This is part of a piece of equipment that is to detect a short. The FUT wil l be a capacitor. It is not the only function of the unit, I am working on the rest. This seems so simple but I have doubts for some reason. Since I a m learning LTSpice finally.
ugh to assure saturation - I think. Seems like it anyway. R 2 & 4 should pr ovide enough current to light the LED, which is shunted by Q 1 when there i s no short. When there is the base voltage drops and the transistor cuts of f and the LED indicates the short. In theory.
I don't know, maybe I am too skiddish after years of conditioning to accept that something so simple could just work. I am not looking for advanced ca lculus here, I believe it unnecessary, but I would appreciate a quick look over to see if I made any blatant mistakes. I have missed some duesies in m y time.
The only other thing that would be nice is to get the current drain down as this is to be battery operated. I don't see how without another transistor , and there is no way of getting out of giving the LED enough current. Anyw ay, here it is :
Version 4 SHEET 1 880 680 WIRE 32 0 -112 0 WIRE 224 0 32 0 WIRE 448 0 224 0 WIRE 224 96 224 80 WIRE 336 96 224 96 WIRE 224 128 224 96 WIRE 336 128 336 96 WIRE 448 128 448 0 WIRE 32 176 32 80 WIRE 32 176 -48 176 WIRE 160 176 112 176 WIRE -48 208 -48 176 WIRE 336 224 336 192 WIRE 336 224 224 224 WIRE 448 224 448 208 WIRE 448 224 336 224 WIRE 32 240 32 176 WIRE 448 240 448 224 WIRE 112 256 112 176 WIRE -48 320 -48 256 WIRE -48 320 -112 320 WIRE 32 320 -48 320 WIRE 112 320 32 320 WIRE 448 320 112 320 SYMBOL npn 160 128 R0 SYMATTR InstName Q1 SYMBOL res 128 160 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 3.3K SYMBOL cap 96 256 R0 SYMATTR InstName C1
SYMBOL res 208 -16 R0 SYMATTR InstName R2 SYMATTR Value 62 SYMBOL res 432 112 R0 SYMATTR InstName R3 SYMATTR Value 120 SYMBOL res 432 224 R0 SYMATTR InstName R4 SYMATTR Value 47 SYMBOL LED 320 128 R0 SYMATTR InstName D1 SYMBOL res 16 -16 R0 SYMATTR InstName R5 SYMATTR Value 1K SYMBOL res 16 224 R0 SYMATTR InstName R6 SYMATTR Value 1K TEXT -112 24 Left 2 !6 VOLT TEXT -120 56 Left 2 !SOURCE TEXT -128 296 Left 2 !COM TEXT -128 216 Left 2 !TO INDICATE TEXT -128 240 Left 2 !SHORT HERE
Cheap shots are OK, I have been around here a while...