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　　A brief analysis of the current status of IGBT drive technology

　　The design of high-power device drive circuits in switching power supplies has always been one of the key technologies in the power supply field. Ordinary high-power transistors and insulated gate power devices (including VMOS field effect transistors and IGBT insulated gate bipolar high power transistors, etc.) have very different specific driving requirements and technologies due to different device structures. The former is a current control device and requires a suitable current waveform to drive; the latter is an electric field control device and requires a certain voltage to drive. This article only introduces the latter situation.

　　The source and gate of VMOS field effect transistors (and devices such as IGBT insulated gate bipolar high-power transistors) are insulated silicon dioxide structures. DC power cannot pass through, so the low-frequency static driving power is close to zero. However, a gate capacitance Cgs is formed between the gate and the source, so a certain dynamic driving power is required during high-frequency alternate turn-on and turn-off. The Cgs of low-power VMOS tubes is generally within 10-100pF. For high-power insulated gate power devices, since the gate capacitance Cgs is large, ranging from 1-100nF or even larger, larger dynamic driving power is required. Moreover, due to the Miller capacitance Cdg from drain to gate, the gate drive power cannot be ignored.

　　In order to reliably drive insulated gate devices, there are many mature circuits. When the driving signal and the power device do not need to be isolated, the design of the driving circuit is relatively simple. There are also some excellent driving integrated circuits, such as IR2110. When electrical isolation between the input end and the output end of the driver is required, there are generally two ways: using a photocoupler, or using a pulse transformer to provide electrical isolation.

　　The advantage of the optocoupler is its small size, but the disadvantages are: A. The response is slow, so it has a large delay time (high-speed optocouplers are generally greater than 500ns); B. The output stage of the optocoupler requires an isolated auxiliary power supply. .

　　There are three ways to use pulse transformer isolation to drive insulated gate power devices: passive, active and self-contained power drive.

　　The passive method is to use the output of the transformer secondary to directly drive the insulated gate device. This method is very simple and does not require a separate driving power supply. However, since the gate-source capacitance Cgs of the insulated gate power device is generally large, the gap between the gate and source The waveform Vgs will be significantly deformed, unless the primary input signal is changed to a large signal with a certain power, and the corresponding pulse transformer should also be larger in size.

　　The transformer in the active method only provides isolated signals, and there is a shaping amplifier circuit on the secondary side to drive the insulated gate power device. Of course, the driving waveform is good, but an additional isolated auxiliary power supply is required to supply the amplifier. If the auxiliary power supply is not handled properly, it may introduce parasitic interference.

　　The existing technology of the self-sufficient power supply method is to perform high-frequency (above 1MHz) modulation of the PWM drive signal. The signal is added to the primary of the isolation pulse transformer, and the self-sufficient power is obtained through direct rectification at the secondary. The original PWM modulation signal needs to be decomposed Obviously, this method is not simple, and the price is certainly higher. The advantage of modulation is that there is no limit to the duty cycle that can be delivered.

　　The finished drivers currently on the market can be divided into direct drive and isolation drive based on the electrical relationship between the drive signal and the driven insulated gate device. The isolation components for isolation drive include photocouplers and pulse transformers.

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