US Patent 7636226 Current protection circuit using multiple sequenced bipolar transistors

A current protection circuit that uses a sequence of bipolar transistors to provide or draw current from a protected circuit node. An initial bipolar transistor has its emitter terminal coupled to the protected circuit node, with its collector terminal coupled to a current source or sink. One or more additional intermediary bipolar transistors are also provided in the sequence. Each additional intermediary bipolar transistor has its emitter terminal coupled to the base terminal of the previous bipolar transistor in the sequence, and has its collector terminal coupled to the current source or sink. To complete the sequence, a reverse-biased diode is coupled between the base terminal of the final intermediary bipolar transistor and the current source or sink. This allows for effective triggering of current protection for a protected circuit node without requiring a zener diode.