OK I am trying to design a circuit that uses an lm61 to monitor the temperature inside a computer case. If the temp goes over a preset value the op-amps will power a darlington array that drives a fan.

I have not gotten very far with is yet because I keep popping the lm61's. On the spec sheet it is shown connected directly to a 3-12V power source. I am using the I did that and it blew instantly. Then I tried limiting the current to around 2 mA with a 6k resistor between +12 and the lm61. Now the new lm61 wont work properly.

Can anyone tell me how to hook these things up? Do I need a minimum load on the output to get a legit output? What value resistor do I need to limit current?

I would normally keep trying but I have popped $12 worth already and have 2 left. I have tried looking for designs online that use the lm61 but I could not find anything after numerous serches and going through 50 pages of google results.

 

On this page they have a schematic for a typical application. Are you hooking it up the same way?
JB

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Nothing is impossible for the man who doesn't have to do it himself - Weiler's Law

 

quick check - are you sure you don't have the pinout backwards? chips act like two series diodes if you put them in backwards - which on a computer power supply will pop them instantly...

 

The recommended max supply voltage is 10V. It is not guaranteed to work with 12V.
Its max output current rating is only 10mA so it might fry if it drives a low resistance.

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Uncle $crooge

 

Post the schematic and don't run it from the 12V rail as it could easilly be damaged by the smallest surge, use 5V or a 9V regulator.

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Well that figures. I got the 12V from a spec sheet for the lm34 which can take up to 20V. I had both spec sheets in front of me when laying out the design and got the wrong value. I will throw in an lm7805 with a cap and see what happens. Thanks everyone.
I have the schematic as an attachment.

Here is my theory behind its operationfor those who are interested:
V2 in the diagram is the representation of an lm61 (lm7805 not shown). (multisim7 didnt have an lm61 so I used a battery)
The first op-amp subtracts the difference between the output voltage of the lm61 and U2(which buffers a potentiometer adjusted voltage reference). This part of the circuit will (ideally) output a voltage only if the output of the lm61 rises above the set reference voltage.
The output of U1 is then added to a reference voltage of 8.5V(fan will not run until it has 8V supply). This setup keeps the fan running at around 8V, and if the temperature rises then the voltage of the fan will rise quickly. I think I have it set up with the gain to provide full power to the fan when the temp is around 10C over the set value.
I have it set up this way because the fan is EXTREMELY noisy. It is pushing 130cfm at 12V. Running at 8 or 9V it is tolerable.
I think I may have to add a resistor to the U3 output still.

Attached Images

Fan Contoller.JPG (43.8 KB, 8 views)