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Ballast design assistant (BDA) Software
A software program (BDA V4.0) has been developed for easy design and prototyping of electronic ballasts. This program includes a graphical interface with a 5-step design procedure. The steps include selecting the control IC, the ballast input configuration, the lamp type, and the lamp configuration. The final step will calculate the ballast parameters and output the schematic, bill of materials and inductor specifications.
An advanced display is also available (Figure 6) that provides all input and output data and allows the user to modify parameters and view the calculation results. An operating points Bode diagram and time-domain graph are also generated so the actual ballast operating points and actual time-domain waveforms can be analyzed in more detail.
Figure 6, Advanced display page with calculations, Bode diagram and time-domain waveforms
When the calculations, operating points and time-domain waveforms look acceptable, the software can then generate the necessary schematic, bill of materials and inductor specifications for the complete ballast. This output data can be directly used to build a ballast prototype on the bench.
Other features include a custom library for user-specific lamp types, website links to obtain more information about each control IC, and export or print diagrams, plots, data and tables.
Dimming Ballast Prototype
An actual T5/35W dimming ballast prototype has been built and tested on the bench. The ballast was designed using the BDA V4.0 software and the bench results were summarized and compared against the software calculations. The schematics generated by the software include (Figure 7) an EMI filter at the mains input to block ballast noise, a power factor controller (PFC) boost converter to provide sinusoidal input current and regulate the DC bus voltage, the IR21592 dimming ballast control IC to drive the half-bridge MOSFETs and control the lamp dimming level, and final resonant output stage for preheating, igniting and dimming the fluorescent lamp.
Figure 7, T5/35W dimming ballast schematics. (Please note: EMI filter is not optimized and dimming input is non-isolated. More EMI filtering and an additional isolated dimming interface may be required.)
The ballast measurements include preheat, ignition and dimming lamp modes (Figure 8), dimming at 100% (Figure 9), and dimming at 5% (Figure 10).
Figure 8, Lamp voltage during preheat, ignition and dimming operating modes
Figure 9, Half-bridge output (green) and lamp current (yellow) during 100% dimming level
Figure 10, Half-bridge output (green) and lamp current (yellow) during 5% dimming level
The final ballast parameters have been summarized (Table II) and compared against the software calculations. Such deviations between calculated and measured values are normal and are due to component and lamp tolerances.
| Parameter |
Description |
BDA Calculations |
Measured |
| LRES |
Resonant inductor |
4.0 mH |
3.95 mH |
| CRES |
Resonant capacitor |
3.3 nF |
3.28 nF |
| fPH |
Preheat frequency |
53.7 kHz |
55.4 kHz |
| fIGN |
Ignition frequency |
49.6 kHz |
48.5 kHz |
| f100% |
100% dimming frequency |
44.8 kHz |
45.5 kHz |
| f5% |
5% dimming frequency |
55.4 kHz |
54.1 kHz |
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Table II, Calculated and measured ballast parameters
Conclusions
An overview of a dimming electronic ballast has been presented. A simplified lamp model and requirements have been discussed for understanding fluorescent lamp electrical behavior. The resonant output stage has also been analyzed and a phase angle dimming control method has been described. The actual design of a complete dimming ballast has been facilitated using a new ballast design software program that gave good results compared to actual measurements. The prototype has been demonstrated to fulfill the lamp preheat, ignition and dimming lamp modes, with only minor tuning necessary to adjust the final dimming levels. Designing a dimming ballast is a difficult task that requires knowledge of fluorescent lamp electrical behavior, control theory experience and resonant converter design skills. The BDA software greatly simplifies this task and has proven to be an invaluable design aid allowing rapid analysis, design and construction of a fully-functional working prototype. This will result in simplified designs, shorter ballast design cycles, faster time to production, and faster time to market.
About the author
Tom Ribarich is Director of the Lighting Design Center at International Rectifier based in El Segundo, CA. Tom is responsible for defining and developing high-voltage control ICs for the global lighting market, including devices for fluorescent, halogen, HID and LED applications. Mr. Ribarich holds a BSEE from California State University (Northridge), a Masters in ASIC design from the University of Rapperswil (Switzerland), and has 16 years experience in IC design.
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