Electronic Ballast Boost Voltage TRIAC Conduction
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Solution Overview
Problem
Existing electronic ballasts for compact fluorescent lamps (CFLs) face issues with flickering and buzzing due to non-linear load characteristics, particularly at low dimming levels, as they do not continuously draw a current higher than the holding current over a half-cycle, leading to premature conduction cutoff and resonant frequency changes that are difficult to manage.
Innovation Solution
The solution involves augmenting the charging voltage for the input capacitor in the electronic ballast, using a secondary winding of a transformer to generate a boost voltage that increases the charging potential, ensuring continuous conduction of the TRIAC and reducing the size of the input capacitor, thereby stabilizing the resonant frequency and maintaining even brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a charge pump circuit is used to drive the CFL, then the lamp can operate at high frequency, but the current drawn from the mains falls below the holding current of the TRIAC, causing flickering and buzzing
Solution Approach 1:
The patent applies preliminary action by charging the input capacitor to a higher voltage before the TRIAC turns off. This is achieved by adjusting the charge pump circuit to charge the capacitor to a voltage significantly higher than the peak mains voltage. When the TRIAC turns off during the next half-cycle, this pre-charged capacitor provides sufficient current to maintain TRIAC conduction throughout the entire half-cycle, preventing flickering and buzzing.
2Reliability
If the value of the charge pump input capacitor is increased to maintain TRIAC conduction, then the holding current requirement is met, but the resonant frequency of the inverter changes significantly when the TRIAC switches, making feedback control difficult
Solution Approach 1:
The patent applies parameter changes by modifying the charging voltage parameter of the input capacitor rather than changing its capacitance value. By charging the capacitor to a higher voltage (significantly above peak mains voltage), the system maintains TRIAC conduction with a smaller capacitor value. This keeps the resonant frequency changes manageable and simplifies feedback control while still meeting the holding current requirement.
3Reliability
If a larger charge pump input capacitor is used to ensure sufficient current, then the TRIAC conduction is maintained, but the ballast size and cost increase
Solution Approach 1:
The patent applies parameter changes by increasing the charging voltage of the input capacitor rather than increasing its capacitance value. This allows the system to maintain TRIAC conduction with a smaller capacitor, reducing the overall ballast size and cost while still providing sufficient current to maintain conduction throughout the half-cycle.
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 approach effectively prevents flickering and buzzing by maintaining the conduction of the TRIAC, allowing for smooth dimming and reducing the complexity of feedback control, while also enabling a more compact design by minimizing the size of the input capacitor.
Implementation Method 1
using a secondary winding of a transformer to generate a boost voltage that increases the charging potential
Data Source
Figure 1~2
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AI summary
An electronic ballast for lighting applications is disclosed. The electronic ballast comprises a first charge pump having an input capacitor (13) charged with a supply current drawn from a power source by application of a charging voltage to the input capacitor (13), the magnitude of the supply current being proportional to the magnitude of the charging voltage; and a voltage booster (16, 17) for generating a boost voltage, which is used to augment the charging voltage, thereby increasing the current drawn from the power source.