Author Topic: Bypass Digispark 5v 500ma current limit?  (Read 629 times)

Synchro

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Bypass Digispark 5v 500ma current limit?
« on: January 13, 2018, 12:10:40 am »
Greetings fellow creators,

been playing around with the digispark to control and power ws2812 LEDS (neopixels) and noticed a current limit that prevents (safely) powering more then 30 or so pixels without an external PSU.

looking at the schematic and reading through a good post on here on powering the digispark and neopixels. we can see that there is a diode that drops the voltage to the VIN pin on the board...as i understand it that pin is there to prevent external power from feeding back into the usb port...what i am wondering is if a person bridges over that diode (D3 on schematic) and simply draws straight from the usb port...will more current be avaliable at the VIN point? allowing connected devices to draw more then limit of the voltage regulator (up to the limit of the usb power supply, have a 2.1Amp adaptor here)

does this make sense to do if one does not intend to provide another VIN voltage source, and just wants the most current possible from the usb port?, allowing for many more pixels to be powered simply from the single already supplied usb port?

i currently have only one digispark to play with and do not want to fry it...but i intend on trying this, when more come in the mail...just curious of any thoughts on the subject before i give it a shot...

Digispark Schematic Referenced:
https://i.stack.imgur.com/Iv2bq.png

Powering the Digispark Thread:
https://digistump.com/board/index.php?topic=1166.0

look forward to hear if anyone here has tried this, or any feedback on the matter.
big ups to the Open Source community!

PeterF

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Re: Bypass Digispark 5v 500ma current limit?
« Reply #1 on: January 13, 2018, 04:26:13 pm »
Yeah, it looks like that diode, the MBR0520LT, has a forward current of 0.5A / 500mA, so will be limiting the current flow from the USB to VIN, so you would need to either bypass it to get all available power at the VIN pin (i.e. more than 500ma and also remove the voltage drop), or power the Digispark via the VCC pin directly instead as well as your led strip, thus bypassing the diode anyway.

I haven't tried it, but what suggested does make sense to do if you are running from things like power banks or wall adapters with higher amperage capabilities and you don't want to mess around with dual-voltage rails or using a custom (USB) lead to power it via VCC.

https://www.onsemi.com/pub/Collateral/MBR0520LT1-D.PDF
« Last Edit: January 13, 2018, 04:32:41 pm by PeterF »