DEC H744 +5 supply

[Noel Chiappa]

    > From: Brent Hilpert

    > In typical "down-converters" there are additional current paths in the
    > supply, paralleling the input path, that can provide the 'additional'
    > electron flow rate. ... the whole rationale of a switching supply is to
    > use time (varying switching periods) and temporary energy storage to
    > change that EI relationship from input to output without energy loss.

So, two more questions (if you have the time):

I can see that there's a nice synergy between the switching concept and the
buck converter (since the switch does exactly what the buck converter needs,
in terms of turning the input current off and on), _but_ - are there switching
supplies that operate the way I described (up-convert the frequency, then use
a transformer to get directly to more or less the right voltage)? I.e. without
needing to use a buck converter to do the conversion from low current at
higher voltage to higher current at lower voltage? (Although I guess the coil
for the buck might be cheaper than the transformer - even though the use of a
high frequency would reduce the size of the latter - making the buck approach
superior.)

To put it another way, there's no _necessary_ connection between the switching
concept, and the buck converter is there? Does that mean it is in theory
possible to stick a buck converter on the output of a linear supply to do the
V1I1-> V2I2 conversion? (Although I know it's probably a stupid design, because
you'd still need some sort of switcher for the buck converter, so the linear
supply would be basically pointless.)


    > If the heatsinks seem huge compared to modern day supplies, that's more
    > likely the result of technology improvements - faster devices, and
    > moving from bipolar switching transistors to mosfets. Bipolar
    > transistors have a near-fixed voltage drop which can't be reduced

Right, I knew bipolars had the fixed drop, but I hadn't made the connection
to that being the cause of the large amount of heat needing to be dumped.
Useful enlightenment!


    > If you supply a link & location to a schematic I'll take a look

Here:

  http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/H744.tif
  http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/H744.jpg

Thanks to everyone for taking the time and energy to reply!

	Noel