Li-Ion/Li-Po Power Supply controller

For another project I wanted to use a Li-Ion or Li-Po battery charger and controller that gave a 3V3 and 5V output. The power demands were not high. After searching the internet a few days I did not found any controller that fit my demands: USB connector, small form factor, stay on even when very low current is drawn from the battery.

I tried to combine a 5V controller and charger and combine it with a 3V3 regulator. This did not work when the battery was empty, the power switched on and off before it became stable.

Own design

So I designed and made my own:

The size is 26.5 x 20.2 mm. Maximum power output is about 500mA. This is not checked yet, I use it for low power applications. Charge current is 500mA max. Output voltage 5.1V and 3V3. LED will signal when battery is fully charged. You can connect a 3.7V Li-Ion or better a 3.7V Li-Po cell with charge and discharge protection.

Warning

The unload of a Li-Ion 3.7V cell will not stop with this controller when the battery voltage is below 3.0V. You have to use another circuit to protect a 18650 Li-Ion cell. I have now a good experience with a Li-Po cell with protection module:

Schema

PCB design

Building and Costs

I have designed and ordered the PCB at JLCPCB. I used LCSC parts in my design and ordered these parts separate. I soldered the components myself on this PCB using a heat gun and solder paste. I did not use a solder mask.

Cost of PCB: $5.00, Shipping cost: $ 11.79, total cost $ 16.79 for 10 PCB’s. So total about $1.68 per PCB.

Cost of Parts: $ 10.53, Handling cost: $3.00, Shipping cost: $ 8.91: Total cost $ 22.44 for building 5 controllers. So total about $ 4.50 per controller.

Total cost: about $ 6.20 (at writing € 5,15) per controller. Soldering is done by myself.

Shared information

The schematic, PCB design and BOM are shared at
https://oshwlab.com/Leo/li-ion-power-supply

Technical info

Charger via Micro USB connector

MCP73831: Miniature Single-Cell, Fully Integrated Li-Ion, Li-Polymer Charge Management Controller

  • Thermal Regulation
  • Package used: SOT-23
  • Programmable Charge Current set to 500mA
  • Reverse Discharge Protection
  • Charge Complete Mode: No Charge Current: Status = HIGH
3V3 output direct from battery voltage, max 250mA

MCP1700: Low Quiescent Current LDO Voltage regulator

  • 1.6 μA Typical Quiescent Current
  • 250 mA Output Current for Output
  • Low Dropout (LDO) Voltage: 178 mV
  • Short Circuit Protection
  • Overtemperature Protection
  • Package used: 3-Pin SOT-23
5.2V output from Boost Converter, max 250mA

TPS61041: Low-Power DC-DC Boost Converter

  • 1.8V to 6V Input Voltage Range
  • 250 mA Internal Switch Current
  • 28-μA Typical No-Load Quiescent Current
  • Thermal Shutdown
  • Overload protection (250mA cut off)

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