I've been working off and on for a while on designing a brushless motor controller just because I want to understand how to design one (I know I can buy them cheap). Of the designs I have studied, they all seem to have a single PWM output channel on a micro, and then use AND gates to drive the motor control transistors. I was trying to mimic this using comparators since they are very easy to get and already included in eagle and LTSpice (I figured simulate first). I'm having trouble in the simulator getting the op-amps to pull the transistors all the way on and off. Can I actually do this, or will I have to go to AND gates. I'll post a schematic if this arrangement doesn't make sense.Thanks.

 

A lot of opamps can't output all the way to zero volts. Maybe giving them a simulated negative supply voltage will fix the problem, or, specify a different opamp. So many people come here after trying to use 741 opamps and expecting them to work.

 

I'll post a schematic

Yes please. What components were you using for your simulation (including power transistors)?

 

I have attached a screen shot of my LT-spice model (or at least I think it attached). The power mosfets are IRF7309's. I probably won't use those in production, but I will use something very similar. I was trying to avoid logic level gates. The op-amps are LM324's, even though it doesn't say that on the schematic. All the small 5V sources are to simulate micro controller outputs, and the 10V source is the PWM channel. Thanks for your help.

 

I'm not very good at this but I think I see a P-channel mosfet with a positive voltage on its drain.

PS, it's good to attach datasheets for each device in question
I provided them to make easier work for the other helpers.

 

You're right. I put all three in upside down. I do that every time thinking the symbol is drawn the way I think it should be rather than the way it actually is (if that makes sense).