[time-nuts] Switching regulator replacement for 7805

Dan Kemppainen dan at irtelemetrics.com
Mon Dec 5 12:21:46 EST 2016

On 12/5/2016 12:00 PM, time-nuts-request at febo.com wrote:
> This is exactly the PWM to PFM mode switch I described earlier.
> The 850mA are probably high enough that the DC/DC converter works
> in PWM mode, thus switching with a constant frequency, even if the
> load changes. On the other hand 200mA of a 1A converter is low enough
> that it's most likely in the PFM region, where every small change
> (or noise) causes the switching frequency to change.

I would guess at 200mA the switcher is still operating PWM. With that 
tiny little inductor, the inductor has probably fallen into 
discontinuous current mode. Usually this is bad for noise generation. It 
would be interesting to see what a scope trace of the switched leg of 
the inductor looks like in both cases.


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