LED should be driven by a constant current (CC) source due to its diode-like characteristic. The redundancy design for CC drivers is different from that for conventional CV power supplies. Different redundancy solutions are discussed in this paper. The stability issue for N+1 redundancy system is analyzed based on the small signal model. Related solution is suggested and verified by experimental results.

Anasymmetric PWM controlled LLCC LED driverwith capacitor connected in series with secondary windingof the transformer is proposed. Due to the presence of the secondary side resonant capacitor, the DC bias of the magnetizing current can be eliminated when asymmetric PWM control is employed. Because the switching frequency is fixed regardless of the load variation, the efficiency of light load is improved compared to conventional frequency controlled LLC topology, especially in dimming applications. The operating principle and circuit simplification of the secondary side circuit are presented. A two outputsLED driver prototype with 100V-200V output, 0.035A-0.35A/channel is built up to verify the theoretical analysis.

The present invention provides a method for controlling two-wire dimmer circuit, an auxiliary source, the auxiliary source circuit comprising: a source capacitor constituting an auxiliary disconnecting switch and the series branch; branch in parallel with the series chopper switch; the said method comprising the steps of: detecting a current of an auxiliary voltage source, the auxiliary source voltage is determined is lower than a set lower limit value, if yes, further determines whether the chopper switch is in a chopper period, and if so, the auxiliary source capacitor is not charged; if not, the auxiliary source capacitor. Using the embodiment of the present invention can solve the drawbacks of the prior art, and the circuit is simple and low cost.