Dear all StackExchange users,
I want to make a circuit consisting of 8 valves. Each valve has 55mH and 33 ohm. I want to control them with an Arduino board and a proper MOSFET. Valves reaction time is 0.05ms and I want to drive them about 10 times per second, 5 times off and 5 times on. Valves are 12Vdc. The battery is also 12 Vdc.
I know that I have to add a sort of flyback diode to protect the MOSFET from high voltage while I switch each of the valves off. I know how a single flyback diode, flyback diode + resistor and a Zener & diode can protect it.
Also I know that Zener is much faster than a single diode.
My main problem is that I don't know which part of I-t or V-t signal I should look to see the valve is turned off. I am using LTSpice. So I'd be thankful if you could guide me through this. In other words, When the valves are off after 5vdc is gone?!
Also in the simulation when I generate the 5vdc to MOSFET I see that the Voltage of the line that goes to ground is going from 12VDC to 0VDC. I really don't understand what's happening. Because when I connect the 12VDC directly to the coil and the coil to the ground, it remains 12VDC and doesn't go from 12VDC to zero!!
It is about 10 years since I passed electronics course in my bachelor years... so please forgive me if I am asking for the obvious.
Also I am coming from here "Can a Zener diode that protects a switch against inductance when the switch opens, affect turn on speed of the valve while you close it again?" Isn't the energy dissipation normal?
UPDATE: I checked the response time experimentally: 70v Zener = 8ms, with simple Diode 25ms.