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[SOLVED] 12V, 5V, 3.3V, 1.8V, -12V, -5V power supplies on PCB

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phanikodali

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Hello,

For my mixed signal PCB to work i need the following low noise power supplies:

+12V/5A
+5V/3A
+3.3V/2A
+1.8V/0.2A
-12V/2A
-5V/3A
my application includes noise sensitive components like 16 bit high speed ADC, several low noise and precision op-amps, 12 bit DAC and noise generating components like Stepper motors(+12V/0.4A each) and digital circuitry.

i would like to generate the above mentioned supplies from +15V/-15V SMPS (having sufficient current rating) using dc to dc switching regulators(single output like national's LM22678TJE-5.0,LM22670MRE-5.0,LM20333MH or multiple output like LTC1876 from Linear) for positive supplies and LDO's for negative supplies(as high current rating negative switching supplies are difficult to obtain), is it the correct approach?
can anybody suggest me the best solution for the above requirements?

Thanks in advance
 

exnol

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Switchers usually produce more noise than LDOs. are you sure you want to use switchers? Have you checked the ripple chara of the above mentioned switchers?
 

goldsmith

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Switchers usually produce more noise than LDOs
Dear exnol
Hi
But you can use a good filter at the out put to eliminate those high frequency noises , simply.
Best Wishes
Goldsmith
 

Raza

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The easy low cost solution is simply use a Computer Power Supply, you will get current than your requirement and a noise free (almost) supply. For extra safety you can add additional capacitors if needed after checking the ripples on the output lines of the supply.
 

phanikodali

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@exnol: when i simulated the circuits in webench, up to 30mV of noise is observed in the absence of filter at the output, can it be eliminated using filters?, if possible, suggest me with such filter topology

@goldsmith: i heard that a ferrite core inductor-capacitor LC filter could eliminate the switching noise well, could it eliminate 30mV ripple is it a good solution for precision 16bit ADC power supply?

@raza: Your idea is good, but i found the below two problems
1) The ATX supply can't give out enough current on negative supplies.
2) -5V is removed from ATX standard, so, modern ATX supplies are coming without -5V supply.

Thank you all,
please suggest me if any
 

goldsmith

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Dear phanikodali
Hi
It depends on your filter . if you use a 4th order filter ( two section that each section consists a two order filter , and second section contain a low value LC ) , there won't be any problem .
Best Wishes
Goldsmith
 

phanikodali

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Dear Goldsmith,

thank you very much for your valuable solution, it worked very well.
 

qayyoum

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i think raza give u very good and also low cast solution here all of required supplies is available
 

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