Smallest DC-DC converter?

This isn't terribly Arduino-related, but I figured this is the right community to ask. What's the smallest DC-DC converter I can get that takes 5V or USB plug in and ~19-20V output? I looked at the XL6009 but looking for something smaller if possible.

(I hate chargers that aren't USB. I want to hack my electric shaver to use USB charging so I don't have to carry a separate charger for it around anymore.)

What output current is needed.

Whoops forgot to specify. 360mA on the output end. So ~1.5A on the input side accounting for inefficiencies (and yes I have a 2.1A USB charger)

Watch out for start-up inrush current - you may need some large 5V decoupling to allow a boost converter to start up (it has to charge the output side decoupling caps and may pull higher currents for a few ms, or shutdown if it cannot).

If you want a tiny package converter it'll require an external MOSFET(s), integrated DMOS FETs aren't particularly low resistance (that XL6009 chip has the highest performing DMOS I've ever seen BTW - do they make H-bridges too I wonder?).

Pololu offers a very nice selection of tiny, high current boost regulators. Here are two that seem to meet your specs: http://www.pololu.com/product/799 http://www.pololu.com/product/2571

Whats is supplying the 5V? USB ports are limited to 500ma , and some in laptops can only supply 100 ma. You may find the DC - DC convertor wont start.

I also want to toss a mention here for Polulu. Their converters are small and perfect for low current conversions (less than 1 amp)

mauried: Whats is supplying the 5V? USB ports are limited to 500ma , and some in laptops can only supply 100 ma. You may find the DC - DC convertor wont start.

I always travel with a compact, 40-watt, 5-port USB charger with a max of 2.1A on each port; I just want to make this my only charger and not have to carry separate chargers for anything else. It's also generally easy to find other people who have 2.1A USB chargers (anyone with a tablet PC, pretty much) while travelling.in case I happen to not carry it.

jremington:
Pololu offers a very nice selection of tiny, high current boost regulators. Here are two that seem to meet your specs:
http://www.pololu.com/product/799
http://www.pololu.com/product/2571

This is awesome. Thank you so much!