Kyle L. Carithers
REU 2006
Power
A custom power board was designed for the MiniRanger using Eagle Layout Software. A 7.2V 2400mAh lithium ion battery powers the board. Two National Instruments LM338T voltage regulators were used to regulate to 5V and 6V. The power board provides twenty 5V outputs, ten 6V outputs, and ten unregulated outputs. Two National Instruments LM338T voltage regulators were used to regulate the 5V and 6V outputs. This regulator provides guaranteed 5A output with a peak output of 7A.
Also guaranteed is a thermal shutdown to keep heat from damaging the regulator. The thermal shutdown will prevent the regulator from reaching the guaranteed 5A output without some type of mechanism to prevent the regulator from reaching thermal shutdown. A heat sink would likely be necessary. For MiniRanger’s power board, the regulators were bolted to the board to transfer heat to the copper side of the PCB. Doing this required inspection of the traces to verify that the sections allocated for each regulator were isolated from the rest of the board. Each regulator has metal protruding from the top for dissipating heat. On most regulators, this is connected to the input, output, ground, etc. Care must be taken to assure this part is isolated from other parts of the circuit or a short could occur.
The LEDs are used to signal the board’s status. If the main switch is enabled, which mean the 5V and unregulated outputs are receiving power, then one LED lights up green. If the 6V output switch is enabled, both LEDs light up green. The LEDs are bidirectional and are red if the polarity into the board is reversed. Therefore, it would be immediately known that the battery is plugged in incorrectly.