USB powered portable light

The circuit of this portable lamp is shown in the figure below. The lamp is powered by two nickel-metal hydride batteries, which are charged by a DC 5V power supply of the USB standard interface of the PC. When charging, insert the USB into the USB interface of the PC. At this time, the ① and ④ pins of the USB will have an output voltage of +5V, which is sent to the emitter of the transistor T1 through the current limiting resistor R1. T1 is a PNP type tube, which forms a constant current source with the peripheral related circuit. The collector of T1 charges the nickel-metal hydride current (+2.4V) through the isolation diode Dl. R2 and LED1 in the circuit provide a fixed bias current for the base of T1, so that the charging current of the constant current source to the battery is 50mA. The capacitor C1 in the circuit can suppress the high-frequency component of the USB output voltage and play a role in current filtering. When not charging, the diode Dl plays an isolation role to prevent the battery voltage from being added to the transistor T1. Here it is explained that the current output of the USB can reach 100mA. Here, two (7#) nickel-metal hydride rechargeable batteries are connected in series for a total of +2.4V. L1 is a flashlight bulb for simple emergency lighting. A reflective device can be added when installing the bulb.
When making it, the circuit in the figure below can be made into a printed circuit board (PCB) circuit. For easy carrying, the printed board can be placed in a small box. The USB plug cable in the figure should not exceed 1m. When welding, check the USB pins ① and ④ to make sure they are not wrong!
As shown in the figure, this circuit can be used as a charger for rechargeable batteries (4 cells) - at this time, just remove the L1 bulb.