This is a description of Preamp Power Supply.

The primary consideration of the new power supply is to keep changes to the existing system at a minimum. Water and AC power will be sufficient to operate the new system. Secondary to this is to physically reduce the dimensions of the supply to allow it to fit completely in the available space.

Increasing the speed of the electronics has caused the power requirements to go from 520 Watts to 1810 Watts delivered, and yet the volume the supply occupies actually needs to be reduced. In order to meet this new power requirement a switching type supply will have to be utilized.

The presence of a magnetic field further complicates supply construction. Although the field is not considerably high, 200-300 gauss, its volume is very large (over 6 m x 6 m x 6 m). The supply volume 10-1/2 x 10-1/2 x 18 makes shielding somewhat difficult. The supplies will be built around a commercial Vicor MegaPAC that will operate from the present 20Amp 208VAC source. Here are the views of the Vicor, Top Side and Back.

Testing has shown that these supplies fail when operated in a field of more than 175 gauss with the orientated in the vertical direction. To reduce the field to an adequate level, a two part shielding scheme will be utilized.

The first level for shielding is in the form of a thick hot rolled steel box. This provides the main reduction of the magnetic field to a manageable level and is the main chassis that houses the supply module.

The second level of field reduction is a smaller magnetic shield, which surrounds the Vicor supply. This second shield directly encloses the Vicor chassis.

Since the supply will be enclosed in a steel chassis cooling is required. Cooling water will be used on heat producing objects inside the box. Each Vicor module is fitted with a copper tube for cooling.

The Preamp supply will provide three separate voltages to power the Preamp hybrid circuits. The power levels are 12.5V @ 48Amps, 8.5V @ 100Amps and 6.5V @ 30Amps. This power will be supplied to each column of 24 motherboards. Monitoring will be implemented so the voltage and current can be monitored via a computer connection. In addition if any voltage or current exceeds a set level all output voltages will be disabled. This is done to prevent the application of partial power to the hybrids. The supplies have fuses on the primary 208VAC input and a solid state 3-phase relay to control main power to the Vicor supply. There is a local On/Off, Reset and Local/Remote switch on the front panel. There are LED indicators for local information.

The Vicor supplies have a built-in analog temperature sensor that is used for monitoring. This signal is 2.5V/25C and has a range of 0-100C. There are signals for Phase Fault, Over Temperature Warning and AC Power OK that will be inputs to the logic control circuitry.

There will be two conditions that will turn the supply off in the event of a fault condition. The first condition occurs when a monitored supply exceeds a preset level for more than 30 milliseconds. This can be considered a normal fault condition. This type of fault only inhibits the outputs of the Vicor and latches the fault until cleared.

The second condition occurs when either an External Interlock, phase fault or temperature warning from the Vicor is false. The main 208 AC power to the supply will be removed when this occurs. The thought here is that a more serious fault or problem has happened and more direct measures should be taken. This might be caused by a direct failure of a module which fails to respond to a normal inhibit signal or smoke or water was detected. This fault must last for more than 8 milliseconds before the fault is issued.

A third and final level of protection are in-line fuses on each output. This will ensure that wire currents will not exceed NEC code. The fusing is above the normal operating levels and should not open under a normal fault condition.

Logic control will be implemented with a programmable logic gate array. This provides the best flexibility and size reduction for the power supply system.

Control power (+5V and +/- 15V) will be a separate supply that will be ON whenever the AC is applied to the box. This small supply is fused.

Additional temperature sensors will be instrumented to reflect the plate temperature for the current sensing shunts and the blocking diodes on the output.

A hall probe will provide magnetic field information inside the steel shell but outside the final magnetic shield around the Vicor supply.

The supplies run without remote sensing, therefore the voltage dropped on the power harness must be adjusted for. Each master module has a connector that can accomidate a resistor to increase the output voltage of each rail. The values are...
600K for the A(+12V)
360K for the B(+8V)
188K for the C(-6V)
. These trim resistors will increase the output by about 0.5V which is the approximate drop of the cabling. The trimmers are placed on the first and third pin in the upper part of the connectors as seen here.

The complete supply
Front
Back
Left
Right