Active Clamping protects the IGBTs/MOSFETs from excessive collector-emitter voltages
Active Clamping(for over-voltage protection) has been widely used for many years to limit the collector-emitter voltage of an IGBT during the turn-off event . The IGBT is partially turned on as soon as its collector-emitter voltage exceeds a pre-defined threshold. The IGBT is then maintained in linear operation, thus reducing the fall rate of the collector current and therefore the collector-emitter over-voltage.
Basic(conventional) active clamping topologies implement a single feedback path from the IGBT’s collector through transient voltage suppressor devices (TVS) to the gate
The TVS placed between collector and gate ensures that the gate is switched on again when a defined voltage is exceed at the collector.The IGBT then becomes conducting and the result is a reduced IGBT turn-off over-voltage
The turn-off transistor of the driver is switched on ,this reduce the charge that flows from TVS path to IGBT gate
This impact the IGBT conducting and the performance of over-voltage protection
Of course you can increase gate resistance to relieve effect, but sacrifice efficiency
Advanced Active Clamping
Most SCALE-2 products support Power Integrations' Advanced Active Clamping, where feedback is also provided to the driver’s secondary side at pin ACL
The turn-off MOSFET of the driver stage is progressively switched off in order to reduces the charge that flows away from the IGBT gate to COM over the turn-off gate resistor
This improve the effectiveness of the active clamping and reduce the losses in the TVS
The gate resistor is no longer responsible for the active clamping and no impact with efficiency