Metal tab (heat sink) · Ø 3.7 mm holeEpoxy bodyPins G-D-S · 2.54 mm spacing

Black TO-220 body, metal tab with a hole, “IRF9540N” text on the front
TO-220 body ≈ 10 × 15 mm, metal tab with a hole · Example shown: IRF9540N-class P-channel MOSFET, TO-220

Transistors

P-channel MOSFET

In simple terms

What is this?

The mirror image of the N-channel; a valve that opens when its gate is pulled down.

What is it for?

It switches the positive side of the load; it also protects against a battery connected in reverse.

Where do you see it?

In battery-powered devices, in power cut-off and reverse battery protection circuits.

How do you spot it?

A body with a metal tab and three legs; you tell it apart from the N-channel by the code on top.

Caution:

The source goes to the plus supply; if you mix it up with an N-channel, it will not turn on. It is sensitive to static electricity.

Technical definition

The complement of the N-channel MOSFET: the source connects to the positive supply and it conducts when the gate is pulled down relative to the source. Used for a positive-side switch and reverse polarity protection. Its on-resistance is higher than an N-channel of the same size.

ExampleIRF9540N

VDS−100 V

ID−23 A

Schematic symbol Same in IEC and ANSI

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 3

1Gate (G)With the marked face toward you, legs at the bottom, 1 from the left.G

2Drain (D)Middle leg; the metal tab is also connected to the drain, goes to the loadD

3Source (S)Right leg; goes to the positive supplyS

Features typical

VDS: −100 V
ID (continuous): −23 A
RDS(on): ≤ 0.117 Ω (VGS −10 V)
VGS(th): −2 … −4 V
Max. VGS: ±20 V
Driving: Pull the gate ≈10 V below the source
Package: TO-220
Example part: IRF9540N (TO-220)

Common mistakes

Thinking of the gate voltage with the wrong referenceA P-channel turns on when the gate is lower than the source. With the source at 12 V, it is off when the gate is at 12 V and turns on when pulled down to 2 V.

Driving directly with a pinIf the source is higher than 5 V, the pin cannot pull the gate up to turn the MOSFET off. Put a pull-up on the gate and pull it down with an NPN.

Exceeding the gate limitIf VGS exceeds ±20 V, the gate oxide breaks down. On a high supply such as 24 V, limit the gate with a zener.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

High-side load switchReverse battery protectionCutting power in a battery-powered deviceHigh-side leg of an H-bridge

Try it in the Lab