Battery Changeover Switch Control for Reverse Current Suppression
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Solution Overview
Problem
In-vehicle power supply systems face challenges in preventing reverse current flow from a second power supply to a first power supply due to small potential differences, which is difficult to detect using software control, leading to increased size and cost of control circuits.
Innovation Solution
A switch control device and method that uses a voltage-controlled semiconductor switch, driven by a gate drive circuit, to maintain the semiconductor switch in specific states based on predetermined voltage differences between the power supplies, employing PWM signals to manage the switch's state transitions and prevent reverse flow without increasing circuit size or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an analog circuit including a comparator is used to detect potential difference between power supplies, then reverse current flow can be prevented, but the number of mounting components increases, substrate size increases, and cost increases
Solution Approach 1:
The patent replaces the mechanical/analog comparator circuit with a software-based detection system using a microprocessor. The microprocessor reads voltage values from A/D conversion results and determines potential difference through software logic, eliminating the need for physical comparator components and reducing circuit complexity.
Solution Approach 2:
The patent changes the detection threshold parameter by comparing A/D conversion results directly rather than using an analog comparator. The microprocessor determines when the potential difference exceeds a predetermined threshold through software comparison of digital values, allowing flexible parameter adjustment without hardware changes.
2Device complexity
If software control using a microprocessor is used to reduce circuit size, then component count decreases, but detection of small potential differences becomes unreliable, leading to delayed switching element control
Solution Approach 1:
The patent performs preliminary A/D conversion of both power supply voltages and stores the digital values in memory before comparison. This preliminary action allows the microprocessor to quickly retrieve and compare pre-converted values, reducing detection time and improving responsiveness to potential difference changes.
Solution Approach 2:
The patent implements a feedback mechanism where the microprocessor continuously monitors the potential difference by comparing stored A/D conversion results, determines when the threshold is exceeded, and immediately outputs a drive signal to the switching element. This closed-loop feedback ensures rapid and accurate response to voltage changes.
3Device complexity
If the switching element is controlled by software based on small potential differences of several mV, then circuit size is reduced, but the timing of open state control becomes delayed after reverse flow has occurred
Solution Approach 1:
The patent implements periodic sampling of voltage values from both power supplies through A/D conversion, storing the digital results in memory for continuous comparison. This periodic action ensures that voltage changes are detected at regular intervals, reducing detection delay while maintaining circuit simplicity.
Solution Approach 2:
The patent performs preliminary A/D conversion and stores voltage values in memory before they are needed for comparison. This preliminary action prepares the data in advance, allowing the microprocessor to immediately compare and detect potential difference changes without conversion delay, thus reducing overall detection time.
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
Effectively suppresses reverse current flow from the second power supply to the first power supply by rapidly detecting and responding to potential difference changes, reducing detection delays and maintaining control circuit efficiency.
Implementation Method 1
a voltage-controlled type semiconductor switch, which connects a first power supply and a second power supply having a rated voltage lower than that of the first power supply and whose gate is driven by a gate drive voltage supplied from a gate drive circuit
Implementation Method 2
The semiconductor switch is set to an ON state in a case where a potential difference ΔV (=V1−V2), which is a difference between a voltage V1 of the first power supply and a voltage V2 of the second power supply, is equal to or greater than a positive first predetermined value
Data Source
AI summary
A MPU controls a changeover switch, which is an FET switch that connects a main battery and a sub-battery having a low rated voltage. The changeover switch is set to an ON state in a case where a potential difference, which is a difference between a voltage of the main battery and a voltage of the sub-battery, is equal to or greater than a positive first predetermined value. A PWM signal is output to a driver to cause the changeover switch to be in a half-ON state in a case where the potential difference is less than the first predetermined value and is greater than a second predetermined value equal to or less than 0. The changeover switch is set to an OFF state in a case where the potential difference is equal to or less than the second predetermined value.