Siemens Aktiengesellschaft

Siements Aktiengesellschaft

Robert Murr

Herbert Zimmer

Thomas Roehrl

Bernhard Foerstl

A circuit for detecting a state of at least one electrical actuating element is described. The circuit has a signal input for receiving an input signal representing the state of the actuating element, a signal output for emitting an output signal representing the state of the actuating element, a control output for emitting an activation signal for an evaluation unit, to change over the evaluation unit from an inactive operating state to an active operating state, and a control unit. The control unit is connected to the signal input on the input side and to the control output on the output side and serves for generating the activation signal in a manner dependent on the input signal. The input signal at the signal input is an analog signal, the control unit generating the activation signal for the evaluation unit if the input signal lies within a predetermined range.

Circuit configuration for detecting the state of at least one electrical actuating element

When a short-circuit transistor is switched on, an impedance of an emitter-collector path through a switching transistor in a driver stage becomes higher as a load current becomes greater, and the load current and power loss in the switching transistor thus become lower. This effect is increased by connecting a voltage divider in parallel with the emitter-collector path through the switching transistor, by a parallel transistor. When the switching transistor is switched off, the parallel transistor blocks the current path via the voltage divider and the load for undesirable residual currents.

Driver stage for switching a load

An anti-theft system for a motor vehicle includes a portable transponder carrying an item of code information. A stationary antenna has a resonant circuit with components and a resonant frequency being determined by the components. An oscillator oscillates at an oscillator frequency and has an output variable being used as an exciter variable with an exciter frequency for compelling an oscillation of the resonant circuit. The oscillation is amplitude-modulated as a function of the code information of the transponder. An evaluation unit receives the oscillation of the resonant circuit. The evaluation unit detects the modulated oscillation and demodulates the code information out of the oscillation. A comparator compares the code information with command code information and supplies an enable signal if a match occurs. A security unit receives the enable signal. The exciter frequency or the resonant frequency of the resonant circuit is varied if initially no code information is recognized by the evaluation unit.

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Barbing, Germany

Robert Murr