Active fly-back clamp shrinks GaN USC-C chargers Power integrations has moved to active clamp fly-back conversion, zero voltage switching and a GaN transistor to shrink the size of its ac-dc USB-C charger circuits. The chipset implementing the topology are InnoSwitch4-CZ and ClampZero – consumer brand Anker announced products using them yesterday: the 30, 45 and 65W USB-C Nano II chargers ( photo). Implemented by the ClampZero IC, the active clamp deals with the transformer’s turn-off leakage inductance energy spike with less loss compared with the passive RCD clamp used in InnoSwitch3 for the same purpose. At turn off, with both passive and active clamps, a diode directs leakage inductance energy into a capacitor. In the passive case this is then dissipated by a resistor, while in the active case it is stored in the capacitor awaiting the next time the main switch needs to be turned on.