| 主权项 |
1. A control circuit used in a LED driver, the LED driver includes an input port configured to receive an input signal, an output port configured to provide a driving voltage to a LED string, an intermediate node, a step-up stage having a first power switch coupled between the input port and the intermediate node, and a step-down stage having a second power switch and a third power switch coupled between the intermediate node and the output port, the control circuit comprising:
a phase detector, having an input terminal coupled to the input port to receive the input signal, a first output terminal configured to generate a phase detecting signal indicative of phase information of the input signal, and a second output terminal configured to generate a cycle detecting signal indicative of cycle information of the input signal, wherein the cycle detecting signal is a short pulse signal; a step-up comparator, having a first input terminal configured to receive a reference signal, a second input terminal configured to receive a voltage feedback signal indicative of a voltage at the Intermediate node, and an output terminal configured to generate a step-up comparison signal based on the reference signal and the voltage feedback signal; a logical OR unit, having a first input terminal coupled to the second output terminal of the phase detector to receive the cycle detecting signal, a second input terminal coupled to the output terminal of the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a step-up enable signal by executing logical OR operation on the cycle detecting signal and the step-up comparison signal; a step-up controller, coupled to the logical OR unit to receive the step-up enable signal, to get enabled or disabled by the step-up enable signal, and to generate a step-up control signal, the step-up control signal being used to control the first power switch; a logical AND unit, having a first input terminal coupled to the first output terminal of the phase detector to receive the phase detecting signal, a second input terminal coupled to the step-up comparator to receive the step-up comparison signal, and an output terminal configured to generate a logical AND signal by executing logical AND operation on the phase detecting signal and the step-up comparison signal; an average circuit, coupled to the output terminal of the logical AND unit to receive the logical AND signal and to generate an average signal; and a step-down controller, having a first input terminal configured to receive a LED current sense signal indicative of a current flowing through the LED string, a second input terminal coupled to the average circuit to receive the average signal, and an output terminal configured to generate a step-down control signal to control the second power switch and the third power switch. |
