How can the same wall wart supply 5V as well as 9V?

Thread Starter

livelongpranav

Joined Oct 18, 2017
19
I saw a 18W wall wart which could supply 5V 3A or 9V 2A or 12V 1.5A. It had only one USB output and no way to select output voltage.

How does a thing like that work? I know that devices draw varying amounts of current, but can they draw(?) specific voltages also? How does the device tell the wall wart what voltage to supply?

Hope my question is clear.

Thanks.
 

Audioguru

Joined Dec 20, 2007
11,249
A cheap wall-wart does not have a voltage regulator. With no load its voltage is much higher than its loaded voltage, maybe double.
The cause is the output resistance of the wall-wart.
 

AlbertHall

Joined Jun 4, 2014
9,845
I saw a 18W wall wart which could supply 5V 3A or 9V 2A or 12V 1.5A. It had only one USB output and no way to select output voltage.

How does a thing like that work? I know that devices draw varying amounts of current, but can they draw(?) specific voltages also? How does the device tell the wall wart what voltage to supply?

Hope my question is clear.

Thanks.
Were these three different versions of the supply where you select which one you want to buy?
Where did you see this?
 
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