Electronic – Solenoid driver schematic

circuit-designmosfet-driversolenoid-valve

Here is a circuit I'm working on. Its purpose is to accept a PWM signal (PID control) and drive a small solenoid valve that consumes ~200 mA at 12V. I have some questions I would love to get a second opinion on.

Driver_circuit

  1. The driver IC's UCC27512 reference design shows what I assume to be an AC choke? (L3), they don't specify any max/min value, so I have just chosen 1uH – I would like some feedback on how to choose this value.

  2. The MOSFET data sheet specifies that, with a VGS = 10 V, the ID = 300 mA – so I assume the 12V output from the driver IC will be fine.
    Now the driver IC can source and sink a few amps when pulsed and around 300 mA and 600mA continuously.
    Should I keep R16 as a current limiting resistor. Do I even need it?
    I would 100% keep it if I was driving directly from my MCU as the GPIO's can't sink that amount of current.

Best Answer

If you want to control the valve, then you need a current source. I have depicted a sketch for high side driven N-MOSFET that needs a high side gate driver with a charge pump or bootstrap circuit. The current is sensed with a shunt resistor, that needs to be filtered to elimiate the switching pulses. This measured current is than subtracted from setpoint and processed with a PI controller with PWM generator.

schematic

simulate this circuit – Schematic created using CircuitLab

EDIT:

The valve current is filtered with RC low pass filter, then a TVS diode is used to protect the opamp buffer that is supplied with same supply as MCU 3.3V or 5V. The MCU samples the current actual value with high speed ADC and then does digital filtering on it, IIR or FIR. The MCU does the PI control and PWM generation.

schematic

simulate this circuit

With one another ADC and analog front end, the flow is measured. The MCU does one additional closed loop control, we call this cascaded loop control. The inner current loop shall execute very fast, meanwhile the outer flow loop has to execute slower, since the system has slower response than current loop.

schematic

simulate this circuit

EDIT 2:

You could even replace the gate driver and MOSFET with an intelligent automotive high side switch that is capable of PWM control. In my opinion fsw = 5-10kHz is just enough for your application, but it is subject to solenoid inductance/resistance ratio.

The MMBF0201NL is just to small, it is rated to 300mA only. You have to choose more suitable device, something at least 4A continous then it has to be derated due to switching losses and PCB size.

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