Referring now to FIG. 9, shown is a schematic block diagram of an example multichannel constant current LED controlling circuit employing a constant off time control mode, in accordance with embodiments of the present invention. Multichannel constant current LED controlling circuit 500 can include transconductance amplifier 501 and a corresponding compensation circuit, comparator 502, and RS flip-flop 503. An inverting input terminal of transconductance amplifier 501 can connect to a current sensing circuit (e.g., including a sensing resistor) to receive current feedback signal VFB, and a non-inverting input terminal can receive reference voltage Vref. A current error signal may be generated at an output terminal of transconductance amplifier 501. Capacitor C51 and resistor R51 can connect in series between the output terminal of transconductance amplifier 501 and ground to form a compensation circuit. Alternatively, the compensation circuit can include only capacitors.

The current error signal can be compensated by the compensation circuit in order to generate a compensation signal. A non-inverting input terminal of comparator 502 can receive current feedback signal VFB, and an inverting input terminal can receive the compensation signal. An output terminal of comparator 502 can connect to a reset terminal of RS flip-flop 503, and a set terminal of RS flip-flop 503 can receive clock signal CLK. RS flip-flop 503 may provide a control signal (e.g., Gate) to a power switching transistor through its output terminal.