The circuit is a LED night light; triggered by a PIR motion sensor; just enough light to keep from stumbling in the dark.
[TL;DR_the value of R2 is required in order to make a 100uF capacitor work, but there is now a ~1.5 sec delay before forward voltage of the LED is met and fade-in begins. A larger capacitor is too bulky for the project; R4 was later added to mitigate the delay.]
Is R4 the right way to pre-charge a transistor gate?
Besides running out of 1M-ohm resistors, R4 seems wasteful, especially if this was driven with a battery. Is this a circumstance for a voltage comparator to be used? This began by forcing a 100uF cap to perform as desired by changing resistor values, and it has revealed new challenges.
To the peanut gallery: I'm not looking to install a boat anchor, please do not comment on the glories of larger value capacitors. The focus is manipulating a transistor gate correctly or a better way to go about it. The transistor may not be necessary for this design, but this is a proof of concept and what is learned will be used for larger scale designs. If anything, I'd try to make an even smaller capacitor perform the same task.
I didn't realize on the breadboard how much of a difference 1.5 seconds makes; the time it takes to achieve the LED's forward voltage due to R2's value. In practice, when walking into a dark room, it's a lifetime. I may have oversized R3 (somewhere I read (R2 x 7 = R3)); but the capacitor cannot be increased for size constraints.
I added R4 to keep the gate "precharged" to mitigate the delay-on time, I believe I've seen this done similarly, but I don't remember exactly how. 13M Ohms is arbitrary; I started with 9M and kept adding to hunt for the right gate voltage; just added two more and it's holding at 340-350mV on the gate; LED seems to light just above that, but I don't know how to test for certain besides visually.
I've seen tons of posts on the LED fade subject, like most all forums, threads get swamped with unhelpful responses. I searched for "precharging transistor gate" and found nothing, so I posted this. To me, it is a different topic.
[TL;DR_the value of R2 is required in order to make a 100uF capacitor work, but there is now a ~1.5 sec delay before forward voltage of the LED is met and fade-in begins. A larger capacitor is too bulky for the project; R4 was later added to mitigate the delay.]
Is R4 the right way to pre-charge a transistor gate?
Besides running out of 1M-ohm resistors, R4 seems wasteful, especially if this was driven with a battery. Is this a circumstance for a voltage comparator to be used? This began by forcing a 100uF cap to perform as desired by changing resistor values, and it has revealed new challenges.
To the peanut gallery: I'm not looking to install a boat anchor, please do not comment on the glories of larger value capacitors. The focus is manipulating a transistor gate correctly or a better way to go about it. The transistor may not be necessary for this design, but this is a proof of concept and what is learned will be used for larger scale designs. If anything, I'd try to make an even smaller capacitor perform the same task.
I didn't realize on the breadboard how much of a difference 1.5 seconds makes; the time it takes to achieve the LED's forward voltage due to R2's value. In practice, when walking into a dark room, it's a lifetime. I may have oversized R3 (somewhere I read (R2 x 7 = R3)); but the capacitor cannot be increased for size constraints.
I added R4 to keep the gate "precharged" to mitigate the delay-on time, I believe I've seen this done similarly, but I don't remember exactly how. 13M Ohms is arbitrary; I started with 9M and kept adding to hunt for the right gate voltage; just added two more and it's holding at 340-350mV on the gate; LED seems to light just above that, but I don't know how to test for certain besides visually.
I've seen tons of posts on the LED fade subject, like most all forums, threads get swamped with unhelpful responses. I searched for "precharging transistor gate" and found nothing, so I posted this. To me, it is a different topic.
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