Hi Jason, You're quite welcome, happy to help. All three methods have losses when there is PWM of any sort. Option 3 will heat up your motor even if you sit at 50% duty cycle, your lo= sses are continuous because you are basically putting AC into a DC motor. A= t 50% PWM the DC voltage is 0, so the motor isn't running, but you're still= pumping AC into it. Depending on your motor's losses, it may not be much o= r it might be a lot. That's why you'd want to shut off the h-bridge when yo= u want the motor idle. Filtering between h-bridge and motor (series inductors in both legs and the= n a cap in parallel with the motor) will really reduce the motor losses, no= matter what choice of PWM you make. If you put the LC filtering right at t= he h-bridge and then a smaller cap at the motor it will reduce the EMI too. PWM of any sort is stressful to a brushed DC motor. Filtering reduces the b= rush and commutator wear(and heat). You might give all three PWM methods a try and see what works best for you. Basically, for most motors, if you don't plan on filtering, stick with one = of the first two methods. Best regards, Bob ________________________________________ From: piclist-bounces@mit.edu on behalf of Jason = White=20 Sent: Tuesday, July 3, 2018 3:50 PM To: Microcontroller discussion list - Public. Subject: Re: [EE] DC Motor PWM, Average Voltage? Bob, I am curious about method (3). Would the efficiency/load/stress be any different than the On-Braking case? This has been very helpful. Thanks, -Jason White On Tuesday, July 3, 2018, Bob Blick wrote: > Your frequency is not low, so what happens is this. When the h-bridge goe= s > HI-Z, the energy stored in the inductance dumps back into the supply rail= s > and your net motor voltage is 0 and the current waveform is based on the > inductance and frequency. Current means you have some motor torque, but n= o > voltage means no speed. > > But when you raise the duty cycle to 50% and above, remember your supply > rails clamp the voltage through those back diodes. The voltage is the > same(you use lossless transistors and diodes, right?) as when ON, just th= e > polarity is now reversed. Being an inductor, when you go Hi-Z the curren= t > can't increase, it ramps down. There isn't enough time before the next ON > cycle for the inductor current to go to zero, and current will build up > over subsequent cycles. > > In order for things to be happy, the average motor voltage will move away > from 0, and your motor will actually spin. > > So what you have is a voltage profile that is not a straight line startin= g > from 0% duty cycle such as you would have with an ON/shorted PWM cycle > train. > > Either way works, it's just the result that's quite different. You need > good strong caps across the supply rails close to the H-bridge either way= .. > > The third way is to not use Hi-Z or braking, just drive the H-bridge for > AC out and then you get 0 voltage at 50% duty cycle. That method is easy = to > calculate, but losses are continuous so you will want to shut off the > H-bridge when you are not running the motor. > > Hope this helps. > > Bob > > > ________________________________________ > From: piclist-bounces@mit.edu on behalf of > Jason White > Sent: Tuesday, July 3, 2018 1:26 PM > To: Microcontroller discussion list - Public. > Subject: Re: [EE] DC Motor PWM, Average Voltage? > > Supplementary information: > > PWM frequency =3D 25kHz > Motor Wattage 15W, 20V (I suppose low wattage could imply lowish > inductance, I don't know the actual motor) > Duty Cycle is always between 50% and 100%. > > -Jason White --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .