Circuit for reducing input voltage

Details Circuit for reducing input voltage Circuit for reducing input voltage

2000-03-08

2001-08-14

Berhane, Adolf Deneke (Department: 2816)

Electricity: power supply or regulation systems

In shunt with source or load

Using a three or more terminal semiconductive device

C363S062000

Reexamination Certificate

active

06275015

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circuit arrangement for reducing an input voltage, which in particular is pulsed, and to a corresponding method.
2. Description of the Prior Art
It is known to use inductive transducer arrangements for detecting rotary speeds, or rpm. By means of a gear wheel or pulse wheel rotating in front of an induction coil, a voltage proportional to the change in the magnetic field over time and thus to the rpm of the gear wheel is induced in the induction coil. These voltages can be delivered to a threshold stage that furnishes an rpm-dependent signal train.
One such circuit arrangement for generating an rpm-dependent signal train from the periodic voltage of an inductive transducer arrangement is known from German Patent DE 3127220C2for, instance.
For certain applications, it is usual to use gear wheels with a low number of teeth, for instance four teeth, as the pulse wheels. Then, however, the problem arises that during the relatively long intervals between two pulses, interference signals can impair the rpm detection, if their amplitudes exceed a threshold stage of an evaluation circuit. Such interference signals fluctuate to approximately the same extent as the input signal to be evaluated. To circumvent the attendant imprecision in rpm detection, it is known to perform a followup of the threshold value of the threshold value stage as a function of the rpm. The expense for circuitry required to create threshold value followup, however, must be viewed as considerable.
SUMMARY OF THE INVENTION
It is an object of the invention to create a circuit arrangement with which voltages of variable amplitude, which occur particularly in the operation of an inductive rpm transducer, can be reduced in such a way that incident interference signals can be distinguished, for instance by means of a threshold value stage, from measurement signals in a simple way.
According to the invention, with only a few, inexpensively obtainable components, a circuit arrangement can be created with which for instance in the operation of an inductive rpm transducer, measurement signal voltages can be separated or distinguished from incident interference signal voltages. To that end, rpm-dependent input voltages of an rpm transducer and interference voltages that occur for instance along the signal paths can be reduced in such a way that the signal voltages are reliably higher, and the interference voltages reliably lower, than a response threshold of an evaluation circuit. This is attained by providing that the division factor, generated by a variable voltage divider, is raised for relatively high input voltages and vice versa (that is, at relatively high input voltages, the operating voltage delivered to the evaluation circuit corresponds to a correspondingly lesser percentage of the input voltage.
Expediently, the operating voltage U
z
, U
arb
can be regulated to a substantially constant value. As a result, it is possible to make the evaluation circuit, to which the operating voltage is supplied, especially simple.
In a preferred embodiment of the circuit arrangement of the invention, the voltage divider has at least one first resistor and one field effect transistor acting as a variable resistor.
With a field effect transistor of this kind, the desired voltage regulation can be done in a very simple and effective way.
Advantageously, a control input of the field effect transistor can be acted upon by a control voltage U
s
derived from the operating voltage U
z
, U
arb
. This makes use of the fact that the only resistance of field effect transistors is determined solely by a control voltage applied between their controller gate terminal and their source terminal. Such a control voltage is especially simple to control or regulate voltage.
Expediently, the circuit arrangement of the invention has a further voltage divider provided between the first voltage divider and the evaluation circuit. The provision of a second voltage divider enables optimal adaptation of the operating voltage to threshold voltage values of a downstream evaluation circuit.
In a further preferred embodiment of the circuit of the invention, the circuit is designed to divide downward or reduce an input voltage, present in differential form, to produce a differential operating voltage. This makes the signal lines ungrounded, and as a result interference factors can be reduced.


REFERENCES:
patent: 3636382 (1972-01-01), Crouse
patent: 4270166 (1981-05-01), Immler
patent: 5521488 (1996-05-01), Stockstad et al.
patent: 31 27 220 C2 (1983-04-01), None
patent: 0 665 437 (1995-08-01), None

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