Whta's wrong with this- proteus simulation....

[MAXPAYNE]

Hi, What's the problem with this ckt ? When Q1 and Q5 is high, the LED  shouldn't glow except for all time it should glow. But it remains glowing all the time...

How resistor is choosen to be anlog or digital in proteus?

[ppa88]

Both R1 and R2 should be selected as ANALOG for proper biasing of the transistor. Also change R2 to somewhere around 330 ohms to drive enough current through the LED.

[MAXPAYNE]

I did it as u said ppa88. But still the same problem exists.....

[o2]

Hi,MAXPAYNE
I try edit your file tst.dsn

Regards

O²

[MAXPAYNE]

wow ! it works now......

What change u have done o2

one more qstn: how can I understand a resistor should be analog or digital ?

[o2]

My change R2 to analog and D3 Current to low same ppa88 said

[ppa88]

Maxpayne,

I am not an expert in simulation but my guess  regarding selection of digital and analog property of resistor (or for that matter any device) is as follows:

1. Whenever you intend to do mixed mode simulation i.e. one which combines non linear nodal analysis of SPICE3F5 (engine used by proteus) with event driven digital simulation (DSIM), then you select the required component to have analog property.

2. Whenever you do purely digital simulation (one which uses only DSIM), eg. I2C bus simulation, you select the property as digital.

Hope it helps.

[MAXPAYNE]

I changed the LED from analog to digital and made all resistor analog and it works..!!!

[ppa88]

Maxpayne,

What you have observed is not wrong. The active LED used in your design has analog a well as digital mode of operation. In analog mode, it will be modelled as a real LED and its intensity etc. will depend on the current flowing (depending on where it is biased in its V-I characteristics). A red LED typically has around 2 volts when it is conducting with normal intensity. You can see that if R2 is made 100k the LED will not glow since the current is not enough. But in digital mode, it is designed to respond to a high or low only irrespective of current (!!), and will glow even if R2=100k ( which is not possible in practice).

So the bottom line is use analog mode for these devices as much as possible (puts more pressure on the spice engine ), but use digital mode if all that you are interested in is a HIGH or a LOW.

Experiment more with these features and you will discover much more.
All the best.

[omidsht]

you are great man PP , i didnt know these things . maybe you should share your other experiments in proteus

omid

[ppa88]

Certainly omidsht, will do so as and when such queries arise, these type of questions are the ones which will help us to learn more about the package.