Patent ID: 9089026
Filing Date: 2015-07-21
Classification: H05B,Y02B

Abstract:
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.