Sensor Device Negative Surge Suppression via Base Current Limiting
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Solution Overview
Problem
Conventional sensor devices experience voltage drops and malfunctions due to negative surges in the power supply line, particularly because diodes on the power supply path cause a forward voltage drop, limiting the output voltage range and requiring large diodes to handle high current consumption, which occupies significant chip space.
Innovation Solution
Incorporating a restriction mechanism at the base terminal of a transistor to control current flow from the ground terminal, using a backflow preventing diode connected to the base of an NPN transistor to block reverse currents during negative surges, thereby maintaining stable voltage and reducing diode size requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a diode is inserted on the power supply path to prevent reverse current during negative surge, then malfunction resistance is improved, but voltage drop increases and output voltage range becomes narrow
Solution Approach 1:
The patent introduces a restriction part as an intermediary element that selectively restricts current flow only during negative surge conditions. This mediator component (implemented as a PN junction or diode connected between base and emitter) activates only when reverse current attempts to flow, preventing malfunction while avoiding continuous voltage drop during normal operation. The intermediary nature allows the system to gain protection benefits without the continuous energy loss of a always-on series diode.
Solution Approach 2:
The patent applies local quality by implementing the restriction function at a specific location (the base terminal of the transistor) rather than in series with the entire power supply path. The PN junction or diode is connected locally between base and emitter, creating a localized protection mechanism that restricts current only where needed (at the base terminal) without affecting the overall power supply voltage available to the load circuit.
2Power
If a diode is enlarged to handle high current consumption, then current capacity is improved, but chip area occupied by the diode increases
Solution Approach 1:
The patent changes the dimensional arrangement by connecting the restriction part in parallel between base and emitter rather than in series with the power supply path. This dimensional change allows the diode to handle base current (which is much smaller than load current) without needing to be enlarged for full load current capacity. The parallel connection in the base-emitter dimension provides sufficient current handling capability for the base terminal without requiring large chip area.
3Reliability
If a diode is placed on the power supply path to block reverse current, then reliability during negative surge is improved, but the forward voltage of the diode limits the output voltage range
Solution Approach 1:
The patent implements preliminary action by proactively restricting current at the base terminal before reverse current can propagate through the transistor and cause malfunction. The restriction part is positioned and configured to prevent reverse current flow at its location (base-emitter junction), stopping the harmful effect before it reaches the power supply path and load circuit. This preliminary restriction eliminates the need for series diodes that would limit output voltage range.
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
This configuration suppresses voltage drops in load circuits during negative surges, enhances malfunction resistance, and allows for a wider output voltage range while minimizing diode size, enabling efficient operation with lower input voltages.
Implementation Method 1
A technology described in PTL 1 includes a diode between a power supply line and a collector terminal of an NPN bipolar transistor for load driving (hereinafter referred to as NPN transistor). Since this diode prevents a reverse current that flows from the load side to the power supply line at the time of the negative surge impression, the malfunctions described above can be suppressed.
Implementation Method 2
it is characterized by including a restriction part for restricting a current flowing from a ground terminal to a base terminal of a first transistor element in the control circuit
Data Source
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AI summary
Provided is a sensor device wherein malfunction due to a negative surge is suppressed. This sensor device is provided with: a sensor element wherein electrical characteristics change corresponding to physical quantities; a signal processing circuit that processes output signals of the sensor element; a first transistor element that supplies currents to the sensor element and the signal processing circuit; a control circuit that controls a base current of the first transistor element; a power supply terminal; and a ground terminal. The sensor device is characterized in that the control circuit is provided with a limiting section that limits a current flowing from the ground terminal toward a base terminal of the first transistor element.