And what are the IGBT MOSFET isolation drives?
Isolated drive of IGBT and MOSFET is a reliable drive insulated gate device, and there are many mature circuits at present. When there is no need to isolate the driving signal from the power device, the design of the driving circuit is relatively simple, and there are many excellent driving integrated circuits at present.
1. Optocoupler isolation driver
The advantages of optocouplers are small size, but the disadvantages are: A, slow reaction, so the delay time is long (high-speed optocouplers are generally over 300ns); The output stage of photoelectric coupler needs isolated auxiliary power supply.
2. Passive transformer drive
There are three ways to drive insulated gate power devices with pulse transformer isolation: passive, active and self-powered driving. The passive method is to drive the insulated gate device with the output of the secondary DC of the transformer. This method is very simple and does not need a separate driving power supply. The disadvantage is that the output waveform distortion is large, because the gate-source capacitance Cgs of insulated gate power devices is generally large. The method to reduce the distortion is to change the primary input signal into a large signal with a certain power, and the corresponding pulse transformer has to take a larger volume, but it is still unsatisfactory under high power. Another disadvantage is that when the duty ratio changes greatly, the positive and negative amplitude of the output driving pulse changes too much, which may lead to abnormal operation, so it is only suitable for occasions where the duty ratio changes little.
3. Active transformer driveIn the active method, the transformer only provides isolation signal, and there is another shaping amplifier circuit in the secondary to drive the insulated gate power device. Of course, the driving waveform is good, but a separate auxiliary power supply is needed for the amplifier. However, if the auxiliary power supply is not handled properly, parasitic interference may be introduced.
4. Transformer isolation driver for modulating self-contained power supply
Self-sufficient power supply technology with only one transformer is of course a good method, which not only saves the auxiliary power, but also can get faster speed. At present, there are two ways to generate self-sufficient power: modulation and time sharing.Modulation technology is a classic method, that is, the PWM drive signal is modulated at high frequency (more than several MHZ), the modulated signal is applied to the primary of the isolated pulse transformer, and the secondary is rectified directly to obtain self-sufficient power, while the original PWM modulation signal needs to be demodulated. Obviously, this method is not simple. Another disadvantage of modulation is that the demodulation of PWM increases the signal delay, which is suitable for PWM signals with low transmission frequency.
5. Transformer isolation driver with time-sharing self-contained power supply
Time sharing technology is a relatively new technology. The principle is that the transmission of signal and energy is carried out separately, that is, the information is transmitted at the rising edge and falling edge of the input PWM signal of the transformer, and the energy required for driving is transmitted at the flat top level of the input signal. Because only the signal is transmitted at the rising edge and falling edge of the PWM signal, there is basically no energy transmission, so the delay and distortion of the output PWM pulse are very small, and a steep driving output pulse can be obtained. The disadvantage of time-sharing self-powered driver is that the transformer is bulky when used at low frequency. In addition, due to the limitation of self-powered energy, it is difficult to drive the IGBT exceeding 300A/1200V.
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