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PWM circuit to control hydraulic proportional valve

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IDEngineer:
I've searched the site and found a few references (such as https://www.eevblog.com/forum/projects/proportional-valve-control-with-npn-transistor-(tip-120)-using-pwm/msg3087566) but no real discussions of any better or worse circuits for controlling a proportional valve.

It's a solenoid (actually, two) but unlike most solenoid applications you need to control its position linearly as opposed to just bang-bang on/off. Most discussions of solenoid drivers seek to optimize for pull-in vs. holding current vs. heat dissipation, where a short-term greater current is used for pull-in and then a lower current can be used to hold the solenoid in the pulled-in position. Proportional valves typically use PWM to achieve linear control, with the frequency set low enough to act as dither to improve hysteresis response. 150-200Hz is common.

The obvious and traditional approach would be a suitable FET, either high or low side, with a flyback diode. But before I commit to this I wonder if someone has devised a more optimized driver circuit for this rather specialized situation.

Thanks!

oschonrock:

--- Quote from: IDEngineer on August 02, 2020, 10:19:03 pm ---I've searched the site and found a few references (such as https://www.eevblog.com/forum/projects/proportional-valve-control-with-npn-transistor-(tip-120)-using-pwm/msg3087566)

--- End quote ---

Sorry, link not working for me.

OM222O:
I'd personally go with constant current circuit. If you need high effeciency then also add a buck converter that adjusts it's voltage with respect to the load, otherwise just strap on a heat sink and fan. If you provide more details I can draw up a schematic.

IDEngineer:

--- Quote from: OM222O on August 02, 2020, 10:49:04 pm ---I'd personally go with constant current circuit.
--- End quote ---
I considered that but we already have a closed control loop so we don't have to control based on current. This is a hydraulic motor application and we have RPM sensing, so even if conditions change we can vary the pulse width to maintain the target RPM. If you have a different reason for current management, I'm all ears! But otherwise I think we just need to have PWM control into the coil... the question is whether there is a better way than the traditional FET+flyback diode.

OM222O:
If you want to go the PWM route then no.

But the constant current method allows for closed loop control and reliable operation automatically without needing fancy control algorithms / feedback. You mentioned a proportional valve (coil + magnet that changes the flow rate) but then you mention a motor and RPM control? Those are two completely different things? The pump creates a certain amount of pressure, resistance to that pressure determines the flow (just like voltage (pressure) and current (flow))

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