Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Proportional valve control using a Raspberry

Status
Not open for further replies.

Rikr09

Member level 3
Joined
Feb 14, 2013
Messages
59
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,745
Hello!

I have a pair of these valve:s https://kellypneumatics.com/download_files/MidPVspec.pdf. We tried to control them using a PWM signal from a Raspberry Pi but this is not working causing some vibrations and notable fluctuations on the output. So i decided to write you to help us with a configuration to control them.

Attached the image of the circuit that im using for now:
WhatsApp Image 2020-04-23 at 12.25.23 AM.jpeg

Thanks for your attention.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
48,910
Helped
14,332
Reputation
28,927
Reaction score
13,077
Trophy points
1,393
Location
Bochum, Germany
Activity points
282,225
Unsuitable high gate pull-up resistor. Try 1kohm.

What's the PWM frequency? Do you have an idea of suitable PWM frequency for this valve?
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
20,493
Helped
4,461
Reputation
8,931
Reaction score
4,490
Trophy points
1,393
Activity points
135,517
Hi,

you need some overvoltage protection for your MOSFET, because you are driving an inductive laod.
Zener, MOV, ..
Even a freewheeling diode may work. But mind the slow decaying current.

To simplify the circuit I recommend to use a logic level MOSFET.

If you want to drive multiple valves, then consider to use a ready to buy low side switch (driver) IC.

Klaus
 

Rikr09

Member level 3
Joined
Feb 14, 2013
Messages
59
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Activity points
1,745
Unsuitable high gate pull-up resistor. Try 1kohm.

What's the PWM frequency? Do you have an idea of suitable PWM frequency for this valve?

Ok, thanks for your reply, i will test with 1k.

According with the PWM frequency i did it till 2Khz and the behavior geot better but still the vibrations. The datasheet does not recommend any PWM. :???:

- - - Updated - - -

Hi,

you need some overvoltage protection for your MOSFET, because you are driving an inductive laod.
Zener, MOV, ..
Even a freewheeling diode may work. But mind the slow decaying current.

To simplify the circuit I recommend to use a logic level MOSFET.

If you want to drive multiple valves, then consider to use a ready to buy low side switch (driver) IC.

Klaus

Hello Thanks for your answer.

With this circuit we onlye wan to control one valve, is to say, one configuration for each valve. On the other side, why to use a Logi Level Mosfet? cand you recommend me one?
 

srizbf

Advanced Member level 5
Joined
Apr 3, 2010
Messages
1,995
Helped
417
Reputation
840
Reaction score
328
Trophy points
1,363
Activity points
10,985
The circuit given is not for proportional control
for a conventional PWM method.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
20,493
Helped
4,461
Reputation
8,931
Reaction score
4,490
Trophy points
1,393
Activity points
135,517
Hi,

why to use a Logi Level Mosfet?
As already said: to simplify the circuit. You can drive it from the Raspberry without a bjt.

cand you recommend me one?
There are so many, and many will suit your application. Just go to any electronic parts distributor or Mosfet manufacturer and use their interactive selection guides.
Then you have all at once: V, I, price, availability, package, R_DS_ON... it´s much faster when you do this on your own.

Klaus
 

srizbf

Advanced Member level 5
Joined
Apr 3, 2010
Messages
1,995
Helped
417
Reputation
840
Reaction score
328
Trophy points
1,363
Activity points
10,985
Replace the input NPN with a PNP transistor
with appropriate biasing.
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
48,910
Helped
14,332
Reputation
28,927
Reaction score
13,077
Trophy points
1,393
Location
Bochum, Germany
Activity points
282,225
Freewheeling diode is in fact required for PWM operation, I didn't notice it's missing.

PWM frequency has to chosen so that you get almost continuous current with a certain ripple to overcome valve hysteresis. Several 100 Hz up to some kHz are typical values, depending on the valve mechanical time constant. Missing freewheeling diode will however cause abrupt current decay and thus higher vibration.
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
20,493
Helped
4,461
Reputation
8,931
Reaction score
4,490
Trophy points
1,393
Activity points
135,517
Hi,

I agree with FvM.
A valve is an inductive device, it's movement is controlled by magnetic field, which is proportional to current (not voltage).
Thus - with the freewheeling diode - and a suitable PWM frequency you can control the valve with PWM duty cycle.
I've done this already with hydraulic proportional valves.

I don't understand the PNP approach.

Klaus
 

LNS Electronics

Newbie level 3
Joined
Jul 28, 2015
Messages
3
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
11
Hi,
try to use uln2003 instead of 2n2222, from 100k to 1k-0.5W and STP55nf06
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top