Battery vs. line power sense

rtarbell · 20th July 2010, 02:33 PM

A question about devices (USB stick, laptop computer, iPod, etc.) that can be powered from a battery, or from line voltage:

What is the basic sense circuit that tells a device whether it is being powered from a battery, or from wall voltage? I am curious as to how the device "knows" where its power is coming from.

-RT

bob91343 · 20th July 2010, 06:15 PM

A diode circuit will work, and the higher source voltage is where the power will be from. There are other circuits too but the basic idea is the highest voltage delivers the power.

davidcookie · 23rd July 2010, 08:26 AM

Hmmm, good question and good answer there.
thanks, bob.
i remember the highest voltage delivers the power.

20th July 2010, 02:33 PM	#1
rtarbell diyAudio Member Join Date: Sep 2005	Battery vs. line power sense A question about devices (USB stick, laptop computer, iPod, etc.) that can be powered from a battery, or from line voltage: What is the basic sense circuit that tells a device whether it is being powered from a battery, or from wall voltage? I am curious as to how the device "knows" where its power is coming from. -RT

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20th July 2010, 06:15 PM	#2
bob91343 diyAudio Member Join Date: Mar 2010	A diode circuit will work, and the higher source voltage is where the power will be from. There are other circuits too but the basic idea is the highest voltage delivers the power.

23rd July 2010, 08:26 AM	#3
davidcookie diyAudio Member Join Date: Jun 2010	Hmmm, good question and good answer there. thanks, bob. i remember the highest voltage delivers the power.

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