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Phase-lead controllers are commonly used in various control systems to enhance response speed and stability. Adjusting the brightness on a television screen offers a practical example of phase-lead control. When contrast is enhanced, a phase-lead controller is employed. Mathematically, phase-lead control is identified when the first parameter is smaller than the second.
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Proportional Integral (PI) controllers are a fundamental component in modern control systems, widely used to enhance performance and mitigate steady-state errors. They are particularly effective in applications such as automatic brightness adjustment on smartphones, where they excel at mitigating steady-state errors for step-function inputs. Unlike PD controllers, which require time-varying errors to function optimally, PI controllers leverage their integral component to address residual...
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Phase-lag controllers are widely used in control systems to improve stability and reduce steady-state errors. A dimmer switch controlling the brightness of a light bulb serves as a practical example of phase-lag control, gradually adjusting the bulb's brightness. Mathematically, phase-lag control or low-pass filtering is represented when the factor 'a' is less than 1.
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The power transmission to a factory involves the transfer of apparent power, a combination of active and reactive power. The power factor measures how effectively electrical power is converted into useful work output. The ratio of the real power (KW) that does the work to the apparent power (KVA) supplied to the circuit.
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Understanding the working function of different types of controllers can be illustrated with practical analogies, such as adjusting a stereo's volume equalizer. Cranking up the bass involves a phase-lead controller, which functions as a high-pass filter, while increasing the treble uses a phase-lag controller, which acts as a low-pass filter. PD controllers, similar to high-pass filters, enhance the system's response to high-frequency components. PI controllers, akin to low-pass...
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Related Experiment Video

Updated: Nov 27, 2025

Development of an Innovative LED-based Illumination Device for In Vitro Application of Photodynamic Therapy with Rose Bengal
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Development of a LED light therapy device with power density control using a Fuzzy logic controller.

Duc Tri Phan1, Ngoc Thang Bui1, Tan Hung Vo1

  • 1Industry 4.0 Convergence Bionics Engineering, Pukyong National University, Republic of Korea.

Medical Engineering & Physics
|December 2, 2020
PubMed
Summary

This study introduces a novel fuzzy logic controller for light-emitting diode (LED) therapy devices to maintain stable power density during battery discharge. The design ensures consistent LED output, enhancing device performance and battery longevity.

Keywords:
Fuzzy logicLED light therapy deviceLED power density control

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Area of Science:

  • Biomedical Engineering
  • Photonics
  • Control Systems

Background:

  • Light-emitting diode (LED) therapy device efficacy depends on irradiation parameters like wavelength and power density.
  • Battery power in LED devices leads to power density variations during discharge, impacting treatment consistency.
  • Stable LED power density, extended battery life, and operational time are critical design challenges.

Purpose of the Study:

  • To design an LED light therapy device with independent control over different LED color power densities.
  • To implement a fuzzy logic controller for maintaining constant LED power density.
  • To improve energy efficiency and operational stability of battery-powered LED therapy devices.

Main Methods:

  • A fuzzy logic control system was developed, correlating LED power density with operating time.
  • The controller was integrated into an LED light therapy device prototype.
  • Experimental validation was performed to assess power density stability across varying voltage conditions.

Main Results:

  • The fuzzy logic controller successfully maintained stable LED power densities: 40 mW/cm² (red), 50 mW/cm² (blue), and 60 mW/cm² (green).
  • The designed controller demonstrated consistent power output despite a broad range of voltage variations.
  • The system achieved energy savings compared to conventional designs.

Conclusions:

  • The proposed fuzzy logic controller effectively stabilizes LED power density in light therapy devices.
  • This advanced design offers improved energy efficiency and reliable performance under fluctuating battery voltage.
  • The developed LED therapy device represents a significant advancement in stable, battery-powered phototherapy applications.