Hello everyone, I hope you're all doing well. I'm working on a circuit to control the intensity of a load using PWM, and I'd appreciate your feedback to help me understand an issue I'm facing. The PWM signal comes from a microcontroller at 3.3V, and I'm using a 2N3904 transistor to shift the signa…

Thank you for your response! Use a logic level MOSFET instead, like the IRLZ44N, and drop the rest of the circuit. You're right, the IRLZ44N is definitely better suited for low logic levels like 3.3V or 5V. However, if I use the IRFZ44N and adapt the PWM signal to 12V, there shouldn't be any pro…

[image] ingyou: there shouldn't be any problem, right? Sure, but since you say that the MOSFET is heating up, there is a problem. What that might be is not clear from the scope traces, as it isn't clear which points in the circuit are monitored. I suspect that your MOSFET driver design (whic…

[image] ingyou: IRFZ44N MOSFET. The schematic shows IRLZ44N. So which one are you actually using? Is the load actually a 5 ohm resistor?

Thank you for your response! The schematic shows IRLZ44N. So which one are you actually using? Is the load actually a 5 ohm resistor? I'm using an IRFZ44N in my prototype, with a 5 ohm resistor as a simulated load for testing.

isn't clear which points in the circuit are monitored. The yellow signal is the PWM output from the microcontroller, and the blue signal is the PWM signal on MOSFET gate. MOSFET driver design (which is not the best) doesn't match what was actually built and tested. I’m curious about your comm…

Well if the MOSFET was fully on (100% PWM) then it would only generate about 100mW of heat. Power = I²R = 2.4²*18mΩ So if it is getting HOT it must be due to switching losses. However your signals look like they do have fast rise and fall times. Look at the drain signal.

[image] ingyou: How would you improve it? I would use a MOSFET driver IC. There are many problems with the posted schematic, primary among them the value of R4. This is a quick simulation of the circuit with a much lower value of R4 (R1 in the figure below, which is not supported by the cho…

Try a NE555 Timer (bipolar version), 24v can be 12v. [image]

Thanks for the simulation and explanation! I understand now that driving the gate directly or with only a 1 Ω resistor would indeed switch the MOSFET very fast—but at the cost of multi‑ampere current spikes, extreme EMI, and likely overloading my small signal transistors. I would use a MOSFET driv…

IRFZ44N Heats Up with PWM – Suspecting Gate Drive Issues

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jremington June 29, 2025, 2:17pm 2

Use a logic level MOSFET instead, like the IRLZ44N, and drop the rest of the circuit.

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IRFZ44N Heats Up with PWM – Suspecting Gate Drive Issues

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