A emitter follower will match the voltage of the base minus the BE drop. The first illustration shows a classic Common Collector configuration (AKA, voltage follower, emitter follower). This is not a good idea, but I can't interpret the schematic that far.
What is the target output of the LM317 regulator? And do you have the bridge circuit connected to the mains? Have you trying wiring this concept? The LM317T must have a 120Ω minimum resistance between the output and adjust, to satisfy the 10ma minimum current requirement. It is obvious you are trying to use it as a voltage follower feeding a LM317.įunny thing, a BJT would be a drop in replacement, a Darlington BJT even more so. This is why they work well for emitter followers (the other name for common collectors). BJTs are linear, not all the way across, but for wide region of their curve. I could be wrong, but I don't think I am. If you try to use them as such you will not have good results. I will repeat, MOSFETs are not linear devices. This board isnt finished, no fet driver yet, but I have an earlier itteration with the fet gate pulled up by resistors which is whats driving the genny now, badly I might add.Ĭlick to expand.Doesn't invalidate anything I said, the design is flawed from the gitgo. The 317 puts out about 6V at startup and as soon as the fet begins to turn on that will quickly rise to 10.4v The FET hold its source at about 25v, zener - VGS(th) In theory at this point the PWM would have kicked in (b) is the output of an opamp with a max 50mA sink capability, no source to speak of. This is the power board for an AVR I am trying to build, the origional is toast. I would appreciate a leg up and some recommended reading, BJTs for dummies perhaps!! Thanks in advance looking forward to learning. Particularly as I want to make sure it keeps working. Well it works, but it occurred to me that it might be a really good idea to find out why and how.
How wrong can you be with just the one head? I found several examples, pulled a couple of GP transistors from my box (2N3906 / 2N3904) And shoved them onto a breadboard. I am trying to understand how this works, I am using an N-Channel FET I sort of expected, when I started looking that the PNP to be at the top with its collector to the gate and the NPN below it in a similar fashion. Hi folks, I suspect this has been asked and answered many times but I couldnt find anything definitive when I searched. This circuit will not invert the original signal, and will give a high current boost. As it's a DC-DC converter you must want that. Totem pole driver is only neccesary when you want very low transition time.
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