Power outage emergency lights (3)

The transistor VT forms a typical inductive three-point oscillator with a frequency of 100 kHz. The capacitor C2 is a positive feedback capacitor.
Its function is to feed back part of the energy of each inductor oscillation to the base circuit of the transistor VT for further amplification. After amplification,
the current flows from the collector The electrode output feeds back part of the energy to the base via the inductor L2 and capacitor C2. In this way, the circuit can
maintain oscillation over and over again. T is a step-up transformer. The high-frequency oscillation current is boosted by L3 and directly added to both ends of the fluorescent tube to make the tube
ignite and glow. Using a high frequency of 100kHz is beneficial to improving the luminous efficiency of fluorescent lamps. By adjusting the potentiometer RP,
the oscillation frequency can be fine-tuned, thereby achieving the purpose of adjusting the brightness of the lamp. R4 is a protective resistor to prevent the transistor
from being damaged due to excessive base current when RP is adjusted to zero .     When charging. The 220V alternating current is reduced and current limited by CI and R2, bridge rectified by VD1~VD4, and then charged to battery G through VD5 . LED is the charging indicator light. VD5 is a charging protection diode. When the battery G is sufficient, the diode VD5 is cut off due to the increase in negative electrode potential, and charging automatically stops, thus effectively preventing battery overcharging. Since the capacitor voltage reduction has a constant current effect, the charging current is limited to less than 220 X2ⅡfCl, which is about 55mA.