Today I was impressed. While being at the university, some 20 years ago I 've had a hard time understanding the principles of Transistors and MOSFETs. That was partly because I was starting reading 1 or 2 weeks before the exams and just taking notes during the semester, and partly because I was not lucky enough with the professor that had taken on to teach my class (don't ask but if you do he was a syndicalist and he was splitting the time of the lesson by 70% for syndicalism and by 30% for the lesson which was performed on fast forward). Today creating something I needed a P-MOSFET and not being able as it was proved at last, since in the beginning I thought did not know (and indeed you know only what you can remember), not being able thus to recall the exact knowledge for this and not wanting to go through a lot of YT Videos to get what I want, I asked ChatGPT for this. Here is the dialog and it rings a lot of bells (maybe almost 100% right if I recall correctly now but will check it). If anyone wants to step in to verify the info, please don't be shy...
USER
Hi, how are you?
ASSISTANT
Hello! I'm an AI, so I don't have feelings, but I'm here to help. How can I assist you today?
USER
Do you know what a P-MOSFET is?
ASSISTANT
Yes, I'm familiar with P-MOSFETs.
A P-MOSFET (P-channel Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of MOSFET where the majority charge carriers are holes. It is constructed using a p-type substrate, which is typically made of silicon. The operation of a P-MOSFET is controlled by applying a positive voltage on the gate terminal to create a depletion region and control the flow of holes between the source and drain terminals.
P-MOSFETs are commonly used in complementary metal-oxide-semiconductor (CMOS) technology, where they work in conjunction with N-MOSFETs to create logic gates and other digital circuitry.
USER
So the conduction is only from Drain to Source or can it be also from source to drain if the mosfet is on?
ASSISTANT
In a P-MOSFET, the conduction occurs from the source to the drain when the transistor is in the on-state. When a positive voltage is applied to the gate terminal, it creates a depletion region in the p-type substrate, allowing the flow of holes from the source to the drain. This is referred to as the active mode or the on-state of the P-MOSFET.
In the off-state, when the gate voltage is low or zero, the depletion region expands, blocking the flow of holes between the source and drain. In this state, the P-MOSFET acts as an open circuit, preventing current flow.
USER
If I set the source in a higher voltage than the drain will there be conduction from source to drain?
ASSISTANT
No, in a P-MOSFET, the conduction will not occur from the source to the drain if the source voltage is higher than the drain voltage, even if the transistor is in the on-state.
In a P-MOSFET, the flow of current (conduction) occurs when there is a positive voltage applied to the gate terminal relative to the source. This creates a depletion region in the substrate, allowing the flow of holes from the source to the drain.
If the source voltage is higher than the drain voltage, there will be a reverse bias across the P-N junction between the drain and the substrate, which prevents current flow from the source to the drain. The P-MOSFET will effectively be in the off-state, and the conduction will only occur from the drain to the source when the proper gate voltage is applied.
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