Novel Voltage Limiting Concept for Avalanche Breakdown Protection

Destructive over-voltage breakdown of cellular phone power transistors is prevented by using a new voltage-limiting concept. The output voltage is detected by an avalanche-based detector, and limited by decreasing the output power when needed. The voltage detector contains a low voltage bipolar NPN transistor with a well-defined lower breakdown voltage than the high voltage power transistor. Avalanche current in this detector is used to adapt the output power. In this manner the maximum collector voltage is limited to the breakdown voltage of the detector. Measurements show actuation current of the detector for extreme mismatch conditions. The maximum collector voltage is reduced from 15.1 V to 11.5 V once the protection loop is closed. This is in accordance to simulation results