When the electronic ballast is in the abnormal state of poor contact with the fluorescent lamp foot, dark tube, broken tube, broken filament and so on, the fluorescent lamp cannot start normally, and the output current of the inverter increases continuously, usually this current will rise to 3 to 5 times of the normal current. So it is necessary to install a temperature switch. When there is over-current or over-temperature, the thermal protector senses the temperature and controls the circuit on and off.