Hey all,
First time post, long time lurker.
So I tried building myself a linistepper board and I can't get it to work. Since understanding is the source of all solutions, I'm trying to understand how the thing actually works.
It starts with this schematic:though I'm actually building the variant with aligned devices. It has eagle files that I used to adjust to the parts I have.
Anyway, as I understand it, the diodes and resister form a divider network intended to yield different voltage levels. The BC337 devices are to pick which leg of A or B to activate. The TIP122 are the drive resistors.
ok, in order for the TIP122 to turn on, Vbe must be > 2.5 (per the data sheet). To get the desired current, we want the input to them to be 1 volt higher than that. This automatically turns the devices off when the current drop across the sense resisters reaches 1 volt.
So we want 3.5 volts the input of a TIP122 to get full current.
Looking at the resistor network, I don't see how we attain 3.5 volts unless both BC337s are off. This would counter the idea of selecting one of the two.
At first I tried working the numbers on paper, but then I tried it in LTSpice:
I did not include the TIP122s in the simulation because I assume that the gate draw will be low due to the high beta.
What am I missing?
Thanks in advance for any thoughts anyone may have on this.
Miles