Low-frequency Square-wave Electronic Ballast Research Articles

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.

Low-frequency square-wave electronic ballast for multiple metal halide lamps

A novel electronic ballast for multiple metal halide lamps is proposed. The lamp power control stages are composed of two-output flyback converters. The lamp driving stage is a half-bridge inverter that is used to drive lamps with a low-frequency square waveform. Implementation of the proposed topology is easy, useful, and low cost. A laboratory prototype of the electronic ballast used to drive four 20 W metal halide lamps is implemented.

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.

Design of a two-stage low-frequency square-wave electronic ballast for HID lamps

This paper presents a two-stage low-frequency square-wave electronic ballast for high-intensity discharge lamps. The ballast consists of a power-factor-correction stage to achieve power-factor correction and an inverter to supply the lamp with low-frequency square-wave current. Due to its low-frequency operation, no acoustic resonance occurs. Ignition, warmup process, and end-of-life detection are analyzed in detail. The presented circuit was verified with simulation and experimental results.