In order to maintain operation of the silicon-controlled rectifier dimmer, bleeder circuit 1′ can sink the bleeder current greater than or equal to latching current IL until direct current bus voltage VBUS is greater than lighting voltage VLED. When direct current bus voltage VBUS rises to a voltage greater than lighting voltage VLED, transistor Q1 can be be turned on and operate in the linear region to adjust the current flowing through the LED load. Further, since the voltage at the inverting input terminal of error amplifier EA1 is greater than bleeder current reference signal Ref1, the output signal of error amplifier EA1 can be negative and transistor Q2 may be turned off. After direct current bus voltage VBUS decreases to a voltage less than lighting voltage VLED, transistor Q1 can again be turned off, and transistor Q2 again turned on to operate.

In this approach, silicon-controlled rectifier dimmer TRIAC may chop a sinusoidal alternating current signal at different angles, and the chopped signal can be rectified and output to the direct current bus to drive the LED load. In FIG. 2, a waveform on the left side shows direct current bus voltage VBUS and drive current IQ1 of transistor Q1 at a relatively large conduction angle, and a waveform on the right side shows direct current bus voltage VBUS and drive current IQ1 of transistor Q1 at a relatively small conduction angle. In FIG. 2, drive current IQ1 can be controlled to be maintained at desired current value Ip. Ripple amplitude ΔI of drive current IQ1 may be expressed by the following formula (1).

$\begin{array}{c}\Delta ?\end{array}$