Voltage control circuit

Details Voltage control circuit Voltage control circuit

1989-12-04

1992-04-14

Stephan, Steven L.

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

323280, 330257, 330261, G05F 328, H03F 345

Patent

active

051051451

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a voltage control circuit, in particular a voltage control circuit for use with a high supply voltage.


BACKGROUND OF THE INVENTION

Without special protective measures, transistors can only be actively operated with collector-emitter voltages which lie below a value U.sub.CEO characteristic of the transistors (for example U.sub.CEO =20 volts). In the blocked condition (U.sub.BE =0), however, a higher voltage up to U.sub.CES can be applied to the transistor without damage thereto (for example U.sub.CES =40 volts). Thus the value U.sub.CES is also a transistor characteristic.
The present invention seeks to provide a circuit, in particular a negative-feedback amplifier circuit or voltage controller, which can be actively operated with voltages above U.sub.CEO but below U.sub.CES. The characteristic values or parameters U.sub.CEO and U.sub.CES are determined by the process of manufacture of the transistors as component parts of an integrated circuit. The present invention also seeks to provide a circuit suitable for use in motor vehicles or other applications in which the supply system is subject to high voltage peaks. The invention also seeks to provide an improved circuit suitable for construction by integrated circuit techniques.


SUMMARY OF THE INVENTION

According to the present invention there is provided a voltage control circuit comprising an amplifier with including at least one transistor having its collector-emitter path connected between a first reference potential U.sub.V and, via a resistive element, or a current source, a second reference potential C, characterised in that selectively conducting means is connected between said transistor and, via switching or controlling means (T8), said second reference potential G.
An advantage of this circuit is that it permits operation with a higher supply voltage than previously, i.e. a greater voltage difference between the two sources of reference potential U.sub.V and reference potential C, without the danger arising of a breakdown in the collector-emitter path of the transistor T1, followed by destruction of the transistor and failure of the circuit.
The circuit is particularly suitable for manufacture by integrated circuit techniques. The selectively conducting means, which preferably comprises a diode D or a transistor T, is conveniently fabricated in the same manufacturing process as the usual circuit components.
The selectively conducting means may be connected between the base of the amplifier transistor T1 and a potential which can become lower than the emitter-potential of T1. This has the advantage of quickly diverting the base current and thus blocking the transistor T1 to prevent damage thereto.
In a preferred arrangement the voltage control circuit comprises an input differential amplifier and an output multi-stage amplifier including transistors T1 and T2 wherein, the collector-emitter path of an additional transistor T8 in the multi-stage amplifier provides a convenient connection between the diode D or transistor T and ground potential or the reference potential (G). The use of a transistor T as the selectively conducting means is particularly advantageous in that it reduces the current loading of the additional transistor T8.
The circuit has the ability to fully block the transistors T1 and T2, but such full blocking is only transient. The control circuit operates in the same manner at high and low 35 values of the supply voltage U.sub.v, but in the case of a high U.sub.v value it can happen that base currents otherwise supplied to transistors T1 and T2 are dropped. The output voltage U.sub.A of the circuit remains substantially constant.


BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, of which:
FIG. 1 is a circuit diagram of a voltage control circuit in accordance with a first embodiment of the present invention; and
FIG. 2 is a circuit diagram of a voltage control circuit in

REFERENCES:
patent: 3569849 (1971-03-01), Cassidy et al.
patent: 4857862 (1989-08-01), Brokaw

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