Low-frequency Square-wave Research Articles

Analysis and implementation of an integrated electronic ballast for high‐intensity‐discharge lamps featuring high‐power factor

This paper proposes a high-power-factor electronic ballast for metal-halide (MH) lamps. In the proposed circuit, two buck–boost converters and a buck converter are integrated with a full-bridge inverter by sharing the four active switches of the full-bridge inverter. Two active switches are switched at high frequencies, while the other two are switched at lower frequencies. The buck converter is used to step down the DC-link voltage of the full-bridge inverter and filter out the high-frequency components to drive lamps with a low-frequency square-wave (LFSW) current. The buck–boost converters are operated at discontinuous-conduction mode to perform the function of power-factor correction (PFC) to ensure almost unity power factor at the input line. By tactful arrangement of diodes, the DC-link capacitors are discharged in parallel; this helps to operate the high-frequency active switches at a high duty ratio, achieving a small peak value of the PFC-converter current and correspondingly smaller conduction losses. Detailed operation modes and the design equations are provided. A prototype electronic ballast for a 70 W MH lamp is built and tested. Experimental measurements have proven that the proposed electronic ballast has the advantages of high-power factor and being free of acoustic resonance. By integrating the active switches of the converters and the inverter, the proposed electronic ballast is advantageous in terms of cost-effectiveness and high energy-conversion efficiency.

Size Reduction in Low-Frequency Square-Wave Ballasts for High-Intensity Discharge Lamps Using Soft-Saturation Magnetic Material and Digital Control Techniques

This paper presents an approach to reduce the size of low-frequency square-wave (LFSW) ballasts by using a single stage for resonant ignition and LFSW operation together with soft-saturation magnetic material and digital control techniques. Inductor design constraints are developed to leverage the nonlinear inductor behavior and achieve both size reduction and desirable performance in lamp ignition, warm-up, and normal operation modes. The digital controller provides multiple functions, including 1) a phase-controlled resonant sweep to achieve reliable lamp ignition and device protection with zero-voltage switching despite the nonlinear tank inductance, 2) lamp ignition detection and rapid transition to LFSW mode for lamp warm-up, 3) fast LFSW polarity transitions with optimal timing control for acoustic resonance free operation, and 4) two-loop feedback control. A fast current control loop limits and stabilizes the lamp current and rejects large ripple from the power factor correction (PFC) stage in order to reduce the size of the PFC output capacitor. A slow power control loop rejects variations in the lamp characteristics during warm-up and lamp aging. Experimental results are presented showing successful ignition and operation of a 150-W high-intensity discharge lamp.

Digitally Controlled Low-Frequency Square-Wave Electronic Ballast With Resonant Ignition and Power Loop

This paper proposes a digital controller for a low-frequency square-wave (LFSW) electronic ballast that includes the ignition sequence, a double control loop, and the selection of the positive and negative operation modes. The whole ballast is a two-stage circuit, where the first part is a power factor correction (PFC) stage and the second is a full-bridge (FB) converter used for both ignition and square-wave drive. Ignition is achieved by approaching the resonant frequency of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter when the lamp is in the off state and the FB is working as a resonant inverter. After ignition, the converter operates as an LFSW inverter by controlling the FB to act alternately as a buck converter supplying positive or negative current. While ignition occurs at the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter resonance frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> = 20 kHz), the buck converter switching frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sw</sub> = 200 kHz) is selected significantly higher than <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> to attenuate high-frequency harmonics and avoid exciting acoustic resonance. Lamp stability is achieved by controlling the inductor current of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> filter, and power mode control is achieved by adjusting the average current and voltage supplied by the PFC stage. The solution is experimentally validated for different types of 150-W high-intensity discharge lamps. A coupled-inductor single-ended primary inductance converter operating in continuous conduction mode is used for the PFC stage.

Experimental investigation about the effect of non-axisymmetric wake impact on a low speed axial compressor

Non-axisymmetric wake impact experiments were carried out after the best exciting frequency for a low speed axial compressor had been found by axisymmetric wake impact experiments. When the number and circumferential distribution of inlet guide vanes (IGV) are logical the wakes of non-axisymmetric IGVs can exert beneficial unsteady exciting effect on their downstream rotor flow fields and improve the compressor’s performance. In the present paper, four non-axisymmetric wake impact plans were found working better than the axisymmetric wake impact plan. Compared with the base plan, the best non-axisymmetric plan increased the compressor’s peak efficiency, and the total pressure rise by 1.1 and 2%, and enhanced the stall margin by 4.4%. The main reason why non-axisymmetric plans worked better than the axisymmetric plan was explained as the change of the unsteady exciting signal arising from IGV wakes. Besides the high-frequency components, the non-axisymmetric plan generated a beneficial low-frequency square-wave exciting signal and other secondary frequency components. Compared with the axisymmetric plan, multi-frequency exciting wakes arising from the non-axisymmetric plans are easier to get coupling relation with complex vortices such as clearance vortices, passage vortices and shedding vortices.

Digital Control of a Low-Frequency Square-Wave Electronic Ballast With Resonant Ignition

This paper proposes a two-stage low-frequency square-wave (LFSW) electronic ballast with digital control. The first stage of the ballast is a power factor correction (PFC) stage, and the second is a full-bridge (FB) converter used for both lamp ignition and LFSW drive. As a novelty for LFSW ballasts, ignition is achieved without an additional igniter circuit by operating the FB during start-up as a high-frequency resonant inverter. After ignition, the converter operates as an LFSW inverter to avoid exciting acoustic resonances by controlling the FB as a buck converter and regulating alternately positive or negative current to the lamp. Lamp power is regulated by adjusting the average current supplied by the PFC stage. Another contribution of this paper is to utilize digital control as a simple solution to achieve multimode control, including resonant lamp ignition, LFSW transitions, and lamp current and power regulation.

Arc Dynamic Stabilization in Low-Frequency Square-Wave Electronic Ballast for Metal Halide Lamps

Discharge lamps present a negative dynamic characteristic that makes necessary to use a current limiting element. In high-frequency resonant ballasts, current limitation is performed by the output resonant tank; but in low-frequency square-wave electronic ballasts, arc stabilization is accomplished by the stage feeding the square wave inverter. Therefore, the design of the input converter must be made taking into account the lamp dynamic characteristic. In the present paper, a new procedure to obtain the small-signal dynamic characteristic of metal halide lamps is proposed. Using the proposed methodology, the small-signal characteristic of a 70-W lamp is obtained. This characteristic is then used for the design of an electronic ballast based on a buck-boost converter followed by a full bridge inverter. The limits for stable operation obtained are verified using a laboratory prototype.

Study of Igniter in Low-Frequency Square Wave Electronic Ballasts for Metal Halide Lamps

Metal halide lamps (MHLs) have serious acoustic resonance problem. The most widely used method to achieve acoustic-resonance free is to use low-frequency square wave (LFSW) electronic ballasts. There are two ignition methods commonly used in LFSW electronic ballast: high-frequency resonance ignition and additional pulse igniter. This paper analyzed the problems during ignition while using the conventional additional pulse igniter and proposed some solutions. A novel high-frequency resonance igniter is also proposed, where no extra semiconductors and feedback control circuit are needed to perform the ignition. High-voltage ignition pulses are obtained by utilizing the fast polarity inversion of the output voltage of full-bridge inverter. Theoretical analysis, simulation, and experiment results of a prototype for 70-W MHLs verified the effectiveness of both the proposed solutions and the igniter.

A Novel Constant Power Control Circuit for HID Electronic Ballast

This paper presents a constant power control circuit for a three-stage high-intensity discharge (HID) electronic ballast. The three-stage electronic ballast is composed of a boost pre-regulator to achieve a high power factor, a DC/DC buck converter to regulate lamp current with constant lamp power, and a full-bridge inverter to drive the HID lamp with a low-frequency ac squarewave current. The buck converter operating in current mode utilizes current sense level-shift technique to achieve constant power output. The proposed constant power control circuit is easily designed and implemented for the three-stage HID electronic ballast. Finally, a laboratory prototype of a 70 W HID electronic ballast is implemented. The measured results show that the proposed ballast can be applied for various HID lamps with low lamp power variation (less than 0.6%).

The Development of the Buck Type Electronic Dimming Ballast for 250W MHL

In this paper, we studied the development of the electronic ballast for 250W MH (Metal-Halide) lamps. We were able to improve the input power factor by using a PFC IC. To provide the lamp with the rated voltage required, we used the buck-type dc-dc converter. The stress of the switching devices in the inverter could be reduced by this method. To eliminate the acoustic resonance phenomena of MH lamps, the voltage of the lamp added the high frequency sine-wave to the low frequency square-wave by using the full bridge typed inverter. We have developed a simple igniter using the L and C elements. We could control the dimness of the lamp by varying the output voltage of the buck converter. The buck converter output voltage could be controlled by using a microprocessor.

Allowed Level of the Power Ripple in Low Frequency Square-Wave Ballasts of Metal-Halide Lamps

In order to avoid the acoustic instabilities in metal halide (MH) lamps a proper method is to supply the lamp with a low frequency square-wave current. Due to the topology of electronic ballasts for such an application, there is a high frequency ripple in the current or voltage waveform. It is known that such ripples with sufficient energy at the proper frequency are able to excite acoustic resonance in MH lamps. The threshold value for high frequency ripples in order to excite an acoustic mode and destabilize the lamp is under debate. This threshold is lamp dependent and should be measured experimentally for each lamp type. This paper addresses an automated experimental method to determine the threshold value of the power ripple in a frequency range of 10–400 kHz. The implementation of the proposed method which is based on the light flicker factor has been explained in a preceding paper. The experimental results show that less than 1 percent of power ripple at the resonance frequency is sufficient to excite a detectable (perceptible to the human eye) acoustic instability.

26.1: Low-Frequency Square-Wave Drive for Large Screen LCD-TV Backlighting Systems

paper presents a low-frequency square-wave drive, consisting of a single high voltage converter, an ac lamp ignition circuit, current control devices and a single backlight controller, capable of driving an arbitrary number of parallel cold cathode fluorescent lamps (CCFLs) with independent accurate lamp current regulation. Key to the architecture is a proposed capacitive coupling approach for ac lamp ignition that results in reliable, simultaneous ignition of parallel lamps with a maximum ignition voltage near the normal lamp operating voltage. A brief summary of the lamp model and behavior is presented to explain the findings during the capacitive ignition and low-frequency operation. Experimental results are presented demonstrating parallel lamp ignition and current regulation for four, 250 mm CCFLs. 1. Introduction screen LCD TV backlighting systems, generally consisting of 16 or more cold cathode fluorescent lamps (CCFLs), require a ballast capable of driving all or groups of lamps in parallel with accurate current control and regulation. The most common electronic ballasts, based on high frequency LCC resonant inverters, are capable of driving at most four lamps in parallel and require complex multi-winding transformers and specialized control circuitry. This solution suffers from several disadvantages, the major limitation being the inability to simultaneously maintain high efficiency, proper lamp ignition, and individual lamp current regulation (1, 2). We present a suitable architecture, capable of driving a large parallel CCFL array with high efficiency, accurate lamp current control and near operating voltage lamp ignition. The system block diagram, shown in Fig. 1, is based on low-frequency square-wave (LFSW) drive and removes many of the drawbacks associated with a high frequency drive, including energy loss through capacitive coupling, the thermometer effect luminance uniformity degradation and electromagnetic interference (EMI). The proposed architecture is capable of driving a large parallel CCFL array with only a single high voltage and high efficiency converter, resulting in reduced size, weight and cost over existing designs. Reduced ignition voltage (at near operating voltage) is achieved by a unique capacitive coupling approach, based on the similar principles to normal operation of electrodeless or external electrode fluorescent lamps. However, the displacement current is only required in our proposed architecture as a short high frequency pulse during cold lamp ignition, which triggers simultaneous lamp ignition of all parallel lamps. High impedance current source circuit (based on MOSFET current mirror) is connected in series with each lamp to ensure individual lamp current regulation and control. In this paper, we discuss a suitable architecture for large CCFL arrays and study new approaches for lamp ignition to enable low frequency drive.

Production of nanometric particles in radio frequency glow discharges in mixtures of silane and methane

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by plasma-enhanced chemical vapor deposition (PECVD) are promising new materials for sintering ceramics, for making nanoscale filters, or for supporting catalytic surfaces. Common characteristics of these powders are their high purity and the easy control of their stoichiometry through the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon–carbon alloys exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor using mixtures of silane and methane at low pressure (&amp;lt;1 Torr) and low frequency square-wave modulated rf power (13.56 MHz). The a-Si1−xCx:H powders were obtained from different precursor gas mixtures, from R=0.05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a-Si1−xCx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of these powders in the infrared. Silicon–hydrogen groups were present for every gas composition, whereas carbon–hydrogen and silicon–carbon bonds appeared in methane-rich mixtures (R&amp;lt;0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660 °C that were ascribed to hydrogen bonded to silicon and carbon, respectively. The estimated hydrogen atom concentration in the sample was about 50%.

A Two-Component Electromagnetic Ship's Log

A ship's log is described which works on the principle of electromagnetic induction. The measuring head contains a coil with a vertical axis and is arranged so that voltages are picked up proportional to the two components of water flow past it. The electronic circuits are designed to give a true and stable zero by using a low-frequency squarewave energizing current. Laboratory tests show the output to be linearly related to water velocity. Because of the complicated flow patterns round a ship, the log must be calibratedin situat sea. Calibration of the forward component meter follows the usual procedure and this meter is accurate to about ±0·1 knot or ± 1 per cent, whichever is greater. However, calibration of the athwartship component meter is difficult and time-consuming, and the sensitivity is dependent on forward speed. With care, it seems that an accuracy of ±0·2 knot or ± 10 per cent, whichever is greater, should be possible with this meter, but more experience of such calibrations is required. The paper is discussed on p. 319.

Electrocutaneous pain thresholds in humans to low frequency square-wave pulses.

Electrocutaneous pain thresholds in humans to low frequency square-wave pulses.

Burst noise of silicon planar transistors

An important random phenomenon has been observed on low-level silicon planar transistors which has the aspect of a low-frequency squarewave of constant magnitude and random frequency. The step magnitude depends on temperature and biasing current; their probability of duration may be approached by a random Poisson process.