Solenoid valve driver

[adithya.rp]

Hello,

I'm doing a project on driving a solenoid valve in BOSCH. The input is a 0-10V sine wave (Which is actually an output from a D/A converter) and it is to be converted to a PWM signal of 300Hz with 0-100% range dutycycle. This duty cycle is to be used to inject current to drive a solenoid valve. For 100% dutycycle, the current should be ideally 1.4A to close the valve completely.
Would using a micro controller give a more accurate PWM signal? Please help me out.

Thank you.

 

[inventor(y)]

I can make a quote for this if you want. No really, this is very easy. I know three ways without thinking to hard.

 

[adithya.rp]

Really? Then please help me out ... We need to complete our project in 3 weeks

 

[inventor(y)]

Convert the sine wave to an absolute value using some op-amps.
for a full description on how to do this:
http://focus.ti.com/lit/an/sboa068/sboa068.pdf

Option 1:

take a micro controller with an AD converter and measure the absolute value. Then you use a timer of the micro to generate a PWM signal.

Option 2:

Use an LM3524 to convert the absolute value to a PWM signal. The test circuit on page 7 in the date sheet below might be helpful.

**broken link removed**

Option 3:

Design a sawtooth generator with some op-amps and use a comparator to generate a PWM signal from the absolute value.

A drawing can be found here under 2. Sawtooth PWM:

Pulse Width Modulation (PWM) Basics

Hope this gets you going.

 

[adithya.rp]

Thank you... But my major issue is, how do I convert this PWM signal's dutycycle into corresponding current to move the solenoid valve?

 

[inventor(y)]

Thank you... But my major issue is, how do I convert this PWM signal's dutycycle into corresponding current to move the solenoid valve?

That wasn't clear from what you wrote.

-You can use a simple voltage source. The voltage should be set to U= R . I.
-Switching the voltage on/off with a PWM signal: use the output of your circuit to drive a mosfet.
Fig 8: 8. Power MOSFET PWM Motor Driver
Some power PWM drivers for electric DC motors

Can you post the technical specification of the valve in question?

 

[chuckey]

What you are trying to do is to convert a 0 ->100% PWM into a 0 -> 1.4A current source. Why?, why not convert your 0 -> 10V AC V into a 0 -> 1.4A current source. Or for a 1V ac input, are you are applying your 300Hz based PWM directly to the solenoid, so for 1V (10%), a pulse of 1.4A of .33mS length is applied every 3.3 mS?
If its just the 0 -> 10 V into a 0 ->1.4A, then build a precision rectifier as per inventor's suggestion, then use an op-amp with a power transistor using the solenoid as its collector load, and a low value resistor (1 ohm) in the emitter circuit. So now you have a monitoring point for the solenoids current. At 1.4A out, there will be 1.4V dropped across this resistor. So connect your feed back resistor from this point to the - input of the amp with another resistor to earth also from the - input. These resistors set your range in terms of Vin/Iout. Feed the actual voltage into the + input of the op-amp.
Frank

 

[inventor(y)]

Hi Frank, indeed. I don't understand why people need an explanation like the one you have given. Shouldn't they be able to design a simple circuit like this all on their own? I think i will stop posting answers to questions like this. People should at least try to find out how to do things and then ask questions if things go wrong. That's how we all learned how to get things done. I still remember making buck regulators with op-amps and transistors when i was 14. PWM controllers where not available at our local electronics store back then. It gives me the advantage that I'm able to read schematics as if it where books.

 

[elactis]

Hi everyone! The solution is not so simple. Why? because proportional valves have a very ugly tendency to heat terribly. Therfore chopping the supply voltage with a given duty cycle will not give a reproducible current. Furthermore, you have to do something with the magnetic hysteresis of the valve which may produce up to 50% error on flow. The easiest solution is to buy a driver on the market. They all have at least two buttons where you can set the gain and offset values. It costs around $50 to $200 depending where you buy it. Otherwise, you may spend 3-6 months before you have the working solution. (By the way, Bosch has also a driver)

 

[inventor(y)]

Hi elactic, you are right about that. I-rms² R losses at low duty cycles will be high indeed. About the reproducible current: the original poster wanted to use a modulated current source for that reason. But ruling hysteresis problems like you describe, can only be done with feedback I think. If you know more about the subject, let me know. Sounds interesting.

Regards, Inventor

 

[kovibb]

Hi everbody,

I build proportional solenoid valve controled by PWM too. In my project I want to use current sensing across solenoid as one of two feedback indicator. thing what i need to know is what input to A/D converter - instant value or average value of current. Thank you for advice