Interface Circuit Overvoltage Protection Using Voltage Reduction
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Solution Overview
Problem
Power and data signal interface circuits, such as USB interfaces, are vulnerable to damage from overvoltage conditions exceeding the standard specifications, particularly in applications involving automotive systems where voltages can reach up to 20V, and require protection that does not interfere with normal operations, even in the absence of an internal power supply.
Innovation Solution
A power supply and data signal interface circuit with overvoltage protection is designed, incorporating a switch and controller that can withstand and manage high voltages, using a voltage reduction connection and zener diodes to limit internal node voltage, ensuring safe operation during both normal and standby conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If overvoltage protection is added to protect from high voltage (e.g., 20V automotive systems), then device reliability improves, but device complexity increases
Solution Approach 1:
The protection circuit is designed to be pre-configured and automatically activated when overvoltage conditions are detected, without requiring complex real-time control logic. The circuit includes pre-biased transistors and reference voltages that immediately respond to voltage excursions above the safe operating range, providing protection before damage can occur.
Solution Approach 2:
The invention introduces intermediate protection elements (such as series resistors, clamping diodes, and voltage divider networks) between the external high-voltage source and the sensitive internal circuitry. These intermediary components gradually reduce or limit the voltage step-by-step rather than requiring a single complex protection mechanism.
2Adaptability or versatility
If the interface circuit is designed to withstand high voltage (e.g., 20V), then overvoltage protection capability improves, but normal operation reliability deteriorates due to potential interference with standard voltage levels
Solution Approach 1:
Different parts of the circuit are designed with different voltage handling characteristics. The input stage includes components rated for high voltage (20V) while the core processing circuitry operates at standard USB voltages (5V/3.3V). Protection elements like Zener diodes and voltage clamps are strategically placed to provide high voltage tolerance only where needed, while maintaining standard operating conditions in the sensitive areas.
Solution Approach 2:
The circuit dynamically adjusts its electrical parameters based on the input voltage level. During normal operation at standard USB voltages, the circuit maintains its standard impedance and operating characteristics. When overvoltage conditions are detected, protection elements activate to change the circuit's effective impedance and voltage distribution, limiting the voltage reaching sensitive components while maintaining signal integrity for normal operations.
3Reliability
If the protection circuit activates during overvoltage conditions, then device safety improves, but data signaling capability deteriorates due to potential interference with data lines
Solution Approach 1:
The protection circuit is segmented into voltage-specific protection paths for different signal types. Power lines (VBUS) have dedicated voltage clamping and current limiting protection, while data lines (D+, D-) have separate protection mechanisms that preserve signal differential characteristics. This segmentation allows each protection subsystem to optimize for its specific function without interfering with other signal types.
Solution Approach 2:
For data line protection, the invention uses intermediary differential signaling techniques and balanced protection networks that maintain the differential voltage relationship essential for USB data communication. Protection elements are configured to clamp absolute voltages while preserving the differential signal, ensuring that overvoltage protection does not corrupt data integrity.
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 protects the interface and device from overvoltage damage, allowing normal operation and signaling even when the internal power supply is off, and limits voltage to safe levels during high-voltage conditions, preventing component damage.
Implementation Method 1
a first voltage reduction connection including a first zener diode having a first cathode connected to a first internal node and a first anode connected to ground, and a second voltage reduction connection including a second zener diode having a second cathode connected to a second internal node and a second anode connected to ground
Data Source
AI summary
A data processing device with a power supply and data signal interface circuit has a switch for connecting an external line and an internal node. The power supply and data signal interface circuit also includes a controller for applying an enabling voltage to the switch enabling the switch to supply current between the external line and the internal node in the presence of power supply to the controller and in the absence of the overvoltage condition on the external line. The power supply and data signal interface circuit also includes a voltage reduction connection from the external line for applying a control voltage to the switch in the absence of power supply to the controller. The control voltage from the voltage reduction connection limits a voltage applied to the internal node through the switch in the presence of the overvoltage condition.