Patent ID: 8836304

Claim:
A switching mode power supply, comprising: a power stage comprising a first power switch and a second power switch coupled in series; a real current sense circuit configured to monitor a current flowing through the first power switch during a first power switch on time, wherein the real sense circuit has an input terminal and an output terminal, and wherein the input terminal is coupled to the first power switch, and wherein the real current sense circuit is configured to provide a real current sense signal at the output terminal, the real current sense signal corresponding to the current flowing through the first power switch during the first power switch on time; a virtual current sense circuit configured to monitor a current flowing through the second power switch during a second power switch on time, wherein the virtual current sense circuit is configured to provide a virtual current sense signal that is related to the current flowing through the second power switch during the second power switch on time; a sense capacitor coupled to the real current sense circuit and the virtual current sense circuit to receive the real current sense signal during the first power switch on time and the virtual current sense signal during the second power switch on time, and to provide a current sense signal based thereon; a controller coupled to the sense capacitor to receive the current sense signal, and to provide a control signal based on the received current sense signal; and a driver coupled to the controller to receive the control signal, and to provide a driving signal to the power stage based on the received control signal; wherein the real current sense circuit is further configured to provide (1) a maximum signal that represents a peak magnitude of the current flowing through the first power switch, (2) a minimum signal that represents a valley magnitude of the current flowing through the first power switch, and (3) an on time signal of the second power switch to the virtual current sense circuit; and wherein the virtual current sense circuit is further configured to calculate the virtual current sense signal based on the maximum signal, the minimum signal, and the on time signal.