There is a cheap LED flashlight on the market, which has 5-8 high brightness light emitting tubes at the front end and uses 1-2 batteries. Due to the use of ultra-high brightness light emitting tubes, the luminous efficiency is very high and the working current is relatively small. In actual measurement, a 5-head flashlight from a No. 5 battery was used, with a current of only about 100mA. Very power saving. If a large capacity rechargeable battery is used, it can be used continuously for more than ten hours, so I bought one.

After turning on the power, VT1 cannot experience sudden voltage changes at both ends of c1 due to R1 being connected to the negative pole. The potential of VT1 (b) pole is lower than that of E pole, VT1 is conductive, and there is current flowing into VT2 (b) pole. VT2 is also conductive, and the current flows from the positive pole of the power supply through L and VT2 (c) pole to E pole, and back to the negative pole of the power supply. The power supply charges L, stores energy, and the self induced electromotive force on L is left positive and right negative. Through the feedback effect of c1, the base potential of VT1 is lower than the emitter potential, and VT1 enters a deep saturation state, while VT2 also enters a deep saturation state, that is, Ib>Ic/ β （ β Is the magnification factor). As the power source charges c1, the voltage at both ends of C1 gradually increases, that is, the VTI (b) pole potential gradually increases, and Ib1 gradually decreases. When Ib1<=Ic1/ β When VT1 exits the saturation zone, VT2 also exits the saturation zone, reducing the charging current to L. At this point, the self induced electromotive force on L. becomes left negative and right positive, with feedback from c1. The base potential of VT1 further increases, VT1 quickly shuts off, and VT2 also shuts off. The energy stored on L is released, and the power voltage on the LED is applied to L to generate self induced electromotive force, achieving the purpose of boosting voltage. This voltage is sufficient to cause the LED to emit light.