[time-nuts] Switching regulator replacement for 7805

Bob Camp kb8tq at n1k.org
Sun Dec 4 16:53:02 EST 2016


I doubt that there is a significant demand for 10 ma output switchers. The 
benefit of going from 12V to 2V as a switcher compared to linear is mighty 
small. As a guess, I’d say that anything much under a watt is not worth doing
in this arena. That gets you up to at least 100 ma at the normal conversion 
ranges. I would also suggest that the regulator you are replacing is only a 
1A part. That places an upper limit on what makes sense. 

If you really want the SMT parts, get an oven. A converted toaster oven is 
a dirt cheap way to do it. 


> On Dec 4, 2016, at 4:09 PM, Attila Kinali <attila at kinali.ch> wrote:
> On Sun, 4 Dec 2016 15:45:55 -0500
> Bob Camp <kb8tq at n1k.org> wrote:
>> Given that the parts to build one are fairly easy to get and that we likely have “nutty” 
>> EMI requirements. Maybe a small board that drops into a 78xx footprint is the 
>> better solution. 
> I don't fully agree. To go full "nutty" you would want to use the chips
> in the QFN packages, as those have shorter leads and a large ground pad
> to keep EMI down. But soldering an 0.5mm QFN by hand is impossible
> (believe me, I tried) and not everyone has an oven. Also a lot of the
> EMI performance depend on what output current you expect. Using a 1A
> design for 10mA is a good way to get poor EMI performance as the
> chip will go from PWM (aka fixed frequency) to PFM (aka fixed on time)
> mode under low load to increase efficiency. The same goes for input
> voltage. So we would need to do multiple designs for different 
> output current and input voltage ranges... which kind of defeats
> the purpose of "a small board that drops into....".
> What could be done, though, is a small board with all components,
> but the inductor on it. So then one could select the right inductor
> for the application and solder it on. Using an inductor that is easy
> to solder (like e.g. WE-PD3) with a wide selection of values should
> do the trick.
> 			Attila Kinali
> -- 
> It is upon moral qualities that a society is ultimately founded. All 
> the prosperity and technological sophistication in the world is of no 
> use without that foundation.
>                 -- Miss Matheson, The Diamond Age, Neil Stephenson
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