Weird behaviour of logical mosfet in proteus

Question

I'm trying to drive a P-Mosfet logical from a 2-3Decoder 74HC238, the problem is whatever the Input to the MOSFET's gate, I always get a high output on the drain.

Kindly find the attached schematic, if there is a faulty mistake.

Q1 is the output, DEM1 is the input from the 74HC238 ( directly connected )

Answer 1

I think your circuit was intended to be like the following and you have connected the Source-Drain inverted (and a P type instead on N type).

^{simulate this circuit – Schematic created using CircuitLab}

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Proteus simulation, showing both states

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Proteus simulation, showing both states using 74HC238 to drive the gate

Answer 2

It looks like you have the right components in the wrong places. Try one of these.

Implementation with a P-channel FET:

^{simulate this circuit – Schematic created using CircuitLab}

Keeping the P-channel FET, a logic low input will result in the FET conducting, current through R1, and a logic high at the output.

Implementation with an N-channel FET:

^{simulate this circuit}

Replacing with an N-channel FET, a logic low input will result in the FET not conducting, no current through R1, and a logic high at the output.

Both schematics assume your supply voltage, Vcc, is equivalent to your input voltage. If all you have is a P-channel FET, go with the first schematic. However, N-channel FETs are usually cheaper than a P-channel with similar capability. It also depends when you want a voltage across R1 as well.