Protective Circuit for Sensor Output Stage Faulty Contacting
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Solution Overview
Problem
Existing output stages in sensors are prone to destruction due to faulty electrical connections, as integrated ESD protection diodes are not robust enough to withstand short-circuit currents, leading to damage or destruction during incorrect voltage supply connections.
Innovation Solution
A protective circuit is introduced, comprising a first transistor with a resistor between its collector and base, and a second transistor connected to the negative supply, which can operate inversely or normally to make the first transistor highly resistive in case of faulty connections, thereby interrupting current flow and protecting the driver stage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sufficiently powerful protection diode is connected in parallel to the analog output against ground with a resistor to limit short-circuit current, then the output stage is protected against faulty connections, but the device size increases and cost rises making installation difficult and uneconomical
Solution Approach 1:
The invention changes the resistance parameter of the series resistor dynamically. During normal operation, the resistor has low resistance to minimize voltage drop. Upon detecting a fault condition (reverse polarity or short circuit), the resistor's resistance increases dramatically to limit current and protect the output stage. This parameter change approach allows using a smaller, less expensive resistor compared to a continuously high-power protection design.
Solution Approach 2:
The protection circuit transitions from a static high-power design to a dynamic response system. The series resistor's resistance value changes based on operational conditions - low during normal operation and high during fault conditions. This dynamic behavior enables effective protection while reducing component size and cost, as the resistor only needs to handle high power temporarily during faults rather than continuously.
2Object-affected harmful factors
If the ESD protection diodes are used to protect against voltage transients, then protection against normal handling is achieved, but the diodes are destroyed when short-circuit currents flow due to incorrect voltage supply connections
Solution Approach 1:
The invention implements preliminary protective action by placing a series resistor in the output path before the ESD protection diodes. This resistor is designed to limit current under fault conditions before the diodes can be damaged. The resistor acts as a first line of defense that prevents excessive current from reaching the ESD diodes during reverse polarity or short circuit events, allowing the diodes to continue functioning for their intended ESD protection purpose.
Solution Approach 2:
The series resistor serves as an intermediary element between the output stage and the ESD protection diodes. During fault conditions, this intermediary component absorbs and limits the harmful short-circuit current, protecting the ESD diodes from destruction. The resistor mediates between the external fault condition and the internal protection circuitry, allowing the ESD diodes to maintain their protection function without being overwhelmed by excessive current.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The added transistor circuits provide a cost-effective and efficient means to prevent damage from short-circuit currents, ensuring the output stage remains functional even under faulty connection conditions by maintaining a low resistance in normal operation and becoming highly resistive during faults, thus protecting the driver stage.
Implementation Method 1
the second transistor circuit influences the first one such that it becomes highly resistive and thus provides a resistance which interrupts the current flow and thus protects the driver stage against the destruction caused by a short-circuit current
Data Source
AI summary
A protective circuit for protecting an output stage in the event of faulty contacting of the electrical connections, wherein the output stage includes a driver unit and has an analog or digital signal output is provided. Accordingly, in order to protect the output stage from a faulty connection in a simple and economical manner, the protective circuit comprises a first transistor circuit, which is connected in series between the output stage and the signal output, and a second transistor circuit, which is connected in series between the negative supply connection and the signal output. The second transistor circuit is connected to the base of the first transistor circuit in order to influence the first transistor circuit in such a way that the first transistor circuit becomes highly resistive in the event of a fault.