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Small thermal switch

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Hey all.. I've been searching google, but have yet to find what I need.

What I am looking for is something thats ideally really small... like the size of a transistor, that is normally closed and when it reaches 120 degrees F, it opens until it cools.

Now it doesn't exactly have to be a switch type deal... It can be something that sends a signal or something when the cutoff temp is reached..

I remember finding something close to what I needed on the net a few weeks ago, but can't find it anymore... I think the thing I saw had 3 leads and looked just like a transistor...

Anyways... If anyone could point me in the direction of where I could find something like this that would be great... Or just tell me what this thing I'm looking for is called.

I've searched for "Thermal switches" but everything i've found under that are really big and bulky..

Thanks in advance!


It's going to be a safety measure to prevent overheating. So it doesn't need to handle large currents. Just send some kind of signal when overtemp occurs.

It is going to go on the body of a heater far away from the actual heating part. The heater has its own thermostat and such.

I just want to add a small device near the body so if for some reason it does get too hot (above 120F) ... It shuts the whole heater down until the body of the unit cools down.

and I must stress the size factor.

I know the tiny transistor sized units like this exist.. I've seen them.

I think the one I found a while ago had 3 leads. A ground, a positive, and the trigger.

I also think it was programmable too...

I need a unit that is as standalone as possible.
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The DS18B20 an LM34 are both TO-92 but both require extra circuitry. Since the OP hasn't indicated what it'll be switching we can only guess.

Open drain is similar to open collector. It can pull a signal to GND


Would it be ok to just build a circuit around a thermistor to accomplish the same end?
No... to much to deal with...

Actually... that open drain method sounds like it would work...

I could simply hook it up to the heater control circuit so that it cuts the power to the heater when it gives the over temp signal.. be it GND or V+.

Now I just need to figure out how to wire it.... Ill be back in a bit. Going to play with a few different circuit layouts.
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