Error in LM324 SPICE Model?

[skeatz]

I created a simple 2x inverting amplifier circuit using the LM324 opamp IC, with +/- 12V supplies. The output voltages for a given input can exceed the supply voltages!! For example, with a 10V input, I get a 20V output - theory tells us that the output voltage should clip at around 10.4 V.

When I tried simulating the same circuit using a 741 opamp IC, the circuit behaved as predicted, with the output voltage clipping at +/- 10.4 V.

Is there a bug in the LM324AD SPICE model? Is there some way for me to check the SPICE model parameters to verify?

thanks.

[skeatz]

OK - found out the reason why the simulation wasn't accurate - the LM324 model is a simplified SPICE model (Virtual 3 terminal opamp) and doesn't take into consideration the supply voltages of the opamp.

Does anyone know how I can replace the 3-terminal opamp model with a Virtual 5-terminal opamp or the full model? I have downloaded the full model from the NatSemicon website, but am not sure how to make use of the data.

Any help appreciated.

[M.I.]

Hi Skeatz,

You can follow the steps below to replace your current model with a 5 terminal version from the Multisim database. 

1.  If you double click on your LM324 component and click on the "Replace" button the Component browser should appear 
2. There should be a list of available models in the "Model manuf./ID:" section of the window. Choose another model (see attached screen shot)
3. To view the contents of the model, click on the "View Model" button (See attached screen shot)
4. Once you're happy with the model, click on the OK button to replace the component on the workspace with the selected component/model.

Hope that helps.

[skeatz]

Hi M.I.,

I replaced the LM324 model with that of the LM224 as per your suggestion - the output voltage now clips at +10.355V and -12.771V during simulation. It is much better than previously (using the 3-terminal model), but is still not quite accurate - my supply is +/- 12V, so the negative output should be around -10.4V (and definitely not -12.771V !!).

Do you know how I can go about replacing the LM324 model with the manufacturer SPICE model? The instructions in the Multisim User Manual is not quite clear as far as this is concerned.

thanks again,
skeatz.

[M.I.]

Hi Skeatz,

I've attached a document from one of our tutorials to guide you through the process of adding your own model (or a manufacturer model) to an existing component

I've also attached a simple circuit file with the component (using the National Semi model) in it, just in case you have problems with creating it using the tutorial.

Let me know if this helps,

[skeatz]

Hi M.I.

Thanks; I will go through the tutorial & sample circuit that you have included in your post and update you on my progress.

As I mentioned to Graham in another post, my institution intends to purchase many copies (> 500 licences) of NI Circuit Design Suite Education version for use in our courses. One of my key selling points to my staff who are concerned about the 'lack' of support for NI Circuit Design Suite in our country is the very helpful & active NI forum.

You guys are proof of that.

thanks again for your help,
skeatz

[M.I.]

Thank you Skeatz, was glad to help. Feel free to post any of your questions/concerns and we will try our best to get back to you as soon as possible.

The forums are usually the best place to look for answers, as many users with varying backgrounds tend to share ideas and experiences with the rest of the community. So if one of us (NI Staff) is unable to answer a question, you're sure to find someone else who may be able to.

Have a great day.

[skeatz]

Hi M.I.

Just thought I'd keep you updated... I followed the instructions in the tutorial that you posted - and successfully incorporated the NS Spice model for LM324 into my User database. I've also managed to created the 4 section version of the model & simulated the circuit successfully.

Thanks a heap for all you help.

best rgds,
skeatz