So I have an interesting challenge. I have an LCD screen from a laptop which I am driving with a control board. The problem is the backlight needs around 19 volts to run while the control board I have is designed for LCD panels with a 5 volt backlight. Everything else runs fine, just not the backlight. I have a 19 volt power supply that I intend to run everything off of (the 5v control board will be powered of a buck converter from this 19v source). The problem is, when the control board is off or in power saving mode, it is supposed to cut power to the backlight, but since I am driving it directly off the 19v power supply, it stays on. To solve this problem I acquired myself a TIP31AG power transistor from the local radio shack (yes they do still exists) assuming that it could be used like a relay, or atleast in the same situations. As you can imagine this turned out not to be the case.
- I have a 19v load of an unkown and probably variable current draw and resistance (it has a separate PWM brightness control which probably varies things).
- I have a 5v control wire which can provide a decent amount of current (greater than logic level that is)
- I need to control the VCC into the load (not the ground connection, due to the way the control board works)
- I have a TIP31AG power transistor, and all the tutorials I have looked at have their TIP31 (which is NPN btw) downstream of the load (that is between the load and ground)
Can this be done with my TIP31 or do I need a TIP32 (the PNP variant) and another PNP control diode to control the load on the VCC side?