Powering a USB port directly would require major changes to the circuit. The circuit is designed to operate on AC voltage, hence the simple zener diode power supply and TRIAC used to switch.
In order to make the circuit safely power a USB port (the basic supply included in the circuit is NOT isolated) then the power supply would need to be reworked to use a small transformer, and a regulator (like the 7805) would need to be used to provide appropriate current to a USB port @ 5V and to power the circuit. The TRIAC would need to be switched out with a simple pass transistor, U3 could be eliminated and the Q output of U3 would need to be inverted. Basically, an entirely different circuit after the right side of U3.
Circuit to be manufactured
Posted - Dec 16 2009 : 11:03:40 PM
