Current-Mirror Signal Paths for 12V/48V Ground Offset Protection
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Solution Overview
Problem
Existing solutions for transmitting signals between electrical systems with different supply voltages in motor vehicles are either too large and expensive or fail to handle ground offsets during fault conditions, leading to potential short circuits and component damage.
Innovation Solution
A multi-voltage on-board electrical system uses current-mirror circuits and low leakage diodes to ensure safe signal transmission between 12V and 48V systems, limiting current flow and handling ground offsets without requiring complete galvanic isolation, as specified in the VDA 320 standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolating means such as optocoupler or electromagnetic coupler are used for information exchange between different voltage systems, then short circuit prevention is achieved, but the components become relatively large and expensive
Solution Approach 1:
The patent introduces an intermediary circuit configuration using diodes and resistors that mediates between the high-voltage and low-voltage systems. This intermediary structure allows signal transmission while preventing direct short circuits, replacing the need for bulky optocouplers or electromagnetic couplers with a more compact electrical circuit solution.
Solution Approach 2:
The patent replaces mechanical or optical isolation mechanisms (optocouplers, electromagnetic couplers) with an electrical circuit solution based on diodes and resistors. This substitution maintains the isolation function while reducing component size, cost, and complexity.
2Reliability
If diodes are used to prevent short circuits from high voltage to low voltage side, then short circuit protection is provided, but the solution cannot handle ground offset voltages during fault conditions
Solution Approach 1:
The patent applies beforehand cushioning by introducing resistors in series with the diodes before the high-voltage side. These resistors are pre-configured to limit current and provide voltage division, cushioning the circuit against ground offset voltages that may occur during fault conditions. This prevents excessive power dissipation and component damage before faults occur.
Solution Approach 2:
The patent changes the electrical parameters of the protection circuit by adding resistors that modify the voltage and current characteristics. This allows the circuit to handle varying ground offset conditions by adjusting the voltage division ratio and current limiting, enabling the system to adapt to different fault scenarios including negative ground voltages in recuperating devices.
3Reliability
If complete galvanic isolation is implemented between high voltage and low voltage systems, then short circuit prevention is maximized, but signal transmission complexity and cost increase
Solution Approach 1:
The patent applies partial isolation rather than complete galvanic isolation. By using diodes with reverse blocking capability combined with series resistors, the circuit achieves sufficient protection against short circuits and ground offsets without the complexity of full galvanic isolation. This partial approach provides adequate protection while maintaining simpler signal transmission.
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 effectively prevents short circuits between different voltage supplies, manages ground offsets, and maintains system integrity during faults, ensuring reliable communication without excessive power dissipation or component damage.
Implementation Method 1
it is indeed necessary to prevent short-circuiting the systems, and in particular, to prevent a higher supply voltage from 'breaking through' into the lower supply voltage
Implementation Method 2
in each signal path at least one current-mirror-circuit (CM1, CM2, CM3) is inserted
Data Source
Figure 1~2
Figure 3
AI summary
The invention is related to a multi-voltage on-board electrical system with at least two different voltage levels and at least one signal path between components of the electrical system with different voltage levels, in such a way, that in each signal path at least one current-mirror-circuit (CM1, CM2, CM3) is inserted.