Device for monitoring the functon of an electric load, its drive

Details Device for monitoring the functon of an electric load, its drive Device for monitoring the functon of an electric load, its drive

1991-12-13

1994-05-10

Wieder, Kenneth A.

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

In vehicle wiring

324509, 324522, 340650, G01R 3102

Patent

active

053111389

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to circuitry for monitoring the function of an electric load, the output stage and control circuit that drive the electric load, and the lines that connect these elements.


BACKGROUND OF THE INVENTION

Function monitoring circuits are known. These known circuits, however, do not distinguish between load drop-outs and short circuits to earth of an assembly, do not have any fault storage capacity which means that there can only be on-line fault detection, handle fault detection using a control circuit, and require extensive software search routines for fault detection and detection of the fault path and type.
One of the known function monitoring circuits uses the drive pins for signalling the output potentials of the output stage. During this process, it is determined whether the output stage which contains a transistor has assumed the "high" or "low" output potential. As a result, it can be determined after a software comparison of the input and output signal whether a short circuit of the output stage to the supply voltage or to the positive potential or to earth is present.
In another known function monitoring circuit, the output potentials of the output stages are signalled via a serial interface.
Another function monitoring circuit which is known signals several output stages simultaneously. These output stages, which are signaled by the function monitoring circuit, short circuit to the supply voltage and the load drops out on one side, and the load short circuits to earth on the other side at one connection pin each.
In this circuit, it is not possible to distinguish between faults--load drop-out and short circuits to earth. To make it possible to allocate the fault to one output stage, an extensive software search routine is necessary.


SUMMARY OF THE INVENTION

The circuitry according to the present invention is for monitoring the function of an electric load, the output stage and control circuit for driving the electric load, and the lines that connect these elements. The fault monitoring circuit of the present invention has ability to reliably distinguish between possible fault conditions such as the short circuits to earth, short circuits to positive potentials, and load drop-outs, with little hardware and software expenditure, particularly, without extensive software search routines. The function monitoring circuit of the present invention also detect the proper operation of the output stage, electric load, control circuit, and lines connecting the output stage to the electric load and control circuit.
In the circuit arrangement for the electric load disclosed herein, the electric load may be connected to earth and be driven by a so-called high-side output stage and it can connected to a positive potential and be driven by a so-called low-side output stage. The present invention also permits monitoring of both inverting and non-inverting output stages. In addition, the circuitry according to the present invention may be included in existing control circuits without difficulty. In the overall concept, the functioning monitoring circuit of the present invention, and each of the monitoring circuit's individual components can be constructed, hybridized, and integrated.
The circuitry of the present invention has at least one fault detection circuit connected in parallel with the output stage that with the control circuit is used for driving a load. The faults that are detected can be distinguished by a comparison of the input and output potentials. To detect the load drop-out, a further potential is applied to the output stage. This potential can be evaluated when a connecting line to the load drops out. This potential can be generated, for example, by means of a voltage source and an internal resistance, an operational or comparator circuit or by means of a current source and so forth. Due to the fact that the function monitoring circuit is connected in parallel with the output stage of the load, no intervention into the control circuit is requi

REFERENCES:
patent: 4306270 (1981-12-01), Miller et al.
patent: 4574266 (1986-03-01), Valentine
patent: 4694372 (1987-09-01), Sibeud
patent: 4884033 (1989-11-01), McConchie, Sr.
patent: 4962350 (1990-10-01), Fukuda
patent: 5173832 (1992-12-01), Giorgetta et al.

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