Single Cell (AA or AAA) Boost Circuit

Following on as part of this remote "monitor" gadgets I’m playing with, it would be good to use a single cell (battery) to power the remote devices. In the past some cool step-up devices form Pololu Robotics & Electronics: NCP1402 and S7V7F5 (both shown below).

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These allow using a single AA or AAA battery to power +5V devices and fit within the regular footprint of a TO-220 regulator. But I also must include with them the case to hold the AA or AAA battery. So upon further research I found a really neat reference design from Microchip using their MCP1640: MCP1640 Single Quadruple-A Battery Boost Converter Reference Design.

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That is so simple, small, and elegant; I figured I had to give that a try. Now I don’t use AAAA-size batteries, but if they did such cool stuff with a smaller size (and packed more complexity), I had to be able to create a similar profile for the larger AAA and AA cases. The task was to provide +5V (or close) from a AA/AAA battery, have a means to enable/disable it, and not exceed the case of the AA battery holder. Since the design was to be common to both AA and AAA; it had to accommodate both cases.

I again turned to OSH Park for the PWBs, and again they turned out great (and really fast – 2week turnaround).

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The boards turned out excellent. Two assemblies are shown above; one with the AAA case and another one with the AA case. Pretty cool uh?

So now I have a neat little single (1) cell case which supports +5V operation for both AA and AAA batteries. Following are scope pictures showing the actual output and the ripple on the output. This particular MCP1640 has an internal switchover which produces PFM function for light loads and PWM (@500kHz) for heavier loads. The circuit was built with values to produce around +4.8V, and tested at no-load and 50mA load conditions. The no-load shows the PFM operating around 30Hz and +4.82V; and the 50mA load shows PWM operating around 498kHz and +4.81V. Another good point worth noting is that the PFM shows ripple of approximately 0.150Vpp and the PWM show ripple of approximately 0.020Vpp. All of these matches the datasheet expectations.

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