Proportional valve control current with PWM

[Rikr09]

Hello,

I need to control a 10V proportional valve using a current control with PWM, i checked some forum related to this topics but no one gave some answer for this. So, i would like you to help me with this. Cutrrently i have this on my board but the manufacturer says that we are controlling voltage and this is not the idea.



Thanks for your attention.

 

[FvM]

How's the question related to your previous thread? https://www.edaboard.com/threads/proportional-valve-control-using-a-raspberry.389741/ Particularly are you asking about the same proportional valve linked there? The datasheet does not specify current control. The relation between valve voltage and current is set by the the coil resistance. Current control results in an almost temperature independent characteristic if your application is open loop.

 

[danadakk]

I think what you are looking for is a VCCS (Voltage Control Current Source).

You can use a DAC to drive this, if its onbard, or a PWM followed by a LPF to convert
pulses/duty cycle into a VDAC like output.

A classic VCCS, for a ground referenced valve, would look like -

https://www.ti.com/lit/an/sboa046/sboa046.pdf

A PMW DAC, see filter design in attached doc.

If you need high resolution, accuracy I can show you a possible base design using
fdbk to manage/monitor current accuracy in the valve, single chip for the low power
portion of design.


Regards, Dana.

 

[KlausST]

Hi,

Why no low side control? It makes hardware more simple: logic level Mosfet, diode...

When one sees a valve as a LR series connection...
Then the average of the 10V current times the voltage gives the power.
You may calculate back to the valve current by: P = I x I x R.

Klaus

 

[danadakk]

Could be either low or high side. Just thinking maybe valve is grounded
such that high side is required. Clearly if power is isolated from valve body
low side easier, and one less error to manage.in the simple current source
shown. Eg, one would use current sink -

Obviously diode across valve coil to protect against transients prudent.
Of course MOSFET could be used, but with gate series R to decouple gate C
from OpAmp.


Regards, Dana.

 

[KlausST]

Hi,

I referred to the OP's circuit.

Klaus

 

[Rikr09]

How's the question related to your previous thread? https://www.edaboard.com/threads/proportional-valve-control-using-a-raspberry.389741/ Particularly are you asking about the same proportional valve linked there? The datasheet does not specify current control. The relation between valve voltage and current is set by the the coil resistance. Current control results in an almost temperature independent characteristic if your application is open loop.

Yes, you are right, i forgot that i was wondering about this before in this forum.

 

[Rikr09]

Could be either low or high side. Just thinking maybe valve is grounded
such that high side is required. Clearly if power is isolated from valve body
low side easier, and one less error to manage.in the simple current source
shown. Eg, one would use current sink -

View attachment 163800

Obviously diode across valve coil to protect against transients prudent.
Of course MOSFET could be used, but with gate series R to decouple gate C
from OpAmp.


Regards, Dana.

Hello, thanks for your help, i did this and anything happens... is not working; the output voltage is not varying.

 

[KlausST]

Hi

Are you sure you tested exactly the shown circuit?
No modifications?

Show your circuit (schematic and photo), wiring, test conditions, test results..

Klaus

 

[danadakk]

Hello, thanks for your help, i did this and anything happens... is not working; the output voltage is not varying.

You added the LPF to the PWM and built the constant VCCS ? Subbed a R for the coil R and verified
for varying PWM out duty cycle you get changing DC levels ? Then verified constant current source
changes its current with input V ?


Regards, Dana.