Originally posted by petersone
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1) When the switch (MOSFET) is on and conducting, I think we all agree that: a) the current direction through the coil is from terminal 1 to terminal 2; b) the voltage potential across the coil is 1+ and 2-; c) the diode is reversed-biased with no forward current through it; and d) the MOSFET conducts the same current as the coil.
2) When the switch turns OFF, and due to the collapsing magnetic field of the coil, the voltage potential across the coil reverses such that: a) the voltage potential across the coil is now 1- and 2+; b) the switch is OFF and effectively isolated from the coil and diode; c) the coil, diode, and coil capacitance effectively forms its own isolated circuit because the lower end is now effectively floating; d) with the coil voltage as it now is, this forward-biases the flyback diode and it forms the major current path around the coil; e) the current through the flyback diode must be from bottom to top (anode to cathode) in order for it to conduct, and I think we all agree that it does indeed conduct while the field is collapsing; f) as the current exits the top of the diode, it can not go into the 24V supply because there is no electrical path to the negative side of the supply, so it conducts around down through the coil (and capacitor) again in the same direction it was when the switch was ON.
If RA concedes that the flyback diode does indeed conduct during the collapsing field of the coil, how can the current be reversed as she proposes?
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