throbscottle
Well-Known Member
So, I finally went back to my ridiculously over-complicated automatic drill feed controller after abandoning it for many years. Took a few days to figure out how it works. I was obviously smarter back then!
Anyway, I re-visited the H-bridge design and added a couple of driver transistors to it. The gates of the P and N mosfets which form each leg of the bridge are tied together and have a pullup resistor, and are driven by a level shift transistor which can pull it to ground, or the resistor can pull it up. Well known simple design.
But the major flaw with the design is that there is plenty of opportunity for shoot-through, which I think is happening (drive is PWM from a 555 timer gated through a 4066 where it is the signal, not the control). It's ok if you're just changing direction with it, but it doesn't like PWM.
The PWM signal is gated through two channels of a 4066 quad analogue switch.
So I changed the design so that the four bridge transistors all have separate gate pullup resistors so the N mosfets are still always on, and the P mosfets are still always off, but now with separated control, and the inverse of the gating signal for the PWM turns off the N mosfets, and the gated PWM drives the P mosfets via the driver transistors, which is great for one leg, but the other leg doesn't have an inverse gating signal, so that's a small problem.
Rather than add yet another transistor to the design, I tried changing the input signal of the 4066 switch to 0v, and applying the gating signal to the emitter of the driver transistor, leaving PWM input to it's base.
It looks as if it will work fine but I wanted to get some more experienced eyes to take a look at my one-transistor "gate". The mosfet in the simulation represents one P-mos from the H-bridge, and the motor model is arbitrary, I have no idea what real values to use.
What do you think?
Anyway, I re-visited the H-bridge design and added a couple of driver transistors to it. The gates of the P and N mosfets which form each leg of the bridge are tied together and have a pullup resistor, and are driven by a level shift transistor which can pull it to ground, or the resistor can pull it up. Well known simple design.
But the major flaw with the design is that there is plenty of opportunity for shoot-through, which I think is happening (drive is PWM from a 555 timer gated through a 4066 where it is the signal, not the control). It's ok if you're just changing direction with it, but it doesn't like PWM.
The PWM signal is gated through two channels of a 4066 quad analogue switch.
So I changed the design so that the four bridge transistors all have separate gate pullup resistors so the N mosfets are still always on, and the P mosfets are still always off, but now with separated control, and the inverse of the gating signal for the PWM turns off the N mosfets, and the gated PWM drives the P mosfets via the driver transistors, which is great for one leg, but the other leg doesn't have an inverse gating signal, so that's a small problem.
Rather than add yet another transistor to the design, I tried changing the input signal of the 4066 switch to 0v, and applying the gating signal to the emitter of the driver transistor, leaving PWM input to it's base.
It looks as if it will work fine but I wanted to get some more experienced eyes to take a look at my one-transistor "gate". The mosfet in the simulation represents one P-mos from the H-bridge, and the motor model is arbitrary, I have no idea what real values to use.
What do you think?
