Single-ended (SE) resonant inverters are widely used as power converters for high-pressure rice cooker induction, with 1200 V insulated-gate bipolar transistors (IGBTs) being used as switching devices for kW-class products. When voltage fluctuations occur at the input stage of an SE resonant inverter, the resonant voltage applied to the IGBT can be directly affected, potentially exceeding the breakdown voltage of the IGBT, resulting in its failure. Consequently, the resonant voltage should be limited to below a safety threshold—hardware resonant voltage limiting methods are generally used to do so. This paper proposes a sensorless resonant voltage control method that limits the increase in the resonant voltage caused by overvoltage or supply voltage fluctuations. By calculating and predicting the resonance voltage through the analysis of the resonance circuit, the resonance voltage is controlled not to exceed the breakdown voltage of the IGBT. The experimental results of a 1.35 kW SE resonant inverter for a high-pressure induction heating rice cooker were used to verify the validity of the proposed sensorless resonant voltage limiting method.
A new low-voltage detecting method for a multichannel LED back lighting unit is proposed. The proposed method detects the lowest voltage drops among the multichannel LED strings with a reduced number of devices, and it provides feedback voltage to control the stages of the boost converter for minimising the power consumption in the LED driving circuit.Introduction: A backlight unit is needed in LCD applications, and two major backlighting sources are widely used: the cold cathode fluorescent lamp (CCFL) and the light emitting diode (LED). Recently, LEDs have gradually substituted CCFLs as the backlighting source for their better colour gamut, longer lifetime and thin structure. LED back lighting units (BLUs) can also provide a local dimming function that significantly enhances the contrast ratio (CR) in LCD TVs, and its colour spectrum is even larger than NTSC [1,2].In general, the LED backlighting system consists of a boost converter and current driving channels. The boost converter supplies sufficient voltage to ensure the normal operation of LED strings, and the current drive channels regulate the current of each LED string. LEDs have an inherent forward voltage drop deviation. Moreover, the forward voltage drop of LEDs depends on the junction temperature. For these reasons, the channel voltage drop in the LED driving circuit should be kept as low as possible to minimise the power consumption. To achieve this, a low-voltage detection circuit is required to control the output voltage of the boost converter in an LED BLU.The most common method for controlling low voltage in LED strings is sensing the cathode voltage of each LED string with small-signal diodes and regulating the voltage of the boost converter [3,4]. Although they are simple to implement, these methods are inaccurate because sensing diodes also have variations in forward voltage drop as well as temperature dependence, which results in higher cost and poor sensing accuracy.
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