Power supply circuit having voltage control loop and current control loop

摘要

A power supply circuit includes two pass transistors that conduct current from a voltage supply terminal to an output terminal. One of the pass transistors is smaller whereas the other is larger. Current through the smaller transistor is controlled by the voltage control loop such that the voltage on the output terminal is regulated to a predetermined voltage. Current through the larger transistor is controlled by a high gain current control loop such that the current flowing through the larger transistor is a multiple of the current flowing through the smaller pass transistor. By reducing current flow in the smaller transistor, the power supply rejection ratio (PSRR) of the power supply circuit is improved for frequencies up to 100 kHz. Die space occupied by the two pass transistors is reduced in comparison to the amount of pass transistor die space in a conventional power supply circuit of similar performance.