Speed Controller Design

[Geek 2.0]

Originally Posted by kamocat

I understand what you're saying; there doesn't seem to be an input to chose between HDRV and LDRV. The reason is, they're both used together.
If you look at the datasheet for the PWM driver, it says the low is 180 degrees out of phase of the high. That means the "off" period for HDRV is the "on" period for LDRV. On the Jaguar (unlike the Victor) the H-bridge switches between 12v and 0v, not 12v and "open".

There are then two ways to stop the motor: brake (driving both sides at 50% duty cycle, or 6v) or coast (using the OD pin).

What's especially interesting about this is that you don't *need* to dedicate a microcontroller output to each side; you just swap the high and low on one side of the h-bridge, and you can use the same PWM signal to control both PWM drivers.

You are absolutely right that you could make a less expensive speed controller with less features. Something like that might actually be quite useful. Let me recommend that you use an aluminum heat sink instead of just a fan. A little thermal mass is useful in preventing accidents.

Okay I'm starting to get there... but still a bit confused.

If I were to want to run at half speed, so about 6V, I would think I should use a 50% duty cycle, but that runs the motor in forward 50% of the time and reverse 50% of the time, thus braking as you stated. The same holds true for any other speed; The time the PWM is low, the motor is doing the opposite of what I want. So, to run at half speed, would I do what I tried explaining and hold PWM high and then send a 50% duty cycle to OD? Or is there something I'm still missing?