RF Generator Power Monitoring Using Estimated Voltage Feedback
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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 current flow to patients and medical personnel, and existing solutions like software controls and throttling schemes are inadequate or complex.
Innovation Solution
The proposed solution involves 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, and a microprocessor to control the RF waveform generator, eliminating the need for costly RMS converters and transformers, thereby reducing leakage current.
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 output side and relocates it to the DC input side. Instead of measuring RF voltage through inductive couplings across the isolation barrier, the system measures DC voltage at the input and uses it to calculate the equivalent RF output voltage. This removes the problematic capacitive coupling elements that cause leakage current.
Solution Approach 2:
The patent replaces the electromagnetic/inductive measurement system with a computational approach. Instead of using physical inductive couplings to sense RF voltage, the system uses DC voltage sensing combined with microprocessor-based calculations that account for the known transformer ratio and circuit characteristics to determine the equivalent RF output voltage.
2Object-generated 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 a feedback control system that continuously monitors the calculated RF output voltage and adjusts the DC input voltage accordingly. The microprocessor compares the calculated output voltage with the desired setpoint and dynamically adjusts the PWM duty cycle to maintain accurate voltage control, enabling the system to achieve both low leakage current and proper coagulation performance through precise real-time regulation.
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 effectively minimizes leakage current, improves cost-efficiency, and ensures safe operation by accurately regulating RF energy delivery while complying with safety standards like IEC 60601, even under fault conditions.
Implementation Method 1
an RF waveform generator (60) configured to convert the direct current into an RF signal
Implementation Method 2
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
Implementation Method 3
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
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.