In autumn 2012 asked me about the development of a power supply for his next three fursuits with a few more functions as I designed in the last power supplys I build for other fursuits (for and ).
So we made up a spec sheet and after that I designed it until end of 2012 including necessary software.

(long text is long...) you have not to read it, if you're not into electronics or specially interessted in how this circuit works.


Main requirements are:
- poweres 3 fans at rated spec (9/12VDC 0.16A)
- poweres 12 colored LEDs at rated spec ( 20mA each)
- switchable fans and colors of the LEDs by 2 reed contacts
- powered from a single LiPo-cell (3.7V nom)
- backup powered from a 9V-cell
- last for about at least 4h of runtime with one charge
- overview the LiPo not to run into damage
- charge the LiPo by an standard USB-Port
- small enough to put into a fursuits head
- ...

Following a detailed description of the function.
My intention was to power the fans and LEDs out of a single LiIon/LiPo-cell, cause of the great Wh/kg of these cells and because of the easier charging-circuit of the cell-voltage is below USB-voltage (5V). Because of a single cell only provides 3.7V of nominell voltage and the fans are driven by at least 9V an internal step-up intermediate circuit was necessary.
That lighten the way to a back-up inlet by a 9V-cell, too.

So I desigend a switchable DC/DC-converter, so boost the voltage and to save energy if it isn't needed. To recognize all possible necessaries and stages I decided to controll the DCDC by a microprocessor.
The LEDs are attached to six constant-current supplies, so they're driven inner their optimal specs.

That processor overviews the connected inlets (LiPo-cell, backup-cell, USB), measures all innert voltages (cell-voltage, output-voltage, charging-voltage), currents (drain-current, fan- and led-currents, charging-current), the temperature and processes the switches.

That makes it easier to ensure the wished function, of a time based behaviour of the LED-switch (short activation: change the color, long activation: rainbow-effect. With a security time gap between, to not run into the rainbow to fast) and also the fan-switch (delayed switching behaviour).

So the processor ensures an always safe cycling in every possible state (prevent exhaustive discharge of the LiPo cell and so on) and charges the LiPo out of the USB-port with an optimal charging curve for maximum lifetime. The Charging is fully software-adjustable in charging voltage and -current and is provided by fast impulses, followed by extensive measurement.

The OS onto the processor is one of my babies, developed over the last few years and selfcontrolled and -managed. By any error rougfox got a beep-error-code (beside the empty-battery-warning) thru the attached piezo.

CPU: Atmel ATTINY861A (2k used) 8MHz 3.30V
DCDC: MC34063 + PISR68uH + 2N6292 + 2x MBRS320 3.0-4.4Vin 8.6-12Vout (adaptable), Uripple: <0.1V
Measure: U_cell, Uout, U_usb, U_9V, I_cell, temp
Uref: dedicated constant voltage: 1.100V
dimension: 70x 60 mm (2.75x 2.35 ")

Schematic and layout created via EAGLE with wires down to 12MIL and SMD0805. Printed, etched and assembled by me at home.
Programmed in ASM and C.