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Coolling fan electronic thermostat

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fjpompeo

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I need a simple circuit to turn on a fan when the power transistor's heat sink temperature reaches 50ºC if possible using a transistor as temperature sensor. In my country is less expensive build your own stuff instead of import one.

Thanks in advance,

Fernando - PU2PLL
 

Hi,

Browse online for variations on that circuit. I wonder if using a bjt as the temp sensor will require an op amp to amplify the tens of mV the bjt vbe will change between say 25ºC and 50ºC or also maybe level shifting the signal to a suitable level. Have you been simulating diode connected BJTs (and strategic resistors) across temp range, like 0 to 125ºC? Worth the time.

Personally, not sure how accurate using a BJT is as a temp sensor, I think if it were me, I'd look at op amp/comparator based solutions or the NTC one to see if it works (well).

I think this may be a suitable alternative choice for a very simple circuit ; it uses a trimpot, a MOSFET and an NTC, Build yourself a fan temperature control - are NTCs available where you are?
 

Maybe you can include a small microcontroller with a temperature sensor like the LM35
 

I need a simple circuit to turn on a fan when the power transistor's heat sink temperature reaches 50ºC if possible using a transistor as temperature sensor. In my country is less expensive build your own stuff instead of import one.

Thanks in advance,

Fernando - PU2PLL
The simplest way is to use a thermostat switch.There are tons of thermostat switches for different temperature values.All you have to do is to connect this thermostat in series to Fan.
Be aware which voltage and current is used for Fan and then select the proper thermostat switch.The accuracy has not to be very precise, %20 is good enough.
 

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