Comments on: H-Bridge Fundamentals

By: Roko

Roko — Sat, 28 Jan 2012 00:46:29 +0000

Hi RobotJay,

You’re correct on both counts. The intent of the circuit in Figure 3.2 is to simplify the control slightly by reducing the number of required control lines, and allowing for a single PWM line. Nothing is preventing shoot-through if A and B are enabled at the same time, so care still needs to be taken when using that circuit.

A long time ago, when it was harder to source microcontrollers with a high pin-count in the hobby world, controlling motors with as few pins as possible was important to save the few pins available for other important uses, however ultimately this reduced the functionality and flexibility of controlling motors.

Nowadays, it’s easier to get larger microcontrollers with enough pins that such a circuit is not required. To be honest, on most of my H-bridges nowadays, I control each MOSFET individually, with it’s own pin from the microcontroller. This allows me to be much more creative in firmware with how I control the H-bridge, allowing for more advanced control than would be possible with the circuit in Figure 3-2.

Hopefully that makes sense, it’s been a long day at work and my brain is shutting down.

Cheers,
Roko

By: RobotJay

RobotJay — Sat, 28 Jan 2012 00:40:39 +0000

Ahhhhh… nevermind. I see now. P-Mosfets are “ON” when ground is applied. And although Q1 and Q3 will always be logic high at the same time, Q1 and Q3 will always be opposite of each other. Sorry for bugging you. Again, great article.

By: RobotJay

RobotJay — Sat, 28 Jan 2012 00:34:55 +0000

Similarly, when A and B are on together, what prevents shoot through then?

By: RobotJay

RobotJay — Sat, 28 Jan 2012 00:21:43 +0000

Maybe I’m just dumb, but according to Figure 3.2, won’t Q1 and Q3 ALWAYS be on together? Won’t Q2 and Q4 also do the same? Thanks for clarifying for me. Great article.

By: motor controller comparison

motor controller comparison — Thu, 01 Sep 2011 02:10:49 +0000

which motor you should use…

H-Bridge Fundamentals « Roko.ca…

By: Lonnie

Lonnie — Fri, 19 Aug 2011 13:07:28 +0000

I have built several H-bridges and have had a problem finding mosfets that work well in a 3V system. I need a small package, 3 amps peak current, .5 amp run current. Anyone know of good P & N ch devices that fit this application?

By: Manny

Manny — Fri, 10 Jun 2011 01:19:24 +0000

Hi, we are trying to control an AC motor using H-Bridge with PWM at the inputs of our IGBTS. when we increase the DUTY CYCLE, the motor suddenly stutters or stops. it works fine at 50-60% dutycycle. what could be the problem?

By: Valerie

Valerie — Wed, 11 May 2011 10:34:16 +0000

I just discovered this site — I’ve been exploring it for a while. Great stuff!

By: Emily

Emily — Tue, 10 May 2011 13:51:43 +0000

Thanks for the post — Much appreciated!

By: Abdullah

Abdullah — Sat, 07 May 2011 20:35:48 +0000

Man you have definitely mixed up the MOSFET’s operating modes. You mention that analog amplifier use the triode region and that is untrue because they use the saturation region, when the MOSFET is exhibiting current source like behavior. You also say that you want the transistor should operate in saturation when switching, or turning load on and off, and that is also untrue. You would want it to operate in the triode region, so that vDS is as small as possible and so that most of the source voltage is applied across the load.