26 Feb
2005
26 Feb
'05
11:22 p.m.
At 10:35 PM 2/25/05 -0500, you wrote:
basically to get the constant voltage output even when
the AC supply goes
from 90 to 120. A normal transformer will "follow" the line voltage. The
power supply board uses schottky diodes and the transformer puts out just
enough voltage to be regulated to five volts with minimal power loss (there
are a couple of other secondary windings for + and - 12 for RS232). With a
normal transformer, the power supply design would have to been different to
deal with the higher wattage that it would have had to dissipate.
I understand all that but AC power is cheap and so is a fan to dissapate
the excess heat. It's surprising to see a company spent money for features
like this unless there is a very real requirement for them. Even HP doesn't
go to this length with their power supplies.
The
transformer was custom wound for AMC.
And expensive I'll bet!
By the way, the EM189 was a 6809 emulator...
Oops. I guess it was late and I was tired. I had it setting right in
front of me and I still got it wrong. I should have said EM-180B. I'd sure
like to find a pod for it but it doesn't look likely. BTW I'm assuming
that the transformers for the various models all put out the same voltage.
Is that true?
Joe
the resonant tran
At 10:09 PM 02/25/2005, you wrote:
Thanks for the info Steve. I have a EM-189
(Z-80) that's missing the pod
so I guess I can rob the x-former out of it.
I'm curious, why did they use a resonant transformer?
Joe
27 Feb
27 Feb
12:55 a.m.
first, you can't consider an under the covers part a feature... there are
plenty of small companies out there doing transformer winding so cost
wasn't that much more than a standard transformer. Keep in mind that this
product was developed back in the late 70s/early 80s. It was before small
switching supplies and you couldn't find a standard transformer with three
secondary taps anyway. There was room for one transformer and adding a fan
would have made noise. In the long run, you would have had to dissipate
more power, require larger parts for the power supply section along with
heatsinks, require a larger cabinet, and added a fan that made noise. The
box retailed for around $4K and these were sold in the hundreds. If it was
a higher quantity product, then cost reduction would have been more important.
secondly, all the EM series used the same transformer for 110V 60Hz.
best regards, Steve
At 08:22 AM 02/27/2005, Joe R. wrote:
At 10:35 PM 2/25/05 -0500, you wrote:
basically to get the constant voltage output even
when the AC supply goes
from 90 to 120. A normal transformer will "follow" the line voltage. The
power supply board uses schottky diodes and the transformer puts out just
enough voltage to be regulated to five volts with minimal power loss (there
are a couple of other secondary windings for + and - 12 for RS232). With a
normal transformer, the power supply design would have to been different to
deal with the higher wattage that it would have had to dissipate.
I understand all that but AC power is cheap and so is a fan to dissapate
the excess heat. It's surprising to see a company spent money for features
like this unless there is a very real requirement for them. Even HP doesn't
go to this length with their power supplies.
The
transformer was custom wound for AMC.
And expensive I'll bet!
By the way, the EM189 was a 6809 emulator...
Oops. I guess it was late and I was tired. I had it setting right in
front of me and I still got it wrong. I should have said EM-180B. I'd sure
like to find a pod for it but it doesn't look likely. BTW I'm assuming
that the transformers for the various models all put out the same voltage.
Is that true?
Joe 
6:01 a.m.
----- Original Message -----
From: "Joe R." <rigdonj at cfl.rr.com>
I understand all that but AC power is cheap and so is
a fan to
dissapate
the excess heat. It's surprising to see a company spent money for
features
like this unless there is a very real requirement for them. Even HP
doesn't
go to this length with their power supplies.
CVTs (resonant xfmrs) have the big advantage that they significantly
reduce lots of noise and transients and such nasties that would
otherwise cause havoc on a logic supply rail. They also provide a
pre-regulating function to reduce the voltage range the following DC
regulator has to handle.
I think pre-regulators used to be fairly common in higher power
regulated DC supplies- always thought it was due to limitations in the
semiconductors available at the time. Saturable reactors on the
primary side were often used - SCR based secondary side stuff came a
bit later.
DaveB, NZ
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