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Old 9th August 2004, 08:46 AM   #1
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Default power supply pspice simulation problem

Hi,

I am simulating a choke-input power supply with 2 section LC filters in both psud and pspice. While I am getting about 20V, 100mV, 500uV ripple voltages after chokes in psud as expected, pspice gives about 60V, 30V and 30V ripple after chokes. Transformer resistance, choke resistances and capacitor esrs are modeled in simulation, and load is simulated as a current source. What can be the problem with spice ?

Thanks in advance.

MB
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Old 9th August 2004, 09:26 AM   #2
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Can you post a diagram? Are the sources the same in both cases? Sometimes you have to specify Vac RMS, sometimes VacAmplitude. But without a diagram it is difficult to advise.

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Old 10th August 2004, 05:27 AM   #3
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The buzzing of the choke in an LC filter can be reduced by adding a small smoothing capacitor (about 0.68 uF) directly following the rectifier and before the choke. It will still behave as a choke-input filter to all intents and purposes.
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Old 10th August 2004, 07:10 AM   #4
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here are the schematic and probe results...
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Old 10th August 2004, 07:12 AM   #5
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sch..
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File Type: gif psu.gif (7.4 KB, 104 views)
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Old 10th August 2004, 07:15 AM   #6
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probe...
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File Type: gif probe.gif (22.1 KB, 78 views)
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Old 10th August 2004, 08:45 AM   #7
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One question I have, did you make sure that there is 180 degree phase shift between the sources V1 and V2? If not, you are only using only half of the 50Hz waveform. That will give more ripple.

Your probes look weird indeed, I need to look at it some more. Can you do a probe of a realistic time frame, like from 0 to 200mSecs. What is the signal at pin 3 of the tube?

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Old 10th August 2004, 10:45 AM   #8
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I dont think there must be 180degree phase shift between V1 and V2. I have also simulated it. Keep in mind they are connected like (+-) (+-) not the otherwise.

Moreover, I am getting the correct results now. I think pspice is messed up. I think I need to install service pack for orcad.

Thanks...

MB
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Old 10th August 2004, 11:23 AM   #9
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Quote:
Originally posted by metebalci
[sni]Moreover, I am getting the correct results now. I[snip]

Good! What did you change to make it work?

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Old 10th August 2004, 01:59 PM   #10
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Nothing ! We were using Orcad at school, so I try to use it right now too. But I think there are many bugs in Orcad that are not related with simulator code but interface and general software issues. LTspice seems to be very good. I will try to use it.

MB
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