Hi I need help explaining a simple switch circuit to activate a solenoid with a capacitor and FET transistor. L1 is the solenoid and is activated when the X1-1 and X1-2 short is opened, sending current through the transistor causing the cap to instantaneously discharge and activate the solenoid.
I have not yet learnt transistors, and have only done 1 subject on capacitors so far. I am not sure how the transistor causes the capacitor to discharge when the short is opened? Also it was explained to to me that R1 & R2 form a voltage divider dissipating 6V across each. Why are these not included when we find the time constant for charge or discharge (I thought you would have found Req (R1 + R2 || R4), seeing as they are dissipating voltage.
Also I am trying to calculate the time it takes to discharge the capacitor when the circuit is switched off (Should be over 60 secs).
I have the time it takes to charge T = CR = 2200 * 10^-6 * 2400 = 5.28 secs (Time constant). Then, 5.28 * 5 = 26.4 secs to fully charge.
I have been unable to calculate the time it takes to discharge though, have been trying to use the formula, V(t) = V(0) = e^(-t/RC)
I have uploaded the circuit for you guys to see.
Many thanks.
I have not yet learnt transistors, and have only done 1 subject on capacitors so far. I am not sure how the transistor causes the capacitor to discharge when the short is opened? Also it was explained to to me that R1 & R2 form a voltage divider dissipating 6V across each. Why are these not included when we find the time constant for charge or discharge (I thought you would have found Req (R1 + R2 || R4), seeing as they are dissipating voltage.
Also I am trying to calculate the time it takes to discharge the capacitor when the circuit is switched off (Should be over 60 secs).
I have the time it takes to charge T = CR = 2200 * 10^-6 * 2400 = 5.28 secs (Time constant). Then, 5.28 * 5 = 26.4 secs to fully charge.
I have been unable to calculate the time it takes to discharge though, have been trying to use the formula, V(t) = V(0) = e^(-t/RC)
I have uploaded the circuit for you guys to see.
Many thanks.
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