Gating circuit having current measuring and regulating elements

Details Gating circuit having current measuring and regulating elements Gating circuit having current measuring and regulating elements

1996-07-01

1998-11-24

Callahan, Timothy P.

Miscellaneous active electrical nonlinear devices, circuits, and

Gating

Compensation for variations in external physical values

327108, 327491, 327513, 323285, 361 87, H03K 1714

Patent

active

058413120

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a gating circuit having a current measuring resistor and a power transistor and, more particularly, to a gating circuit of this type in which the current flowing through the power transistor is measurable by pickup of the voltage drop at the current measuring resistor and which has a current regulating transistor whose collector is connected to the base via a resistor and whose emitter is connected to the emitter of the power transistor so that the base of the power transistor is triggered by the voltage drop at the current measuring resistor.


SUMMARY

It is an object of the invention to provide an improved gating circuit of the above-described type, in which current flow through the power transistor is reduced as a function of component temperature.
This object and others which will be made more apparent hereinafter is attained in a gating circuit having a current measuring resistor and a power transistor, in which the current flowing through the power transistor is measurable by pickup of the voltage drop at the current measuring resistor and which has a current regulating transistor whose collector is connected to the base via a resistor and whose emitter is connected to the emitter of the power transistor so that the base of the power transistor is triggered by the voltage drop at the current measuring resistor.
According to the invention, the gating circuit is provided with a temperature measuring transistor, a further transistor which is triggered by the temperature measuring resistor when the temperature exceeds a predetermined temperature and means for varying a voltage applied to the base of the current regulating transistor by means of the current flowing through the further transistor so that the current flow through the power transistor is reduced.
The integrated circuit according to the invention has the advantage over the prior art that the current flow through the power transistor is reduced as a function of the component temperature. This provision provides protection of the power transistor against overheating.
By means of the provisions recited in the dependent claims, advantageous further features of and improvements to the integrated circuit defined by the independent claim are possible. By the use of a temperature measuring transistor with a larger emitter surface area than the current regulating transistor, the temperature dependency of the circuit can be controlled especially exactly. By the use of a current measuring transistor connected parallel to the power transistor, the current measurement is effected with low losses, since no measuring resistor needs to be disposed in the emitter circuit. By the use of a voltage divider, the switching potential for the current regulating transistor and the temperature measuring transistor can be adjusted to a suitable level. By the use of diodes connected in the conducting direction, the positive temperature coefficient of the current regulation can be adjusted to the desired value. By the suitable dimensioning of a coupling resistor, the magnitude of the thermal cutoff is adjusted. Varying the potential through the current flow of the further transistor is done especially simply via a third node of the voltage divider. By using Darlington transistors or additional current regulating transistors, the corresponding gains can be increased.


BRIEF DESCRIPTION OF THE DRAWING

Exemplary embodiments of the invention are shown in the drawings and described in further detail in the ensuing description.
FIG. 1 is a circuit diagram of the integrated gating circuit;
FIG. 2 shows the integrated circuit in combination with an inductive load; and
FIG. 3 is a graph showing the course over time of the current through the integrated circuit.


DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a circuit diagram of the integrated gating circuit is shown. The circuit has a collector terminal C, a base terminal B, an emitter terminal E, and transistors T1, T2, T3, TE, T5, T6, T9 and T10. The transi

REFERENCES:
patent: 5008586 (1991-04-01), Miyazaki et al.
patent: 5281872 (1994-01-01), Mori
patent: 5406130 (1995-04-01), Hennig
patent: 5486781 (1996-01-01), Im
Tietze & Schenk pp. 522-525 1974.

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