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???
11/29/08 06:14
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 		 #160400 - High frequency ripple
Responding to: ???'s previous message
Thanks Mr.Klaas and Mr.Erlacher for informative posts,
In one occasion(about a year ago) I needed to use a SMPS for a very sensitive board, if I remember correctly SMPS frequency was about 70KHz. and because sometimes high quality low current voltages were needed and SMPS ripples are terrible in low currents I looked for a linear regulator. At fist I wanted to use LM338 reading datasheet and simulation with SPICE led me to this conclusion that this regulator is terrible in anything above a few KHz. Then I investigated LM723, SPICE simulation led me to believe that this regulator is quite respectable at about 70KHz (if I remember correctly ~60db attenuation). I never measured the actual performance of LM723 in that frequency so I just trusted the SPICE but I also used about 13200uF capacitance at input(before regulator stage) of the device, the device works fine and I'm not sure whom should I thank, LM723 or fat capacitors.

regards,

List of 26 messages in thread
TopicAuthorDate
Decoupling capacitance can kill the regulator?            01/01/70 00:00      
   Yes, LDOs are sensitive...            01/01/70 00:00      
   and that's not all ...            01/01/70 00:00      
      was there a supervisor?            01/01/70 00:00      
         No ...            01/01/70 00:00      
            you have yourself posted re ....            01/01/70 00:00      
               as often happens ...            01/01/70 00:00      
                  who 'injected'?            01/01/70 00:00      
                     It's on you, Erik!            01/01/70 00:00      
                        what was 'injected'            01/01/70 00:00      
                           What I injected was potential failure modes ...            01/01/70 00:00      
                              not if Vdd drop below            01/01/70 00:00      
                                 This is not the place to argue that matter!            01/01/70 00:00      
                              reset vs supervisor            01/01/70 00:00      
                                 I think it is equally important that ...            01/01/70 00:00      
                                    Lethal ramp-down            01/01/70 00:00      
                                       a funny thing happened ...            01/01/70 00:00      
                                          Brownout interrupts can be nice            01/01/70 00:00      
                                 RESET is not germane to this thread            01/01/70 00:00      
      diode in reverse bias (from output to input)            01/01/70 00:00      
         The best way to pass the ce testing...            01/01/70 00:00      
      High frequency ripple            01/01/70 00:00      
         Use a LRC-lowpass-filter!            01/01/70 00:00      
            What kind of L in the filter?            01/01/70 00:00      
      Big caps at output were used in the past            01/01/70 00:00      
         They used large L in the input in the past, too            01/01/70 00:00      

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