How do these things work? From what I'm reading it appears tha you can get say 11.7V output from a 12V source at 1A -> is this correct? How does it work if you need 1.7V across the transistor minimum? I'm considering using this as a voltage follower in place of a power transistor as I could get a higher output voltage.
[I'm trying to make a fan speed controller buffer to handle multiple fans on a single controller line (eg there are 3 fans on my PC watercooling radiator) but I want to be able to get as close to 12V as possible for max speed when things get hot. Pulse width modulation (with 3 lead fans) makes the tach signal worthless so can't go that way btw]
They use a different topology than the standard NPN pass transistor regulators (like LM317s and 7805s). It probably uses a single P type FET as the pass transistor.
They use a different topology than the standard NPN pass transistor regulators (like LM317s and 7805s). It probably uses a single P type FET as the pass transistor.
Thanks! I really liked that tutorial. I was just wondering about the physics of the gating etc as to how the PNP can turn on with such a small voltage drop. Sometimes I can understand such explanations like the basics of how transistors work, so I was just wondering what is different about this configuration. Just curious.
If you use an n-channel MOSFET and a small boost converter so you can drive the gate at a higher voltage than the supply, you can get a very low drop out voltage.
It's a wonder that some ICs don't use this technique. There could be an on-chip voltage doubler so all you need to do is add a couple of ceramic capacitors to give an ultra low dropout regulator.