Electrical transmission or interconnection systems – Personnel safety or limit control features – Interlock
Patent
1988-12-23
1989-12-12
Miller, Stanley D.
Electrical transmission or interconnection systems
Personnel safety or limit control features
Interlock
307255, 307270, 307300, H03K 326, H03K 3013, H03K 1760
Patent
active
048869856
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a transistor arrangement serving as an output transistor, particularly for switching inductive loads.
A transistor circuit arrangement with a power transistor designed as a Darlington transistor is already known from the DE-OS No. 34 39 366. The transistor arrangement serves as an ignition output stage for controlling transistor ignitions in motor vehicles. For this purpose, the primary winding of an ignition coil is connected in the collector-emitter circuit of the power transistor. According to the law of induction, it is necessary to switch off the current through the primary winding of the ignition coil as quickly as possible in order to achieve the highest possible ignition voltage at the secondary side of the ignition coil.
As is known, when switching off a transistor, a certain time passes until the transistor has achieved its full blocking ability after the controlling of the base is terminated. This turn-off timee is caused primarily by charge carriers stored in the base region of the transistor. One also often speaks of a charged collector-base capacity of the transistor. The turn-off time of the transistor is therefore relatively long if, in order to switch off the collector current, the base current is simply interrupted. It can be clearly reduced if the charge carriers stored in the transistor are removed by means of a reversal of the base current. The same is also true for power transistors in Darlington circuits, wherein, however, the minimum switching time can only be achieved when not only the base of the driver transistor but also the base of the output transistor is dicharged. In many cases of the application, however, it is not possible to reverse the base current in order to achieve a quick cut-off process for reasons relating to circuit technology.
Therefore, it is the object of the present invention to find a transistor arrangement with a power transistor which enables a turn-off time of the power transistor which is as short as possible, even when the base current is only interrupted for switching off.
The object is met by means of the transistor arrangement, according to the invention, wherein a first- and a second transistor are interconnected as a Darlington pair having a base terminal, an emitter terminal and a collector terminal; a third transistor having its collector connected to the base of the first transistor and its emitter connected to the emitter terminal; and a fourth transistor of a conductivity type opposite to that of the first, second and third transistors and having its base connected to the collector terminal, its emitter connected to the base terminal, and its collector connected to the base of the third transistor.
ADVANTAGES OF THE INVENTION
The transistor arrangement, according to the invention, has the particular advantage that it is monolithically integrable in a very simple manner. Since its function is substantially independent of the respective transistor data, it has a very small dispersion of turn-off time within a series. It can therefore be used particularly reliably where a high demand for quality is placed on the tolerance of the turn-off time, that is, particularly when it is used as an ignition output stage for controlling transistor ignitions in motor vehicles. It is particularly advantageous when a follower transistor, which takes over the actual discharging function, is connected downstream of the discharging transistor. Accordingly, the discharging transistor serves only to control the follower transistor and can therefore be realized in monolithic integrated technology so as to be particularly small and low in output, accompanied by the use of structural component elements adjoining diffusion regions. In addition, it is particularly advantageous if the Darlington pair has its base-emitter diodes bridged by means of parallel resistors. The base regions of the transistors in the Darlington pair are then also discharged via the resistors and a short turn-off time is achieved.
DRAWING
An embodiment exam
REFERENCES:
patent: 4128742 (1978-12-01), Davis
patent: 4234805 (1980-11-01), Carlsen, II
patent: 4616144 (1986-10-01), Hideshima et al.
patent: 4695807 (1987-09-01), Annacker et al.
Flohrs Peter
Heyke Klaus
Michel Hartmut
Nelle Ulrich
Miller Stanley D.
Robert & Bosch GmbH
Striker Michael J.
Thai Nancy
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