What to look for in OP AMP comparator

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jlawley1969

Joined Feb 22, 2021
97
I am trying to implement an OP AMP with a thermistor to make an adjusted thermal shut down for my flyback circuit. I am using TNY290 and it has "Multifunction Pin" which is said that if the pin reaches 9mA that it will cause shut down . So my plan is to use a two voltage dividers one for each of the OP AMP pins and include the thermistor into one of the voltage dividers so when it reaches the temperature the OP AMP sinks current to the pin.

Now the point I am at is I don't really know what OP AMP to get because they all have so many different characteristics like slew rate and gain and such. I am under the impression that most of the characteristics(aside from absolute maximums) don't matter because I am just using it as a comparator.

Is there an industry standard OPAMP the way the TL431 is for voltage references??
thank you
 

BobTPH

Joined Jun 5, 2013
4,322
If you want a comparator, why not use a comparator? Opamps can perform as a comparator, but a chip designed for that purpose would be better.

Bob
 

LowQCab

Joined Nov 6, 2012
1,635
I made the Schematic.
What are your questions ?

The Pot can be replaced with a single resistor when the "trip" Temperature is established,
by either bench-testing, or by obtaining a Resistance-Graph for the
Temperature-Dependent-Resistor that You intend to use.

I think a Diode could replace the TDR, but I have not investigated that possibility.

This Circuit does not "latch", and the only Temperature hysteresis is mechanical.

Electrical / Temperature-Hysteresis can be added with an additional single Resistor.
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