Inverter Driver Soft Start Using PWM Duty Ratio Control
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Solution Overview
Problem
Existing inverter drivers for discharge lamps require complex and costly soft starting methods, such as digital-analog converters or capacitors, which increase the size and cost of the driver due to the need for additional components and increased area for the soft start block.
Innovation Solution
An inverter driver that implements a simple soft start function using a control signal with a specific waveform to control the duty ratio of switches and charge/discharge a capacitor, allowing for gradual voltage increase during the soft start period without the need for a digital-analog converter, utilizing an amplifier, comparators, and a soft start unit to manage the capacitor voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a soft starting method using a capacitor or digital-analog converter is implemented in the inverter driver, then the discharge lamp life is extended, but the device complexity and size are increased
Solution Approach 1:
The patent merges the soft start function with the existing PWM control circuit by utilizing the existing capacitor and control signal generation capabilities. The soft start is achieved by controlling the duty ratio of the PWM signal during the startup period, combining two functions (PWM control and soft start) into a single integrated control mechanism, thereby avoiding additional components while extending lamp life
Solution Approach 2:
The existing capacitor in the inverter driver circuit is made to serve dual purposes: both its traditional function and the soft start function. By controlling the charging and discharging of this existing capacitor through duty ratio adjustment, the system achieves soft start capability without requiring separate dedicated components, reducing overall device complexity
2Reliability
If a digital-analog converter is added to implement soft start, then the discharge lamp life is extended, but the manufacturing cost is increased
Solution Approach 1:
The patent replaces expensive digital-analog converter components with a simpler, more cost-effective control approach using basic PWM duty ratio adjustment. This uses readily available control circuit elements that are cheaper to manufacture and integrate, reducing the overall manufacturing cost while achieving the same soft start functionality
Solution Approach 2:
The patent extracts the essential soft start functionality from the complex digital-analog converter and implements it through a simplified control mechanism. By taking out only the necessary function (gradual voltage increase) and implementing it through duty ratio control of existing components, the solution eliminates the need for expensive converter hardware
3Reliability
If a separate output pin is added to implement soft start using a capacitor, then the discharge lamp life is extended, but the device complexity is increased
Solution Approach 1:
The patent makes the existing capacitor and control signal output serve multiple functions: both the primary control function and the soft start function. By controlling the duty ratio of the existing PWM output, the same signal path and components are used for both normal operation and soft start, eliminating the need for separate output pins and reducing device complexity
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 enables a cost-effective and compact implementation of the soft start function, extending the life of discharge lamps by gradually increasing the output voltage during startup, thereby reducing the overall cost and size of the inverter driver.
Implementation Method 1
a capacitor, and an inverter driver. The inverter converts an input voltage into a driving voltage of the discharge lamp using at least one first switch for switching according to a duty ratio. The capacitor is charged and discharged by a current corresponding to a difference between a feedback voltage corresponding to a current flow to the discharge lamp and a reference voltage.
Data Source
AI summary
A load driver includes an inverter and an inverter driver. The inverter converts an input voltage into a driving voltage of a discharge lamp using at least one first switch for switching according to a duty ratio, and the inverter driver controls the inverter. The inverter driver controls the duty ratio using a voltage of a capacitor and a control signal having a waveform that is repeated with a predetermined frequency. The capacitor is charged and discharged by a current corresponding to a difference between a feedback voltage corresponding to a current flow to the discharge lamp and a reference voltage. Such inverter driver controls to gradually increase the output voltage of the inverter in the soft start period by setting the voltage of the capacitor as a voltage corresponding to the control signal.