9 May
2023
9 May
'23
5 p.m.
On 2023-May-09, at 12:28 AM, Brent Hilpert via cctalk wrote:
I thought I must be off somewhere by 10^n when first
doing the calc. The 51Ω is 3 orders of magnitude away from the 0.01Ω on the other outputs,
so a similar diff could be anticipated on the current sense.
The low current sense might be explained as follows:
...
I'm speculating the unusual shunt regulator in the
-12V output is actually a 'controlled freewheeling diode' for a -12V bucking
step-down. The choke would be stepping down the voltage from the -12 output secondary from
something higher down to the actual -12V output. With a higher V from the secondary, a
lower current is needed for the same energy throughput, and thus sense on a lower max
current from the secondary. However, one would anticipate the regulation V sense point in
such operation to be on the other side of the choke than what's shown in the
schematic.
Thinking further this morning. The TIP121 is the wrong orientation or polarity to be
acting as a freewheeling conductor (--explanation). However, that's the transistor
section. The 121 has a built-in flyback diode which is the right orientation
(++explanation). Still some things that don't make sense though, like the high EI
ratio needed from the order 100 I difference (--explanation), and how the load current
would be supplied during the charge portion of the cycle (--explanation).