Does a Photoresistor Exist in LTSpiceIV ? - Page 1
Forum section: electronics / beginners

author: joydivisionman
author_rank: Newbie
timestamp: October 01, 2015, 12:18:33 am
content: 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?

author: DimitriP
author_rank: Super Contributor
timestamp: October 01, 2015, 12:54:17 am
content: 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

author: IconicPCB
author_rank: Super Contributor
timestamp: October 01, 2015, 07:42:35 am
content: Go to Yahoo groups and find LTspice group ( there are two ) join up and search extensive model database .

author: tron9000
author_rank: Frequent Contributor
timestamp: October 01, 2015, 12:25:53 pm
content: Quote from: DimitriP on October 01, 2015, 12:54:17 amAs 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

author: liquibyte
author_rank: Frequent Contributor
timestamp: October 01, 2015, 04:29:46 pm
content: Join the Yahoo group and thenhttps://groups.yahoo.com/neo/groups/LTspice/files/%20Lib/Light_Dependent_Resistor/

author: Neilm
author_rank: Super Contributor
timestamp: October 01, 2015, 07:16:03 pm
content: 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.I've remembered the syntax. Set the resistor value to "R=V(x)" where x is the voltage you want to represent. See attached

author: Ian.M
author_rank: Super Contributor
timestamp: October 01, 2015, 07:41:43 pm
content: http://ltwiki.org/index.php5?title=Undocumented_LTspice#Behavioral_Resistors

author: codeboy2k
author_rank: Super Contributor
timestamp: October 01, 2015, 07:56:49 pm
content: 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.

author: macboy
author_rank: Super Contributor
timestamp: October 02, 2015, 02:09:02 pm
content: Quote from: codeboy2k on October 01, 2015, 07:56:49 pmI 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.

author: eetech00
author_rank: Regular Contributor
timestamp: October 02, 2015, 11:40:42 pm
content: 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.