release time:2022-03-17Author source:SlkorBrowse:939
MOS tube heating is a common problem in circuits, which often bothers us. Next, a small series summarizes several problems and reasons of MOS tube heating:
The problem is not detailed enough, but there are generally several kinds of mos tube heating: 1. Excessive load leads to over-current heating of mos tube. 2. The driving excitation signal is insufficient, which causes the mos tube to heat up. 3. If the excitation signal is too strong, the mos tube will also heat up. Generally, the working temperature of mos tubes is below 120 degrees Celsius, and all of them can work.It usually doesn't exceed 70 degrees.No, the maximum working temperature of most mos tubes is below 120 degrees, but it is not absolute, and some of them have low working temperatures. Some work at several hundred degrees.
Causes of MOS tube heating:
1. The problem of circuit design is to make the MOS tube work in a linear working state, not in a switching state. This is also one of the causes of MOS tube heating. If N-MOS is used as a switch, the voltage of G-stage must be several V higher than the power supply before it can be fully turned on, while P-MOS is the opposite. The voltage drop is too large when it is not fully opened, resulting in power consumption. The equivalent DC impedance is relatively large, and the voltage drop increases, so the U*I also increases, and the loss means heating.
2. The frequency is too high, mainly due to the excessive pursuit of volume sometimes, which leads to the increase of the frequency and the loss on the MOS tube, so the heat generation is also increased.
3. The current is too high, and there is not enough heat dissipation design. The nominal current value of MOS tube generally needs better heat dissipation to achieve it. Therefore, if the ID is less than the maximum current, the heat may be severe, and enough auxiliary fins are needed.
4. Wrong selection of MOS tube, wrong judgment of power, insufficient consideration of internal resistance of MOS tube, resulting in increased switching impedance.
The MOS tube is unsaturated and has high voltage drop. The reason may be the driving problem of MOS tube, so an intermediate stage should be added. Oscillation frequency is too low. Energy storage inductance is too small or leakage inductance is too large.
MOS is hot. It must be a power loss. The reason is that it is not working in the switch state.Check the MOS drive, whether the drive current is enough or not, and whether the voltage is enough.In addition, don't use 1N4007 for D1, it's better to use faster switching diodes, such as SK34. I think it's normal for the building owners to heat up. The drain and source of mosFET have voltage drop Vds. This voltage multiplied by the drain current will generate power consumption, so it will heat up. I hope it can help the building owners mos to heat up because the current is too large. The current is almost 1A at 1V voltage. Change the MOS tube. Why is the output not connected with capacitor for energy storage and filtering? ?
No matter what the power supply is, there are only three reasons why MOS tubes burn out: overvoltage, overcurrent and overheating.When designing products, R&D will consider the working loop mirror of MOSFET, which can debug the overcurrent point from light load to full load, the overvoltage point from low voltage to high voltage, and the overtemperature point for a long time.When you blow up, you should consider whether the voltage loop and the current loop are open-loop, etc!If it will blow up again, it is necessary to consider the causes of over-temperature, such as MOS high-frequency loss, transformer loss, heat dissipation, etc!
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