Thermistor solves the problem of cathode preheating of fluorescent lamps

Thermistor and copper-spraying equipment, with aluminum and silver, transform energy-saving materials. In order to solve the problem of cathode preheating of fluorescent lamps, a positive temperature coefficient thermistor (commonly referred to as PTCR) is utilized.

After the body temperature of the PTCR is higher than the TB point, the resistance of the PTCR will suddenly change to a very high value as the temperature rises, and the preheating start circuit designed by this characteristic of the PTCR is used. When the circuit is turned on, the output voltage V0 of the high-frequency power source is applied to both ends of the lamp.

At this time, since the thermistor PTCR is shunted to the resonant circuit, the Q value of the circuit is very low, and high voltage cannot be formed at both ends of the lamp tube, so that the lamp tube cannot be lit. At the same time, the high-frequency current is preheated through the inductor L filament Rf and the thermistor PTCR. After t1 (GB is more than 0.4 seconds), the PTCR increases rapidly due to the passing current, and the resistance value increases rapidly. The shunting of the resonant tank is reduced. When the resistance increases to a certain value, the resonant circuit starts to oscillate, and the resonant voltage amplitude V2 increases to illuminate the lamp. When the lamp is lit, t2, the lamp has a negative resistance characteristic, that is, the lamp current increases, the voltage V3 across the lamp falls to the rated working voltage value, the preheating start process ends, and the lamp is turned into normal operation.

The problem is that after the lamp is working normally, the thermistor PTCR is always in thermal equilibrium state. This is because the thermistor cannot completely block the shunting of the lamp cathode. The temperature of the thermistor body affects the magnitude of the passing current. The magnitude of the passing current affects the change in the thermistor body temperature.