IRFZ40FI MOSFET — Specifications & Equivalents
Manufacturer: Commonly produced by International Rectifier (now Infineon)
About the IRFZ40FI
The IRFZ40FI is an N-channel MOSFET with a drain–source voltage (VDS) rating of 50 V, a continuous drain current (ID) of 27 A and an on-resistance (RDS(on)) of 0.028 Ω. It can dissipate up to 45 W and is rated to a junction temperature of 175 °C. It is supplied in the ISOWATT220 package.
At a glance
- Type: N-channel MOSFET
- Max drain–source voltage (VDS): 50 V
- Max continuous drain current (ID): 27 A
- On-resistance (RDS(on)): 0.028 Ω
- Gate threshold (VGS(th)): 4 V
- Power dissipation (PD): 45 W
- Max junction temperature (TJ): 175 °C
- Package: ISOWATT220
- Manufacturer: Commonly produced by International Rectifier (now Infineon)
Typical applications
With its 50 V drain–source rating the IRFZ40FI sits in the low-voltage class of switching MOSFETs, typically found in 12 V and 24 V automotive and industrial rails, synchronous buck converters, load switching and reverse-polarity protection and H-bridges for small motors.
The low 0.028 Ω on-resistance keeps conduction loss down, which suits synchronous rectification and continuous high-current paths.
Gate drive and switching notes
With a gate threshold (VGS(th)) of 4 V this is not a logic-level device: driving the gate directly from a 3.3 V or 5 V microcontroller pin will leave it only partly on and cause it to overheat. Use a gate driver or level shifter, typically taking VGS to 10 V.
Keep gate–source voltage within the ±20 V maximum; exceeding it punctures the gate oxide and destroys the device permanently.
Total gate charge (Qg) of 50 nC sets the drive current required: average gate current is roughly Qg × switching frequency, so faster switching needs a stronger driver.
Switching behaviour is characterised by a rise time of 110 ns and an output capacitance (Coss) of 630 pF, which together with the gate drive determines switching loss and the practical upper frequency limit.
Choosing a replacement for the IRFZ40FI
A drop-in substitute for the IRFZ40FI must be the same N-channel type and offer a drain–source rating of at least 50 V, a continuous drain current rating of at least 27 A, an on-resistance no higher than 0.028 Ω if efficiency and heat matter and a comparable gate threshold, so your existing gate drive still fully enhances the device.
Mechanically, check the replacement against the ISOWATT220 footprint and confirm the pin order — parts sharing a package outline do not always share a pinout.
Where the application switches inductive loads or runs near the voltage limit, keep extra headroom rather than choosing a part that only just meets the original numbers.
Frequently asked questions
What is the IRFZ40FI?
The IRFZ40FI is an N-channel MOSFET (metal-oxide-semiconductor field-effect transistor). It is rated for 50 V drain-source and 27 A continuous drain current.
What is the maximum voltage of the IRFZ40FI?
The IRFZ40FI has a maximum drain-source voltage (Vds) of 50 V. Treat this as an absolute maximum and design with margin, especially when switching inductive loads.
How much current can the IRFZ40FI handle?
It is rated for 27 A of continuous drain current, with power dissipation limited to 45 W. Real-world capability depends on your heatsinking and ambient temperature.
What is the on-resistance of the IRFZ40FI?
On-resistance (Rds(on)) is 0.028 Ω. Multiply by the square of your load current to estimate conduction loss.
Is the IRFZ40FI logic-level compatible?
No. The gate threshold is 4 V, so a 3.3 V or 5 V logic output cannot fully turn it on. Use a gate driver and take Vgs to around 10 V.
What package does the IRFZ40FI come in?
It is listed in ISOWATT220. Verify the pinout of the specific variant, as one outline can carry different pin assignments.
What can I use to replace the IRFZ40FI?
No verified equivalents are listed yet. Choose a part of the same polarity that meets or exceeds every rating above and shares a compatible package and pinout.
Key Specifications
| Type | MOSFET |
|---|---|
| Channel Type | N -Channel |
| Drain-Source Voltage (Vds) | 50 V |
| Gate-Source Voltage (Vgs) | 20 V |
| Gate Threshold Voltage (Vgsth) | 4 V |
| Drain Current (Id) | 27 A |
| Drain-Source On-Resistance (Rds) | 0.028 |
| Total Gate Charge (Qg) | 50 nC |
| Rise Time (tr) | 110 nS |
| Output Capacitance (Coss) | 630 pF |
| Junction Temperature (Tj) | 175 °C |
| Package | ISOWATT220 |
| Power Dissipation (Pd) | 45 W |
Equivalent & Replacement Parts
No verified equivalents are listed for IRFZ40FI yet.