9 volt usb charger

Getting 750mA from a 9V battery for any length of time will be a problem.

However, for maximum efficiency what you'd be looking for is a switchmode regulator with an input voltage that includes 9V and a fixed or variable output that can be set to 5V

 

It would, but not for long. (What kit?)

You are throwing away almost half the power in the battery as heat.

 

You could go for an integrated switch mode regulator that is 7805 compatible but has a much better efficiency. See e.g. http://www.dimensionengineering.com/de-sw050.htm

Harald

 

No,
this kit includes the 7805T regulator which is a linear regulator with all the drawbacks already noted.
Jameco doesn't seem to have switch mode 7805 compatible regulators in stock.
Google >7805 switch mode< will give you lots of results, if you're lucky one of your favorite retailers has something similar to the on eI posted first in stock.

Harald

 

You'll have to describe more of what you want to do.

If you have a signal that provides a max of (say) 10mA and you need to switch something that draws 1A, then yes, a transistor may be what you need.

If your power supply is only capable of 100mA and you need 750mA, then there's no way to do that. You need a power supply rated for a higher current.

 

Not really. It may be better to tell me where that thread is and I'll move your new post to it so we have some context for your question.

I guess we may have suggested that the current you'll get out of a 9V battery isn't very high, and that the phone may require certain indications to be present to charge at high speed.

We may also have suggested that a linear regulator means that you'll be wasting a substantial amount of power as heat.