For motor control, which IC woild make the better PWM with variable Freq. and variable Duty Cycly? Perhaps the introduction of a dead band as well...?

Requirements:
Frequency between 20kHz and 40kHz
Duty Cycle between 0% and 100%
IC operating Voltage of 5V - 12V DC

Are there advantages or disadvantages of one or the other?

Or................neither, IC "x" would be better!

 

Ahh, neither.
The LM324 is just too slow for 20kHz-40kHz when you're looking for a square wave output. It runs out of steam at just a few kHz.

The 555 timer can still crank pretty well up to around 100kHz, but you mentioned deadband - so that's out as well.

I'm thinking that a synchronous buck controller would be a mighty spiffy application for a motor controller. You'd practically eliminate the losses you would otherwise have in the diodes across the motor. Besides, you wouldn't be accused of trying to turn an Escort into a Lincoln.

A TI UC3638 is specifically made as a current mode PWM motor controller.
http://focus.ti.com/docs/prod/folders/print/uc3638.html

 

Lots of choices...Google: PWM controller IC

Ken

 

Just did a quick search on National's website. Their "Buck Syncronous Switching Controllers" starting freq. are at 50kHz. The driver board I was considering accepts up to 40kHz. I'll have to admit, the whole concept you have just presented is absolutely new to me.

Any other Op-Amp IC that might be able to handle around 30KHz of the top of your head?

By the way, how would I know what the switching frequency limit is on the LM324 or any other OpAmp for that matter?

 

The datasheet for a low power (which means very slow) National Semi (its inventor) LM324 quad or LM393 dual opamp shows a slew-rate graph where it drops its output into a triangle-wave above about 1kHz at full output. Most audio opamps work perfectly up to 100kHz.

 

Well, opamps are slow because they're compensated, and the way their outputs are configured. If you want something a lot faster, you can use a comparator, like an LM339 quad comparator.

It will run circles around most opamps for bandwidth. However, it makes for a lousy opamp, as it isn't compensated and has an open-collector output.

I'd thrown together an LM339 PWM circuit for some fellow months back.

 

Ah Ha! just found the TL494CN from TI. It includes dead time control and an oscillating frequency between 1 and 300kHz.

 

Check out the SG3525A, UC3525, UC3825, UC28025 current mode PWM regulators. The TL494 was really designed for driving transistors. If you're planning on feeding a TTL signal to something, these will be easier to connect.

 

Thanks, the SG3525A looks real good.