Browse Prior Art Database

Auto Preregulating Converter with Surge Control

IP.com Disclosure Number: IPCOM000051300D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 4 page(s) / 47K

Publishing Venue

IBM

Related People

Dobberstein, EA: AUTHOR

Abstract

Converter circuits are used to derive a DC voltage from an AC source, such as a utility line. The usual technique is well known and quite simple, and consists of rectifiers in a bridge or doubler arrangement followed by a large filter capacitor. In typical applications, AC-to-DC converters are used as a source for a higher frequency switching circuit that provides the low voltage power supply functions of line isolation, transformation, and regulation.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 41% of the total text.

Page 1 of 4

Auto Preregulating Converter with Surge Control

Converter circuits are used to derive a DC voltage from an AC source, such as a utility line. The usual technique is well known and quite simple, and consists of rectifiers in a bridge or doubler arrangement followed by a large filter capacitor. In typical applications, AC-to-DC converters are used as a source for a higher frequency switching circuit that provides the low voltage power supply functions of line isolation, transformation, and regulation.

These simple converters have some shortcomings, among which are (1) extremely high surge currents that occur upon initial application of the AC input or upon recovery of the AC input following an interruption of several cycles and
(2) variations in the DC output that are at least as great as the AC input voltage variations.

Usually high surge current is corrected by a series resistor which is bypassed by an electromechanical relay after power-on or by thermo resistive devices which have high resistances when cool. Voltage variation has been corrected by following the converter with a time ratio controlled switching preregulator. Through effective, the series switching transistor must accommodate the highest expected line input voltage.

The circuit of the figure is intended to provide both surge control and "coarse" regulation of the broad range of line voltage variations without either relays or thermo-resistive devices for surge control, and without feedback from either the DC converter voltage or some subfunction of it. As a result, no amplifiers, optical isolators, or special bias supply voltage are required, and the response to line voltage variations is especially fast. To accomplish this result, the circuit makes use of an unusual application of silicon unilateral switch (SUS), reference diodes, and resistor-capacitor networks which establish the gating angle for silicon- controlled rectifiers (SCR).

Referring to the figure, the combination of C11, D7, D8, SCR-1 and SCR-2 represent a full-wave bridge rectifier with filter. A rearrangement of the SCR and diodes will form a "doubler" circuit. When C11 is large enough, it becomes a "peak" filter. If the SCRs are triggered after the peak of the wave, the C11 voltage becomes a function of point-in-time of the triggering (e.g., phase control).

In the past, the control function was obtained by sensing the DC converter voltage (or some subsequent function thereof), comparing it to a reference, amplifying the difference, and adjusting the gating angle as a function of that difference. The circuit in the figure, in contrast, uses certain properties of the SUS to establish the phase control. The parameter sensed is the instantaneous value of the AC input voltage, as opposed to the converter DC voltage output.

The preregulating circuitry consists of two symmetrical halves, one of which includes SUS-1, C1, R3, Z1, R1, C3 and D1, and the other of which includes SUS-2, C2, R4, Z2, R2, C4 and D2...