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Old 29th October 2006, 04:38 AM   #1
lineup is offline lineup  Sweden
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Smile LM7812 Test, PSRR 60dB at 100Hz ripple

hi

Trying to figure out how to setup
Power Supply Rejection Ratio = PSRR testing
using my Multisim spice simulator.

Have a look at my attached test circuit.

1. I am feeding 100mV ripple 100Hz onto a 12V regulator input.
2. Then I measure the AC voltage at the output.
3. In this setup I use 100mA DC load with a normal electrolytic decoupling capacitor.
------------------------------------------------------------------
Result:
Ripple at input: 100mV
Ripple output: 114uV = 0.114mV

Ratio: 100 / 0.114 = 877
20 x LOG10( 877 ) = 58.8dB

PSRR = 58.8dB at 100Hz ripple ( with ripple level 100mV )
This looks as a value that may be correct and valid.

------------------------------------------------------------------

Questions:

->> Is this a good method of estimate PSRR?

->> What setup do you use?

->> Is there some standard method used for example by Op-Amp manufacturers?



Thanks
lineup
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Old 29th October 2006, 07:08 PM   #2
lineup is offline lineup  Sweden
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Arrow The Best Audio Lab - Lineup

okay
never mind
I understand now:

I am the only one diyaudio amateur constructor
that actually design my amplifier
to have a good PSRR and try to make this sure by
doing some simulations and tests


lineup
The Best Audio Lab
The Most Serious Audio Lab:
Lineup Audio Lab

http://lineup.awardspace.com/
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Old 3rd November 2006, 06:54 AM   #3
mrjam is offline mrjam  Italy
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OK! Never mind!
You understood what??
You're the only one diyaudio amateur constructor that actually design your amplifier using Electronic WorkBench!

Maybe it's the reason why people ignored your "discovery"! Nobody cares about PSRR "measured" with a sim!

You talk about music you can hear and loose time with EWB ....stop sims and connect a "real" function generator and a "real" oscilloscope to your "real" 7812 connected to a "real" circuit! You will discover parasitics, oscillations and other "real" things

Good luck with your beloved simulations!
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Old 3rd November 2006, 07:21 AM   #4
edl is offline edl  Hungary
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Hi HALOJOY,

I visited your webpage, Lineup.
Had a good laugh, thanks!

Mrjam is right, in EWB measuring 7812's PSSR means nothing. Measure it in your Lab. In such a serious laboratory I'm sure you have the needed gears. I'm sure you have a really nice workbench.

"I am the only one diyaudio amateur constructor
that actually design my amplifier
to have a good PSRR and try to make this sure by
doing some simulations and tests"

haha...
http://lineup.awardspace.com/labtour-1.html This is that Audio Lab?!

Regards,
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Old 3rd November 2006, 08:01 PM   #5
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Hi lineup,

1->> Is this a good method of estimate PSRR?

2->> What setup do you use?

3->> Is there some standard method used for example by Op-Amp manufacturers?

1- yes!

2- the same, but you can "save" R1.

3- I donīt know but why not,
may be You ask Bob Pease?

"I am the only one diyaudio amateur constructor
that actually design my amplifier
to have a good PSRR and try to make this sure by
doing some simulations and tests"

Of course not : Itīs always the best to try some simulations
b e f o r e one build and test!

Regards
Heinz!
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Old 5th November 2006, 12:25 PM   #6
BWRX is offline BWRX  United States
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You can just capacitively couple your AC signal to the supply voltage as is shown in this diagram: http://i.cmpnet.com/eet/news/03/july/SS1278_ADI.gif
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Old 5th November 2006, 01:53 PM   #7
sss is offline sss  Israel
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i use simulation only for digital circuits . the the only case it works the same as in reality
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Old 6th November 2006, 02:12 AM   #8
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Default we do what we needed

Hi, Lineup

I have visited Ur web, it's interesting, I want to know what's the purpose of Ur Lab, for business, for fun, or an ad.

anyway, we do what we needed. the way to measure 78XX is not important, the point is we buy a component that can meet our application is enough. Too precise is a waste. We only consider price verse perfomance. any component manufacturer can provide spec. for their products. no necessary to do extra work on testing.

I've been using the 78XX series regulators for decade, and they gave our performance is over their value. to measure their spec. is meanningless.




WE CONSIDER PRICE AND PERFORMANCE
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