Integrated Overvoltage Protection Circuit for ICs
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Solution Overview
Problem
Conventional overvoltage protection circuits for ICs increase size and cost, emitter follower circuits may not operate when input voltage is reduced, step-up power supply devices lead to unnecessary power consumption, and power supply ICs for liquid crystal displays require external resistors increasing manufacturing costs.
Innovation Solution
An overvoltage protection circuit using P-channel field-effect transistors and Zener diodes to prevent surge voltages, a step-up power supply device with controlled discharge, and a power supply circuit integrated with a variable current source to generate gate voltages for liquid crystal displays, reducing external components and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an anti-ESD element or high-voltage resistant LDO chip is added outside the IC, then overvoltage protection is improved, but device size and cost increase
Solution Approach 1:
The patent integrates the overvoltage protection function directly into the IC chip by incorporating a protection circuit that includes a first transistor, first resistor, and short circuit mechanism. This merging of the protection function into the chip eliminates the need for external anti-ESD elements or LDO chips, thereby reducing device size and complexity while maintaining overvoltage protection capability.
Solution Approach 2:
The protection circuit is designed to perform multiple functions: it provides overvoltage protection when surge voltage occurs, and simultaneously allows normal power supply operation when voltage is within the safe range. The circuit uses a transistor that can operate in different states (normal conduction vs. cutoff during surge) to achieve both protection and normal functionality within a single integrated structure.
2Reliability
If an emitter follower circuit is provided within the IC, then surge voltage protection is improved, but operation fails when input voltage is reduced
Solution Approach 1:
The protection circuit employs a dynamic switching mechanism where the first transistor transitions between conductive and cutoff states based on voltage conditions. During normal operation, the transistor conducts to allow power supply. During surge voltage, the short circuit mechanism activates to cutoff the transistor, preventing overvoltage. This dynamic response allows the circuit to adapt to different voltage conditions, maintaining both protection capability and normal operation across voltage ranges.
Solution Approach 2:
The circuit changes its electrical parameters (transistor state, circuit connectivity) based on the input voltage level. When voltage exceeds the breakdown voltage threshold, the short circuit mechanism changes the circuit configuration to protect internal elements. When voltage is within normal range, the circuit returns to its normal power supply configuration, enabling operation across different voltage conditions.
3Reliability
If a high-voltage resistant emitter follower circuit is provided, then surge voltage protection is improved, but power consumption increases
Solution Approach 1:
The protection mechanism operates periodically or event-driven rather than continuously. The short circuit mechanism is activated only when surge voltage is detected (when voltage exceeds the breakdown voltage of the Zener diode), and remains inactive during normal operation. This on-demand activation minimizes power consumption while providing protection when needed, avoiding the continuous power drain that would result from always-active protection circuits.
4Reliability
If multiple discharge circuits and overvoltage detection circuits are used, then ESD and EOS protection is improved, but circuit complexity increases
Solution Approach 1:
The patent combines multiple protection functions (overvoltage detection, ESD protection, EOS protection) into a single integrated protection circuit. The first transistor, first resistor, and short circuit mechanism work together to provide comprehensive protection against various voltage anomalies including ESD and EOS, eliminating the need for separate discrete protection circuits and reducing overall complexity.
Solution Approach 2:
The protection circuit is designed with multi-functionality to handle various protection scenarios. The same circuit components (transistor, resistor, short circuit mechanism) provide protection against multiple types of voltage anomalies including overvoltage, ESD, and EOS, making a single circuit structure serve multiple protection purposes and reducing the need for separate specialized circuits.
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 solutions enable efficient overvoltage protection, controlled power discharge, and reduced manufacturing costs for ICs and liquid crystal display devices, ensuring operation and cost-effectiveness.
Implementation Method 1
a Zener diode having the breakdown voltage characteristic of a predetermined voltage (for example, 5 V)
Implementation Method 2
a first transistor which is a P-channel field-effect transistor, whose source is connected to an input terminal and whose drain is connected to an internal circuit
Data Source
AI summary
An overvoltage protection portion (14) includes a transistor (P1) that achieves continuity with an input voltage (VIN) used as an output voltage (VOUT) to an internal circuit when the input voltage (VIN) applied to an external terminal (T1) is not in an overvoltage state. The overvoltage protection portion (14) also includes: a transistor (P2) operating as a short circuit that short-circuits the source and the gate of the transistor (P1) and that interrupts the input voltage (VIN) when the input voltage (VIN) is in the overvoltage state; a resistor (R2); and a Zener diode (ZD1). The overvoltage protection portion (14) also includes: a transistor (NTr1) operating as a bypass circuit that supplies a constant output voltage (VOUT) from the external terminal (T1) to the internal circuit when the input voltage (VIN) is brought into the overvoltage state; a resistor (R3); and a Zener diode (ZD2).