fetled
In the circuit above, when S1 is pressed and released, the LED turns ON and stays ON. Why is this so? I can't directly measure the Gate Voltage with a DMM since connecting the DMM results in the LED not staying ON.
If the LED is ON (S1 pressed then released), when S2 is pressed and released, the LED turns OFF, as expected.
I skimmed my intro ECE book chapter on FETs and it didn't seem to mention anything about this phenomenon…
Alright, I investigated this today a little and found out that it works as expected if I turn down the PWM frequency to some good 100Hz. Now I just need to fine tune the visual perception and I'm good to go. Still, if anyone knows what good Rext2 is for (or has any other improvements), I'd be happy to know.
This one is fairly simple: -
Each time you press the button, the output latches in the opposite sense to what it previously was. Lots of good ideas.
Picture stolen from this stack exchange question: Make a Latching Relay using SPDT Relays
Is this question all but identical?
Best Answer
When you press S1, you're storing a charge on the gate which has a small capacitance Cgs. This charge maintains the electric field which keeps the channel between the drain and source. Once you press S2, the charge on the gate is deplected and the channel is turned off