The standard DEC power supply configuration uses three-phase power. The H760 power supply uses three ferroresonant transformers with their primaries wired in a three-phase delta arrangement. The secondaries are are each wired to a half-wave bridge rectifier, and the rectifiers are paralleled to provide -12V DC at 490A.
A capacitor assembly of thirteen 300,000 uF capacitors is connected between the H760 and the H761 in order to provide a 20mS delay from power failure to the time the DC level reaches -7.5V.
The H761 Regulated Series Pass Assembly consists of multiple linear regulators with sensing. It provides ten outputs of -5.2V at 35A (only nine of which are used), and four outputs of -2.0V at 35A.
Since linear power supplies are used, this provides a rated output of 1918W, while requiring around 6000W of input power. Approximately two thirds of the power is lost in the power supply!
This is why I want to replace the ECL power supply system of the KL10 with modern switching power supplies. Modern switchers are around 85% efficient, so they can supply the 1918W of DC while only requiring only about 2257W of input power.
Commonly available 5V switching supplies are readily adjusted to 5.2V. However, 2V switchers are somewhat more difficult to find.
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Last updated July 26, 1997
Copyright 1997 Eric Smith
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