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P-Channel MOSFET always on

AAnkur

Feb 7, 2022
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Hello

I am using a MOSFET driver circuit with SI2303 as p-channel mosfet and SI2302 as n-channel mosfet.

I have given control signal (of 5V) on the gate of n-channel mosfet to turn-on and off the p-channel mosfet.



However, the p-channel mosfet is not getting off and I am constantly finding voltage on Output (marked as Point-A).

Please let me know what is the problem in this circuit.

Thanks
 

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Harald Kapp

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Nov 17, 2011
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Show the FET pins (S, D, G). When you swap D and S, the body diode will be conducting. We cannot see this since you haven't used the conventional MOSFET symbols which makes it difficult to read your "schematic".
 

crutschow

May 7, 2021
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Yes, sounds like you have the P-Channel source and drain reversed.
The source must go the the +12V.
 

CircutScoper

Mar 29, 2022
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Hello

However, the p-channel mosfet is not getting off and I am constantly finding voltage on Output (marked as Point-A).


Thanks

What is the magnitude of said voltage and with what kind of voltmeter are you measuring it?

Even when off, mosfets, like any real switch, will have a bit of leakage. The S12303 datasheet speaks of as much as 100nA, which would produce a reading of 1V in a standard 10Megohm input impedance multimeter.

If this mysterioius voltage is of the order of 10s to 100s of millivolts and you're measuring it with a high input impedance meter, try adding a 10K resistor from output to ground. It might disappear.
 

ETechnoG

May 29, 2022
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May 29, 2022
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Check the following points,
  1. Polarity of connection
  2. Components are in good condition
  3. Is there any short circuit
  4. Is transistor goes into breakdown mode
 
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