I am trying to do a charging and a discharging Circuit. R8 is the load that Capacitor C1 needs to discharge into when P12V_IN is low.

My question is Why is Vsolenoid low in the interval shown on the waveform when P12V_IN is low? I am expecting that P-FET M2 is OFF during this time so the voltage/charge of C1 should discharge into R8 since NMOS M3 is ON.

I am sure I am screwing up somewhere silly.

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  • \$\begingroup\$ Please don't take a photo of the screen. You can export decent graphics from LTspice. \$\endgroup\$ – Elliot Alderson Jan 11 at 2:00

You must use two Pch FETS to make high side switches to charge and discharge.


simulate this circuit – Schematic created using CircuitLab

Otherwise V discharge needs to be 2.5Vgs(th) greater than V+. for an Nch FET. This is often done in half bridges using low side PWM and a boost negative clamp cap ac coupled to a diode to V+ to raise the gate driver voltage.

However this still may not do what you want.

How much energy do you need to move the solenoid depends on force and distance as well as current and time duration.

If your 6 Ohm load is 1 Henry, You might need 1 Farad to power it. Then if there is an opposing spring force , it will retract depending on the reactive:resistive time constant.


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