I'm using transistors to switch external loads for my PIC project. I'm using NPN transistors (specifically these: **broken link removed**) with the PIC's output pins connected to the base of the transistors. I have a base resistor of 10k, which I know is too high but that's not my problem. The load it is switching is NOT 5v - it's about 14-15v (automotive relays eventually, but still on the bench right now.) It's actually switching the GROUND for the device, not the power. So the emitter is tied to the ground plane and the collector goes to the screw terminal to be connected to the device's ground wire.
When I test it using the regulated 5v on-board, the transistors completely turn on/saturate to 5.00v, and turn off to 0.00 volts. But if I use my volt meter on the ~14v supply voltage, it turns on/saturates fully to about 14.8 volts, but it only "turns off" to about 6.38 volts. Why is it still letting through 6 volts with a 14/15v load but totally turning off for a 5v load? The PIC pin is low at 0.00v measured - so the transistor base is getting no voltage or current. It seems to be "leaking" through the transistor despite being turned "off." Any ideas?
When I test it using the regulated 5v on-board, the transistors completely turn on/saturate to 5.00v, and turn off to 0.00 volts. But if I use my volt meter on the ~14v supply voltage, it turns on/saturates fully to about 14.8 volts, but it only "turns off" to about 6.38 volts. Why is it still letting through 6 volts with a 14/15v load but totally turning off for a 5v load? The PIC pin is low at 0.00v measured - so the transistor base is getting no voltage or current. It seems to be "leaking" through the transistor despite being turned "off." Any ideas?