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Power supply OPAMP

Hello!

 

This is my first time posting here on this forum. 

I am trying to simulate my power supply using multisim from 0 to 30V. When I use opamp TLE2141 it is working fine but if i want to use similar opamp like MC34071 i get some strange readings in kV.

So what i am doing wrong, i am just a begginer using multisim. Please help me! I am trying to solve this for several days now.

Below is my schematic of PSU. 

 

Thank you in advance

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Hi

 

Welcome on NI Forums!

 

Please give us some more info:

- which TLE2141 version are you using (there are many in Multisim database)

- which of 3 opamps are you replacing - all or just one of them?

- can you give us a brief description of your circuit? I know that it's a power supply, but there are a few potentiometers and the circuit is quite complex to analyze it deeply. Give us a short overview and give an idea on what values are you expecting to see in certain parts of the circuit.

- which exactly version of Multisim are you using?

 

With this info we'll try to find the source of your problems. 

 

So far I've tried replacing all opamps with TLE2141ACD and the output is 80.547mV, while for MC it is 62.043V - but I don't see any kV. Is this the incorrect value you see?

Best regards,
Maciej Antonik
National Instruments Poland
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Hi there,

 

It looks like the issue here lies in the model you have chosen.  The MC34071 opamp is a simplified version that does not take into account the power supplies.  As a result, there is no power supply clipping, and therefore the opamp has the ability to achieve very high gains (and hence why you are getting the strange readings in the kV-range).

 

Before using a model, it is always a good idea to take a look at what is modeled.  To do this:

  1. Double-click on the component in your design and choose Edit Component in DB to invoke the Component Properties
  2. Select the Model tab
  3. In the Pin Mapping Table, notice that VS+/VS- use model nodes NC (Not Connected)

Alternatively, when placing a component you can select View Model.  Here you will see that the comments in the header indicate that this is a 3-Terminal Opamp (ie. Inputs and Output only).

 

Hope this helps to explain the strange results.

Message Edited by NatashaB on 09-14-2009 04:25 PM

Natasha Baker
R&D Engineer
National Instruments

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