DIY Desktop Flashlight with AX2002 LED Driver

If you're interested in DIY desktop flashlights, this article is worth a look.

At night when you're browsing the web or watching videos, if you don't like turning on the ceiling light and prefer a slightly warm background light, you might flip an 18650 flashlight upside down to shine at the ceiling for diffuse lighting, but the battery life usually isn't enough, you have to swap batteries after a few hours, and you end up rotating through several flashlights, so you can try the following modification.

You can prepare a few flashlight parts and make a desktop flashlight with an external 5V power supply, and it can be powered by either a power bank or a charger.

For the LED, you can use an OSRAM 3W warm yellow emitter with a matching lens. The power input connector can be a DC 5.5 jack salvaged from an old board.

Flashlight circuits are usually powered by 3V–4.5V, and feeding in 5V directly might burn them out, unless you add a buck converter in between, which is more troublesome. In the end, you can use an AX2002 driver that supports wide-voltage input from 3V to 12V with three lithium cells and provides a 1A output current.

The picture above shows the Arthur Light Technology AX2002 (2A) / AX2003 (3A) series PWM LED driver ICs. The AX2002/2003 series is an asynchronous DC buck converter with PWM output, using a feedback resistor to control the LED current, and the feedback voltage is only 0.25V, which significantly reduces power loss on the feedback resistor. Its input voltage range spans from a minimum of 3.6V to a maximum of 23V, and the output can drive up to seven LEDs in series, making it very suitable for LCD TVs and displays, flashlights, cup lights, and similar devices.

In applications, the AX2002/2003 offers high conversion efficiency and stable operating voltage, and it integrates complete system protection functions including soft start (SS), short-circuit protection (SCP), over-temperature protection, and over-current protection (OCP), with a fixed switching frequency of 330kHz or 500kHz and a maximum efficiency of up to 91%.

The AX2002/2003 uses a standard SOP-8L lead-free package, and with very few external components it can greatly reduce PCB area, while its thermal design allows heat to be conducted to the PCB, significantly lowering the component surface temperature to meet application requirements.

The PCB has a diameter of 17mm, a thickness of 1.2mm, a component height of 4.8mm, a single-sided component layout, and a double-sided gold-plated board.

Note: The recommended supply voltage is around or below 12V; with a single lithium cell, it automatically cuts off at 3.3V; single-level dimming; default current is 1000mA for a single 3W LED.

The finished unit is palm-sized, with thermal grease applied to the LED star board and the circuit fixed using thermally conductive double-sided tape. At 1A, it's still very bright, gets slightly warm, and has good heat dissipation.

The downside is that the white lamp cover leaks a bit of light, but you can just cover it with some black tape.

The end.