IRF9540NPBF

The IRF9540NPBF from Infineon Technologies (formerly International Rectifier) is a -100V P-channel HEXFET power MOSFET rated for -23A continuous drain current with 117mΩ maximum on-resistance at VGS=-10V. As a P-channel device, it is the natural choice for high-side switching: the source connects to the positive rail, and pulling the gate below the source by 10V turns the MOSFET on. This eliminates the need for a gate driver or bootstrap circuit required by N-channel high-side switches. The complementary N-channel IRF540NPBF (100V, 33A, 44mΩ) pairs perfectly in H-bridge motor drive and push-pull amplifier circuits. The 140W power dissipation rating (at TC=25°C) with 1.1°C/W junction-to-case thermal resistance allows substantial current handling with adequate heatsinking. The avalanche rating provides protection against inductive kickback from motors and solenoids. The PBF suffix denotes the lead-free (Pb-free) version in TO-220 package.

The IRF9540NPBF is a P-channel enhancement-mode MOSFET. Unlike N-channel MOSFETs where VGS must be positive relative to the source, the P-channel requires VGS to be negative (gate below source) to create a conductive channel. When VGS = 0V (gate = source), the MOSFET is off. When VGS reaches the threshold (-2V to -4V), an inversion layer forms under the gate oxide, creating a conductive channel between source and drain. At VGS = -10V, the channel is fully enhanced, and RDS(on) drops to 117mΩ max. In a high-side switch configuration, the source is connected to the positive supply rail (e.g., 12V), and the load is between the drain and ground. To turn on the MOSFET, the gate must be pulled at least 10V below the source, i.e., to 12V – 10V = 2V or lower. A simple GPIO-controlled NPN transistor can pull the gate to ground, providing VGS = -12V for full enhancement. When the GPIO goes low, the NPN turns off, and a pull-up resistor (10kΩ) pulls the gate to the source (12V), making VGS = 0V and turning the MOSFET off. The 64.7nC total gate charge means the gate capacitance requires this amount of charge to switch; with a 10kΩ pull-up, the turn-off time is approximately R × Ciss = 10kΩ × 1300pF ≈ 13µs, which is acceptable for load switching but may need a gate driver for PWM applications.

IRF9540NPBF pin assignment (TO-220-3, front view, pins down): Pin 1 (left) = Gate, Pin 2 (center) = Drain/Tab, Pin 3 (right) = Source. P-channel MOSFET for high-side switching: Gate pulled to GND = ON, Gate at Source = OFF. The tab is connected to Drain. Complementary N-channel: IRF540N (100V/33A). For lower on-resistance P-channel at 60V, consider FQP47P06 (60V/47A/26mΩ).

• High-Side Switch: Source to +12V battery; gate driven by NPN to GND; load between drain and GND; simple on/off control
• H-Bridge: IRF9540N (high-side) + IRF540N (low-side) per half-bridge; bidirectional DC motor control
• Reverse Polarity: Source to battery+, drain to load; gate tied to source via zener; blocks reverse current automatically
• Buck Converter: High-side P-ch switch; VGS driven by controller; 117mΩ at 5A = 2.9W conduction loss
• Battery Disconnect: Source to battery+, drain to system; MCU-controlled NPN drives gate; 0.5µA gate leakage preserves battery

IRF9540NPBF is a -100V/-19A P-channel MOSFET from Infineon in TO-220 with 117mΩ RDS(on). The FQP47P06 from onsemi provides -60V/-47A with 26mΩ for lower on-resistance. The IRF9Z34N offers -60V/-12A with 100mΩ in a smaller footprint. The IRF4905PBF provides -55V/-74A with 78mΩ for higher current. The STD20P06 from ST offers -60V/-20A with 65mΩ in D2PAK. For surface-mount, IRF9540NSPBF provides the same in D2PAK. Complementary N-channel: IRF540N (100V/33A).