


September 23, 1986


To: Norm Kelly


From: Robert Briody


Subject: Diskless Node power supplies


I have looked at over 30 power supply manufactures in hopes of finding a 
supply for the Diskless Node. Power General and Todd appear to be the only
manufactures of supplies that will closely suit our electromechanical
requirements. The other manufacturers build supplies which have inadequate
electrical output given our mechanical needs. The supplies which meet our
electrical needs are typically 12 to 15 inches in length. The maximum power
supply chassis length the Diskless Node can accomodate is 9.75 inches without
any modifications, 11.00 inches if the control logic PCB is relocated, and
11.50 inches if the control logic PCB is relocated and a different AC power
entry module is used.

The following OEM power supply manufactures were looked at during my search
for a switching supply for the Diskless Node:

ACDC Electronics
Boschert
California DC
Calex
Cherokee International
Condor
Computer Products - Packaged Power
Conver
Deltron
Digi-Power
Elpac
GFC Hammond
KEC
Kepco
Lambda
Modern Power Conversion
National Power Technology
Poineer Magnetics
Power One Electronics
Potter & Brumfield
Power General
RTE Power Mate
RO Associates
QSI
Sierracin Power Systems
Standard Power
Switching Power
Switching Systems International
Todd
Ulveco
Xentek

Conver said they could build a custom supply to meet our needs. The cost of the
supply would be as follows:  NRE charge: $8,000.00, 100 piece pricing: $460.00,
200 piece pricing: $380.00. UL and CSA certification would be an additional
$2,000.00 each!

Power General responded to our requirement and said they would have to redesign
their 4300 supply and re-layout the PC board. Jeff Kelly of Power General said
he would talk to their engineering group and come up with new pricing (and
the NRE charge). I expect this figure to be between $8000.00 and $15,000.00.
The OEM price for 100 pieces would be approximately $175.00. Unless the yearly
volume of Diskless Nodes shipped reached the 1,000 to 1,500 pieces per year 
level, a custom supply is not a cost effective solution to our problem.

According to an engineer at Todd, the 220 watt supplies' +5 VDC supply output
is current limited by a schottky diode and not the transformer. The MBR3045PT 
diode's maximum forward current rating of 30 amps is a limitation of its die
and NOT a thermal limitation. It would be necessary to parallel a second
schottky diode across the existing diode. An applications engineer at Motorola
said the forward voltage of the rectifier varies approximately 50mV between
devices. A V(f) difference of 50 mV will mean a minor imbalance in forward
current shared by the two paralled devices. A +12VDC to -5.2 VDC inverter
would have to be added to the supply as the Todd is configured as a 3 output
supply. This could be easily done on a separate PCB and mounted to the 
heatsink of the Todd supply with an "L" bracket. Both of these modifications
could be done without disassembling or drilling holes in the supply frame.

This leaves us three possible solutions to the Diskless Nodes' power supply
problems: 1) Power General could manufacture a custom supply that would be
taylored to the systems needs. 2) Its possible that ISI could modify a Todd
220 watt supply to suit our application. The Todd 220 watt supply costs $209.00
in the 100 piece volume. (Note that a fully configured Diskless Node consumes
207 watts.) 3) Todd manufactures a 300 watt supply that is physically smaller
than other manufacturers 220 watt supplies. Its outputs are capable of handling
the Diskless Node in all of its configurations including a disk-based version.
The 300 watt supply is 11.50 inches in length. The control logic PCB would have
to be relocated and a new AC power entry module would have to be used. A new 
piece of sheet metal would have to be fabricated to accomodate a change in the
power entry module. The 300 watt Todd has a 100 piece price of $296.00.

It is important to note that if solution 1 is chosen, the supply may not
support the disk-based version of the Node.



cc:	Doug Swartz

