Mcu 0137-SLA-charge-controller

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For me this charge controller is part of a bigger project, but since it should work fine as a stand-alone solution I thought I'd put it here for the world to see and use.

I will be using the 8-pin 8-bit ATtiny84 for this design.

This charge controller aims to do the following:

  • use battery voltage sensing to detect whether the charging circuit should be activated or not.
  • use a fixed charge current in combination with an LM317 to regulate charge current
  • set final charge voltage using a trimpot
  • enter sleep mode on the microcontroller to save power when the battery is charged.
  • signal charge state with an LED


  • use a boost converter to allow charging from low input voltages (e.g. 5V from a USB port).

The first version of the charge controller schematic:

With these objectives defined, the next steps will be to work out the following features:

  • complete a rough schematic of the design (diptrace)
  • voltage detection of input and output
  • current detection of input and output
  • auto-adjustment of boost converter output voltage from mcu
  • design charge regime (boost - bulk - float)
  • minimise current draw when not charging (hopefully less than a few uA's)

(to be continued..)