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Load control using PWM and temperature sensor

Discussion in 'Sensors and Actuators' started by udhaya, Apr 4, 2016.

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  1. udhaya

    udhaya

    17
    0
    Feb 26, 2016
    Hai Alec_t,
    Am also tried 12v for 555 timer but the problem is still present.
     
  2. Alec_t

    Alec_t

    2,904
    784
    Jul 7, 2015
    +12V should not be connected directly to the FET drain.
    Do you have your load (lamp, LED with current-limiting resistor, other) connected in series between the drain terminal and +12V?
    Do you have the catching diode at the drain connected with the correct polarity (cathode at +12V)?
     
  3. udhaya

    udhaya

    17
    0
    Feb 26, 2016
    Please have a look on my post(#10) on that am shown the circuit diagram,only change is instead of 2N2222 replaced with IRF740B MOSFET.on that +12v is connected with diode and drain,across the diode only am connected the load.
     
  4. Alec_t

    Alec_t

    2,904
    784
    Jul 7, 2015
    You keep saying that +12V is connected to the drain. That is confusing, since it's not what the schematic shows. If you have indeed connected +12V to the drain, that would account for the FET frying. The +12V rail should be connected only to the diode cathode, to one terminal of the load, and to the supply pin of the 555.
     
  5. udhaya

    udhaya

    17
    0
    Feb 26, 2016
    If you don't mind can you please draw the schematic diagram for that,in my diagram +24v is changed with +12v.
    can you understand that, what am looking for.
    MOSFET is turned on when the 555 output goes high( using multimeter the voltage is displayed ) but it does not turned on the load.
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,567
    2,356
    Nov 17, 2011
    I think that's not the way it's going to work. Show us instead your complete and correct diagram so we may be able to spot possible sources of error.

    This is in contradiction to your post #17, where you tell us that the drain voltage is 12 V even with the gate voltage of the MOSFET being 12V. With Vgs=12V the MOSFET should show VDS~0V, depending on the load current. And when Vds~0V, the voltage across the load is Vload=12V-Vds ~ 12V, so the load should be on.
    How do you verify the MOSFET is on?
     
    Alec_t likes this.
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