I've read that the original A/B had about 50mA of elbow room left from the on-board 3v3 regulator.
Newer Pi's may allow more, however if the 3v3 regulator draws too much, the 5V can be pulled too low, leading to the dreaded lightning symbol indicating low voltage.
How much you can draw depends on:
- your 5V power supply
- quality of USB cable used to provide power
- what other USB peripherals / add-on boards you are driving
- draw off the 3v3 regulator by other devices
Generally for most of my designs I add my own 3v3 regulator (however tempting it is to leave off) and sometimes provide for an external 5V supply.
julyjim wrote:Where can I find (reference please) how much load can Raspberry Pi 3B supply on external (GPIO connector ) 3.3 V bus.
I am using DDS AD9850 and will power it from 3.3 V .
The inputs are OK, in uA range, but output DAC can supply up to 30 mA.