I am limited to a high side layout. I am using the LM324 but it does not return the gates high enough to achieve good cut off. (-1.5V)

The power pfets are SUP90 P06 th about -1.

There is not much information around covering High Side PWM motor control circuits. So I ask here, can anyone recommend a wide rail op amp that will work well as a PWM unit?

 

Why not a comparator? Designed for such a use.

 

Show us your circuit schematic.

 

I would like to use a dedicated comparator if that would be better. However I'm comfortable setting up this quad op amp from a published schematic. I am not yet capable of designing the whole circuit. If you guys can spoon feed me a circuit that does the same as the one posted I would be most grateful.

I am using the Forest Cook published circuit and the second diagram is my adaptation. It's all working well right now but I am concerned that the gates are at threshold when the input is off.

I would like to know that the circuit is optimized for high side. The Forest Cook works for either of course.

 

One way to get a higher output voltage from the LM324 is to add a couple diodes (1N4148 or similar) in series with its output (anodes towards output, with a 2kΩ resistor from the MOSFET gate to V+.

 

That pull up scheme has been recommended by Alec as well. I tried it on my linear version where I have the same issue using the LM 358.

What I found, with that pull up, the opamp doesn't go as LOW. The motor here is being raced so I need every spec of power from that 13.8V diesel truck battery.

Am I right? I don't have the numbers I found but, it was, like, 3volts above ground. I'll try it again.

HOWEVER with all the opamps and comparitors that exist, there must one that will work well High Side.

 

I don't have the numbers I found but, it was, like, 3volts above ground. I'll try it again.

You don't need more that 10V Vgs to fully turn ON any MOSFET.

But if you insist on a rail-rail device you might try the LM6134.

 

You don't need more that 10V Vgs to fully turn ON any MOSFET

I do understand. even at 4v they're on like a boss....enough for the brake short anyway. yes I will revisit the pull up. And I will ponder the 6134. thanks crutschow

 

Cool. So the LM6134 is a quad. Can I assume it will work with the same component values as the Forest Cook version above? do you see any basic improvements needed to that layout?

 

One way to get a higher output voltage from the LM324 is to add a couple diodes (1N4148 or similar) in series with its output (anodes towards output, with a 2kΩ resistor from the MOSFET gate to V+.

The Diode does not need.
See

 

The Diode does not need.
See
View attachment 121666

Your LM324 model is different than mine which needs the diodes.
See



So which one is correct?

 

I made a model for more accurate results. My model is actually a transistor model.
This model correctly reflects the actual behavior. Here, inside the model:

 

Here is my research: