If you're interested in DIY-ing a relatively complete lithium battery charging desk lamp module that may still have some unknown issues, this article is worth checking out.

This article explains how to design and implement a universal lithium battery charging desk lamp module that can replace low-quality circuits with potential safety hazards. The module consists of three main parts: an MCU (STC15W204AS) control circuit, a switch-mode lithium battery charging IC (ETA6002), and an LED constant current driver IC (SDB628x).

The MCU handles user button inputs to control circuit switches and mode selection. It also monitors the battery voltage and automatically shuts down the system if the battery voltage gets too low. The lithium battery charging IC has built-in dynamic power path management, which completely separates the charging and discharging paths. This means that when the USB power supply is sufficient, the battery charges normally while the system runs on USB power. If the system requires more power or the USB supply is insufficient, the battery kicks in to share the load with the external power.

The benefit of this approach is that during simultaneous charging and discharging, the battery stops charging in time, and the system can immediately run on external USB power even if the battery is missing or fully depleted. In traditional designs, the system load is directly connected across the battery. If the system consumes power while the battery is charging, the battery may never fully stop charging. Even if the voltage reaches 4.2V, the charging current may not reach the cutoff condition (usually 0.1× the maximum charging current), leaving the battery in a constant float charge state, which reduces its lifespan. When the battery is low, the system voltage is also low, so the system cannot immediately resume operation when external power is connected.

The LED constant current driver uses the efficient and simple SDB628x boost design, providing over 4W output to drive 8 full-spectrum LEDs arranged in 4 series × 2 parallel. However, this IC has some limitations, such as weak load capacity. In practice, though, a well-designed PCB allows the IC to achieve performance close to the datasheet specifications.

The complete system looks like this:

Front side of the PCB:

Schematic and PCB layout:

Currently, there's a problem: at a certain point, the board's static current rises significantly. This was discovered during a routine long-term discharge test, where the lithium battery was discharged down to 2.5V, which triggered the ETA6002's undervoltage shutdown. The system powered off. However, the MCU-controlled discharge cutoff is designed to be around 3.15V. Even with automatic shutdown, under a standby current of no more than 50μA, the battery voltage shouldn't drop so quickly below 2.5V.

Upon inspection, the standby current had mysteriously increased to around 10mA, far above the 47μA measured when the board was first assembled. You can try cleaning the PCB to rule out self-discharge caused by contamination or leftover flux. If a component has failed, and you have the ability, you can try to troubleshoot and isolate the issue more deeply on your own.

End.