DEC H744 +5 supply

Brent Hilpert bhilpert at
Fri Sep 21 18:56:30 CDT 2018

On 2018-Sep-21, at 4:03 PM, Noel Chiappa via cctalk wrote:

>> 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.)

There are a thousand configurations for power supplies possible depending on what needs to be accomplished: circuit isolation (e.g. mains from load), EI conversion up or down, degree of regulation, economy tradeoffs, etc.

An example that perhaps fits what you're thinking of is the old motor-generator setups which convert 60Hz to 400Hz, the 400Hz then being used as input to a variety of supplies.

It's useful to keep in mind that regulation and EI conversion are different objectives but they can be achieved either separately or in concert.
What we commonly refer to as a "linear power supply" does EI conversion (and circuit isolation) in one stage (the transformer), followed by an independent regulator stage.
Your common modern generic switching supply integrates EI conversion, regulation and circuit isolation into one feedback loop across one transformer (switching at high frequency).

A buck converter is inherently a switching converter, the buck operation requires the switching to function.
There is a corresponding boost converter with a different circuit topology around the inductor, for . .  boosting voltage.
There are also boost-buck converters.

Dropping 5V to 3.3V or 1.xV for ICs is often accomplished with little on-board buck converters which you may not have realised were there, to avoid the losses and heat of a linear regulator.

>> 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:
> Thanks to everyone for taking the time and energy to reply!
> 	Noel

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