PWM Driven LEDs Based on Isolated DC Voltage Measurement
Das, Shuvo (2023)
2023
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Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:amk-2023091525845
https://urn.fi/URN:NBN:fi:amk-2023091525845
Tiivistelmä
Voltage regulated LED driver ICs are commonly used to drive LEDs in variable voltage conditions. The purpose of this thesis work was to design an LED driving circuit without using LED driver ICs for Teknoware company. A PWM controlled average current method was used to cope with the variability of the voltage source. The LEDs are operated in switch mode by a microcontroller generated PWM signals through an isolation barrier. The brightness levels are controlled by varying the duty cycles of the PWM signals. The microcontroller measures the power supply voltage through the isolation barrier and determines appropriate PWM duty cycles to attain specific brightness levels. The average current regulation was designed for 21V to 30V. The 3000K and 5000K color temperature LEDs were used in the circuit. The 5000K LEDs have emergency current paths in the event of missing PWM signal.
Different techniques for the isolated DC voltage measurement were explored, such as linear optocoupler, isolation amplifier based techniques. A PWM based voltage measurement circuit was developed to provide a lower cost solution. The company continued with a TL431 based voltage measurement circuit at the end. The voltage measurement circuits were measured twice; the second measurements were taken by changing ICs with the same models to observe how IC to IC variation affects the measurement accuracy. The linear optocoupler based circuit had the largest voltage measurement error, while the isolation amplifier based circuit provided the best measurement accuracy. TL431 based circuit produced a maximum 676mV difference with the power supply voltage between 20V and 30V, whereas the PWM based voltage measurement circuit produced a maximum of 375mV difference.
The measured PWM duty cycles for different brightness levels and emergency mode current were close to the theoretical values.
The software department of the company utilizes the result of this thesis work to program the microcontroller for driving the LEDs.
Different techniques for the isolated DC voltage measurement were explored, such as linear optocoupler, isolation amplifier based techniques. A PWM based voltage measurement circuit was developed to provide a lower cost solution. The company continued with a TL431 based voltage measurement circuit at the end. The voltage measurement circuits were measured twice; the second measurements were taken by changing ICs with the same models to observe how IC to IC variation affects the measurement accuracy. The linear optocoupler based circuit had the largest voltage measurement error, while the isolation amplifier based circuit provided the best measurement accuracy. TL431 based circuit produced a maximum 676mV difference with the power supply voltage between 20V and 30V, whereas the PWM based voltage measurement circuit produced a maximum of 375mV difference.
The measured PWM duty cycles for different brightness levels and emergency mode current were close to the theoretical values.
The software department of the company utilizes the result of this thesis work to program the microcontroller for driving the LEDs.