Variable Voltage by pulse driven input

[timryder]

I have an application I'm trying to solve which would allow me to vary voltage going to an Electric Solenoid at 24v ~3.0amps DC. What I want to do is create a device to vary the voltage going to the Solenoid using a pulsed digital input. I have a motor controller which has a High Speed output and it is programmable to me. I would like to somehow utilize this output to control this circuit to vary the voltage going to my solenoid.

I don't have MUCH experience with electronic pcb/circuit design so I need lay mens terms...

Anyone have any ideas how I can accomplish this? Again Steady power supply of
24vdc at 3.0a and I need to vary the output voltage from 0-24 based on digital pulsed input.

Thanks in advance!

 

[neddie]

What do you mean by "digital pulsed input".
Does the "digital pulsed input" go to a "black box" that controlls the 0-24Vdc for the solenoid , or is the digital pulsed input going to the solenoid directly.
It sounds to me that you are looking for some sort of PWM control of your solenoid,
to provide the 0-24Vdc. PWM is not really DC , but to the solenoid it will look like DC.
Give a bit more clarity and I'm sure you will get what you need.
Cheers
Rob

 

[timryder]

OK i'll try to explain what i'm looking for a bit better.

I have a device which is like PLC. This device gives me a pulsed output using a MOSFET and I can control the frequency of it's pulsed output to be a steady set # of Hz. If I program it to output at 22khz then it would do exactly that, or if I want 1kz it will also do exactly that. The voltage of this pulsed output is 5vdc.

So what I'm looking to buy/develop is a solution which will convert 120/240vac into 0-36vdc. I want this device to also have 2 terminals to which I can connect my 0v and 5v pulsed signal from my PLC. This device should be able to scale the output voltage depending on the input frequency being received in these 2 terminals between 0 and 36vdc. I can even go with 0-24vdc if not the 36vdc.

So is there anything like this or how can I put something together to do this...

 

[neddie]

Ok :0)
What you are lookig for is some sort of frequency to voltage convertor.
Does your PLC only provide a variable frequency output , or can it also do a PWM output.Frequency is fixed , but the duty cycle changes.
If so , things are easy.
If you only have a variable frequency it's a little harder.Do a search for frequency to voltage convertor.
If you have the ability to program a micro the solution is simple. Measure the input frequency and output a proportional PWM.If you can't use a micro , go analog :0)
Frequency to voltage convertor -> PWM.
I'll attach a LTSpice cct to this post. It will have a simple frequency to voltage convertor , using a 555 , followed by a PWM cct to drive the solenoid.
There are much better chips than the 555 designed exactly for this job(lm2907 comes to mind) , but I'll use what you can probably get hold of easely. The accuracy you need is also a factor.If you need very precise control , with little delay(Voltage to frequency convertors using this scheme have some delay before the voltage settles) , then some other solution is needed. In this case the delay is about 100ms untill the voltage is stable and hence stable pwm is reached. At the low frequency end there will also be a bit of jitter on the pwm , because the voltage out of the F->V convertor has ripple on it.If your input frequencies are higher , say 10khz to 100khz , then the ripple is significantly reduced. This circuit uses frequencies from about 6Khz to 18Khz to give a voltage 0 to 100% pwm.Below 6Khz the FET is off and above about 18Khz it's hard on.PWM'ed in between :0) Just scale the R's and C's for the frequency range you want to use. (within reason :0) )
It runs off 12V with a 5V input. It's not the best circuit you can get for this sort of job , but it will get the job done and uses easy to get components and is fairly simple.If you don'y have LTSpice , you can get it from Linear.com. Its simple to use , unlimited and best of all , free. Ive made the circuit with components that are supplied with the program except for the opamp , I've used a lm358. The subcct is in the schematic , so you don't have to download it.I've go no specs on the solenoid , so I guessed at 1mH inductance. The fet u will use will obvoiusly have to be sized accordingly.
This was supposed to be a quick post , but has become a little long winded. If you have any qusetion , just shout. Hope this will at least get you started though :0)

 

[timryder]

So what if I am looking at this the wrong way... Here is what I am trying to do with this application and I think I trying to control the wrong thing.

I am using this Push type solenoid to Push a Hardened steel pin into a piece of aluminum. It will impact the part repeatedly very fast like a tattoo on skin, but I would like to be able to digitally vary the amount of force the solenoid is applying using my program I developed. But with the existing hardware I have the only way I can think of accomplishing this is to develop this type of solution I am looking for by way of varying the voltage going to the Solenoid there by restricting its' peak force.

So I think instead of controlling the voltage though I think I should be resisting the current? Does that sound correct to you? I am needing it to be a higher current too... I want to be able to restrict it's current from 0-3amps peak at 36vdc.

So what would be a good way to do this instead...

Sorry for the hassle but you're a huge help!

 

[neddie]

The current to the solenoid is going to be a function of the supply voltage to the solenoid. You need to vary the voltage to the solenoid to vary the current.
I think you could still achieve what you want with PWM'ing the drive to the solenoid.
How do you currently drive the solenoid , and what is its current supply voltage.
If you supply voltage is fixed at 36V and you have a output that can be PWM'ed then it's easy.If you drive the output with 50% duty cycle output , the solenoid will
"see" 18V , and will behave as if driven by 18v DC.
If the drive can't be pwm'd then you need to vary the supply voltage. This can be fairly simple.The output of a frequency to voltage convertor can be amplified and buffered to give a variable output supply. You may not get 0-36V , maybe only 4-36V , but I'm sure that would be ok. If the output from the "PLC" can give you a digital protocol like i2c then you could use a DAC to give you a variable voltage.