"Jim Thompson" wrote in message
...
I asked for a description of WHAT you were trying to do. Schematics
and PCB layout did me no good, so I helped others.
I had sent you a fairly complete project outline
ETI_Next_Gen_Test_Set_PI-200.doc with my initial contact email sent on
December 18. But that was rather comprehensive and included the entire
design, whereas I later condensed my requirements to just the high-isolation
DC-DC converter, which mostly involved the transformer design and the driver
to obtain about 6-9 VDC at 300 mA from a 12VDC supply. The schematics
included my design for that subcircuit, and I really just wanted your
opinion on how the board should be laid out to achieve the safety and
isolation of the 480 VAC mains.
My description of this portion of the design, from my email of January 6,
2012:
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I think the most reasonable approach at this point is to have you design a
small, but important, component of the system. The document I sent you
described the unit and some of the components, and most of that has already
been designed. But I am now working on the SCR gate drive, which requires a
high isolation DC-DC converter. I am getting quotes on the transformer I
need for this, but perhaps you can help. Here is what I have sent to some
local transformer shops we have used:
I am designing a new SCR trigger board for a smaller test set (PI-200, for
which you recently provided a transformer quote), but may also be used for
the larger ones, and I will need a special transformer for a DC-DC converter
for the gate drives. I will supply a 12 V P-P square wave to the primary,
and the secondary will be a full wave bridge using Schottky rectifiers to
produce a nominal 8VDC at about 400mA. I was planning to use a switching
frequency of about 20-40 kHz, to keep the transformer size small. But I need
to have isolation and safety for use with nominal 480 VAC mains. The best
commercial DC-DC converters I could find are the:
http://www.powergatellc.com/traco-po...converter.html
They are rated 4000 VRMS isolation but for continuous duty only up to 300V.
I would like a transformer that is no larger than these units (about 1.5â
x 1â x 0.5â), and I can supply the drive and output electronics. I am
designing the circuitry now and I plan to design the PC boards in about a
week, so I need at least the basic form factor that a custom transformer
would take.
I think a split bobbin design might be best, something like the Atech
ATS-075A. (See attached files). It has 3750 VRMS hypot but itâs 600 ohms
impedance. I have one and it appears to have steel laminations. That is
probably OK for 20 kHz but maybe ferrite is better if I use 40 kHz.
The Triad CSE187L is also the right size, but the split bobbin is of unequal
size, since it is a current transformer with a single turn 30A primary.
I have also made a transformer using a ferrite toroid and about 30 turns of
#26 enamel wire. But I donât know if the coated core can be trusted for
480 VAC use.
However, perhaps I can just use some very well insulated wire (perhaps
Teflon) for the primary and secondary of a toroid (or other type). If the
insulation is rated to withstand 480-600 VAC continuous then that would be
another option.
I have also found some laminations from Thomas Skinner
http://www.thomas-skinner.com/index.html that are 0.75âx1.00â (EE-24-25)
of 4-14 mils thickness, and I found a good selection of bobbins from
http://www.cosmocorp.com/en/corp-overview.cfm.
That should be enough to get you started. I have the PCB laid out for the
Atech ATS-075, but I can easily modify the decal for another type. But I
would like to have the size be not much larger. Maximum is about 1â square
and about 0.75â high. Basically I have 12 VDC available and Iâd like to
get about 8 VDC at a minimum of 300 mADC for the gate drive of the larger
SCRs. But if that causes a size problem, Iâd be OK with about 5 VDC at 250
mA.
And a major consideration is the 480 VAC mains. I plan to use the 1.25A 600V
SMT fuses for the gate and cathode wires, as discussed in S.E.D. recently.
Littelfuse 04611.25ER, Newark 34C6800
================================================== ===========
I don't know what more you need. And I was using this as a test to see if
you could offer help for other things in the future. Oh, well. There are
others who may be able to help with other issues. Good luck on your
renovations and main project. And please don't continue this ongoing
argument with Larkin, or at least snip all the previous worthless chatter.
What was it you said about his wife that got him all riled up, anyway?
Paul