How much current can the +5V regulator supply?

dalewheat · October 16, 2008, 4:55pm

I’m adding peripherals to the 3pi that use +5V. How much current can it supply?

Thanks,

jan · October 16, 2008, 5:59pm

Hi, Dale.

Because the 5V goes through two power stages, the answer is not completely clear-cut. The 5V regulator itself has a 900 mW power dissipation limit, so with a 4.3 V drop from the boost voltage to 5V, we get just over 200 mA. The stock electronics typically use under 50 mA (this also depends on what your program is doing, if you are making high-frequency noise with the buzzer, and so on), so you could figure an absolute max of 150mA, with 100 mA being a more comfortable guideline.

However, the boost voltage has a limit of its own of around 1A, which is dependent on your battery voltage. The motors and IR LEDs also use this supply, so using a lot for your 5V will affect what is available for the motors. You can almost stall the motors and still have the full boost voltage on the motors in the stock configuration; if you’re also drawing an extra 200 mA for other electronics, the boost voltage will start dropping as the motors approach stall. That’s not necessarily a bad thing since it will limit the stress on the motors and lower the voltage drop on the linear regulator.

- Jan