DEC H744 +5 supply

[Noel Chiappa]

	> From: Brent Hilpert

    > Your conceptualisation around the role of electrons is perhaps a
    > little off.

Well, I'm not taking into effect things like the velocity of electrons
passing around the circuit (more current, with the same number of electrons,
effectively), etc, but I value the 'electron-based-view' since it led me to
understand the issue of EI conversion (something I don't recall having seen
called out explicitly - e.g. it's not in that DEC tech manual).

(Speaking of reducing the number of electrons: I recall a physicist - don't
recall who - who jokingly suggested the reason they are all identical is that
there is only _one_ - it travel forward in time an an electron, goes back as
a positron; rinse, repeat! :-)

    > You don't need 'more' electrons to generate a higher current, you just
    > need to 'expend them' more quickly, using words like 'more' and
    > 'expend' loosely

Right, particularly since what's really happening (e.g. during the L
discharge phase) is that electrons are being 'borrowed' from the shells in
the atoms of the conductor, run around the circuit, and then returning from
whence they came.


    > Capacitors very much play a role in supplying current to the load.
    > Both the L & C play a role as energy reservoirs.

Right, but the C doesn't play a _direct_ role in the EI conversion, the way
the L does? (Or maybe it does - the voltage across the C could I guess play a
role in mobilizing electrons in the circuit?)


    >>> The transformer is nonetheless much smaller than it would be in a
    >>> straight linear regulator design because the secondary current it has
    >>> to supply is several factors lower than for a comparable linear reg.

    >> That's because of the higher efficiency of this circuit .. ?

    > primarily it's because it's still a higher voltage by several multiples
    > ... and thus the current that the transformer secondary has to deal
    > with is the same factor lower .. meaning less copper for the secondary
    > and less iron for the core.

Ah. Interesting tradeoff!

So it seems like they probably picked the intermediate voltage to be as high
as they could (to reduce the transformer cost), modulo the cost/availablility
of transistors for the switching...


    > I haven't seen/read this TofOp.

Here:

   http://www.bitsavers.org/pdf/dec/pdp11/1140/1140_SystemManual.pdf

if you're (still) interested; the H744 starts on pg 6-10 (pg 112 of the PDF).

	Noel