Portable rechargeable light circuit

The portable household emergency backup light is
composed of a portable flashlight and a rechargeable power box. If there is a power outage
for more than one second, the emergency backup light will automatically light up.
Generally speaking, it can be used for several hours on a single charge. Charging
relies on its charging power supply to charge two ordinary nickel-cadmium batteries
.
    (1) Circuit principle The appearance and circuit of the portable charging lamp
are as shown in the figure.
A low-voltage DC power supply is composed of a transformer T, a full-wave bridge rectifier and a filter capacitor Cl to provide charging current
for the battery B. When the grid voltage is connected, the light-emitting diode LED will emit light, and the resistor R1 is the current-limiting resistor of the light-emitting diode. =The diode VD prevents the battery from forming a discharge loop through the light-emitting diode LED, and the battery charging current is limited by the resistor R3 or R4. When switch Sl is placed in the "slow" position, 33mA current is allowed to flow into the battery through the resistor . "quick". When in the position, 100mA current is provided through the resistor to speed up the battery charging.     (2) The power supply is normal. The DC voltage also supplies power to the relay K coil. A resistor R2 is connected in series to reduce the coil current and keep the coil temperature rise low. The path between battery B and light bulb EL1 is formed by the relay contact Switch control, that is, when the power supply is normal, the battery is charging (switch Sl is turned off), and no current flows through the bulb EL1.     (3) The AC power supply is cut off. When the power supply is cut off, battery charging stops, the coil current of relay K is cut off, and its normally closed contact switch is closed. A path is formed between battery B and bulb EL1, the battery supplies current to the bulb , and the bulb automatically lights up as emergency backup lighting.