RF Generator Power Monitoring Using DC Voltage Feedback Isolation
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Solution Overview
Problem
Radiofrequency (RF) generators in electrosurgical units face challenges in minimizing leakage current due to capacitance in isolation barriers, which can lead to dangerous RF energy exposure to patients and medical personnel, and existing solutions like software controls and throttling schemes are inadequate or complex.
Innovation Solution
An electrosurgical unit with a reduced number of inductive couplings across the isolation barrier, using a DC voltage sensor and current sensor to estimate output voltage feedback, eliminating the need for measuring RMS output voltage feedback, and employing a programmable logic device to control RF energy output within safe limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple inductive couplings are used across the isolation barrier for feedback measurement, then output voltage and power control is achieved, but leakage current increases due to excess capacitance
Solution Approach 1:
The patent extracts the voltage feedback measurement function from the RF path by measuring DC input voltage instead of AC output voltage through transformers. This removes the inductive couplings and their associated capacitance from the isolation barrier, eliminating the source of leakage current while maintaining feedback control capability.
Solution Approach 2:
The patent replaces the electromagnetic measurement system (transformers and inductive couplings) with a direct electrical measurement system (DC voltage sensor). This substitution eliminates the need for magnetic coupling components that contribute capacitance and leakage current.
2Object-affected harmful factors
If peak output voltage is lowered to minimize leakage current, then leakage current is reduced, but coagulation performance degrades
Solution Approach 1:
The patent implements feedback control by measuring DC input voltage and using it to regulate RF power output. This allows the system to maintain optimal peak output voltage for coagulation while dynamically adjusting power delivery to prevent excessive leakage current, resolving the contradiction between therapeutic effectiveness and safety.
3Power
If software control is used to manage output power, then power regulation is achieved, but system complexity increases and software failure risks exist
Solution Approach 1:
The patent replaces complex software-based power control with a simpler hardware-based feedback system using DC voltage sensing and regulation. This reduces computational complexity and eliminates software failure modes while maintaining precise power control capability.
4Reliability
If open circuit detection is implemented, then safety is improved, but voltage spikes occur during sensing delay
Solution Approach 1:
The patent performs preliminary detection of open circuit conditions through continuous DC voltage monitoring before they can cause dangerous voltage spikes. By detecting changes in the DC input voltage that indicate an open circuit, the system can prevent the development of hazardous voltage conditions.
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
This design reduces leakage current by minimizing capacitance and eliminating the need for costly RMS converters and transformers, providing a cost-efficient and effective feedback estimation system that ensures safe RF energy delivery and compliance with safety standards like IEC 60601.
Implementation Method 1
a voltage sensor configured to measure DC input voltage to the RF waveform generator
Implementation Method 2
a current sensor configured to measure output current feedback
Implementation Method 3
a high-turns transformer 22 across an isolation barrier 17, which serves to isolate a supply of RF energy from the electrosurgical instrument
Implementation Method 4
due to the capacitance of transformers in isolation barriers which serve to isolate the supply of RF energy between the RF generator and the delivery device, sometimes stray leakage in the form of RF energy flows from the RF generator to ground
Data Source
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AI summary
An electrosurgical unit having power monitoring circuitry for reducing leakage current in an electrosurgical unit. The electrosurgical unit includes a power source configured to produce direct current, an RF waveform generator configured to convert the direct current into an RF signal, a voltage sensor configured to measure DC input voltage to the RF waveform generator, a current sensor configured to measure output current feedback, and a processor. The processor is configured to estimate output voltage feedback based at least upon the measured DC input voltage and the measured output current feedback, and output a control signal to control the DC input voltage to the RF waveform generator, the control signal based at least upon the estimated output voltage and the output current feedback.