Does a Photoresistor Exist in LTSpiceIV ?

[joydivisionman]

I'm a novice with LTSpice.  I've built simple circuits and I see the value of the software.

For whatever reason, I've tried to find a photoresistor, but have not succeeded.  I've scoured the web, and have found some alternative routes, but they look more difficult than need be.

Certainly I am missing something here.  LTSpice IV certainly has the ability to provide a photoresistor, doesn't it?

[DimitriP]

LTSpice doesn't  seem to care if a resistor value varies due to changes in  light,  temperature or someone  turning a knob.

There is a way to simulate a variable resistor:

http://eecs.oregonstate.edu/education/docs/tutorials/LT%20Spice_VarResistor.pdf

[IconicPCB]

Go to Yahoo groups and find LTspice group ( there are two ) join up and search extensive model database .

[tron9000]

LTSpice doesn't  seem to care if a resistor value varies due to changes in  light,  temperature or someone  turning a knob.

There is a way to simulate a variable resistor:

http://eecs.oregonstate.edu/education/docs/tutorials/LT%20Spice_VarResistor.pdf

As Dimitri put it, its really just varying a resistor value rather than making it change with lumin.

Have a look at this vid, it'll explain a few things in LTSpice that helped me. However don't get the title confused with what your trying to do, you can just apply the same parameters to the actual value of a resistor

[liquibyte]

Join the Yahoo group and then https://groups.yahoo.com/neo/groups/LTspice/files/%20Lib/Light_Dependent_Resistor/

[Neilm]

Rather than using the .step command, you can use a voltage source to program the value of a variable resistor. This means you can vary the value during the run and see how your circuit reacts (for instance if it is going into a comparator circuit that you want to test triggers and releases at the correct values).

Unfortunately, I can't remember the syntax for this. I have it in a simulation at work - I'll try to remember to post it tomorrow.

[EDIT]

I've remembered the syntax. Set the resistor value to "R=V(x)" where x is the voltage you want to represent. See attached

[Ian.M]

http://ltwiki.org/index.php5?title=Undocumented_LTspice#Behavioral_Resistors

[codeboy2k]

a demonstration of what Neil said:

You can use a PWL voltage source, give a name to its output net, and set R=V(the_named_net) and this makes the R follow the voltage source.

In the image below, R1 is the name of the V2 output,  V(R1) is the resistance of R1.

[macboy]

a demonstration of what Neil said:

You can use a PWL voltage source, give a name to its output net, and set R=V(the_named_net) and this makes the R follow the voltage source.

In the image below, R1 is the name of the V2 output,  V(R1) is the resistance of R1.

I do this all the time to test power supply designs. You can check the response of the design to a change in load (or input voltage or ...). By changing the rise or fall time, you can get anything from a gradual change to a sharp step.

[eetech00]

No. but you can use a behaviorial voltage source to generate a voltage representing light intensity,
then use that voltage to control a resistors value.