5SHY3545L0016 3BHB019719R0101 GVC736BE101 5SXE06-0160 ABB high-voltage converter board silicon controlled rectifier

Description

5SHY3545L0016 desaturation detection uses IGBT itself as a current measuring element. The diode in the schematic diagram ensures that the collector emitter voltage of IGBT is only monitored by the detection circuit during the conduction period; In normal operation, the collector emitter voltage is very low (typically 1 V to 4 V). However, if a short circuit event occurs, the IGBT collector current rises to the level that drives the IGBT to exit the saturation area and enter the linear working area. This causes the collector emitter voltage to rise rapidly. The above normal voltage level can be used to indicate that 5SHY3545L0016 has a short circuit, while the threshold level of desaturation jump is usually in the range of 7 V to 9 V. Importantly, desaturation can also indicate that the grid emitter voltage is too low and the IGBT is not fully driven to the saturation region. Desaturation detection should be deployed carefully to prevent false triggering. This may happen especially when the IGBT has not fully entered the saturation state, during the transition from IGBT off state to IGBT on state. The blanking time is usually between the opening signal and the activation time of desaturation detection to avoid false detection. A current source charging capacitor or RC filter is usually added to generate a short time constant in the detection mechanism to filter the filter spurious jump caused by noise pickup. When selecting these filter elements, it is necessary to balance the noise immunity and response within IGBT short-circuit withstand time.

After IGBT overcurrent is detected, the further challenge of 5SHY3545L0016 is to turn off IGBT in abnormal high current level state. Under normal operating conditions, the gate driver is designed to turn off IGBT as quickly as possible to minimize switching loss. This is achieved by lower driver impedance and gate drive resistance. If the same gate turn off rate is applied for over-current conditions, the di/dt of collector emitter will be much larger, because the current changes greatly in a short time. The parasitic inductance of collector emitter circuit caused by stray inductance of wire welding and PCB routing may make the large overvoltage level reach IGBT instantaneously (because VLSTRAY=LSTRAY × di/dt)。 Therefore, during the desaturation event, it is important to provide a high impedance shutdown path when turning off IGBT, which can reduce di/dt and all potentially destructive overvoltage levels.
In addition to the short circuit caused by system fault, the instantaneous inverter direct connection will also occur under normal working conditions. At this time, the IGBT is required to be driven to the saturation area where the conduction loss is the lowest. This usually means that the gate emitter voltage in the on state is greater than 12 V. IGBT shutdown requires IGBT to be driven to the working cut-off area, so as to successfully block the reverse high voltage at both ends when the high-end IGBT is turned on. In principle, this can be achieved by reducing the IGBT gate emitter voltage to 0 V. However, the side effects when the low end transistors on the inverter arm are turned on must be considered. The rapid change of switch node voltage when conducting leads to capacitive induced current flowing through the parasitic Miller grid collector capacitor (CGC in Figure 3) of low-end IGBT. This current flows through the turn off impedance of the low end grid driver (ZDRIVER in Figure 3), creating a transient voltage increase at the low end IGBT grid emitter, as shown in the figure. If the voltage rises above the threshold voltage VTH of IGBT, it will cause the transient conduction of low-end IGBT, thus forming the transient inverter arm direct conduction – because both IGBTs are transiently conducted. This generally does not damage IGBT, but it can increase power consumption and affect reliability.

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