Homebrew PCBs

On Friday 08 July 2005 03:46 pm, Greg Codori wrote:

> Have you seen the schematic link I posted?  Could I just start with
> another power wall wart current (instead of 15v/20va) and feed
> directly into part U6 and U3?  Part U6 is outputting 15v and U3 is
> outputting 5v.  I would assume that U6 amd U3 both have the same
> input voltage (35v per digikey specs?).  Then I could just have the
> power jack and fuse without the bridged rectifier.

Actually the 35v limit is only for the 5v regulator,  the other one will 
handle up to 40v in,  but then you need to consider how much power each of 
those will have to dissipate to regulate things properly.  For example if 
you're putting 20v on the input then the 5v regulator is going to be dropping 
15v -- at an output current of (say) 1A,  that's 15W of power being wasted.  
It'll also need a pretty good heatsink to keep working.

But if current is fairly small,  this shouldn't be a problem.

Yes,  you can do that,  leaving out the bridge and just feeding some DC right 
into those regulators.  Better still would be feeding in two levels of DC,  
closer to what the regulators want to see as a minimum,  but that's not a 
problem if the load currents are small.