PWM controller

[Someone Electro]

Thats what basicly makes DC motors lose tork at high speeds.The inductance of there coil.

I dont see how higher frq. are more eficent anyway. I know that 500Hz is more eficent then 50Hz in AC motors.

 

[Dr.EM]

Yeah, I made the mistake of touching a clamping diode after a few seconds of use and it was burning hot. That was a 6A one, so it really needs a bigger one (the practical solution would be a 10A TO220 diode I think, heatsinked).

I tried both the 120Hz and 3Khz frequencies on it and found the 3Khz to be more effective. For one thing, the 120Hz really was too loud, and it had the typical stalling on lower RPM. 3Khz gave perfectly good control, but like I say the whistling noise is irratating. After a while, you can hear the motor noise over it, and of course on full, it dissapears altogether.

My attempt at hosting the video:

**broken link removed**

 

[Someone Electro]

Ouch this motor give ot a lot of sound when PWM controled!

If it has high enugh resistace try conecting this to a audio amp it would act as a speaker quite good.Hehe

 

[audioguru]

Hi Dr. EM,
I made a motor speed control very similar to yours for an electric powered model airplane. I also used a switching frequency of about 3kHz and it whistles loudly when 1st turned on then the air noise from the propeller drowns it out.
I didn't use a diode across the motor, maybe I should for better efficiency. Instead I rely on the zener diode in the Mosfet to protect it by "wasting" the voltage spike when the controller switches off the current.

 

[Hero999]

audioguru, you're also falling into the all to common trap of believing the protection myth believed by many nubes, the diode isn't used for protection but for efficiency's sake.

What about the inductance of the motor?, as the frequency gets higher the impedance of the motor increases so it gets less power. This is why PMW for motors is normally low audio frequencies.

Another myth, it actually works better at higher frequenies as the self-inductance of the motor is enough to sustain the current flow through the diode in between pulses, think of it like an inductor in a SMPS.
https://www.4qdtec.com/pwm-01.html

 

[Nigel Goodwin]

Another myth, it actually works better at higher frequenies as the self-inductance of the motor is enough to sustain the current flow through the diode in between pulses, think of it like an inductor in a SMPS.

I did tests when I wrote my PIC PWM tutorial, trying different frequencies driving a 6V DC motor - in the end I settled on 2.5KHz, this gave the best performance - moving to 20KHz produced hardly any power at all.

 

[Hero999]

Interesting, possibly the diode wasn't switching fast enough.

 

[Someone Electro]

Then the diode would overheat.The inductance of the motor is restricing the curent flow a lot at such a high freq.

 

[Dr.EM]

I tried this circuit at over 20Khz in prototyping and found it worked very poorly operating a small computer fan.

 

[antpsai]

Hi all. The terms like "efficiency" and "protection" applied to the diode across the motor in a PWM circuit are both correct and both misleading. Its like saying that the wheels in a car are there for efficiency (rolling) and protection (suspension?), yes but the wheel is there to make the car run. Same thing with the diode - it is there to make the circuit run by letting the current circulate (free wheel is the term) through the motor -without the diode the circuit would be a BAD circuit. BTW the diode can be replaced by a transistor to improve efficiency (lower drop) when it is suitably switched.

 

[muki55]

2 Simple PWM

Try this simpliest PWM

 

[svdv]

Hello

Hello the circuits seems good to for study. I would like to know the specifications of Q2, the power MOS and the diode to be place across the load.

Thanks in advance.

 

[audioguru]

I would like to know the specifications of Q2, the power MOS and the diode to be place across the load.

The spec's must match your load's requirements and the switching frequency.
You can lookup the spec's in Google or at www.datasheetarchive.com like everyone else does.

 

[audioguru]

Won't your beer can freeze to your mouth?

 

[AirWalker83]

hi, everybody........
i need some help here.......
i am using power window motor for my project.....
Now i am searching a suitable motor driver in IC package for the power window motor.....
As i know, the L293B is not suitable because it only support up to 1A per channel.......
So, do u all have any suggestion of the motor driver for the power window motor???

 

[chiba]

hi, everybody........
i need some help here.......
i am using power window motor for my project.....
Now i am searching a suitable motor driver in IC package for the power window motor.....
As i know, the L293B is not suitable because it only support up to 1A per channel.......
So, do u all have any suggestion of the motor driver for the power window motor???

Your choice is simple: drive a mosfet and live in peace, or pursue your present course and your ic's face obliteration. We shall be waiting for your answer. The decision rests with you.

 

[AirWalker83]

Your choice is simple: drive a mosfet and live in peace, or pursue your present course and your ic's face obliteration. We shall be waiting for your answer. The decision rests with you.

Mosfet need to build the circuit?
Cause i still a beginner, not quite understand the MOSFET.
Beside MOSFET, got any other motor driver IC that can replace L293D?

 

[chiba]

Do you like Salsa? because trying to drive a Window winder that could draw anywhere from 5-30A is going to bake all your chips. However, using a simple low cost ic to drive one of them awfull mosfet thingys will work out cheaper and easier. I'm sure PWM ic's that can handle 30A are available in the future but first we have to get that time line thing sorted.

 

[Hero999]

Mosfet need to build the circuit?
Cause i still a beginner, not quite understand the MOSFET.
Beside MOSFET, got any other motor driver IC that can replace L293D?

No, not that I know of anyway. I recommend that you should do some Googling and research about MOSFETs, they're not that complex, they're basically electronic switchs.

 

[tankist80]

all, thanks for the info. lurked for month's now and learned a lot of things.
i plan to build H bridge for wheelchair motor and IRF3205 looks very suitable. at least on paper looks like significant improvement over ifrz44n (and not much more expensive) i thought using first.

Also need a very good gate driver to run as cool.

any recomendations for a VERY good one ? HIP4081??