From: invalid@invalid.invalid   
      
   On Tue, 06 Sep 2016 11:22:48 -0700, Big Bad Bob wrote:   
      
      
   > 3.  B+ voltage has a tendency to have VLF 'instability' in it.  As an   
   > example, let's say you use a 10-bit A:D to regulate the voltage,   
   > something like an ATMega processor might have built-in.  That means that   
   > a 350V power supply is off by at lest 0.35V no matter what, and probably   
   > twice that (or more) in actual practice.  The voltage will constantly   
   > vary around that inaccuracy, at a frequency that is related to the   
   > filtering capacitors, etc..  Let's say 2Hz.  I've seen that.   
   >   
      
      
   Surely, if your PSU has VLF instability it's been designed wrongly? The   
   correct way is for the ADC to provide a reference voltage. That is   
   compared, using analogue circuitry, with a sample of the output voltage   
   and the difference is used to correct the output. The ADC output should   
   remain constant.   
      
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