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  1. #1
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    Coolling fan electronic thermostat

    I need a simple circuit to turn on a fan when the power transistor's heat sink temperature reaches 50ēC 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

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  2. #2
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    Re: Coolling fan electronic thermostat

    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 25ēC and 50ēC 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 125ēC? 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?



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  3. #3
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    Re: Coolling fan electronic thermostat

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



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  4. #4
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    Re: Coolling fan electronic thermostat

    Quote Originally Posted by fjpompeo View Post
    I need a simple circuit to turn on a fan when the power transistor's heat sink temperature reaches 50ēC 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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