Help with USB - need a soft start circuit

[Victor hyppolito]

Hello,

I´m new into electronics (i´ve studied theory the last year but now
i´m trying to build some real stuff).
There´s a project i need to do that the device is charged through USB.
My problem is the following:
Once it powers on,a high-power device (it means a device that draws up
to 500mA from the BUS) can't draw more than 100 milliamperes until the
host has said it's OK to do so(this happens during enumeration
process). Up to this point(during enumeration) the rest of the circuit
have to be off. So, I have this soft-start logic circuit
(http://geocities.com/victor_hyppolito/usbproblem) that allows the
power to the load to be switched off and on, and it provides a 'slow
start' feature .
Unfortunately, it isn´t working properly.Suddenly the results on the
computer get lost.
I think its a problem with this soft start circuit. Maybe the
transistor consumes too much power, i don´t know. Or it isn´t slow
enough.
Does anyone know another kind of soft start circuit, like that one?
Maybe suggesting another transistor, I don´t know. Anything will be
helpful.
Thanks a lot and sorry if i´m being "too begginer".
Victor

 

[Ian Stirling]

Hello,

I?m new into electronics (i?ve studied theory the last year but now
i?m trying to build some real stuff).
There?s a project i need to do that the device is charged through USB.
My problem is the following:

I think its a problem with this soft start circuit. Maybe the
transistor consumes too much power, i don?t know. Or it isn?t slow
enough.

Have you checked this?
Put a scope on a small resistor in the +5V line, and measure the current
with a scope.