IRF540N MOSFET: pinout, ratings, 5 V gate drive and the IRF9540N

Read the print on the face. IRF540N is an Infineon part number, from the International Rectifier range Infineon bought; PbF only means lead-free. The IRF540 with no N is a different part from other makers' ranges, so the figures on this page are for the IRF540N only. The IRF9540N is the P-channel part of the same family, with the same pins.

A good IRF540N meters like the test further down and carries a maker's logo and a date code. If a part runs hot at a load far below its rating, check the gate voltage before you suspect a fake.

Both parts take 100 V and ±20 V on the gate. The IRF540N is rated 33 A and 130 W, the IRF9540N 23 A and 140 W, all with the case held at 25 °C. The IRF9540N's voltages and currents are negative on its sheet; the table gives magnitudes.

The 33 A needs the case held at 25 °C, which no real heatsink does. In free air the part has 62 °C/W from junction to air. At 10 V on the gate, with the on-resistance multiplied by 1.5 for a warm die, about 3.8 A keeps the junction 60 °C above the room with no heatsink. Past that it needs one.

The on-resistance row is the one to read. Infineon gives 44 mΩ at 10 V on the gate and nothing lower. The threshold, 2.0 to 4 V, is where the part passes just 250 µA, so it says when the part starts to turn on, not when it is fully on.

The typical curve shows what a 5 V gate can do. Infineon's Fig. 3 plots drain current against gate voltage for a typical part with 50 V across it: about 12 A at 4.5 V, about 28 A at 5 V and about 95 A at 7 V. That is far more than the IRF520 passes at 5 V (about 2 A on Vishay's curve), which is why an IRF540N on a 5 V pin often seems to work. A part at the 4 V threshold limit sits further right and passes about 9.4 A at 5 V.

• Low-side switching of heaters, lamps, motors and LED strips from a few amps up to tens of amps, when something drives the gate to 10 V or more and the part sits on a heatsink.
• 24 V and 48 V loads. At 100 V it has more headroom than the 55 V logic-level parts.
• With the IRF9540N, switching the positive side of a 12 V or 24 V load, or an H-bridge whose gates get a proper driver.

On a microcontroller pin with no driver it is a gamble on the threshold. For that, see IRFZ44N vs IRLZ44N and our guide to choosing a MOSFET for Arduino and ESP32.

A 12 V, 60 W heater measures 2.4 Ω and draws 5 A. The IRF540N switches its low side: source to ground, heater between +12 V and the drain. The gate is fed through 220 Ω, with 10 kΩ to ground on the drive side so the gate stays off while the pin floats at reset. A heater is resistive, so it needs no flyback diode; a motor or solenoid in its place does.

The gate drive lesson covers ways to get 10 V onto the gate from a logic pin, and transistor packages and heat explains the °C/W arithmetic.

The IRF9540N is the P-channel part: source to the positive rail, load from the drain to ground, and it turns on when the gate is pulled below the source. Its sheet gives 117 mΩ at most with the gate 10 V below the source, and a threshold of 2.0 to 4 V below it. On a 12 V rail the simplest drive is a small NPN that pulls the gate to 0 V, which puts it 12 V below the source, inside the ±20 V rating.

The numbers: 2 A × 2 A × 0.117 Ω = 0.47 W, times 1.5 for a warm die is 0.70 W, and × 62 °C/W is 44 °C above the room, about 84 °C at the junction with no heatsink. The pin gives the BC547 about 4.3 mA of base current through 1 kΩ, and the BC547 only has to sink 1.2 mA from the pull-up. Switching off is slow: the 10 kΩ has to charge up to 97 nC of gate, so keep this circuit for on and off, not fast PWM. On a rail above 20 V, add a resistor divider or a zener so the gate never sees more than 20 V.

• Measure drain to source with the load running. About 0.2 V at 5 A is right at a 10 V gate; half a volt or more means the gate is not driven hard enough.
• Plan the heatsink from the watts, not the 33 A. Above about 3.8 A the bare TO-220 runs past a 60 °C rise.
• Keep the 10 kΩ pull-down. A floating gate can leave the part half on, and half on is where it gets hottest.
• The tab is the drain. On a grounded heatsink it shorts the load: use an insulating pad and shoulder washer, then meter tab to heatsink for an open circuit.
• For PWM, the gate charge matters. Up to 71 nC through 220 Ω is fine at a few hundred hertz; at tens of kilohertz use a gate driver.

Where a 5 V pin drives the gate and the load runs from 55 V or less, the IRLZ44N in the same footprint is the fix. The IRF520N fits the same holes but is a much smaller part.

1. Short all three leads together for a moment to empty the gate. Set the meter to diode test.
2. IRF540N: red probe on the source, black on the drain, and the body diode reads about 0.4 to 0.7 V. Reversed, it should read open. For the IRF9540N, swap the probes.
3. IRF540N: touch the red probe to the gate with the black on the source for a second. Now red on the drain, black on the source: a good part conducts. Short gate to source and it goes open again.
4. If step 3 shows nothing, your meter's test voltage may be below the threshold. That is the same problem as the 3.3 V pin, not a dead part.

The transistor testing lesson and continuity and diode test explain what the meter is doing.

Use the IRF540N where the gate gets 10 V or more and the load is several amps or more, on a heatsink sized from the watts. For a 5 V Arduino pin and a load under 55 V, fit an IRLZ44N instead, whose data sheet covers that gate voltage. For the positive side of a 12 V load, an IRF9540N with a BC547 pulling its gate down is simple and runs cool at 2 A.

The IRF540N is stocked by most Indian electronics shops and online sellers, usually beside the IRFZ44N. Check the print for IRF540N and a maker's logo, and meter a part before it goes on a board. If the job is a 5 V Arduino project, buy the IRLZ44N instead. Our guide to buying electronic components in India compares ten online sellers and covers how to spot fakes.