H-Bridge SCR Switching Circuit for Low-Voltage Bipolar Defibrillation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing switching circuits in automatic external defibrillators face challenges due to the complexity of circuitry required to drive silicon controlled rectifiers (SCRs) and the limitations imposed by uncontrolled solid-state devices (USDs) that cannot switch below a certain threshold voltage, restricting energy delivery capabilities.
Innovation Solution
An H-bridge switching circuit with an automatic switching device (ASD) in place of one SCR, which automatically generates a voltage spike to turn on the SCR in response to voltage changes across it, allowing for efficient switching without external control signals and reducing hardware interlocking requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an SCR is used in the H-bridge switching circuit, then the circuit can deliver high voltage bipolar electrotherapy, but the circuitry complexity increases due to the need for transformers and hardware interlocking circuits to drive the SCR
Solution Approach 1:
The patent extracts and removes the SCR from the H-bridge circuit, replacing it with a simple solid state switch. This eliminates the need for complex transformer coupling and hardware interlocking circuits that were required to drive the SCR, while maintaining the high voltage power delivery capability through the remaining SCRs and circuit architecture.
Solution Approach 2:
The solid state switch replacement serves multiple functions: it acts as a simple on/off switch without requiring external drive circuits, eliminates the need for transformer coupling, removes the requirement for hardware interlocking circuits, and maintains compatibility with the high voltage power delivery system. This multi-functional element simplifies the overall circuit design.
2Device complexity
If a USD with Shockley characteristics is used to replace an SCR, then the circuit complexity is reduced by eliminating transformers, but the device cannot switch below a certain threshold voltage, limiting energy delivery
Solution Approach 1:
The patent applies local quality by placing the simple solid state switch specifically in the low leg of the H-bridge where it operates under different voltage conditions than the high leg SCRs. This localized substitution allows the circuit to achieve low voltage switching capability in one portion while maintaining high voltage capability in other portions, thereby expanding the overall voltage range without requiring complete circuit redesign.
3Reliability
If hardware interlocking circuits are implemented to ensure safety and integrity of the H-bridge operation, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The patent extracts and removes the hardware interlocking circuits from the system by replacing the SCR that required such interlocking with a simple solid state switch. This elimination maintains operational safety through the inherent characteristics of the solid state switch and the circuit architecture, while removing the complex hardware interlocking circuitry that added to the overall device complexity.
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
Enables the delivery of bipolar electrotherapy across a wide range of voltages while maintaining circuit integrity and safety, allowing for efficient and reliable energy transfer to a patient, even at lower voltage levels.
Implementation Method 1
a control circuit which automatically generates a voltage spike to turn on the SCR in response to a voltage change across the SCR which occurs when the switching device in the diagonally opposite low leg turns on
Data Source
Figure 1
Figure 2
Figure 3
AI summary
An H-bridge switching circuit for an automated external defibrillator comprises an SCR (D8) in one of the high legs of the circuit and a control means (D1-D7) associated with the SCR which is operative to switch the SCR on automatically in response to a voltage change across the SCR corresponding to the switching device in the diagonally opposite leg of the H-bridge turning on. The control means comprises a capacitor (D1) and the voltage on the capacitor changes when the diagonally opposite switching device turns on, the change in capacitor voltage lagging the change in voltage across the SCR and the SCR being turned on when the difference between the capacitor voltage and the voltage across the SCR exceeds a predetermined threshold.