DEC standard modular regulators

The DEC standard modular regulators (not a formal DEC term) were a series of modular power supply units, used primarily in the H742 Power Supply of the BA11-F Mounting Box and the H765 Power System of the BA11-K mounting box. (They are also occasionally found in other locations.)

Supported regulators include:

• H744 +5V Regulator (and later versions, H7440 and H7441)
• H745 -15V Regulator
• H754 +20V, -5V Regulator

These regulators all used switching techniques (likely one of the earliest switching power supply designs); they differed from later switching supplies (which generally dispense entirely with a large transformer as the first thing on the AC input), in that they take as input 30V AC supplied by the 'mother' system using a large (and heavy!) isolation/step-down transformer.

Although the DEC technical manual does not make this clear, the output stage is increasing the output current, over the input, in order to have high overall efficiency. It uses what it called a buck converter, where some of the energy from a 'block' of incoming high-voltage current is stored in the magnetic field of a large inductor, and then used to supply current when the DC from the initial AC/DC converter stage is turned off by the switching function of the supply.

This allows these regulators to be much more efficient than a linear power supply, where excess voltage (and its energy) on the fixed current throughput is simply discarded. Ironically, the large input transformer would be even larger and heavier were it not for this efficiency gain (which means less input power is needed to reach the desired output), and the fact that the current in the secondary is lower because of the higher output voltage (which the switching supply can use efficiently, above).

The 7014251 +12VB and +5VB Battery Backup Regulator, used with the H775D Battery Backup Unit, is another in the series.

Connectors

All use a common connector (which carries both input and output conductors), an 8-pin 'Commercial MATE-N-LOK', made by AMP. The power harness uses a female shell (housing) with male pins; the regulators use a male shell with female sockets (pins).

The female shell is AMP part # 1-480460-0, pin part # 60620-1; the male shell is part # 1-480459-0, pin part # 60619-1. (There are a large number of different pin options: 30-22, 24-18, and 20-14 gauge; tin and gold plated; and brass and phosphor-bronze material. The part numbers given are for tinned brass, 20-14 gauge.)

The Commercial MATE-N-LOK line is now made by TE Connectivity, who bought AMP. Unfortunately, they have ceased production on these two shells (although the pins are still being made). Some vendors still have stocks, though; as of July, 2018, ConnectorPeople and Quest still had some in stock.

Pins 6, 7 and 8 of the common connector are used for the AC input, but each of the three types of regulator uses a different pair of pins, with the third left un-connected; thus, if a regulator is plugged into the wrong connector on the power harness, no harm results.