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Button battery charger

Overview

I. Design Summary This circuit

can charge an LIR2032 (3.6V) and a 4.2V lithium battery. It only requires configuring a resistor. An external solar panel (voltage range 3.9~6V) can be connected to charge the battery. The charging current is configured using a resistor, with a maximum charging current of 300mA.
II. Hardware Circuit Composition

This circuit is very simple, consisting of two parts
: 1. Charging Interface: The CC pin is connected to a 5.1K resistor to ground for easy C-to-C power supply.

2. Charging IC

Voltage Configuration Resistor R5
R5 value: 80K for LIR2032, 240K for 4.2V lithium battery.
0R 3.3V
80K 3.6V
240K 4.2V
Calculation Formula

Current Configuration Resistor R4
1188V/120KΩ = 9.9mA
The minimum charging current is 10mA, therefore R4 is 120KΩ.
The maximum continuous charging current can reach 300mA.
3. Physical Demonstration

III. Precautions:

SS14 does not require soldering short circuit (for reverse polarity protection solar panel) when not using solar charging function. R1 and R2 do not require soldering.

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It is your responsibility to test the circuit yourself and determine its suitability for you. EEWorld will not be liable for direct, indirect, special, incidental, consequential or punitive damages arising from any cause or anything connected to any reference design used.

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Update:2026-03-26 02:27:05

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