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

 

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

 

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

Not really.
Why an op amp?
A common comparator IC is the LM339/393 which should do what you want.
According to the data sheet you only need to sink 115µA to shut down the TNY290 (below).

 

Not really.
Why an op amp?
A common comparator IC is the LM339/393 which should do what you want.
According to the data sheet you only need to sink 115µA to shut down the TNY290 (below).

View attachment 253994

unless I am missing something that states "current out of this pin" thanks for the comparator suggestion tho.

 

Way too much complexity ..........
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Way too much complexity ..........
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View attachment 254033

oh that super smart!!!
do you have a link to where that image is from because I have some questions about the specifics

 

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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