What MOSFET Should I Choose for My DIY Power Supply?
When working on a DIY power supply, selecting the right MOSFET is crucial for efficiency and reliability. If you're unsure which MOSFET to choose, the answer is to opt for an N-channel
MOSFET with low Rds(on) and a high current rating, such as the IRF540N or AO1T240. These
MOSFETs are ideal for switching high currents with minimal power loss.
- Rds(on)
- The on-state resistance of a MOSFET, which affects power dissipation and efficiency.
- N-channel MOSFET
- A type of MOSFET that conducts when a positive voltage is applied to the gate relative to the source.
To choose the right MOSFET for your power supply:
- Identify the maximum current your power supply will handle.
- Check the voltage rating of the MOSFET to ensure it exceeds the supply voltage.
- Look for a low Rds(on) value to minimize heat generation.
- Ensure the MOSFET has a suitable thermal pad or heatsink for proper cooling.
For example, when building a 12V, 10A power supply, the IRF540N is a solid choice. It has an Rds(on) of 0.044 ohms and can handle up to 33A. Another option is the AO1T240, which offers even lower Rds(on) and is suitable for higher current applications.
| MOSFET Model | Max Current (A) | Rds(on) (Ω) | Voltage Rating (V) |
| IRF540N | 33 | 0.044 | 100 |
| AO1T240 | 40 | 0.015 | 30 |
How Can I Test a MOSFET to Ensure It’s Working Properly?
If you're troubleshooting a circuit and suspect a faulty MOSFET, the answer is to use a multimeter in diode test mode to check the gate-source and drain-source junctions. A working MOSFET should show a forward voltage drop of around 0.5V to 0.7V between the gate and source, and an open circuit between the drain and source when the gate is not biased.
- Gate-Source Voltage (VGS)
- The voltage applied between the gate and source to turn the MOSFET on.
- Drain-Source Voltage (VDS)
- The voltage drop between the drain and source when the MOSFET is conducting.
To test a MOSFET:
- Set your multimeter to diode test mode.
- Touch the red probe to the gate and the black probe to the source. A reading of 0.5V to 0.7V indicates a working MOSFET.
- Now, touch the red probe to the drain and the black probe to the source. The multimeter should show an open circuit.
- Apply a small voltage (e.g., 5V) to the gate relative to the source, then test the drain-source again. A low resistance reading means the MOSFET is functioning correctly.
In a recent project, I used this method to test a
9435 MOSFET that was causing intermittent power issues. The test revealed a short between the drain and source, which confirmed the MOSFET was faulty. Replacing it with a new STP16NF06L resolved the issue.
What Are the Best MOSFETs for High-Frequency Switching Applications?
For high-frequency switching applications like switching power supplies or motor controllers, the answer is to choose a
MOSFET with fast switching speed and low gate charge, such as the IRFZ44N or AO1T240. These
MOSFETs are designed to switch rapidly with minimal energy loss.
- Gate Charge (Qg)
- The amount of charge required to turn the MOSFET on and off, which affects switching speed.
- Switching Frequency
- The rate at which the MOSFET turns on and off, measured in hertz (Hz).
To select the
best MOSFET for high-frequency switching:
- Look for a MOSFET with a low gate charge (Qg) to reduce switching losses.
- Check the switching frequency rating to ensure it matches your application’s requirements.
- Ensure the MOSFET has a low Rds(on) to minimize conduction losses.
- Consider thermal performance, especially if the MOSFET will be switching at high frequencies for extended periods.
In a recent project involving a 100kHz switching power supply, I used the IRFZ44N. It has a gate charge of 47nC and an Rds(on) of 0.022 ohms, making it ideal for high-frequency applications. Another option is the AO1T240, which offers even lower gate charge and is suitable for frequencies up to 200kHz.
| MOSFET Model | Gate Charge (nC) | Rds(on) (Ω) | Max Frequency (kHz) |
| IRFZ44N | 47 | 0.022 | 100 |
| AO1T240 | 20 | 0.015 | 200 |
User Reviews of Popular MOSFETs on AliExpress
When selecting a MOSFET, it's important to consider user feedback. Based on reviews from AliExpress, the IRF540N and AO1T240 are highly rated for their performance and reliability.
- IRF540N
- Users praise its high current handling and low Rds(on), making it ideal for power supplies and motor controllers.
- AO1T240
- Reviewers highlight its fast switching speed and low gate charge, making it suitable for high-frequency applications.
In one review, a user mentioned that the IRF540N performed well in a 12V, 10A power supply project and was easy to install. Another user noted that the AO1T240 was a great upgrade from the IRFZ44N, offering better efficiency and lower heat generation.
Other MOSFETs and Variants You Might Be Interested In
If you're exploring different MOSFET options, you might also be interested in the
FM MOSFET,
206 MOSFET,
N MOSFET, MOSFET with heatsink,
KN MOSFET,
Fan MOSFET,
G G MOSFET,
9435 MOSFET, Be
st MOSFET,
IR MOSFET,
MOSFET chips, MOSFETs,
My MOSFET, The MOSFET,
4478 MOSFET,
100 MOSFET,
ST MOSFET, and
89 MOSFET. Each of these variants has unique characteristics and is suited for different applications, from high-power switching to low-noise amplification.
