A little help with PWM selection?

[Boosted67]

**broken link removed**

Looking to control a 12v solenoid. I find nothing but these chinese deals, so a little timid about it. Seems to fit everything I need. Question is in the description, it says it "comtrol voltage" is 5v. Here's the description.

- Model: 15A
- Quantity: 1
- Color: Green + Black
- Material: PCB + Component
- Working voltage: DC 6V~90V
- Control power: 0.01~1000W (max. 15A current)
- Quiescent current: 0.005A (standby)
- PWM cycle: 0%~100%
- PWM frequency: 15KHz
- Cable length: 19cm
- Control voltage: 0~5V (voltage-controlled, with a PLC can control the motor speed directly)
- Packing list:
- 1 x Speed control


Is the pulse width modulation only going to be 5v? I'm sure it's a super rookie question. Just getting into this kind of stuff and didn't find anything searching.

 

[willis...]

This motor driver board works by accepting a PWM input and using that signal to generate an output. The 5V means that the input signal must be 5.0V logic, although 3.3V will most likely work as well. As an example, if your working voltage is 12V, and you provide a 15kHz signal at a 50% duty cycle, you will effectively create a 6V output, oscillating 15000 times a second. All that this board allows you to do is to modulate the output voltage by providing a PWM input.

Regards,
Willis

 

[Boosted67]

This motor driver board works by accepting a PWM input and using that signal to generate an output. The 5V means that the input signal must be 5.0V logic, although 3.3V will most likely work as well. As an example, if your working voltage is 12V, and you provide a 15kHz signal at a 50% duty cycle, you will effectively create a 6V output, oscillating 15000 times a second. All that this board allows you to do is to modulate the output voltage by providing a PWM input.

Regards,
Willis

Thanx Willis. What I'm not understanding is the 5.0v logic and 3.3v.
The pulse width I get. 60v @ 50% duty cycle would be 30v effectively.
I found 5.0v logic on wiki. Damn lol. Is 6v-90v just the logic family then? Or is it something I really don't need to know and going to over complicate?

I have a solenoid that is already fed 12v. I need to modulate the ground. I'll need to voltage to be about 2-4v as a guess, for this work.
I know it's rudimentary as hell so thanx again

 

[willis...]

You will be controlling this motor board with some sort of logic, probably a simple microcontroller. You will configure that microcontroller to provide your desired PWM output, depending on how you would like to drive that motor. Based on the type of microcontroller you choose, the PWM output will either be 3.3V or 5.0V logic. Here is a well written article that talks about logic levels and voltages...
https://learn.sparkfun.com/tutorials/logic-levels/all

You will also have a voltage source that will be used to drive the load (solenoid); in your case, this will be 12V. The motor driver board will then use the input PWM to create an output PWM that is essentially equivalent to an output voltage. For instance, if you provide a input PWM with a duty cycle of 50%, you will effectively get a 6.0 V output; a d.c. of 25% will yield a 3V output, and so on an so forth.

Sparkfun also provided a nice tutorial on PWMs...
https://learn.sparkfun.com/tutorials/pulse-width-modulation

Regards,
Willis

 

[Boosted67]

Wow had no idea pwm had that side to it. Almost looks like for what I need, pwm is going to be more trouble than it's worth. I need it work on the lower end of the spectrum of about 0-6v. But with all the dead space in the lower voltage area I might be SOL. After reading those articles a simple potentiometer might be the way to go for me. I can have my range of voltage including a full ground w no problems or unknowns.

 

[willis...]

It is all going to depend upon the resolution of your PWM. Even at just 1% resolution you will be able to step at 120 mV increments. Simple increase your resolution to .1% and now you can vary your voltage with up to 12mV of accuracy (in theory).

I suppose you could use a potentiometer, but then you will have an added amount of power dissipation across the resistor. Furthermore, you would have to manually control the pot, unless you selected a digital potentiomenter, in which case it would probably just be easier to stick with PWM in the first place.

Regards,
Willis

 

[FvM]

The 5V means that the input signal must be 5.0V logic, although 3.3V will most likely work as well.

I understand "0~5V voltage-controlled" differently, an analog control voltage that is translated to 0 to 100% duty cycle.

 

[KlausST]

Hi,

The pulse width I get. 60v @ 50% duty cycle would be 30v effectively.

It's not clear.
Often "effective voltage" means RMS voltage.
Then a 0V /60V square wave with 50% duty cycle gives 42.4V RMS.

Why:
Let's say you have a 60Ohms load. It draws 1A resulting in 60W of power.
Now with 50% duty cycle there is 50% of time with 60W and 50% of time with 0W. The power averages to 30W.
If you now calculate back how many volts (DC) is neccessary to generate 30W of heat at a 60Ohms resustor, then you get 42.4V.
This is the method that is used to calculate the RMS voltage. The RMS voltage is the equivalent voltage for a random waveform to generate the same power as DC voltage.

Klaus