Zero-crossing detection circuit

摘要

In one embodiment, a zero-crossing detection circuit can include: (i) a first detection circuit configured to detect a current through a main transistor of a main circuit of a switching power supply, and to generate a voltage sense signal that represents the current through the main transistor; (ii) a second detection circuit configured to detect if quasi-resonance occurs in the main circuit, the second detection circuit being configured to generate at least one pulse signal when the quasi-resonance is detected; and (iii) a control circuit configured to receive the at least one pulse signal and the voltage sense signal, to turn the main transistor off when the current through the main transistor reaches a predetermined value, and to turn the main transistor on when the at least one pulse signal is active.

主权项

1. A zero-crossing detection circuit, comprising:
a) a first detection circuit configured to detect a current through a main transistor of a main circuit of a switching power supply, and to generate a voltage sense signal that represents said current through said main transistor, wherein said first detection circuit comprises a first transistor that is coupled to a source of said main transistor; b) a second detection circuit configured to detect if quasi-resonance occurs in said main circuit, said second detection circuit being configured to generate at least one pulse signal when said quasi-resonance is detected; and c) a control circuit configured to receive said at least one pulse signal and said voltage sense signal, to turn said main transistor off when said current through said main transistor reaches a predetermined value, and to turn said main transistor on by turning said first transistor on when said at least one pulse signal is active.