Patent ID: 9351362
Filing Date: 2016-05-24
CPC Classification: H05B,Y02B

Claim Text:
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 said 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; and a second control circuit configured to generate a dimming signal and control an operation of said second power stage circuit in accordance with said dimming signal to maintain an output current of said second power stage circuit to be consistent with an expected driving current represented by said dimming signal, wherein said dimming circuit operates in one of a first operating mode and a second operating mode, in said first operating mode, an input current of said first power stage circuit is maintained to be a first current which is no less than a holding current of said electronic transformer, when said first output voltage is in a continuously increasing state and is less than said upper threshold voltage, in a time period during which said TRIAC is turned on, in each half-sinusoidal wave period of said AC power supply, and said second control circuit generates said dimming signal in accordance with said first current, in said second operating mode, said input current is maintained to be said first current when said first output voltage is in a continuously increasing state and is less than said upper threshold voltage, and said input current is maintained to a second current after said first output voltage reaches said upper threshold voltage and then decreases continuously, after said TRIAC is turned on, in each half-sinusoidal wave period of said AC power supply, and said second control circuit generates said dimming signal in accordance with said first current and said first output voltage.