High-Frequency Power Supply with Constant-Current Conversion Circuit
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Solution Overview
Problem
Existing high-frequency power supplies for inductively coupled plasma (ICP) emission spectrometers face challenges in maintaining stable operation when the resistance component of the load impedance abruptly changes, leading to potential MOSFET damage and performance deterioration due to excessive current, especially when the plasma suddenly disappears.
Innovation Solution
A high-frequency power supply with a direct current voltage source, half-bridge drive circuits, and a constant-current conversion circuit, where the control terminal of semiconductor switching elements is connected to a transformer secondary winding, and a capacitor is used in parallel, allowing for stable operation by maintaining a constant product of voltage and current, thus preventing abrupt current increases and ensuring safe plasma regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional high-frequency power supply with fixed output impedance (50Ω) is used, then the power supply is simple to design and manufacture, but it cannot maintain stable operation when the load impedance varies, leading to potential MOSFET damage
Solution Approach 1:
The patent applies dynamics by making the output impedance of the high-frequency power supply variable rather than fixed. The control circuit dynamically adjusts the output impedance to match the varying load impedance (induction coil impedance) in real-time, enabling stable operation under different plasma conditions while preventing MOSFET damage from impedance mismatches
Solution Approach 2:
The patent implements feedback control where the control circuit continuously monitors the load impedance and adjusts the output impedance accordingly. This feedback mechanism ensures the power supply adapts to impedance variations caused by plasma formation and disappearance, maintaining reliable operation without requiring complex additional protection circuits
2Reliability
If the output impedance is fixed at 50Ω, then the power supply circuit is simpler, but excessive current flows when plasma disappears causing MOSFET damage
Solution Approach 1:
The control circuit uses feedback to detect when plasma disappears by monitoring impedance changes, and automatically adjusts the output impedance to prevent excessive current flow. This protects the MOSFET from damage without requiring separate protection circuits or complex control logic
Solution Approach 2:
The power supply system performs self-protection by automatically detecting plasma status and adjusting its own output impedance to prevent damage. The control circuit inherently monitors and responds to abnormal conditions without external intervention or additional protection components
3Loss of energy
If a tuning circuit with vacuum variable capacitor is used to maintain 50Ω impedance, then the reflected power can be minimized, but the control mechanism becomes complicated and costly
Solution Approach 1:
The patent replaces the mechanical vacuum variable capacitor tuning circuit with an electronic control system that adjusts output impedance through solid-state components. This substitution eliminates mechanical moving parts while achieving the same goal of minimizing reflected power through electronic impedance matching
Solution Approach 2:
The control circuit changes the output impedance parameter dynamically to match the load impedance, thereby minimizing reflected power. Instead of using a fixed 50Ω output with mechanical tuning, the system electronically adjusts the output impedance parameter to optimize power transfer under varying plasma 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
The solution enables stable and efficient operation by automatically controlling the current flowing into the induction coil, preventing overcurrent and maintaining optimal power supply to the plasma, even when the resistance component of the load impedance decreases abruptly, thereby ensuring safe and continuous plasma generation.
Implementation Method 1
plasma is generated and maintained by introducing a plasma-generating gas such as argon as well as an analysis sample into a plasma torch and supplying high-frequency power to an induction coil
Implementation Method 2
A high-frequency electromagnetic field is produced in a plasma-generation portion by a high-frequency current flowing through the induction coil, and the plasma is heated by induction current caused by acceleration of charged particles in the plasma
Implementation Method 3
A resonant circuit is formed by the induction coil and a capacitor to supply power to the plasma
Data Source
AI summary
A high-frequency power supply apparatus for supplying high-frequency power to a load the impedance of which greatly fluctuates is provided, wherein a stable high-frequency current is always maintained without having overcurrent or overvoltage generated in a drive circuit thereof. In the high-frequency power supply apparatus, a constant-current conversion circuit is connected between an LCR series resonant circuit and a half-bridge drive circuit, high-frequency current of the LCR series resonant circuit is controlled by the voltage of the half-bridge drive circuit, and a constant-current function is applied to impedance variation of the load. Due to the constant-current conversion circuit, the gate of a MOSFET of the half-bridge drive circuit is driven with a parallel capacitor using a transformer inserted in the LCR series resonant circuit, and the phases of the high-frequency current of the LCR series resonant circuit and the output of the half-bridge drive circuit are maintained to be constant.