Inefficient wall warts

B

bigpilot

Well-known member
My Teensy alarm clock is powered by a (regulated) wall plug adapter which outputs 7.5V and a 7805 voltage regulator converts this into the 5V needed to power the device.

It uses about 4W continuously. However, when I power the board through an USB adapter connected to the Teensy 2.0 the clock only uses about 0.3W!! I previously thought the power consumption came from the LCD backlighting but this seems not to be the case.

I'm now planning to power all my devices through an USB thru-hole plug to conserve energy. Something to contemplate when you design your next Teensy powered project.
 
A linear voltage regulator like the 78xx family generates heat to use up the excess voltage. A switching regulator, which is probably what is inside your wall wart, converts a higher voltage at a given current to a lower voltage at a higher current (plus a little heat) and is thus more efficient. Less commonly nowadays, a transformer-based wall wart does the same thing but with significantly larger heat production.
 
Not really sure how a USB breakout will improve a transformer's power efficiency.
Nowadays a basic USB phone charger will be more efficient and you don't need any sort of adapter.
 
jmarsh said:
Not really sure how a USB breakout will improve a transformer's power efficiency.
Nowadays a basic USB phone charger will be more efficient and you don't need any sort of adapter.
Click to expand...
The idea is to completely replace the power adapter and the 7805 regulator with the USB breakout.
 
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