# Hardware for the LNSC-2420 Solar Charger

The LNSC-2420 is a PWM-based solar charge regulator for 24 V systems supporting
up to 20 A charging current.

## WARNING

The version 1.0 currently in the repository contains **a mistake will destroy the
driver MOSFETs** (the power MOSFETs are safe)! Do not build it as-is!

This notice will be removed once the design is fixed.

## Noteworthy Features

- High-side switching with N-Channel MOSFETs:
  - Gate voltage is provided by a charge pump which doubles the battery
    voltage.
  - Using N-Channel MOSFETs allows to drastically reduce the Rds\_on compared
    to P-Channel MOSFETs, resulting in lower loss.
  - High-side switching allows to have a shared ground connection between solar
    panel, battery and all devices connected as load.
- Current and voltage measurement:
  - The solar current, load current, solar voltage, battery voltage and charge
    pump output voltage are measured using the internal ADC of the STM32F030.
  - The voltages are measured via high-resistance voltage dividers which are
    buffered using ultra-low-power OpAmps.
- Low power usage:
  - The charge pump is disabled if both power FETs are off.
  - Additionally, the microcontroller is put into deep sleep (Stop Mode) if no
    solar power is available and the battery voltage is in undervoltage
    protection.
  - During normal operation (with LEDs on), the controller itself consumes
    below 300 mW.
  - In deep sleep, power consumption is below 25 mW.
- LED status display:
  - 6 LEDs show the internal charging and discharging state.
  - The LEDs are controlled using Charlieplexing (i.e. only 3 GPIOs are needed)
- Protections:
  - Solar panel reverse current
  - Battery overvoltage
  - Battery undervoltage
  - Load current limit

## License

The design in this repository is licensed under the [CERN Open Hardware Licence Version 2 - Permissive (CERN-OHL-P](LICENSE).