The Drive Circuit Design of MOS Tube

In the power supply debugging process, the debugging of the drive signal is particularly important, which is not only for the reliability of the power supply, the efficiency of the power supply, the design temperature rise of the power supply, and EMC characteristics are particularly important. Therefore, the design of the drive circuit becomes an important index of the design power supply. The rationality of driving parameters directly affects the performance of the power supply.

It is summarized as the following five points:
1. The drive circuit design of MOS tube with a small power supply (within 50W) is relatively simple, and only one drive resistor (R_G) is needed to drive the MOS tube. In this case, the open resistance of the drive is the same as the off resistance.

Fig.1

2. For small and medium-sized power supplies (50W to 500W) with certain efficiency design requirements, it is necessary to separate R_G(on) and R_G(off), which are generally designed in the following two ways:

Fig.2 R_G(on)=R_G1+R_G2，R_G(off)=R_G1

Fig.3 This design separates R_G(on) from R_G(off) for easy adjustment

3. For medium-power power supply (300W to 1500K), the drive design of the MOS tube not only needs to separate the open resistor and the off resistor but also needs to process the drive Miller platform. In general, a set of RC circuits will be added between the GS of the MOS tube to adjust the oscillation in the MILLER platform of the MOS tube by adjusting RC parameters. The design method is as follows:

Fig.4

The parameter design should be based on the final debugging decision of the design circuit and MOS tube selection

4. It is particularly important for the drive design of MOS tubes for power supply with medium upper power or even high power (1200W to 5KW or even 10KW). At this time, the drive design has a great relationship with many aspects, including MOS tube selection, parasitic parameter differences between different manufacturers, power routing design, driver selection and design, drive loop design, and so on. Generally, MOS tube drive design has the following several design ideas. The main purpose is to suppress the oscillation and reduce the loop between THE GS of the MOS tube. The design method is as follows:

Fig.5

The triode is used to pull G class to S class directly when the drive is turned off.
The drive-off circuit is reduced and the drive anti-jamming ability is enhanced.

Fig.6

NMOS is used to pull the G class to the S class directly when the driver is turned off.
The drive off circuit is reduced and the drive anti-jamming ability is enhanced.

Fig.7

The triode is used to pull G class to S class directly when the drive is turned off. The drive off circuit is reduced and the drive anti-jamming ability is enhanced. At the same time the GS resistor series diode further enhances the anti-interference ability of the drive circuit.

5. The same is true in the design of the driver. The interference of the power loop must be reduced or even avoided. The specific design method is as follows:

Fig.8

The totem pole is adopted as the driver, which is suitable for small and medium power products with low cost and strict requirements on cost.

Fig.9

The drive IC is used as the driver to drive MOS or drive transformer, which is suitable for the design of large power and long drive circuits. The input end of the signal is added with pull-down resistance and RC filter to further process the IC input signal to ensure the signal is clean and enhance the anti-interference ability.