Input voltage on the Propeller proto board

Brian218

Hi,

I'm in the very early stage of a 12V DC project that will be built around the Propeller Proto board. The proto board specs indicate the input voltage is 6 to 9 Volts DC which is regulated by the LM1086 regulators to 3.3 and 5 volts.

The data sheet for the LM1086 indicates the max input voltage is about 30 volts.

My questions are:

1. Is 9 volts the maximum voltage that can safely be·applied to the proto board's power input? If so, why?

2. Unless I'm totally missing something obvious, I should be able to·use a 12 V power supply.·Is this correct?

Thanks
BT

Mike Green

The LM1086 on the Protoboard really doesn't have a heatsink, so it can't dissipate much heat. All the voltage above 5V has to get dissipated as heat (times the current drawn). If you're using only a little current (maybe 100mA), that's only 3/4 W of heat if you're feeding it 12V. If the current goes up, the power dissipated goes up accordingly. Eventually things start to overheat and the regulator will shut down to protect itself. It won't damage the board, but it will stop working at some point until it cools down.

Brian218

Thanks Mike!

The explanation makes perfect sense.



BT