Dimming circuit and method for LEDS

摘要

The present disclosure relates to dimming circuit and method for LEDs. The dimming circuit obtains a DC voltage from an external AC power supply by using a TRIAC, an electronic transformer, and a rectifier bridge sequentially. The dimming circuit comprises a first power stage circuit, a second power stage, a first control circuit, and a second control circuit. The first power stage circuit has an input terminal configured to receive the DC voltage. The second power stage has an input terminal coupled to an output terminal of the first power stage and an output terminal coupled to an LED load. The first control circuit is configured to generate a first control signal in accordance with a first output voltage generated at the output terminal of the first power stage circuit, a first reference voltage and an upper threshold voltage to maintain an average value of the first output voltage to be consistent with the first reference voltage. The second control circuit is configured to generate a dimming signal in accordance with a first current and the first output voltage to control an operation of the second power stage circuit to maintain an output current of the second power stage circuit to be consistent with an expected driving current represented by the dimming signal. The first current is no less than a holding current of the electronic transformer. An input current of the first power stage circuit is maintained to be consistent with the first current by the first control signal when the first output voltage is in a continuously increasing state and is lower than the upper threshold voltage. The first output voltage decreases continuously and the input current is maintained to be consistent with a second current after the first output voltage reaches the upper threshold voltage.

主权项

1. A dimming circuit for LEDs which obtains a DC voltage from an external AC power supply by using a TRIAC, an electronic transformer, and a rectifier bridge sequentially, comprising:
a first power stage circuit having an input terminal configured to receive said DC voltage; a second power stage having an input terminal coupled to an output terminal of said first power stage and an output terminal coupled to an LED load; a first control circuit configured to generate a first control signal in accordance with a first output voltage generated at the output terminal of said first power stage circuit, a first reference voltage and an upper threshold voltage to maintain an average value of said first output voltage to be consistent with said first reference voltage, wherein an input current of said first power stage circuit is maintained to be consistent with a first current by said first control signal when said first output voltage is in a continuously increasing state and is lower than said upper threshold voltage, and said first output voltage is decreased continuously and said input current is maintained to be consistent with a second current after said first output voltage reaches said upper threshold voltage by said first control signal, and wherein said first current is no less than a holding current of said electronic transformer; and a second control circuit configured to generate a dimming signal in accordance with said first current and said first output voltage to control an operation of said second power stage circuit to maintain an output current of said second power stage circuit to be consistent with an expected driving current represented by said dimming signal.