H744 +5V Regulator

The H744 +5V Regulator is one of the DEC standard modular regulators. It can produce an output current of up to 25A at an output voltage of +5V; the later (short-lived and rare) H7440 +5V Regulator could also produce up to 25A, and the replacement H7441 +5V Regulator up to 32A. All had over-current and over-voltage detection and protection.

It was a switching power supply, one of the earliest; however, the basic concept was somewhat different from later supplies of this type. It takes as input AC at a voltage of 20V-30V, runs it through a diode bridge and filter capacitor to convert it to DC. That is then run through a large transistor controlled by a monolithic integrated circuit voltage regulator and an inductor to do VI conversion using a buck converter, and produce the output.

The H744 and H7440 took their AC input on pins 6 and 7; the +5V output was on pins 2 and 5, and the ground return on pins 3 and 4; pins 1 and 8 were not used. In the H7441, pin 1 was also used for +5V output; the other pins were the same. Since it retained the use of only two pins for ground return, it's not clear what the utility of the third +5V pin was - perhaps it allowed machines to differentiate between H744's and H7441's?

External links

• PDP-11/40, -11/35 (21 inch chassis) system manual (EK-11040-TM-002)- the H744 is covered in Section 6.4.3 (pp. 112-114 of the scanned version)
• PDP-11/60 cabinet and power supply manual - the H7440 is covered in Section 3.3.2 (pp. 49-53 of the scanned version)
• PDP-11/40 system engineering drawings - the H744 is covered on pp. 205-208 of the scanned version