Control method and control circuit of electronic ballast of gas discharge lamp (HID)

A control method of an electronic ballast of a gas discharge lamp (HID), to generate PWM signals for controlling a left upper arm switch, a right upper arm switch, a left lower arm switch, and a right lower arm switch of the electronic ballast, wherein the gas discharge lamp (HID) is disposed between a connection point of a left upper arm and a left lower arm and a connection point of a right upper arm and a right lower arm;

• wherein during a normal operation of the electronic ballast, an operation of a controller of the electronic ballast comprises:
• generating the PWM signals;
• wherein the controller generates a PWM1 signal for controlling on/off of the left upper arm switch, a PWM2 signal for controlling on/off of the right upper arm switch, a PWM3 signal for controlling on/off of the left lower arm switch, and a PWM4 signal for controlling on/off of the right lower arm switch;
• the PWM1 signal and the PWM3 signal are low frequency signals and have an identical frequency and an opposite phase, the PWM2 signal and the PWM4 signal are high frequency signals;
• controlling to filter an electrical signal input into the gas discharge lamp (HID);
• detecting a current input into the gas discharge lamp (HID);
• and
• adjusting duty ratios of the PWM2 signal and the PWM4 signal;
• wherein if the current input into the gas discharge lamp (HID) is detected to be greater than a set normal value, the duty ratios of the PWM2 signal and the PWM4 signal are reduced, and if the current input into the gas discharge lamp (HID) is detected to be less than the set normal value, the duty ratios of the PWM2 signal and the PWM4 signal are increased;
• if the current input into the gas discharge lamp (HID) is detected to be greater than a set maximum value, the left upper arm switch, the right upper arm switch, the left lower arm switch and the right lower arm switch are all disconnected.