Preheat Control Device for Gas-Discharge Lamp Voltage Modulation
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Solution Overview
Problem
Conventional electronic ballasts using class-D half-bridge designs face issues with increased manufacturing costs and shortened lamp lifetime due to glow current during the preheat state, as they require additional circuitry or higher DC-link capacitors to manage lamp voltage effectively.
Innovation Solution
A preheat control device employing pulse-width modulation (PWM) to reduce gas-discharge lamp voltage during the preheat state and pulse frequency modulation (PFM) to stabilize current during the steady state, utilizing an analog or digital controller without modifying the existing half-bridge driver and resonant tank network, comprising a PWM circuit, PFM circuit, and timing unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional class-D half-bridge design is used with standard half-bridge configuration, then manufacturing cost is reduced, but lamp voltage cannot be effectively controlled during preheat state leading to glow current and shortened lamp lifetime
Solution Approach 1:
The patent applies dynamic switching control during the preheat state by rapidly switching the lamp voltage between positive and negative values using the existing half-bridge driver. This dynamic voltage modulation prevents glow current while maintaining preheat current, extending lamp lifetime without requiring additional circuitry or increasing manufacturing cost.
2Reliability
If additional external switch is added to set lamp voltage to zero, then lamp voltage control is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent makes the existing half-bridge driver multi-functional by enabling it to perform both the standard half-bridge function and the additional function of dynamically modulating lamp voltage during preheat state. This universal use of the existing driver eliminates the need for additional external switches and circuitry, maintaining simplicity while improving voltage control.
3Stability of the object's composition
If DC-link capacitor is increased to manage lamp voltage, then voltage stability is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces the passive approach of using a larger DC-link capacitor with an active control approach using PWM switching. By dynamically switching the lamp voltage through the half-bridge driver, the system achieves voltage stability without requiring increased capacitor capacity, thereby avoiding additional manufacturing cost.
Data Source
AI summary
A preheat control device for modulating the voltage of a gas-discharge lamp is disclosed, which comprises: a pulse-width modulation (PWM) circuit, for controlling the voltage of the gas-discharge lamp while it is operating at a preheat state; a pulse frequency modulation (PFM) circuit, for controlling the frequency of the gas-discharge lamp while it is operating at a steady state so as to stabilize the current flowing through the lamp; and a timing unit, for determining a preheat period of the gas-discharge lamp.