Bipolar Transistor Sensor Interface Circuit for Low Power Standby
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Solution Overview
Problem
Existing sensor systems for passive keyless entry in vehicles face challenges in minimizing current consumption during standby mode, particularly due to the limitations of standard gate drivers which have insufficient current output capability and increased leakage current at extreme temperatures, leading to potential failure in switching on the transistor properly.
Innovation Solution
A sensor system utilizing a circuitry with NPN and PNP bipolar transistors, along with a CMOS gate supply, to boost power levels and manage current efficiently, including a switch for enabling/disabling the gate supply and resistors for protecting against short circuits, allowing for high current gain operation with standard small transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard gate driver is used to interface with the capacitive sensor, then the device complexity is reduced and ease of manufacture is improved, but the current output capability is insufficient and current consumption increases at extreme temperatures
Solution Approach 1:
The patent introduces an intermediary circuit between the gate driver and the capacitive sensor. This intermediary circuit includes a PNP transistor connected to the gate driver output and an NPN transistor connected to the sensor. The intermediary circuit acts as a buffer that isolates the gate driver from the sensor's current demands, allowing the gate driver to operate with standard components while the intermediary circuit provides the necessary current amplification and temperature compensation.
Solution Approach 2:
The patent changes the operating parameters of the transistor circuit by using complementary PNP and NPN transistors in a push-pull configuration. This allows the circuit to dynamically adjust its current gain and output characteristics based on temperature conditions. The transistors are biased to operate in specific regions that optimize current output capability across extreme temperature ranges while maintaining low quiescent current consumption.
2Reliability
If the driver is switched on during vehicle sleep mode to detect user presence, then the detection function is enabled, but the current consumption increases and may discharge the vehicle battery
Solution Approach 1:
The patent implements periodic sensing action where the capacitive sensor is activated in intervals rather than continuously during vehicle sleep mode. The microcontroller controls the gate driver to enable the sensor only when needed for detection, allowing the system to enter a lower power state between sensing events. This periodic operation maintains detection reliability while significantly reducing average current consumption during standby mode.
Solution Approach 2:
The capacitive sensor circuit is designed to self-activate when a user approaches, using the body capacitance itself to trigger the detection sequence. The sensor circuit monitors its own operating conditions and automatically initiates the detection process when capacitance changes indicate user presence, eliminating the need for continuous active monitoring and reducing overall power consumption.
3Reliability
If a transistor with high thermal capacitance is used to survive short circuit conditions, then the reliability under fault conditions is improved, but the transistor size increases and current gain decreases
Solution Approach 1:
The patent segments the transistor function into two separate transistors: a PNP transistor for current amplification and an NPN transistor for output switching and short-circuit protection. This segmentation allows each transistor to be optimized for its specific function - the PNP transistor can be small with high current gain, while the NPN transistor handles the thermal capacitance requirements for fault survival. The segmentation eliminates the need for a single large transistor, maintaining high current gain while ensuring reliability under short circuit conditions.
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 solution significantly reduces current consumption in vehicles during standby mode, ensuring reliable operation of capacitive sensors and minimizing power consumption, even at extreme temperatures, by effectively managing current flow and preventing short circuits.
Implementation Method 1
The circuitry comprises a NPN bipolar transistor having a base, a collector and an emitter. The circuitry further comprises a PNP bipolar transistor having another base, another collector and another emitter. The NPN bipolar transistor is an input transistor. The PNP bipolar transistor is the output transistor.
Data Source
Figure 1~2
Figure 3~4
AI summary
A sensor system (10) configured to interface a gate supply (12) with a sensor (14) comprises the sensor (14) to detect a user (46), the gate supply (12) to provide power to an apparatus (16). The apparatus (16) comprises an input (28) connected to the gate supply (12) for receiving power from the gate supply (12), a circuitry (17) for boosting a level of the power received from the gate supply (12), and an output (26) connected to the sensor (14) for providing the boosted level of power to the sensor (14). The circuitry (17) comprises a NPN bipolar transistor (22) having a base (34), a collector (32) and an emitter (30). The circuitry further comprises a PNP bipolar transistor (24) having another base (39), another collector (38) and another emitter (36). The NPN bipolar transistor (22) is an input transistor (22). The PNP bipolar transistor (24) is the output transistor (24). The base (34) of the input transistor (22) is connected to the input (28) of the apparatus (16). The collector (38) of the output transistor (24) and the emitter (30) of the input transistor (22) are connected together to the output (26) of the apparatus (16). The emitter (36) of the output transistor (24) is connected to a supply voltage (18) and the collector (32) of the input transistor (22) is connected to the base (39) of the output transistor (24).