On Mon, 26 Dec 2005 18:15:48 -0600, John Fields
wrote:
Aarghhh!!!
There's a gross error in the circuit which I'll fix tomorrow...
Hint: Vbe of the NPN won't allow the MOSFET to turn on, duh...
---
KISS works best...
+V
|
+-------+
| |8
[Rt] +---+---+
| 2|_ Vcc |3
IN---+----------|--O|T OUT|-- OUT
| | 6| |
| +---|TH |
[1000] | 7|_ 7555|
| +-----+--O|D |
| | +| | GND |
| E [Ct] +---+---+
+--B PNP | |1
C | |
| | |
+-----+-------+
|
GND
Unlike the vanilla 7555 which starts timing out when pin 2 goes low,
with the retrigger it starts timing out when pin 2 goes high. That
means that pin 3 will be high for the timeout period (1.4RC) plus as
long as pin 2 stays low:
_
t = (1.4RC) + (tT)
If you don't already have it you might want to download Linear's
excellent simulator at:
http://www.linear.com/company/software.jsp
It's free, and you can use it to build stuff without having to buy
parts, which might be handy for you in your present situation.
Anyway, here's the netlist for the circuit above if you want to
check it out:
Version 4
SHEET 1 960 680
WIRE -432 352 -432 224
WIRE -432 528 -432 432
WIRE -256 336 -256 288
WIRE -256 528 -432 528
WIRE -256 528 -256 416
WIRE -144 224 -432 224
WIRE -144 432 -144 224
WIRE -80 352 -80 80
WIRE -16 528 -256 528
WIRE -16 528 -16 160
WIRE 48 160 -16 160
WIRE 48 224 -144 224
WIRE 48 288 -256 288
WIRE 48 352 -80 352
WIRE 64 432 -144 432
WIRE 272 432 144 432
WIRE 336 80 -80 80
WIRE 336 160 272 160
WIRE 336 160 336 80
WIRE 336 224 272 224
WIRE 336 288 272 288
WIRE 336 288 336 224
WIRE 336 320 336 288
WIRE 336 384 336 320
WIRE 336 528 -16 528
WIRE 336 528 336 480
WIRE 432 160 336 160
WIRE 432 192 432 160
WIRE 432 320 336 320
WIRE 432 320 432 272
WIRE 432 352 432 320
WIRE 432 528 336 528
WIRE 432 528 432 416
WIRE 656 160 432 160
WIRE 656 240 656 160
WIRE 656 528 432 528
WIRE 656 528 656 320
WIRE 656 576 656 528
FLAG 656 576 0
SYMBOL Misc\\NE555 160 256 R0
SYMATTR InstName U1
SYMBOL voltage -432 336 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR Value PULSE(5 0 0 0 0 .1 .5 2)
SYMATTR InstName V1
SYMBOL voltage 656 224 R0
WINDOW 123 0 0 Left 0
WINDOW 39 24 132 Left 0
SYMATTR SpiceLine Rser=0
SYMATTR InstName V2
SYMATTR Value 5
SYMBOL res -272 320 R0
SYMATTR InstName R1
SYMATTR Value 1000
SYMBOL res 416 176 R0
SYMATTR InstName R2
SYMATTR Value 1e6
SYMBOL cap 416 352 R0
SYMATTR InstName C1
SYMATTR Value 1e-6
SYMBOL pnp 272 480 M180
SYMATTR InstName Q1
SYMATTR Value 2N4403
SYMBOL res 160 416 R90
WINDOW 0 63 58 VBottom 0
WINDOW 3 67 59 VTop 0
SYMATTR InstName R3
SYMATTR Value 1000
TEXT -354 616 Left 0 !.tran 0 5s 0 .001s
--
John Fields
Professional Circuit Designer