Voltage Fed Ballast Frequency Boosting for Lamp Preheat
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Solution Overview
Problem
Current voltage fed electronic ballasts lack a reliable method to provide a low current preheat signal in a non-capacitive mode, leading to shortened lamp life due to excessive preheat glow current when using self-oscillating modes without capacitive mode detection.
Innovation Solution
A voltage fed electronic ballast design that includes an inverter portion converting DC to AC, a resonant portion with a filament transformer providing preheat current to lamp cathodes, and a self-oscillating mode that boosts the AC frequency above the resonant frequency for preheating, then lowers it for ignition, while maintaining a non-capacitive mode without external IC control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If self-oscillating mode with inverter clamping is used, then IC controller is eliminated simplifying the circuit, but preheat glow current becomes too high shortening lamp life
Solution Approach 1:
The patent segments the secondary windings of the filament transformer into two separate sets: one set dedicated to providing preheat current to the cathodes, and another set providing drive signals to the gate drive circuitry. This segmentation allows independent optimization of preheat current levels without affecting the inverter control functionality, thereby extending lamp life while maintaining circuit simplicity.
Solution Approach 2:
The patent implements dynamic frequency control where the AC signal frequency is boosted above the characteristic resonant frequency during preheating to minimize glow current, then lowered to the resonant frequency for ignition. This dynamic adjustment of operating parameters enables low current preheating in self-oscillating mode without requiring capacitive mode detection or IC controllers.
2Reliability
If frequency is lowered to resonant frequency for ignition, then lamp ignites successfully, but glow current increases potentially damaging cathodes
Solution Approach 1:
The patent applies preliminary action by providing preheating current to the cathodes through the filament transformer before ignition occurs. The frequency is initially boosted above resonant frequency to minimize glow current during preheating, then lowered to resonant frequency only after cathodes are adequately heated, ensuring reliable ignition without cathode damage from excessive glow current.
Solution Approach 2:
The patent changes the operating frequency parameter dynamically: boosting it above the characteristic resonant frequency during the preheat phase to minimize glow current, then lowering it to the resonant frequency at ignition. This parameter change enables successful ignition while avoiding the harmful effect of high glow current on cold cathodes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution minimizes glow current during preheating, prevents component overheating, and ensures non-destructive lamp ignition, extending lamp life and maintaining soft-switching mode throughout the process.
Implementation Method 1
An inverter portion receives a direct current input from a DC bus and converts it into an alternating current output
Implementation Method 2
A filament transformer in parallel with the resonant portion provides a preheat current to cathodes of the lamps (28, 30, 32, 34) during a preheat phase
Implementation Method 3
A frequency of the AC signal is boosted to a frequency greater than the characteristic resonant frequency of the resonant portion, preventing the AC signal from lighting the at least one lamp. The frequency of the AC signal is lowered to the characteristic resonant frequency, igniting the at least one lamp
Data Source
Figure 1
Figure 2
AI summary
A lighting ballast (10) includes an inverter portion (12) and a resonant portion (14). During a preheat phase, a filament transformer (110) supplies preheat glow currents to lamp cathodes. Also during the preheat phase, the filament transformer boosts the oscillation frequency of the inverter portion (12) to a frequency above a resonant frequency of the resonant portion (14). Once the lamp cathodes are sufficiently heated, the filament transformer (110) is removed from the circuit and the inverter (12) is allowed to start oscillating. A feedback network (150) monitors a high frequency bus (26) and provides input to a shunt regulator (170). The shunt regulator drives the gate of a switch (128) of a bias network (126) and adds or removes the filament transformer (110) to the circuit depending on the conductive state of the switch (128).