Driving circuit for single-string LED lamp

A driving circuit for a single-string light-emitting diode (LED) lamp having an input terminal and an output terminal, comprising:

• a dimming control circuit for receiving a dimming signal of a pulse-width modulation (PWM) waveform, with the dimming signal comprising a plurality of consecutive cycles, with each cycle comprising an on period and an off period;
• a current feedback circuit and the dimming control circuit coupled in series between the output terminal and a ground terminal, wherein during the on period, the dimming control circuit controls the output terminal and the ground terminal to be closed and the current feedback circuit detects a lamp current flowing through the single-string LED lamp and outputs a first feedback voltage to a feedback terminal according to the lamp current;
• wherein during the off period, the dimming control circuit controls the output terminal and the ground terminal to be open and outputs a second feedback voltage to the feedback terminal and the current feedback circuit does not detect the lamp current to stop outputting the first feedback voltage;
• a PWM control circuit coupled to the feedback terminal and the PWM control circuit for outputting two PWM signals which are 180 degrees out of phase with each other when receiving the first feedback voltage, and for stopping outputting the two PWM signals when receiving the second feedback voltage;
• and
• a push-pull converter coupled to the input terminal and the PWM control circuit, the push-pull converter converts, according to the PWM signals, a first direct-current (DC) voltage to a second DC voltage output to the input terminal when receiving the two PWM signals, and stopping converting and outputting the second DC voltage when not receiving the two PWM signals, wherein the dimming control circuit comprises:
• a unidirectional component;
• a first inverter for receiving the dimming signal and outputting an antiphase dimming signal which is 180 degrees out of phase with the dimming signal, with the antiphase dimming signal coupled to the feedback terminal through the unidirectional component to stop outputting the second feedback voltage related to the antiphase dimming signal to the feedback terminal during the on period, and output the second feedback voltage to the feedback terminal during the off period;
• a second inverter coupled to the first inverter, with the second inverter receiving the antiphase dimming signal and outputting an in-phase dimming signal which is 180 degrees out of phase with the antiphase dimming signal;
• and
• a switch and the current feedback circuit coupled in series between the output terminal and the ground terminal, with the switch turned on or off according to the in-phase dimming signal, with the switch turned on to control the output terminal and the ground terminal to be closed during the on period, and with the switch turned off to control the output terminal and the ground terminal to be open during the off period.