Rechargeable Breadboard Power

One of the first projects I published on this site was for a power supply designed to clip onto the end of a breadboard and supply power to the rails on each side.  My first design used a NCP1402 Step-Up Switching Regulator to boost the voltage from a 1.5 volt, AAA cell up to 5 volts.  I find these clip on power modules very useful when wiring up experimental circuits so, over the years, I've continued to make many versions with many improvements to the design. This page describes my latest design, which has the following features:

1. Uses a ICR10440 rechargeable, lithium, AAA Cell which has a capacity of 350 mAh (1.295 Wh)

2. Can also use non-rechargeable 1.5V cell if J1 jumper is set, but you cannot use charger function for these cells

3. Automatic cutoff to prevent over discharge of ICR10440 battery

4. Switch selectable 3.5V or 5V output at up to 500 mA (short duration only, see section on batteries below)

5. Built in charging circuit based on MCP73831 (uses Mini USB jack for Charging Power Input)

6. PTC Resettable Fuse protection on USB Power Input

7. LED indicators for Power On, Battery Charging and Battery Charged

Click either image for a larger view (note: photos show version of PCB before J1 jumper was added)

The following schematic shows the complete design for the circuit which, as designed, is configured to charge the ICR10440 cell at a safe, 100 mA rate.  However, you can get faster, or slower charge rates by selecting a different value for resistor R1 (see the data sheet for the MCP73831 charge controller for the formula you need to calculate the resistor value for a given charge rate.)  Resistors R6 and R6 set the cutoff voltage (to the UVLO input on pin 7) for the cell which, in this case, is calculated for 2.6 Volts.  Likewise, Resistors R2, R3 and R4 form selectable voltage dividers for an output Voltage of either 3.3 or 5 Volts.  See the datasheet for the TPS61200 for the formulas used to calculate these resistor values.

Parts List

Note: all passive SMD parts are 0603 (1608 metric)

10440-type 350 mAh Batteries

I purchased the batteries I used for this project from Amazon.com, but they are available from a variety of sources.  Some places advertise 10440-size batteries with capacities up to 600-700 mAh, but I have not tested these claims and strongly suspect them to be untrustworthy.  The ICR10440 cells I purchased are rated at a maximum continuous discharge rate of 600mA, so it's advisable to limit the current you draw from the boost converter to stay below this limit.  But, for short durations of 10-20 seconds, I was able to verify that the boost converter can output 500 mA at 5 Volts.  The specs says that the ICR10440 can be charged at a rate of up to 300 mA, but I decided to set the limit at a more conservative 100 mA rate.  However, you can change this rate by adjust the value of resistor R1 (see section 5.1.2 of the MCP73831T datasheet for details.)