Rectifier circuit

Rectifier circuits which are usable, instead of diodes, for rectifying alternating voltages, and which, like diodes, form two-terminal networks having a cathode terminal and an anode terminal. The power loss of these rectifier circuits is clearly less that the power loss of silicon p-n diodes. These rectifier circuits also include voltage clamping functions.

FIELD OF THE INVENTION

The present invention relates to a rectifier circuit.

BACKGROUND INFORMATION

For the generation of direct voltages from AC voltages, at the present time mostly rectifier bridges are used which are made up of an interconnection of diodes.

The conversion of an AC voltage to a DC voltage takes place in a motor vehicle, for instance, in which an AC voltage is generated by a generator which is converted by a post-connected rectifier bridge to a DC voltage.

An example for such a voltage supply of a motor vehicle is shown inFIG. 1. This includes a generator device GEN which has an excitation winding G and radially connected phase windings U, V and W. The phase voltages provided at phase windings U, V and W are supplied to a rectifier bridge RF, which provides the desired DC voltage at its output. Rectifier bridge RF includes three bridge branches. In each of these bridge branches two silicon p-n diodes D are provided.

Conditioned physically, during a forward operation of a silicon p-n diode in rectifier applications, diode forward voltages of ca. 800 mV to ca. 2 V come about. These diode forward voltages, at meaningful dimensioning, are usually not able to be lowered below ca. 1 V. Therefore, especially in the case of the rectification of lower alternating voltages, power losses are created at the rectifier diodes. In generators used for the voltage supply of passenger vehicles, the alternating voltages that are to be rectified usually amount to about 17 V peak-to-peak between the terminals of two phase windings. Since the current flows via two rectifier diodes, because of the rectification, a voltage reduction is created averaging about 2 V. In this example, the power loss in the rectifier at corresponding load amounts to about 20% of the power output. The power loss converted in the rectifier has to be eliminated in the form of heat by costly cooling elements. In addition, the power losses directly affect the fuel consumption of the respective vehicle.

SUMMARY OF THE INVENTION

By contrast, a rectifier circuit having the features described herein has the advantage that the power loss is reduced, and for this reason, the expenditure for cooling may also be reduced.

This is achieved essentially in that, in a rectifier bridge, instead of silicon p-n diodes, rectifier circuits according to the exemplary embodiments and/or exemplary methods of the present invention are used, each silicon p-n diode of the rectifier bridge being able to be replaced by such a rectifier circuit. Circuit engineering changes of the overall system are not necessary. The rectifier circuits according to the exemplary embodiments and/or exemplary methods of the present invention require no separate power supply and also no separate signal inputs.

The forward voltages of silicon p-n diodes in rectifier operation can usually not be lowered below ca. 1.1 V. By using rectifier circuits according to the present invention, instead of silicon p-n diodes, the forward voltages are able to be lowered to ca. 25 mV. This makes it possible clearly to reduce the power losses of rectifiers and the expenditure for their cooling.

Further advantageous characteristics of the exemplary embodiments and/or exemplary methods of the present invention are yielded by the following explanation of exemplary embodiments with reference toFIGS. 2-7.

DETAILED DESCRIPTION

FIG. 2shows a rectifier circuit according to a first exemplary embodiment of the present invention.

The rectifier circuit shown inFIG. 2may be used, for example, in a rectifier bridge instead of a silicon p-n diode. It has a cathode terminal K1and an anode terminal A1, the same as a silicon p-n diode. MOS transistor T1and inverse diode D6are connected in parallel, and from a technological point of view, in this circuit, together they form a microelectronic component.

The rectifier circuit shown inFIG. 2has a symmetrically designed differential amplifier, which is formed by transistors T2and T3and resistors R1, R2and R3. A first input of this differential amplifier is connected via a diode D1to cathode terminal K1and the drain terminal of MOS transistor T1. A second input of this differential amplifier is connected via a diode D2to anode terminal A1. This differential amplifier amplifies the potential difference present between cathode terminal K1and anode terminal A1of the rectifier circuit. Because of the symmetrical construction of the differential amplifier, temperature differences and ageing effects act only slightly on the properties of the differential amplifier.

The output signal of the differential amplifier is available at the collector of transistor T3, and is passed on via a resistor R4to the input of a power amplifying stage. This power amplifying stage is made up of transistors T4and T5, whose bases are connected together. Zener diode5acts as a protective element for transistor T1and protects its gate from overvoltages.

In the case of the rectification of an alternating voltage, an alternating voltage of frequency f is present between cathode terminal K1and anode terminal A1. At a positive potential at cathode terminal K1, MOS transistor T1with its integrated inverse diode D6is in blocking operation and capacitor C1is able to charge via diode D3and resistor R5. The voltage present at capacitor C1is used for supplying the additional components of the rectifier circuit.

If, on the other hand, the electrical potential at cathode terminal K1is more negative than the electrical potential at anode terminal A1of the rectifier circuit, then the gate-to-source voltage of MOS transistor T1is positive and greater than its threshold voltage. At these conditions, MOS transistor T1is conductive, a current flow having this current direction causing only a slight voltage drop.

If the electrical potential at cathode terminal K1of the rectifier circuit is again more positive than the electrical potential at anode terminal A1of the rectifier circuit, then the gate-to-source voltage of MOS transistor T1is less than its threshold voltage. Under these conditions MOS transistor T1blocks. For this reason, the current flow through MOS transistor T1is only very small.

If the electrical potential at cathode terminal K1of the rectifier circuit is more positive than the electrical potential at anode terminal A1of the rectifier circuit and if this potential difference exceeds a value set by Zener diode D4, the input potential of the power amplifying stage consisting of transistors T4and T5is raised. This also increases the gate-to-source voltage of MOS transistor T1and a current flow comes about between the drain and the source of MOS transistor T1. At the conditions given, this current flow limits the electrical potential difference between cathode terminal K1and anode terminal A1of the rectifier circuit to a predetermined value. This feature of the limiting of the potential difference represents voltage clamping and constitutes a load dump protection in special cases.

FIG. 3shows a rectifier circuit according to a second exemplary embodiment of the present invention. The design and the functionality of the rectifier circuit shown inFIG. 3agree to a great extent with the design and functionality of the rectifier circuit shown inFIG. 2. The rectifier circuit shown inFIG. 3differs from the rectifier circuit shown inFIG. 2only in that the bases of the two transistors T9and T10, which form the power amplifying stage, are not connected to the cathode of diode D9via a Zener diode and a resistor. Accordingly, the exemplary embodiment shown inFIG. 3does not have the feature of limiting the potential difference between cathode terminal K2and anode terminal A2of the rectifier circuit, that is, the feature of voltage clamping.

FIG. 4shows a rectifier circuit according to a third exemplary embodiment of the present invention. The design and the functionality of the rectifier circuit shown inFIG. 4agree to a great extent with the design and functionality of the rectifier circuit shown inFIG. 2. The rectifier circuit shown inFIG. 4differs from the rectifier circuit shown inFIG. 2in that the functional features of voltage clamping and power amplification are not provided. The control of the control input and of the gate terminal of MOS transistor T11takes place directly from the output of the differential amplifier, which in the exemplary embodiment shown inFIG. 4is formed by transistors T12and T13and resistors R10, R11and R12.

In this exemplary embodiment, by omitting the power amplifying stage, conditioned upon the dimensioning of the additional components of the rectifier circuit, the power consumption of the circuit is able to increase. Furthermore, the maximum frequency f of the voltage that is to be rectified is also able to be reduced, since the charging and discharging of the gate of MOS transistor T11takes place more slowly at these conditions.

FIG. 5shows a rectifier circuit according to a fourth exemplary embodiment of the present invention. The design and the functionality of the rectifier circuit shown inFIG. 5agree to a great extent with the design and functionality of the rectifier circuit shown inFIG. 2. The rectifier circuit shown inFIG. 5differs from the one shown inFIG. 2in that the first input of differential amplifier T15, T16, R13, R14, R15is not connected via a diode, but directly to cathode terminal K4of the rectifier circuit and to the drain terminal of MOS transistor T14, and moreover, in that the second input of this differential amplifier is not connected via a diode, but directly to anode terminal A4of the rectifier circuit. In this exemplary embodiment we assume that the base-to-emitter inverse blocking capability of transistor T15of the differential amplifier is always greater than the maximum voltages present there during the operation of the rectifier circuit.

FIG. 6shows in exemplary fashion the current-voltage characteristics line of a silicon p-n diode and the current-voltage characteristics line of a rectifier circuit according to the present invention. It is clear fromFIG. 6that forward voltage UARF of a rectifier circuit according to the present invention is relatively small compared to forward voltage UPND of a silicon p-n diode.

FIG. 7depicts the implementation of a rectifier circuit according to the present invention in the form of an electronic component. Rectifier circuits according to the present invention may be composed of discrete components or of specially developed components. Such a low-loss electronic component is seen inFIG. 7, which is made up of a MOS transistor MOS, a capacitor C, a mounting rack B and an integrated circuit IC. Integrated circuit IC includes all electronic components of the rectifier circuit except the MOS transistor and the capacitor. The electronic component according toFIG. 7is interconnectable in the same way as a silicon p-n diode. In this context, anode terminal A of the electronic component corresponds to the anode terminal of a silicon p-n diode, and cathode terminal K of the electronic component corresponds to the cathode terminal of a silicon p-n diode.