Nowadays, many cheap rechargeable LED desk lamps use a small 4V battery as the power source. The simple resistor-capacitor step-down circuit is charged, and the circuit has a high failure rate. This article describes in detail the working principle of this rechargeable LED table lamp circuit, in order to facilitate the reference for maintenance.
The circuit is shown above. After the power is turned on, the AC 220V voltage is stepped down by the capacitor C1, the rectifier bridge bridge rectifier and the capacitor C2 filter, and a DC voltage is generated to charge the 4V battery through the diode VD. The charging current of the battery is mainly determined by the capacitor C1. When C1 uses a capacitor of 1μF, the charging current of the battery is about 69mA. LED1 is the charging indicator and resistor R1 is the bleeder resistor.
In the figure, LEDs 2 to 20 (not all of which are shown in the figure) are a plurality of parallel white LED lamp beads, each of which is connected in series with a 51 Ω chip current limiting resistor. K is the power switch of the desk lamp, and K is closed, and LED2~LED20 can be lit. Need to say here, because the voltage at both ends of the battery is high during charging, do not close the switch K during charging, otherwise it will easily damage the LED lamp bead.
The rectifier bridge in the circuit generally uses a rectifier bridge with a chip package. The commonly used models are MB6S and DB107S.
Detailed explanation of the working principle of the rechargeable LED desk lamp circuit ▲ In-line white LED lamp bead for LED desk lamp.
The white LED lamp bead shown in the above figure has an operating voltage of about 3V and a maximum operating current of 20mA.
Explain the working principle of the rechargeable LED desk lamp circuit ▲ 4V battery for LED desk lamp.
Many cheap rechargeable LED desk lamps use 4V batteries as the power source. Because the charging circuit is simple and there is no protection circuit, some batteries of the desk lamp are easily damaged by overcharging. If the battery is damaged or the storage capacity is deteriorated, you can replace the battery of the same specification after confirming that the circuit is not faulty.