A CCFL inverter is an electrical inverter that supplies alternating current power to a cold cathode fluorescent lamp (CCFL). CCFLs are often used as inexpensive light units in electronic devices powered by direct current sources such as batteries. CCFL inverters are small, have a power conversion efficiency over 80%, and offer adjustable light output. They are widely used for backlights for LCDs or for rear lighting in advertising signs. History Voltage resonant self-excited type circuits have been widely used as inverter circuits for cold cathode fluorescent lamps. This is sometimes referred to as the "Royer circuit".[1] However, the proper definition of the Royer circuit requires that the inversion of a switching operation be performed in a state in which the transformer is saturated. An inverter circuit which performs the inversion operation by utilizing resonance in the collector circuit of a transistor is preferably referred to as the "Baxandall converter" in distinction from a true Royer circuit.[2] In the early designs of inverter circuits for cold cathode fluorescent lamps, the resonance method of a secondary circuit was not utilized at all. Instead, a so-called non-leakage type transformer with small leakage inductance was used as a step-up transformer. The size of transformers in inverter circuits during this era was large compared to the power they handled, and their power conversion efficiency was not so good. Resonant transformer and ultra-small CCFL-Inverter Leakage inductance (more precisely, short-circuit inductance) was disliked because it caused a reduction in the output voltage on the secondary side of the transformer. This was considered undesirable, and it was thought to be necessary to reduce it as much as possible. At the same time, the parasitic capacitance of the LCD backlight was also disliked as it caused a reduction in the lamp current.[3] In the next era, methods were invented to dramatically improve efficiency by resonating these disliked components with each other.[4][5] Development of LCD backlight inverters and piezoelectric inverter circuits With the development of liquid crystal display technology, the CCFL inverter circuit was also required to be miniaturized. However, in an inverter circuit using a conventional non-leakage transformer, when trying to miniaturize the transformer, the magnetization current of the primary winding increases and heat generation increases. It was thought that there is a limit to the miniaturization of the transformer. Therefore, major electric manufacturers competed to develop inverter circuits for CCFL using a piezoelectric transformer which invented by Rosen, and the miniaturization of the inverter circuit was about to be realized. [6] This piezoelectric inverter circuit is very small and, at the same time, has very high efficiency compared to the CCFL inverter circuit that uses a non-leakage transformer. As a result, it was expected to be widely used as the LCD backlight inverter for notebook PCs. However, this inverter method is extremely expensive, and there are many failures due to damage of the piezoelectric element, so it was gradually replaced by the winding-type ultra-small inverter circuit which is low-cost, high-efficiency, and highly reliable. Ultra-small inverter In 1992, a Japanese inventor discovered the power factor improvement effect, which led to a significant reduction in the size of the CCFL inverter circuit. This effect is achieved by resonating the secondary side of the step-up transformer, which reduces the magnetization current of the primary winding and allows for a drastic reduction in the number of turns in the primary winding. Moreover, the ferrite core can be uniquely shaped so that the magnetic path is elongated and the cross-sectional area is smaller compared to a standard non-leakage transformer.[7] Over the following decade, it became apparent that resonance on the primary side was unnecessary.[8] Several IC manufacturers then competed to develop new methods, resulting in the creation of two types of drive ICs that used resonance only on the secondary side. With O2 Micro International and MPS (Monolithic Power Systems), two drive methods called external excitation type and current resonant type, combined with this elongated shape transformer, had become widespread. And they became occupied almost 100% of the world's notebook LCD backlight inverters.[9][10][11] For the room illumination For room illumination purposes, CCFL technology has been increasingly adopted due to its high efficiency, comparable costs to compact fluorescent lighting, long lifespan, and eye-friendly light emission. Inverter circuits based on external excitation or current resonant circuits inherited from LCD backlight technology are utilized to power the CCFL. The current resonant circuit utilizes current phase feedback to track changes in the resonant frequency of the secondary side caused by human interaction and adjust the driving frequency accordingly to maintain stable lighting performance.
●初期のnon-leakage type transformerの時代は二次側の共振を利用せず、Baxandall oscillatorの時代。効率は良くない。
●CCFLインバータ回路は電圧共振回路(Baxandall oscillator)の一次側駆動と二次側の直列共振の組み合わせから始まる。(1993年頃〜螢謄ノリウム)
■ワイヤレス給電においてはオークランド大学とダイフク(Baxandall oscillator)から始まる。(1993年頃)
●一次側の電圧共振回路(Baxandall oscillator)は二次側の直列共振周波数と相性が悪いことに気づく(平成8年通産省補助事業実験)
■オークランド大学ジョンボーイズも電圧共振回路(Baxandall oscillator)と二次側共振との相性が悪いことをチュートリアルの中で述べている。
■WiTricityは駆動周波数を85KHzに固定するようにライセンス契約書で強要する。(2023年現在)←WiTricityはイマココ (CCFLインバータの他励型に相当)
●CCFLは電流共振型回路にして一次側電流位相検出で二次側共振周波数をトラッキングする。S-S方式に該当 (2000年頃〜Monolithic Power Systems)
●応答速度ではPLL方式よりも電流位相で直接スイッチングする方法に軍配。(2001年頃〜Monolithic Power Systems)
一次側検出電流共振型 ZCS-ONのSwitching方式
●CCFLは一次側の共振が二次側の共振周波数のトラッキングの障害になることを次第に認識し始め、一次側共振を止める。S-S方式からN-S方式に移行という意味。(2001年頃〜Monolithic Power Systems)
■ワイヤレス給電は途中のS-S方式(CCFLインバータでいえば他励型:2000年頃に相当)で停滞している、という状態である。これはCCFLインバータ回路における"Over the following decade, it became apparent that resonance on the primary side was unnecessary."の最中に該当する。