What should I pay attention to when using IGBT driver?
In recent years, IGBT, a new type of power switching device, has been gradually recognized by people. Compared with the previous power electronic devices, IGBT has obvious advantages in comprehensive performance, and it is increasingly used in various power conversion devices with operating frequency of several tens of kilohertz and output power of several kilowatts to several tens of kilowatts. However, during the use of IGBT, many problems have been found, one of which is the reasonable choice of IGBT driving circuit. Let's talk about some problems that should be paid attention to when using IGBT drive.
The choice of diode V6 is very important. It must be a fast diode, its reverse withstand voltage should be at least the same as that of IGBT, and its forward voltage drop is closely related to the setting of IGBT protection points. For example, Fuji EXB series drive requires the forward voltage drop of V6 to be 3V. If we choose other diodes with low voltage drop, IGBT cannot be effectively protected. On the contrary, if you want to reduce the protection point of IGBT, you can increase the forward voltage drop of V6 by connecting several igbts in series. In addition, the transmission ratio of IGBT produced by different manufacturers is different. Therefore, when using the driver produced by one manufacturer to drive the IGBT of another manufacturer, the forward voltage drop of diode V6 should be adjusted accordingly.
Some manufacturers' drivers (EXB series) do not have the function of timing logic gate voltage control. In the overcurrent state, if the input signal of the driver disappears, its output signal also disappears. In this way, the IGBT in the overcurrent state is easily damaged. Therefore, it is necessary to take measures in the external circuit to ensure that the drive pulse at the entrance of the driver has enough width when the overcurrent occurs, so that the IGBT can reliably complete the turn-off process under the soft turn-off action of the driver. On the other hand, for drivers with logic gate voltage control (such as HR065), in some cases, there is a danger of bridge arms passing through.
When the IGBT is turned on, some normal peak currents often flow. Therefore, drivers usually cannot prevent short-term overcurrent. For example, EXB841 is connected to 4µ S did not protect IGBT from overcurrent before. In addition, after overcurrent occurs, when the driver sends out a protection signal and sends it to the control circuit through the photocoupler, there will be several microsecond delays. Therefore, the current driver is still powerless against the narrow pulse overcurrent, and it still needs to be protected by other means.
To sum up, when designing the circuit, we should have a clear understanding of the characteristics of various drivers, make correct choices according to actual needs, and reduce blindness. For the equipment whose output and input are directly electrically connected, such as frequency converter, it is more appropriate to use optocoupler isolation driver because of the high risk of direct short circuit between inverter and ground and the long waiting time for IGBT to turn off. However, for general switching power supply (such as inverter welding machine, communication power supply, etc.). ), because the possibility of IGBT's direct short circuit to the ground is very small. As long as the bridge arm of the inverter circuit can not pass through and the current transformer is used for overcurrent protection, the IGBT will not be threatened by overcurrent. Generally, the operating frequency of this kind of equipment is relatively high. Considering the technology and economy, it is more appropriate to adopt transformer driver.
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