关键词: 恒频, 可变电感, 软开关;均流, LED 调光 

Abstract: The capactive charge balance scheme is widely adopted to eliminate current imbalance in driving multi-channel LEDs due to the high accuracy of current sharing. In order to get the required LED driving current, variable frequency control directly leads to large reactive circulation and increases the stress of devices, and the EMI circuit is complex. Soft switching can’t be guaranteed by constant frequency operation under load variations. Hence, a multiplex LED dimming circuit based on variable inductance (VI) is proposed in this paper, which completes the constant frequency operation, alleviates the complexity of EMI circuit, and realizes the ZVS to improve the energy conversion efficiency. The proposed circuit with superimposed half-bridge structure will increase the number of outputs and simultaneously share resonant inductor, so that the power density is improved and the LED dimming unit is simplified. This paper describes the working principle of the circuit, and takes 8-channel LEDs to build 18W experimental prototype for verifying the feasibility of the LED driver.

Key words:  constant frequency, variable inductor, soft switching, current sharing, LED dimming