Electronic switch maintaining a predetermined state independent of supply voltage variation

US4159431A · kind A · utility

Assignee

• Robert Bosch GmbH · DE

Inventors

• Herman Roozenbeek · Schwieberdingen, DE
• Werner Jundt · Ludwigsburg, DE

Key dates

• Filing date: Jan 16, 1978
• Grant date: Jun 26, 1979
• Expiry date: Jan 16, 1998

Classification

• Technology area (CPC H): Electricity
• CPC primary: H03F2203/45471
• WIPO field: Basic communication processes
• WIPO sector: Electrical engineering

Abstract

To prevent uncontrolled switching of a Schmitt trigger during supply voltage shutoff, the trigger input transistor is maintained in the conductive state independent of supply voltage by a voltage divider and an additional DC base voltage. A second voltage divider furnishes a voltage blocking the output transistor of the Schmitt trigger after the supply voltage sinks too low to maintain conduction of the first transistor. A first and second so constructed Schmitt trigger is connected, respectively, to the first and second output of a difference amplifier. The inputs of the difference amplifier are connected to a pulse generator. Since the DC operating point of the difference amplifier changes with supply voltage, a controllable current source is connected to the difference amplifier for opposing the changes in the operating point. The controllable current source is controlled by the output signal from a summing and comparator circuit which has a first set of inputs connected to the outputs of the difference amplifier and a reference input.