Breaking the 100mA limit

The TI-89 and TI-84+ USB port can only supply 100mA of power. This is a circuit that bypasses this problem.

The USB Port

The TI-89/84+'s USB port can only supply 100mA of power without crashing the calc. If you have a device that uses more than 100mA of power, not only will you crash your calc, you will run the batteries down faster. This circut bypasses this problem by drawing power from a 9 volt battery.

The Circuit

Here is the schematic for the circuit:

Download schematic and PCB layout in AutoTRAX EDA format: usbpower.zip

Download schematic and PCB layout in PDF form: usbpdf.zip

Operation

When power is applied to J2 (eg. host is turned on) the 5v signal will bias Q1. Q1 will apply ground to Q2, biasing Q2 and supplying 9v to the regulator. The regulator will supply 5v on the other side of D1 to power the client device. R1 lowers the voltage on the host side of R1 so power is not drawn from the host when the client is connected. D2 is a power indicator.