buck boost/sepic-powered usb

Thread Starter


Joined Nov 10, 2010
hi dear friends..

Im looking for some knowledge regarding a project I'm engaged in, relevant to power supply.

main aim of my project is to design a varaible voltage regulator which can be used with powered usb ports(usb pluspower) here are the basic specifications

input- 12V @ 3A (from poweredUSB port)
output voltage-5V to 30V (variable)
output current-1A all through out the range

I was first planing to use a buck-boost/cuk converter as output voltage is less or greater depending on the required output..But sepic topology seems to be like more straight forward as the polarity is not inverted...

So have you guys got any better idea or if you got any knowledge relevant to this kind of a project ur support is highly appreciated...

From basic reading what i understood was most of the times both these topologies are used to give a steady output when input is varying within a certain range..so I doubt how applicable those 2 topologies in to this perticular project..ur ideas are more than wellcomed.

thanks in advance...


Joined Apr 20, 2004
Have you gone over the specs for USB3 (still a bit vaporware-ish). This is from a USB3 FAQ -
A new Powered-B receptable is defined with two extra contacts that enable a devices to provide up to 1000 mA to another device, such as a Wireless USB adapter. This eliminates the need for a power supply to accompany the wireless adapter...coming just a bit closer to the ideal system of a wireless link without wires (not even for power). In regular wired USB connections to a host or hub, these 2 extra contacts are not used.
1000 ma is a long way from 3 amps. I'm not sure that the voltage isn't the standard 5 VDC.


Joined Dec 5, 2009
Usb PLUS POWER is 12v or 24v depending on which flavor you wish.

It is basicially like power over ethernet, but using USB ;)

It is, I believe a 6 wire system. The standard 4 wire usb, then 12v+(or 24v) and an additional power GND

ok, here is the standard:

And I was wrong, it is an 8 wire system ;)
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Thread Starter


Joined Nov 10, 2010

first of all thanks for participating to the thread with ur valuable ideas...

well i think usb3 is not providing enough power :(...at the high end the device should able to prove 30V @ 1A so (30W) but usb3 is well below that limit (5V @ 1amp) so powered usb will be the only option as far as i can see:rolleyes: which gives 12v supply @ 3A current (36W>30W)

so what about toplogies..have you guys got any ideas about ic s supporting sepic topologies..:confused: this is one of them i ve been reading these days..TPS61170 ..But i dobt if i can use it in the reverse manner..I meant typical applcation of this is totake a steady output when input is varying withing a range( as battery power drains slowly).But Im trying to do opposite use the same topology to increase and decrease the output when input stay inside a steady level..

......................................I-->30V @ 1amp[out]
in 12v @ 3A--(sepic)--->I
......................................I-->5V @ 1amp[out]

if you guys know any other chips that you think worth looking in to please mention and im more than willing to look in to the applicability of them:)

thanks again...