A new controller for eliminating the temperature effect of a piezoelectric transformer (PT) in a backlight electronic ballast is proposed in this paper. First, a class-D backlight inverter is employed to simplify the circuit configuration and to raise system efficiency. Next, to reduce the dimensions of the backlight module for satisfying the thin-shaped design trend and to overcome the drawbacks of a conventional transformer, a PT is incorporated instead. Then, a digital phase-locked-loop (DPLL) controller is embedded into the backlight system as a feedback control mechanism to track the optimal operating frequency of the PT, so that the PT's temperature effect is removed; hence, system efficiency and stability is improved. The design considerations are detailed, and the experimental results confirm the validity of the proposed control strategy

Eliminating the Temperature Effect of Piezoelectric Transformer in Backlight Electronic Ballast by Applying the Digital Phase-Locked-Loop Technique

A phase locked loop based system that tracks the resonance frequency of a series RLC circuit is investigated. Assuming that the RLC circuit parameters are slowly and time-varying, a linear time-invariant model that accurately predicts the performance of the system is developed. The results are illustrated by examples.

Tracking the resonance frequency of a series RLC circuit using a phase locked loop

A full-bridge MOSFET DC-to-RF power inverter consisting of four branches, each branch consisting of three MOSFETs connected in parallel to enhance the power handling capability, was built for driving a high frequency, high power ultrasonic transducer with an output power of 600 W operating at 1 MHz. When the power inverter was connected to the ultrasonic transducer through an output transformer with a primary-to-secondary winding ratio of 2 to 1, the load impedance looking into the load from the inverter was 3.5 ohms at 1 MHz, and was high enough to drive the load with high power conversion efficiency, i.e., over 80%. >

https://ieeexplore.ieee.org/iel2/3173/8996/00397760.pdf

Fullbridged MOS-FET DC-to-RF power inverter for use with high-frequency high-power ultrasonic transducer

Described is a full-bridged MOSFET DC-to-RF inverter operating at a frequency of 3 MHz for driving a high frequency ultrasonic transducer for cleaning material surfaces. The full-bridged MOSFET DC-to-RF inverter generates an RF power of 60 W with a power conversion efficiency of 79 to 87% at 3 MHz when an ultrasonic transducer with a very low impedance in the order of 1 to 5 ohms is connected to the inverter. The ultrasonic transducer was satisfactorily operated when the ultrasonic transducer was driven from the full-bridged MOSFET DC-to-RF inverter.

Full-bridged MOSFET DC-to-RF inverter for high frequency ultrasonic transducer at 3 MHz

This paper describes a prototype of a shortwave DC-to-RF inverter used to drive an ultrasonic transducer, which can operate at a frequency in the range of 0.5 to 5.0 MHz. The ultrasonic transducer has a resonant frequency of 1.2 MHz, and it can also resonate at frequencies of 2.0 MHz and 4.6 MHz. The DC-to-RF inverter provides the RF power to the ultrasonic transducer at the respective resonant frequencies. >

Shortwave DC-to-RF inverter to drive ultrasonic transducer

The frequency of the MOSFET DC-to-RF power inverter is precisely set at the series resonant frequency of a megasonic transducer by controlling the oscillation frequency of the PLL when the MOSFET DC-to-RF power inverter is used to drive the megasonic transducer having an impedance of as low as 5 to 6 ohms or less. The frequency control system features a current sensor having an effective internal impedance of as low as 0.25 ohm which is negligible compared with the impedance of the megasonic transducer at the series resonant frequency. The impedance of the inverter load composed of the output transducer, matching capacitor, coaxial cable, megasonic transducer, and current sensor is calculated to determine the frequency control range of the PLL. In accordance with the result of calculation, the performance of the phase-frequency comparator, low pass filter, and VCO is decided. When the RF output power of the MOSFET power inverter was 60 W with a power conversion efficiency of 95%, the frequency control range was 2.8 MHz to 3.2 MHz. The PLL covers the range of frequency shifts and variations in the megasonic transducer and VCO.

Frequency control of MOSFET full bridge power inverter for maximizing output power to megasonic transducer at 3 MHz

Methods to increase the output power while keeping the power conversion efficiency high are discussed. Examples of the DC-RF MOSFET powers inverter operating at both 2.5 MHz and 3 MHz are presented. Despite the difficulties in designing the full-bridged MOSFET power inverter having the output power enhanced by parallel connection of the MOSFETs operating at shortwave frequencies, the experimental versions were operated with reliability and without any extraordinary temperature rise. >

http://ieeexplore.ieee.org/iel2/608/4487/00178354.pdf

S. Shinohara

Papers

Frequency control of MOSFET full bridge power inverter for maximizing output power to megasonic transducer at 3 MHz

Output power and efficiency tradeoff in full-bridged MOSFET power inverter for use at shortwave frequencies