Small +5 volt 1 Amp Li-Ion Power Supply

Original and hacked boards with battery and charger

The original circuit, hacked circuit and battery and charger

This is another project born of necessity. A new costume with a bunch of LEDs needed a +5 volt power supply. After burning out a Sparkfun boost converter module I turned to hacking one of my own circuit designs. For a series of gifts I had designed a small LED controller that drove commonly available +12 volt flexible LED arrays. It used a Linear Technology LT1935 boost converter IC to step the voltage from a Li-Ion CR123A cell up to 12 volts. I had some spare boards and parts laying around so I figured I could just repurpose the converter circuit to generate +5 volts with a change in the feedback circuit. Of course the empty pads where the PIC 16F1825 microcontroller went was too inviting and I ended up writing some code to display the current battery level and provide an automatic low-voltage shutdown so the Li-Ion battery wouldn't be damaged. This circuit can supply up to about an amp of power.
Close-up of hacked board
Close-up of the hacked board. Note the addition of a n-channel MOSFET transistor on the ground leg of the load and the LEDs and series resistors. Because the original board had ground pads in the location I wanted to put the LEDs I configured the firmware to drive an active high signal to light a LED. This is not ideal. A better solution is to sink current in the PIC to turn the LEDs on (active low signal with the LED anodes connected to V+). This is because the act of driving current to a LED momentarily affects the ADC readings being made to measure the battery voltage.
Pressing button on hacked board to show battery level
The Batt Check button being pressed with a fully charged battery while powering my own version of a "Pixel" smart LED module.