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pyBoard v1.1 Power Input Specification

Posted: Wed May 25, 2016 9:28 am
by GeekCharge

pyBoard external power input spec is 3.6-16V. This is quite dangerous, especially for users not aware how the on board voltage regulator works. I run the number for max LDO output of 250mA and ambient temperature of 50C, and this would result in the LDO dissipating some serious power of over 15W resulting in junction temperature of nearly 1500C (which it would never reach since it would most likely fail well before it came close to that). If we assume that the onboard LDO only supplies around 100mA of current to the pyBoard circuitry, we only have a budget of around 1W for the junction temperature to stay below the maximum of 150C. This means the supply voltage should not be higher than around 13.3V. For maximum load current of 250mA, it would need to be no higher than 7.3V. Even then these are calculations which bring it up to its maximum capability. Sensibly speaking, the external power supply should be as close to 3.6V as possible, the bigger the difference between the supply and the LDO's output of 3.3V the more heat needs to be dissipated in the LDO's body.

I hope this helps and prevents users from potentially damaging their pyBoards.

Kind regards,