Hi, monostable mode 555 circuits shall trigger with the falling edge of the input trigger pulse, right?
I am trying to simulate it using NE555 LT spice model, and it seems to trigger with the either edge.
Can anybody please clear it up?

The green curve is the input pulse.
The blue curve is the 555 output.

 

Hi L22,
Please post your asc file.
E

 

Version 4
SHEET 1 1840 680
WIRE 560 -224 448 -224
WIRE 688 -224 560 -224
WIRE 912 -224 688 -224
WIRE 1232 -224 912 -224
WIRE 1424 -224 1232 -224
WIRE 448 -192 448 -224
WIRE 560 -144 560 -224
WIRE 1424 -144 1424 -224
WIRE 688 -112 688 -224
WIRE 448 -64 448 -112
WIRE 560 -64 560 -80
WIRE 560 -64 448 -64
WIRE 448 -32 448 -64
WIRE 976 -16 784 -16
WIRE 1232 -16 1232 -224
WIRE 1232 -16 1200 -16
WIRE 688 48 688 -32
WIRE 688 48 448 48
WIRE 976 48 688 48
WIRE 1424 48 1424 -64
WIRE 1424 48 1200 48
WIRE 976 112 880 112
WIRE 1424 112 1424 48
WIRE 1424 112 1200 112
WIRE 912 176 912 -224
WIRE 976 176 912 176
WIRE 1232 176 1200 176
WIRE 448 256 448 48
WIRE 688 304 688 48
WIRE 880 368 880 112
WIRE 1232 416 1232 176
WIRE 1424 416 1424 112
WIRE 448 528 448 336
WIRE 688 528 688 368
WIRE 688 528 448 528
WIRE 784 528 784 -16
WIRE 784 528 688 528
WIRE 1232 528 1232 480
WIRE 1232 528 784 528
WIRE 1424 528 1424 480
WIRE 1424 528 1232 528
WIRE 448 576 448 528
FLAG 448 576 0
FLAG 448 -32 0
SYMBOL voltage 448 240 R0
WINDOW 3 -406 -76 Left 2
WINDOW 123 0 0 Left 0
SYMATTR Value PULSE(0 5 1u 0 0 2.22u 40u)
SYMATTR InstName V1
SYMATTR SpiceLine Rser=0 Cpar=0
SYMBOL cap 1248 480 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C3
SYMATTR Value 10n
SYMBOL cap 1440 480 R180
WINDOW 0 24 56 Left 2
WINDOW 3 24 8 Left 2
SYMATTR InstName C4
SYMATTR Value 1n
SYMBOL res 1440 -48 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R2
SYMATTR Value 500
SYMBOL voltage 448 -208 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V3
SYMATTR Value 5
SYMBOL cap 544 -144 R0
SYMATTR InstName C5
SYMATTR Value 100n
SYMBOL cap 672 304 R0
SYMATTR InstName C6
SYMATTR Value 10n
SYMBOL Misc\\NE555 1088 80 R0
SYMATTR InstName U2
SYMBOL res 672 -128 R0
SYMATTR InstName R3
SYMATTR Value 10k
TEXT 568 560 Left 2 !.tran 0 10u 0us

 

Hi,
That is not the LTSpice asc file, please recheck.
E

 

I am sorry Eric, this is my schematics file that has .asc extension.
What file do you need?

 

Hi LI22.
This is an example, try and run it in LTS.
E

 

It is working. What is it for?

 

this is my schematics file that has .asc extension.

Yes. but we want the .asc file, not the files contents.

 

Ha! Got it. Thank you.

 

hi LIno,
Try this, change the R and C values to suit your application.
E

Added 555 Apps PDF, may help

 

Below is your circuit, modified for correct operation:

I changed the positive going trigger to a negative going, and increased the one-shot time to be greater than the trigger pulse time.
The one-shot time has to be longer than the trigger pulse, otherwise the output pulse width just follows the input.

 

Thank you very much guys. I may have a few more questions later.