Re: gEDA-user: Switching regulator question

[John Griessen <john@xxxxxxxxxxxxxx>]

John Doty wrote:
> On Jun 16, 2007, at 5:43 PM, Randall Nortman wrote:
  I would think that 120Hz ripple on the input
>> would not bother the thing, even if it's large ripple, so long as the
>> voltage never drops below the minimum required to still enable a 5V
>> output (i.e., about 8V).
> 
> Depends on how much ripple on the output you can tolerate and how  
> fast the control loop is. The regulator acts as a lowpass filter, but  
> it will pass some ripple to the output. Know your requirements. Know  
> the specs of the stuff you're using.
>

Yes, I would not be surprised if that TI controller cycling at 500KHz
can be a low pass filter by changing it's pulse widths as the ripple varies.
Its ripple response might have a shape like a one pole filter with 3db down lower than you think.
The effect on the rectifier caps might be even worse -- more current draw when it sags -- sag further.

Need to read its spec like John D. said.

John Griessen


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