funkyguy4000:
if you need to source 500mA but insist on using 74HC595 shift registers, you can use the UDN2981AT. Its capable of sourcing your 500mA needed.
500mA is the absolute maximum output current of the UDN2981. The recommended maximum is 350mA, and at that current the voltage drop is 1.8V typical, 2.0V maximum. If you drive just 3 of the 8 outputs simultaneously at 350mA, you will already be close to the device maximum power dissipation. So I advise against using the UDN2981 in this application.
The ULN2803 current sinking driver is slightly better, with voltage drop 1.1V typical, 1.6V maximum at 350mA.