N-Channel and P-Channel MOSFET Wiring: A Beginner Practice Circuit

For a beginner wiring exercise, identify the source reference and the load connection before choosing an N-channel or P-channel MOSFET. The gate must be driven relative to its own source. Performance, voltage, loss, and driver requirements still matter when selecting the actual part.

Last updated: October 16, 2026

Two polarities in one picture

An n-channel device conducts when its gate is driven above its source, so it is normally placed between the load and the negative supply — a low-side switch. A p-channel device conducts when its gate is pulled below its source, so it is normally placed between the positive supply and the load — a high-side switch.

The analogy worth holding is a valve in a water main. A low-side valve sits downstream of the load and lets water out; a high-side valve sits upstream and lets water in. Both stop the flow, both can be operated from the same hand, and the choice of which to install depends on where it is convenient to cut the pipe.

The wiring rule beginners can remember

One sentence covers the common cases: n-channel goes below the load, p-channel goes above it. If you find yourself trying to place an n-channel device between the positive supply and the load, you are working against the device’s natural behaviour, and you will need extra circuitry to drive the gate above the supply.

The reason is the gate voltage reference. A MOSFET’s gate voltage is measured relative to its source, not relative to ground. In a low-side n-channel arrangement the source sits at ground, so a gate voltage above ground turns the device on. In a high-side n-channel arrangement the source sits at the load voltage, so the gate has to be driven above that — which needs either a separate supply, a charge pump or a bootstrap circuit.

Symbols that confuse everyone at first

P-channel symbols usually have the arrow pointing in the opposite direction to n-channel ones, and the body diode inside the device also points the other way. That last detail is worth understanding rather than memorising, because it explains the behaviour when the device is off: the internal diode gives current an unintended path, and in a high-side p-channel arrangement that path can be exactly what you wanted, while in other circuits it is a fault.

The practical version of this is simple. Check the body diode direction in the datasheet before deciding that a switch is off when its gate says it should be. A device that is not conducting through its channel may still be conducting through its diode, and the circuit will behave accordingly.

Common wiring mistakes

Four mistakes account for most beginner failures with this choice. Placing an n-channel device high side and driving the gate from logic, which leaves it partially on and hot. Omitting the pull-up resistor on a p-channel gate, so the device turns on whenever the driving circuit is disconnected. Reversing the drain and source, which works for some devices in some circuits and destroys the switching behaviour in others. And forgetting that the body diode conducts, so a circuit that appears to switch off still has a path.

Each of those is visible in the schematic once you know the rule, and none of them is visible in a functional test, which is what makes them worth learning before rather than after building. Our article on gate drive design covers the drive side in more detail.

Practice circuit

The exercise worth doing is switching a small load two ways. Build a low-side circuit with an n-channel device driving an LED or a small motor, and note the gate voltage needed. Then build the same load as a high-side switch with a p-channel device, and note that the gate now has to be pulled to ground to turn it on and returned to the supply to turn it off.

Both circuits work, and the difference between them is the whole subject of this article. Use a low-voltage supply, disconnect before changing anything, and keep the load small enough that a mistake does not damage anything you care about. Our guide to choosing a MOSFET for a first project covers the part-selection side.

Check a low-voltage practice circuit one connection at a time

Before applying power, identify gate, drain, and source from the exact package drawing. Mark the load supply and return, then measure gate voltage relative to source. Use a suitable low-voltage, current-limited practice setup. The engineering polarity comparison handles driver headroom and losses; this page concentrates on tracing the wiring.

FAQ

What to do next

Draw your circuit twice, once with the switch below the load and once above it, and work out what gate voltage each arrangement needs. That single exercise resolves most of the confusion around polarity, because it makes the source reference obvious. If you want the part-selection side next, our beginner checklist covers the four questions that decide which device to buy.

This article is published by Good-Ark, a manufacturer of MOSFETs and other discrete devices. It describes wiring conventions rather than specific parts; gate requirements and ratings belong to the current official datasheet.