Power Design

Posted on Feb 6, 2014

Electronic ballasts for dimming fluorescent lamps require a control interface for the user to set the desired lamp-brightness level. Existing interface circuits include a 1-to-10-Vdc interface, digitally-addressable lighting interface (DALI), triac-based wall dimmers, three-way lamp sockets, power line communications, and wireless communications.

Power Design
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Each of these interface circuits requires additional wiring to each ballast during installation, a special lamp socket or wall dimmer, or an additional signal processing unit. A new circuit implemented in International Rectifier`s IRS2530D DIM8 dimming ballast control IC eliminates the need for any additional interface components by sensing the on/off switching of the ac line voltage and cycling through the dimming range in four steps. This allows for the lamp to be dimmed with any standard on/off switch without any additional wiring. The IRS2530D provides all of the necessary ballast functions, fault detection and dimming control required for operation of fluorescent lamps. A microcontroller and pulse detection circuit is used to sense each recycling of the ac line voltage, change the dimming reference, and store the previous dimming level. This article explains how the IRS2530D operates and presents a complete four-level switch-dimming application circuit built around this IC. A complete set of schematics and waveforms is included to help designers better understand and design the new circuit. The electronic ballast circuit block diagram (Figure 1) includes the ac line input voltage (typically 220 Vac/50 Hz or 120 Vac/60 Hz), an EMI filter to block circuit-generated switching noise, a rectifier and smoothing capacitor, a control IC and half-bridge inverter for dc-ac conversion, and the resonant tank circuit to ignite and...

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