IRFZ44N vs IRLZ44N vs STP60NF06: Full Comparison

All three are N-channel power MOSFETs in the TO-220 package. The IRLZ44N is the logic-level variant - the single most important distinction for anyone driving a gate from a microcontroller. The STP60NF06 is the performance upgrade.

When to Use IRLZ44N

• You're driving the gate directly from a microcontroller: this is the single most important reason. The IRLZ44N's 1–2V Vgs(th) means a 5V Arduino or ESP32 GPIO (via 5V level shifter) fully enhances the MOSFET. At Vgs=5V, RDS(on) is ~28mΩ - higher than the 10V spec, but the MOSFET is solidly on. The standard IRFZ44N at 5V isn't even characterized - you're guessing at RDS(on) and current capability.
• You're building a battery-powered DC load switch: with a gate charge of only 48 nC (vs 63 nC for the IRFZ44N), the IRLZ44N switches faster at lower gate voltages. For PWM below 20 kHz from a microcontroller pin, it works without an external gate driver.
• You want the simplest circuit: no gate driver IC, no bootstrap, no 10V rail. Just a GPIO, a gate resistor, and a gate-to-source pulldown - the IRLZ44N turns on hard at 5V.

When to Use STP60NF06

• You need the lowest possible conduction loss: at 10.5mΩ RDS(on), the STP60NF06 dissipates 40% less heat than the IRFZ44N at the same current. At 40A, that's Pd = 40² × 0.0105 = 16.8W vs 40² × 0.0175 = 28W. The difference is meaningful when heatsink size and fan noise matter.
• You're pushing past 50A: the STP60NF06 is rated for 60A continuous. The IRFZ44N's 49A rating leaves almost no margin in high-current designs. For motor controllers and battery management running 40–50A steady-state, the STP60NF06 gives you rated headroom.
• You need 60V Vds margin: on a 48V battery system, the IRFZ44N's 55V rating is dangerously tight - a 48V nominal LiFePO4 pack charges to 54.6V, and switching transients can spike well above that. The STP60NF06's 60V rating buys you survival margin.

When NOT to Use an IRFZ44N-Type MOSFET at All

• You need 100V+ Vds rating: the IRFZ44N family caps at 55–60V. For 72V or 96V systems (e-bike, solar, industrial), step up to the IRF540N (100V/33A/44mΩ) for moderate current, or the IRFP250N (200V/30A) for higher voltage. The IRFZ44N in a 72V system will avalanche on the first switching transient.
• You're switching above 100 kHz: with 63 nC gate charge and 1,470 pF input capacitance, the IRFZ44N needs a serious gate driver above ~50 kHz. Push it to 100 kHz without one and switching losses dominate - the MOSFET spends too much time in the linear region during each transition. For high-frequency SMPS, use a MOSFET with lower Qg like the IRFB4110 (100V, 120A, Qg 73 nC but optimized for fast switching) or a GaN FET.
• You're paralleling MOSFETs without careful layout: the IRFZ44N has a positive temperature coefficient for RDS(on) at high currents, which helps current sharing - but during switching transitions, Vgs(th) has a negative temperature coefficient. As one MOSFET heats up, its threshold drops, it turns on sooner, and hogs current during the switching edge. Without individual gate resistors and tight thermal coupling, one MOSFET runs hotter and fails first.
• Your gate drive is an op-amp: op-amps like the UA741 or LM358 cannot swing close enough to ground to fully turn off the IRFZ44N, and their output stage can't source/sink enough current to charge the gate quickly. The MOSFET lingers in the linear region. Use a dedicated gate driver IC or at minimum a push-pull BJT buffer stage.

IRFZ44N Alternatives Comparison Table (All Candidates)

The Logic-Level Trap: Why Your IRFZ44N Runs Hot with a Microcontroller

This is the most common IRFZ44N problem on StackExchange and Arduino forums, and it deserves a section of its own.

The IRFZ44N datasheet specifies RDS(on) = 17.5mΩ at Vgs = 10V. At Vgs = 5V - the voltage from an Arduino or ESP32 GPIO - RDS(on) is not specified. The MOSFET is not fully enhanced. In practice, at 5V gate drive, RDS(on) is roughly 30–60mΩ (varies unit-to-unit) and the MOSFET can only pass about 20–25A before exceeding its thermal limits. At 3.3V, it's even worse - the gate voltage is barely above the 2–4V threshold. The MOSFET may only pass a few amps before hitting its RDS(on) thermal wall.

The symptom is always the same: "My MOSFET gets burning hot at only 10A - the datasheet says 49A!" The datasheet's 49A rating assumes you're driving the gate to 10V and keeping the case at 25°C. Neither is true on a hobbyist bench. A TO-220 without a heatsink has a junction-to-ambient thermal resistance of ~62°C/W. At just 5A with RDS(on)=50mΩ (the real value at Vgs=5V), that's 1.25W dissipation → 77°C temperature rise above ambient. The MOSFET is at 100°C and climbing.

The fix: use the IRLZ44N. At Vgs=5V, its RDS(on) is specified at ~28mΩ - still higher than the 10V spec, but characterized and guaranteed. For 3.3V systems, even the IRLZ44N is marginal - use a gate driver to translate 3.3V to 10V, or step up to a MOSFET with sub-1V threshold like the IRLB8721 (30V/62A, Vgs(th) 1.0–2.0V, RDS(on) specified at Vgs=4.5V).

Common IRFZ44N Failure Modes

"The MOSFET was working fine for weeks, then suddenly all three pins shorted"

Catastrophic drain-source short. Most common in switching circuits (inverters, Tesla coils, induction heaters, SMPS). The failure sequence: a voltage spike on the drain exceeds the 55V Vds rating → the drain-source junction avalanches → localized heating melts the silicon → a permanent short forms between all three terminals. Once a single MOSFET fails this way, every replacement fails the same way - because the circuit, not the part, is the problem.

Check: (a) add a proper snubber (R-C or RCD) across the drain-source to clamp switching spikes, (b) verify your layout minimizes drain trace inductance - long traces create larger voltage overshoots, (c) measure the actual drain voltage with a scope during switching - you might be seeing 80–100V spikes that your multimeter averages away.

"The MOSFET stays on even after I remove the gate signal"

The gate is a capacitor. Once charged, it has no discharge path if your drive circuit is high-impedance when "off." The MOSFET remains conducting until the gate charge slowly leaks away - which can take seconds. Always include a 10k–100kΩ resistor from gate to source. This provides a guaranteed discharge path. Without it, the MOSFET can turn on during MCU startup (when GPIOs are floating) or stay on after the MCU enters sleep mode. This is the #1 layout mistake in IRFZ44N circuits on StackExchange.

"I paralleled two IRFZ44Ns and one runs much hotter than the other"

Uneven current sharing. During switching transitions, the MOSFET with the lower Vgs(th) turns on first and carries more current during the critical high-dissipation crossover period. Over many cycles, that device runs hotter, its Vgs(th) drops further (negative tempco), and the imbalance worsens. Fixes: (a) use individual gate resistors (10–22Ω) for each MOSFET - never tie gates directly together, (b) thermally couple the MOSFETs on the same heatsink so they track each other's temperature, (c) add small source degeneration resistors (0.01–0.1Ω) if current imbalance persists in steady-state.

"The MOSFET explodes in my ZVS induction heater"

ZVS (zero-voltage switching) circuits are unforgiving. Common mistakes with the IRFZ44N in these circuits: (a) 5V Zeners on the gates - these are too low. The IRFZ44N's Vgs(max) is ±20V, and a 5V Zener clips the gate drive, preventing full enhancement. Use 12–15V Zeners, or remove them entirely if the supply is below 15V. (b) Gate resistors too small - 220Ω lets the gate current spike and can cause parasitic oscillation. Use 470Ω–1kΩ. (c) Missing asymmetry resistor - a ZVS oscillator needs a slight imbalance to start reliably. Add a 10kΩ resistor across one gate-source to create a guaranteed startup path. Without it, both MOSFETs can sit in the linear region and cook.

"My circuit works on the bench at 12V but fails in the car at 14.4V"

Automotive voltage is not 12V - it's 13.8–14.4V with the alternator running, and load-dump transients can spike to 40–60V for hundreds of milliseconds. The IRFZ44N's 55V rating survives a typical load-dump, but the margin is thin. Worse: if your gate drive is a resistor divider from the battery, the gate voltage rises with the battery. At 14.4V with a 10V Zener clamp, the gate sits at 10V - fine. But if the Zener is missing or fails open, the gate hits 14.4V, which is within the ±20V limit but beyond what the drain can handle with inductive kickback stacked on top. For automotive, use the AUIRFZ44N (AEC-Q101 qualified) or step up to a 75–100V MOSFET.

Where to Buy IRFZ44N Replacements

Contact ICMASS for current pricing on your specific quantity. We stock IRFZ44N, IRLZ44N, STP60NF06, FQP50N06, IRF540N, and AUIRFZ44N with full manufacturer traceability. Volume pricing for TO-220 power MOSFETs typically ranges from $0.30–$0.90/unit depending on part number and quantity. Need to validate a gate drive design or check a substitution for production? We can supply sample quantities and engineering support.

Frequently Asked Questions About IRFZ44N Replacements

Q1: Can I replace an IRFZ44N with an IRLZ44N directly?

A: Yes - same TO-220 package, same G-D-S pinout, same 55V rating. The IRLZ44N gives up 2A of current (47A vs 49A) and has slightly higher RDS(on) at 10V (22mΩ vs 17.5mΩ). What you gain: full enhancement at 5V gate drive. If you're switching from a microcontroller, this trade is worth it every time.

Q2: Why does my IRFZ44N get hot at only 10A when it's rated for 49A?

A: The 49A rating assumes 10V gate drive and the case held at 25°C. At 5V gate drive (typical microcontroller GPIO), RDS(on) rises to ~30–60mΩ. At 10A through 50mΩ, that's 5W dissipation. Without a heatsink (RθJA = 62°C/W), junction temperature hits 310°C - the MOSFET destroys itself. Use the IRLZ44N for 5V gate drive, or add a gate driver to deliver 10V to the gate.

Q3: What gate voltage does the IRFZ44N need to fully turn on?

A: 10V for the datasheet RDS(on) of 17.5mΩ. At 8V, it's mostly on but RDS(on) is higher (~20–25mΩ). At 5V, the MOSFET is in the linear region - RDS(on) is uncharacterized and can be 30–60mΩ. At 3.3V, most units don't turn on reliably. For any production design, drive the gate to 10–12V through a dedicated gate driver or a push-pull transistor stage.

Q4: What's the difference between IRFZ44N and IRFZ44?

A: The IRFZ44 (non-N) is the older version. It has slightly better raw specs - 60V Vds, 55A Id, 16.5mΩ RDS(on) - but slower switching (rise/fall 97/57 ns vs the N-version's 60/45 ns). The IRFZ44N is more widely available and preferred for new designs where switching speed matters. For DC on/off switching, the two are interchangeable.

Q5: Do I need a heatsink for the IRFZ44N?

A: It depends on current. At 5A with proper 10V gate drive (RDS(on)=17.5mΩ): Pd = 0.44W, temp rise = 27°C - fine without a heatsink. At 15A: Pd = 3.9W, temp rise = 244°C - needs a heatsink. At 30A: Pd = 15.8W - needs a substantial heatsink with forced air. The math: Pd = I² × RDS(on) × 1.5 (temperature coefficient at 100°C). If Pd × RθJA > 75°C rise from ambient, add a heatsink.

Q6: Can I use the IRFZ44N with an ESP32 or ESP8266 (3.3V GPIO)?

A: Not directly. The ESP32's 3.3V GPIO is below the IRFZ44N's Vgs(th) of 2–4V for many units. Even if the MOSFET partially turns on, RDS(on) at Vgs=3.3V can be hundreds of milliohms. Use a logic-level MOSFET (IRLZ44N at minimum, or IRLB8721 for better 3.3V performance), or add a 3.3V→10V gate driver stage. A simple NPN transistor + pull-up resistor to 12V works as a cheap level-shifting gate driver.

Q7: What kills IRFZ44Ns in inverter and SMPS circuits?

A: Drain voltage spikes exceeding 55V during switching, caused by parasitic inductance in the PCB traces and transformer leakage inductance. The spike duration is nanoseconds - a multimeter won't see it, but a scope will. Solutions: minimize high-current loop area on the PCB, add an RCD snubber across the drain-source, use a MOSFET with a higher Vds rating (IRF540N at 100V), or add a TVS diode clamp from drain to gate (with a series resistor to limit current). A 47V TVS from drain to gate with a 100Ω series resistor can save MOSFETs during development.

Q8: How do I parallel IRFZ44Ns correctly?

A: Three rules. (1) Individual gate resistors: 10–22Ω per MOSFET, never tie gates directly together - this prevents parasitic oscillation between parallel gates. (2) Thermal coupling: mount all MOSFETs on the same heatsink with thermal paste. As one heats up, its neighbors heat up too, keeping Vgs(th) tracking. (3) Layout symmetry: keep source and drain trace lengths equal for all paralleled MOSFETs. Asymmetric layout → asymmetric inductance → asymmetric current sharing during switching edges. For steady-state sharing, the positive tempco of RDS(on) helps - as a MOSFET heats up, its RDS(on) rises, pushing current to cooler devices. But that mechanism only works in DC; switching transitions are dominated by layout and Vgs(th) matching.