Final stage of a bridge circuit

Details Final stage of a bridge circuit Final stage of a bridge circuit

1989-01-20

1990-08-21

Budd, Mark O.

Electric power conversion systems

Current conversion

Using semiconductor-type converter

363 17, 363 58, 363 98, H02M 75387

Patent

active

049511882

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention concerns a device for controlling and regulating the current through an electromagnetic consumer with a bridge circuit consisting of four current control members, the consumer being located in one of its diagonals, as known e.g. from the DE-OS 34 20 611. In the known device, a diagonal of the bridge circuit comprises only the electromagnetic consumer, and a series connection consisting of an additional current control member and a measuring resistor is connected downstream of this bridge circuit. By means of this, the control of the current through the consumer and the control of the polarity of this current are to be separated in a manner related to circuit arrangement. The current control members in the known bridge circuit are bipolar transistors, specifically two p-n-p transistors and two n-p-n transistors. For turning on and turning off, such bipolar transistors require an energy loss which is converted in the transistors during the switching process.
In addition, a bridge circuit consisting of four bipolar transistors is known from the U.S. Pat. No. 4,520,438, a motor being connected in its diagonal. A base-current shunt transistor is connected in series with an inductance and a diode to each of these transistors via its base-emitter junction. The object of the circuit known from the U.S. Pat. No. 4,520,438 is that the base driver current should change as little as possible during a change in the operating conditions.
The relatively high energy loss of the connected transistors of the bridge circuit poses a problem when it involves low power loss as, for example, in electromagnetic consumers in motor vehicles or in connection with computers. In addition, the aforementioned texts make no mention of a protection for the final stage against short circuiting.


ADVANTAGES OF THE INVENTION

The device, according to the invention, for controlling and regulating current through an electromagnetic consumer with a bridge circuit, the consumer being located in one of its diagonals, consisting of four current control members of the logic level power MOSFET type, to which a voltage regulating circuit for the gate voltage supply and a current control circuit for the gate voltage control are connected, and comprising at least one measuring resistor connected to a connection point of the second diagonal has the advantage over the prior art that only an extremely low power loss is required for operating the circuit because of the extremely low resistance of such power MOSFETs. The measuring resistor can also have a very low resistance value. The gate voltage supply via voltage regulators permits a slight voltage drop of typically 1.2 Volts and an input protection against negative voltages. As a result of the gate voltage control via current sources, no problems occur because of disturbances in the supply voltage and only a low power loss of the drive circuit is required. Another advantage consists in that the device, according to the invention, can operate within a wide voltage range which is defined, at most, by the dielectric strength of the current control members of the final stage.
If the voltage regulating circuit comprises an integrated switching circuit, according to an advantageous embodiment of the device, according to the invention, this results in a particularly simple construction.
In another advantageous construction of the invention, the voltage regulating circuit is constructed from discrete components and comprises a diode whose cathode is connected to the collector of an n-p-n transistor and to a resistor whose other terminal is connected to the base of the transistor, with which the cathode of a Zener diode is connected. Such a construction can be hybridized or integrated in a particularly simple manner, since the capacitance of the gate voltage capacitor for the logic level power MOSFET current control members can be reduced by a factor of 1000 compared with the capacitance required in an integrated switching circuit.
This capacitance is the essential element of a voltage

REFERENCES:
patent: 4520255 (1985-05-01), Bredenkamp et al.
patent: 4545004 (1985-10-01), Kade et al.
patent: 4649321 (1987-03-01), Ferraro
patent: 4672524 (1987-06-01), Toriyama et al.

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