1. Home
  2. Electronics Design
  3. Classical multivibrator fails in LTspice

Classical multivibrator fails in LTspice

Version 4 SHEET 1 1444 1224 WIRE -480 624 -512 624 WIRE -368 624 -416 624 WIRE -288 624 -368 624 WIRE -144 624 -208 624 WIRE -512 672 -512 624 WIRE 0 720 -304 720 WIRE 0 752 0 720 WIRE -304 768 -304 720 WIRE -368 816 -368 624 WIRE -336 816 -368 816 WIRE -144 848 -144 624 WIRE -144 848 -192 848 WIRE -112 848 -144 848 WIRE 0 864 0 832 WIRE -496 880 -576 880 WIRE -368 880 -432 880 WIRE -336 880 -368 880 WIRE -576 912 -576 880 WIRE -304 944 -304 928 WIRE -16 944 -304 944 WIRE -16 976 -16 944 WIRE -16 1088 -16 1056 WIRE -576 1104 -576 992 WIRE -464 1104 -576 1104 WIRE -368 1104 -368 880 WIRE -368 1104 -384 1104 WIRE -288 1104 -368 1104 WIRE -144 1104 -144 848 WIRE -144 1104 -208 1104 WIRE -576 1152 -576 1104 FLAG -512 672 0 FLAG -576 1152 0 FLAG -16 1088 0 FLAG 0 864 0 FLAG -112 848 Vo SYMBOL voltage -16 1072 R180 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 12V SYMBOL Opamps\\\\LT6011 -304 848 R0 SYMATTR InstName U2 SYMBOL voltage 0 736 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 12V SYMBOL res -192 608 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 10K SYMBOL res -192 1088 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1m SYMBOL res -368 1088 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R3 SYMATTR Value 47 SYMBOL cap -416 608 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C1 SYMATTR Value 1µ SYMBOL cap -432 864 R90 WINDOW 0 0 32 VBottom 0 WINDOW 3 32 32 VTop 0 SYMATTR InstName C2 SYMATTR Value 0.1µ SYMBOL res -592 896 R0 SYMATTR InstName R4 SYMATTR Value 1e15 TEXT -98 650 Left 0 !.tran 0 10s 1U

Reply to
Robert Baer
Loading thread data ...

Hello Robert,

Your resistor values are wrong. Please change R2 and R3 to 100kOhm. You have to use also a maximum time step to get it running.

.tran 0 10s 0 .1m

The LT6011 has input protection diodes. See page 11 in the datasheet. They will always conduct in this circuit. You should use an Opamp without such diodes.

Best regards, Helmut

Reply to
Helmut Sennewald

With an added ".ic v(n001)=0" and using the original bad items, it has the brazen impudence to run!. (though with little song in it's heart).

--
Posted via a free Usenet account from http://www.teranews.com
Reply to
john jardine

The values as shown are straight out of the Burr Brown Handbook of Operational Amplifier Applications (C) 1963; Pg 66, middle left diagram. And i do not know one LTxxx from another, i picked one at randumb.

Reply to
Robert Baer

You mean the Burr Brown is (gasp) wrong?

Reply to
Robert Baer

In my experience circuits with positive feedback generally do not simulate well in SPICE (or maybe I am doing it wrong). I have tried many times to simulate self-oscillating converters e.t.c. and got useless results, yet on the bench the buggers work!

Reply to
Frithiof Andreas Jensen

It's because _transient_ analysis is noise-free.

Unless you force initial conditions, most oscillators will not start in simulators.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

"Jim Thompson" skrev i en meddelelse news: snipped-for-privacy@4ax.com...

They start, then wierdness sets in with oscillation dropping in and out, that sort of thing.

Reply to
Frithiof Andreas Jensen

Circuit example please?

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

The problem is that what starts these in the real world is small differences in component values in the two halves of the circuit. In a simulator with exactly equal values it won't work. Try changing one of the capacitors by

10% and see what happens.

HTH

Ian

Reply to
Ian Bell

Naaah! It's Brownian noise. Q-up a multivibrator in its exactly balanced linear region... in the real world it WILL start, in the simulation world it won't, it'll just sit there at the initial Q-point.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

In my experience, this is often due to letting the simulator choose the integration step, especially if there are hard nonlinearities. Limit the time step to 1/100th of your signal period and you should get better (i.e. sometimes very different) results.

Pere

Reply to
oopere

Using the startup directive in the transient analysis also helps. This ramps the voltage sources from zero and shakes up the circuit a bit.

- YD.

--
Remove HAT if replying by mail.
Reply to
YD

LTSpice will require additional massage of the run parameters because of its speedup architecture, optimum for switching power supply analysis but not so good otherwise, wherein it solves for an input, however ridiculous, to satisfy a nontrivial DC output state.

Reply to
Fred Bloggs

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.