TP4056 USB-C Li-Ion Charger
A single-cell lithium charger module — your first SMD solder build, end-to-end.
Difficulty: Surface-mount. Estimated build time: about 90 minutes. Estimated parts cost: about US$8.00. 9-line bill of materials. Compare supplier offers when available. A self-contained linear charger for one 18650 or LiPo cell, built around the TP4056 — a tiny 8-pin SOP that handles every awkward part of lithium charging in hardware: the constant-current ramp from 0 V, the constant-voltage hold at 4.20…
Tin the TP4056 pads
Apply a thin layer of solder paste or pre-tin all eight TP4056 pads. The TP4056 is in an SOP-8 package with 1.27 mm pitch — completely manageable with a 0.6 mm chisel tip. Place the chip with tweezers, lining up pin 1 (the dot, top-left of the package text) with the pin-1 corner.
Solder the TP4056
Reflow the first two diagonal corner pins to lock the chip in position, check it is square, then drag-solder or hand-solder each pin one at a time. Add a tiny bit of flux first — it makes the difference between clean joints and bridges. Inspect with a loupe for shorts.
Place the passives
Solder the 0805 components: 10 µF input capacitor on VBUS, 10 µF output capacitor on the BAT pin, R_PROG (1.2 kΩ for 1 A or 5 kΩ for 240 mA) from PROG (pin 2) to GND, and the LED current-limit resistors (1 kΩ each). Add the red CHRG and green STDBY LEDs to their respective pins (CHRG = pin 7, STDBY = pin 6) — both pull low when active, so anode of each LED goes to VCC, cathode to its TP4056 pin through the 1 kΩ resistor.
Wire the USB-C input
If using a USB-C connector with CC pull-downs, place the two 5.1 kΩ CC resistors — without them USB-C hosts will not deliver power. VBUS goes to TP4056 pin 4 (VCC); ground to pin 3.
First-power validation (no battery yet)
Plug into a USB power bank. Measure between BAT+ and BAT-: with no battery, the voltage may sit near 0 V or briefly hit 4.2 V — both are normal. The CHRG LED should be off (no battery to charge). Now connect a partially-discharged Li-ion cell with battery polarity correct — RED LED should turn on solid (constant-current charging). When the cell is full, RED turns off and GREEN turns on (standby).
Sanity-check the charge current
With the charger active, put your multimeter in series with the BAT+ wire. With a 1.2 kΩ R_PROG you should see ~1 A while the cell is below 4.0 V, dropping smoothly toward zero as it nears 4.2 V. If you see more than 1 A, you measured the wrong R_PROG — verify the value before charging more cells.