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Author Topic: Very simple speed regulator for small DC motors  (Read 983 times)
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PeterMcMonty
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« on: December 20, 2014, 10:48:04 22:48 »

Hello everybody,

I have a very cheap mini drill that uses a small DC motor powered by a 12V wall adapter and I made a little box with a very simple PWM regulator.

The core is a CMOS RC oscillator with variable duty cycle, that can be regulated by a 10k linear potentiometer.

This drives a power mos that switches on and off the drill power supply at around 12 to 13 kHz with a duty cycle that is regulable from few percents to quite close to 100%

The circuit is very simple and can be adapted to different needs. It can be supplied up to 24V or more (depending by the mos you use): a simple zener regulator supplies the CMOS oscillator. I tailored it for a 12V supply, but if you run the motor at 18V or 24V or more you can increase R1 value.

Diode D1 recirculates motor current when the mos is off: I used a standard rectifier (1N4007), but a schottky rectifier would be a better choice.

Despite the fact that I'm not able to run the simulation, the circuit works pretty well in real world: I made two units and they perform as expected.

No more to say. I include the picture of the schematic, a photo of the unit (other photos you can find in the attached rar archive), the Proteus 7.10 files (schematic and pcb layout) , the gerber files (CADCAM.zip) and some photos in Photos.rar archive.

Enjoy! Merry Christmas and happy new year to everybody.
PeterMcMonty

Sorry! I can't upload attachements. Please download all of them at: https://app.box.com/s/vlavp110dty344pwesz9

dec 21th, 2014: I succeded in uploading the most of the attachements. To see the photos, please follow the link above.
« Last Edit: December 21, 2014, 10:55:35 10:55 by PeterMcMonty » Logged

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robotai
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« Reply #1 on: December 27, 2014, 08:29:20 08:29 »

I had built a PWM controller with simple NE555 timer circuit for the same purpose before. Is there any advantage for this circuit compared with general 555 circuit?
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PeterMcMonty
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« Reply #2 on: December 27, 2014, 04:28:30 16:28 »

No, I don't think there are big advantages for this circuit. The same thing you can do in several ways. What I can say is that with this circuit you can vary the duty cycle from few percents to near 100%.
I don't remember if it is possible using a 555, but perhaps it can be done. If it is the case, the two solutions are equivalent, also in terms of cost and simplicity.
Why don't you public your circuit here, just to let people compare the two alternatives?
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TucoRamirez
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« Reply #3 on: December 29, 2014, 05:37:52 05:37 »

i built your circuit PeterMcMonty and i only changed C4 to avoid some humming from the motor.  Nice KISS design Smiley
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PeterMcMonty
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« Reply #4 on: December 29, 2014, 10:05:23 22:05 »

Thank you Tuco! I'm very glad that you appreciate it! I've added C4 on my first revision, to avoid latchup of the oscillator at startup, but 100 pF was a first and only try.

Since C2 sets the oscillator frequency, at a first glance I was thinking you changed it, but then I saw where is C4. I don't understand how it can make the difference in the humming of the motor, unless it contributes to change the oscillator frequency.

As I said, I'm not able to run simulation of this circuit with Proteus: it gives me convergence errors. So I can't experiment with different values of C4.

Probably, depending on the motor, little adjustements may be necessary.

Have fun and I wish you an happy new year!
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TucoRamirez
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« Reply #5 on: December 30, 2014, 03:44:22 03:44 »

yep, a classic 'oscillator pissing of prospice' (even the simple astable with pnp transistors makes prospice to puke without correct settings or stimuli on the supply in order to set a proper initial condition to iterate ^^ )  Anyway real world has no nag windows Smiley   ( what about to simulate it on NI multisim? )

PS: neither do i ^^ but changed to 2X or 3x stopped humming and it worked quite well Cheesy 
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robotai
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« Reply #6 on: December 30, 2014, 05:24:14 05:24 »

The 555 circuit is too simple. However, as requested, here is the schematics I am still using. It should be easy to find this kind of circuit by google. This could simply adjust the PWM duty cycle from almost 0% to nearly 100% (althrough less than 50% is normally useless).
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PeterMcMonty
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« Reply #7 on: December 30, 2014, 06:04:30 06:04 »

yep, a classic 'oscillator pissing of prospice' (even the simple astable with pnp transistors makes prospice to puke without correct settings or stimuli on the supply in order to set a proper initial condition to iterate ^^ )  Anyway real world has no nag windows Smiley   ( what about to simulate it on NI multisim? )

PS: neither do i ^^ but changed to 2X or 3x stopped humming and it worked quite well Cheesy 
I don't have NI multisim and, sincerely, I spent not much time on trying to make simulation run on this circuit, since real world told me that it works. I will try to change C4 to 220 or 330 pF to see what happens.

Thank you for your interest!

The 555 circuit is too simple. However, as requested, here is the schematics I am still using. It should be easy to find this kind of circuit by google. This could simply adjust the PWM duty cycle from almost 0% to nearly 100% (althrough less than 50% is normally useless).
Yes! I admit that 555 circuit is even simpler than mine, at least because of the 8 pin size of 555 compared to 14 pin  of 40106. I will try it too, to see how it performs (probably it can be simulated on Proteus Cheesy )

Thank you for this alternative!
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