Gate drive on the high side
On the high side a small NPN driven by the pin pulls the gate of the IRF9540N down and the gate sees the load supply. Above 80 % of its 20 V gate limit a divider keeps it within range.
| Supply | Gate voltage | Verdict | Why |
|---|---|---|---|
| 5 V | −5 V | Not guaranteed | nothing guaranteed below 10 V |
| 12 V | −12 V | Works | RDS(on) at most 117 mΩ guaranteed from 10 V |
| 24 V | −10.9 V (with a divider) | Works | RDS(on) at most 117 mΩ guaranteed from 10 V |
Specifications
| Type | P-channel MOSFET |
|---|---|
| Package | TO-220 |
| Maximum voltage | 100 V |
| Maximum current | 23 A |
| Threshold VGS(th) | −2 … −4 V |
| RDS(on), maximum | 117 mΩ at −10 V (11 A) |
| Gate voltage limit | ±20 V |
| Gate charge | 97 nC at −10 V |
| Thermal resistance | θJA 62 °C/W · θJC 1.1 °C/W |
| Maximum junction temperature | 175 °C |
| Datasheet used | Infineon (IR) |
Pinout
| Pin | Function |
|---|---|
| 1 | Gate |
| 2 | Drain |
| 3 | Source |
Printed face toward you, leads down: pin 1 is on the left. The metal tab is connected to pin 2.
Similar parts
| Part | Package | RDS(on), guaranteed | Max voltage | Max current |
|---|---|---|---|---|
| IRF9540N | TO-220 | 117 mΩ at −10 V | 100 V | 23 A |
| AO3401A | SOT-23 | 85 mΩ at −2.5 V | 30 V | 4 A |
Tips
The gate swings by the whole supply voltage: keep it below 80 % of the MOSFET’s 20 V limit, with a divider or a 16 V Zener above that.
Every coil needs a flyback diode across it, cathode to the positive supply. Without it the voltage spike at turn-off can destroy the transistor at the first switching.
A TO-220 in free air sheds little heat: fit a heatsink, insulated if the tab must not touch it (the tab is the drain or collector).
Open the calculator →Check the IRF9540N with your own load, supply, PWM frequency and temperature.
Other transistors
2N2222A 2N3904 BC547 S8050 TIP120 2N7000 BS170 AO3400A Si2302 IRLML6344 IRLZ44N IRLB8721 IRF520 IRF540N AO3401A
Frequently asked questions
How do I drive the IRF9540N from a microcontroller?
Source to the positive supply, a 10 kΩ resistor from gate to source, and a small NPN driven by the pin that pulls the gate to ground. RDS(on) is guaranteed from 10 V, so the supply must reach that; above 80 % of the 20 V gate limit add a divider.
What is the IRF9540N pinout?
TO-220: 1 gate, 2 drain, 3 source. Printed face toward you, leads down: pin 1 is on the left. The metal tab is connected to pin 2.
Source of the figures: Infineon (IR) datasheet (PDF)