and if you intend e.g. feedback resistors to provide hysteresis. Provided you drive the PNP in common collector configuration, you don't need a base resistor. A pull-up can be omitted only if the comparator's up to 100 nA output leakage isn't an issue.
 
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treez

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thanks, ...i was just worried that it might drive high instead of just pulling high....

i have resistors from B->E and C>B, so that the comparator can switch the PNP on by driving low.

....interesting that i dont need a base resistor for the PNP....there are no hysteresis resistors, ...i believe the internal hysteresis will be enough, and also, this is a comparator that only gets tripped when the customer pulls the battery out without turning off the equipment...which i believe will not happen often....so even if there is some jitter when it trips, i dont think it will be too serious
 

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To avoid misunderstandings, I would prefer to see a schematic.
 
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