Bridge rectifier circuit having active switches and an active control circuit

[54] BRIDGE RECTIFIER CIRCUIT HAVING ACTIVE SWITCHES AND AN ACTIVE CONTROL CIRCUIT

[75] Inventor: Stephen Wong, Scarsdale, N.Y.

[73] Assignee: Philips Electronics North America
Corporation, New York, N.Y.

[21] Appl. No.: 268,705
[22] Filed: Jun. 29,1994

[51] Int. CI.6 H02M 7/217

[52] U.S. CI 363/127; 363/125

[58] Field of Search 363/127, 128,

363/147, 123, 125, 126, 181, 84, 89; H02M 7/217

[56] References Cited

U.S. PATENT DOCUMENTS

3,883,701 5/1975 Zelinaetal 321/5

4,473,757 9/1984 Farago et al 307/127

4,535,203 8/1985 Jenkins et al 179/81

4,590,547 5/1986 Goinga 363/127

4,618,922 10/1986 Hartranft et al 363/127

4,716,514 12/1987 Patel 363/127

4,777,580 10/1988 Bingham 363/127

4,819,147 4/1989 Bingham 363/127

4,866,585 9/1989 Das 363/8

4,922,404 5/1990 Ludwig et al 363/89

5,055,994 10/1991 Schoofs 363/127

5,103,389 4/1992 Kleffstra et al 363/127

FOREIGN PATENT DOCUMENTS

0112119 6/1984 European Pat. Off. .

63-64572 2/1988 Japan.

2131635 6/1984 United Kingdom 363/127

85/01161 3/1985 WIPO 363/127

OTHER PUBLICATIONS

"MOSFETs Move in on Low Voltage Rectification", R.
Blanchard, Director of Engineering and R. Severns, Sr. Staff
Engineer, Central Applications, PCI Oct. 1984 Proceedings,
pp. 213-222.

Primary Examiner—Peter S. Wong
Assistant Examiner—Adolf Berhane
Attorney, Agent, or Firm—Steven R. Biren

[57] ABSTRACT

A bridge rectifier circuit uses active switches for at least two of its four rectifying elements, and employs an active control circuit to control the state of the active switches. The active control circuit receives its input from the AC input to the bridge rectifier circuit, is powered by the DC output of the bridge rectifier circuit, and provides control outputs to the active switches. In this manner, a bridge rectifier circuit having improved performance and decreased power dissipation is achieved.

7 Claims, 2 Drawing Sheets

1

BRIDGE RECTIFIER CIRCUIT HAVING ACTIVE SWITCHES AND AN ACTIVE CONTROL CIRCUIT

BACKGROUND OF THE INVENTION

This invention is in the field of bridge rectifier circuits, and relates more particularly to bridge rectifier circuits having active switching elements.

Typical prior-art bridge rectifier circuits use four diodes in a bridge configuration having two AC input terminals and two DC output terminals, and serve to convert an AC input voltage into a DC output voltage. Perhaps the most common use of such bridge rectifier circuits is to convert an AC input 15 voltage derived a power line into a DC voltage which is subsequently filtered and used to power electronic circuits.

Although the simple four-diode bridge rectifier circuit performs its intended function adequately, it does suffer from a number of drawbacks, particularly in high-current 20 applications. Because of the inherent forward voltage drop (typically 0.7 volts or higher) across each diode, significant amounts of power can be dissipated in the bridge, particularly when large currents are involved. This unwanted power dissipation requires the use of larger components and gen- 25 erates unwanted heat, drawbacks that are particularly bothersome in integrated circuit applications.

To overcome these drawbacks, prior-art bridge rectifier circuits were developed in which MOS transistors were used to replace at least two of the diodes in a conventional bridge 30 rectifier circuit. The advantage of using transistors instead of diodes in this application is that an MOS transistor, when turned on, provides a substantially lower voltage drop (in the order of 0.2-0.3 volts) thus reducing power dissipation and heat generation as compared to diode rectifiers. 35

When MOS transistors are used as rectifying elements, however, additional circuitry must be provided to turn the transistors on or off at the appropriate times. In the prior art, this function is accomplished by connecting the gates of the MOS transistors (either directly or through a network of 40 passive components) to the AC input voltage terminals, thus providing a simple and reasonably effective source of control voltage to appropriately switch the MOS transistors. However, since this technique results in a sinusoidal control voltage, with a slow transition from low to high voltage, the 45 MOS transistors will not be efficiently switched, and will be only partially on during a significant portion of the duty cycle. This results in a relatively high on resistance during this portion of the duty cycle, thus resulting in higher power dissipation and substantially reducing the advantage 50 achieved by substituting MOS transistors for diodes as rectifying elements. Furthermore, the variable resistance of the MOS transistors may result in undesirable "glitches" in the output waveform when the circuits are required to carry large currents. 55

Accordingly, it would be desirable to have a bridge rectifier circuit in which voltage drop, power dissipation, heat generation and output waveform "glitches" are all minimized.

SUMMARY OF THE INVENTION

It is thus an object of the invention to provide a bridge rectifier circuit having active switches such as MOS tran- 65 sistors, in which an active control circuit is used for greater switching efficiency, in order to minimize power dissipation,

2

heat generation, voltage drop and undesirable "glitches" in the output waveform.

It is a further object of the invention to provide a bridge rectifier circuit having the aforementioned advantages which is relatively simple and compact in design, and relatively economical to manufacture.

In accordance with the invention, these objects are achieved by a new bridge rectifier circuit in which at least two of the rectifying elements are active switches, and in which an active control circuit is provided for controlling the state of these active switches. The control circuit receives its input from the AC input terminals of the bridge, provides control outputs to the active switches, and is powered from the DC output terminals of the bridge.

In a preferred embodiment of the invention, the two rectifying elements of the bridge rectifier circuit which are at the lower DC potential are provided as MOS transistors, with the control circuit outputs being provided to the gates of these MOS transistors.

In a further preferred embodiment of the invention, the control circuit is composed of a comparator circuit for sensing the level of at least one of the AC input terminals with respect to a reference voltage, such as the lower DC potential. The comparator circuit can be formed of a bipolar transistor having a main current path coupled between the DC output terminals of the bridge rectifier circuit and a control electrode coupled to one of the control inputs by a diode.

When the bridge rectifier circuit of the invention is used in high-voltage applications, a voltage regulator circuit may advantageously be provided to supply a regulated DC voltage derived from the DC output terminals to the comparator circuit.

BRIEF DESCRIPTION OF THE DRAWING

The invention may be more completely understood with reference to the following detailed description, to be read in conjunction with the accompanying drawing, in which:

FIG. 1 shows a partially-schematic and partially block diagram of a bridge rectifier circuit in accordance with the invention;

FIG. 2 shows a schematic diagram of a bridge rectifier circuit in accordance with a first embodiment of the invention;

FIG. 3 shows a bridge rectifier circuit in accordance with a second embodiment of the invention;

FIG. 4 shows a schematic diagram of a comparator circuit suitable for use in the bridge rectifier circuit of FIG. 2;

FIG. 5 shows a comparator circuit suitable for use in the bridge rectifier circuit of FIG. 3; and

FIG. 6 shows a voltage regulator suitable for use in the bridge rectifier circuits of FIGS. 2 and 3.

DESCRIPTION OF THE PREFERRED
EMBODIMENTS

Abridge rectifier circuit 10 in accordance with the invention is shown in partly-schematic and partly-block diagram form in FIG. 1. The bridge rectifier circuit includes four rectifier elements 20, 22, 24 and 26 connected in a bridge configuration between AC input terminals 28, 30 and DC output terminals 32, 34. An AC input signal source 36, typically an AC mains or line voltage input, is applied across the AC input terminals 28 and 30, and a filter capacitor 38