The "ref" supply NEEDS to be bipolar (have 3 output posts), that is, have +12V, 0V/GND, and -12V outputs.
Measuring DCV between +12V and -12V posts with a multimeter should read +24V.
That GND must be connected to +S/+OUTPUT.
My ref transformer is a DP241-5-28 2x14 .400 mA centertap. That will give me my ground for the TL431s, and the fully isolated supply. At least that is what I think will happen.
Using the center tap as GND, am I correct?
Yes.
See attached (first power supply) and
simulation here.
Falstad doesn't have 7812/7912 regulators so I just labelled the place where they belong; follow your full schematic. Notice the GND symbol on the transformer CT, between bulk caps, 7812/7912 middle pins, anode of lower TL431, and center output connection.
The +5VREF is derived from the +12 as you've done with resistor+2*TL431 to GND (not the -12V post).
This is good to know because I used -12v for it. I am still not sure how they work to create 5v. But they sure do.
TL431 work like zeners; they shunt/clamp the voltage to their Vz voltage (or programmed via divider resistors on the adjust pin). The 1K resistor is important otherwise you'll kill the zener/TL431. However, shunt regulators are only good for low current loads or for reference use (your case). See
here and
here.
The "bulk" supply can be just +12 (to +20V) between 2 output posts (not bipolar).
One of the supplies must be fully isolated from PE; have NO continuity from any output post to PE or the (wide) neutral prong (on a polarized wall plug). The latter shouldn't really exist but check anyway.
I have the Transformer a 266L24 2x12 and it can be a 2a or 4a depending on using one or two windings selected by the range switch. I understand I can wire it and use it like a center tap. GND the chassis with the PE not the center winding like the REf. Is that correct?
I think I am just going to wire the Transformers and the bridges and at least know my power is correct.
See attached (second "bulk" power supply).
You still want to keep both ref and bulk supplies isolated from PE; leave that option for the user on the front panel.
Fortunately, the
266L24 secondaries
can be wired in series or parallel. See attached for how to wire a DPDT switch for series/parallel duty (from
this "Series/Parallel Switching" diagram). The 470R resistor (R1) is to discharge the cap when changing the switch position to the lower voltage. However, you'll likely need another pole (3PDT) for the switch to short R32+R33 in the CREF generation part of the complete schematic (not shown here).
Wire the primaries for the
DP241-5-28 transformer the same way as shown in the
Hammond connection diagram (notice the dots on the windings). In the DP251-5-28 case, F2 connected to F1 is one mains phase and S2 connected to S1 is the other mains phase. Don't make a mistake or you'll kill the transformer; wire up the mains fuse.
Before proceeding with the regulator parts, wire-up the ref and bulk supplies and confirm that they are producing:
ref: +12V, +5V, -12V relative to 0V/GND (black multimeter lead).
bulk: +12 or +24V (depending on switch position) relative to 0V (black multimeter lead).