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Rechargeable flashlight: 21700 cell, USB-C TP4056, clicky switch, 2.8 A driver and a 10 W LED

Bench build · Everyday gadgets · Beginner · about 25 minutes

A 950-lumen torch with four modes, charged from any USB-C charger. What is inside a good rechargeable flashlight. One 21700 cell (5 Ah) is charged by a USB-C TP4056 board, which also cuts it off at 2.5 V. The tail switch feeds a constant-current driver (eight 350 mA regulator chips in parallel, 2.8 A) that holds the LED at the same brightness from a full to a half-empty cell, then, as the cell empties, falls into direct drive (it can no longer hold 2.8 A, so the light dims) and steps down to low below 3.0 V. The 10 W LED sits on an aluminium star pressed against the metal head: at 2.8 A it makes about 950 lumens and nine watts of heat, so the body is the heatsink. Click the driver board to step through high, medium, low and strobe.

Rechargeable flashlight: 21700 cell, USB-C TP4056, clicky switch, 2.8 A driver and a 10 W LED: the finished build running on the simulator's bench

Build it in the labGuided build, test sheet and fault finding, free in your browser.

zencircuitlab.com/l/rechargeable-flashlight

Parts list

Test procedure

Each test has an expected value and a pass range, like a factory test sheet:

  1. High: LED current
  2. Low: LED current
  3. Switch off, plugged in: charge current
  4. Nearly flat cell: out of regulation, dimmer

How it works

What it does: A 950-lumen torch with four modes, charged from any USB-C charger.

Build it (guided or ready-made), then run its test procedure below. Every test has an expected value and a pass range, just like a factory test sheet.

Background

Linear AMC7135 drivers and XM-L class LEDs have been the heart of hobby flashlights since about 2011.

More builds: everyday gadgets