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Home » Hardware » Interfaces » problem with bus power (can't turn on ULN2 from MBPr without EXT. power)
problem with bus power [message #85660] Tue, 05 February 2013 14:20 Go to next message
alifatemi is currently offline  alifatemi
Messages: 1
Registered: February 2013
Junior Member
I can't power on ULN2 directly from my MBP retina, connected via thunderbolt to firewire adaptor. I have to first turn on ULN2 with its external power then it stays on even if I disconnect it from Ext. power. Can I turn it on directly with my MBPr without initiate it from Ext power supply from the first place?

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Re: problem with bus power [message #85661 is a reply to message #85660] Tue, 05 February 2013 14:25 Go to previous message
Allen is currently offline  Allen
Messages: 156
Registered: July 2011
Senior Member
No, the bus doesn't supply enough turn on current to start the box. You will need to use the power supply at all times, use the power supply to start the box and then bus power, or build a "jumpstarter" battery pack as described in the FAQ.

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