Load Driving Circuit Frequency Control and Burst Dimming
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Solution Overview
Problem
Existing load driving circuits for fluorescent lamps and light-emitting diodes face challenges in adjusting the frequency variation range and maintaining luminance levels effectively, particularly in achieving zero power supply and reducing power loss and audible noise.
Innovation Solution
A load driving circuit with a main transformer, error amplifiers, an oscillator, and a burst current source that uses pulse frequency modulation (PFM) and pulse width modulation (PWM) to control the frequency and duty ratio of the driving signal, allowing for adjustable frequency range and intermittent power supply to maintain target luminance levels while reducing power loss and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pulse frequency modulation (PFM) is used to adjust the driving signal frequency, then the frequency can be dynamically changed to control luminance, but the frequency variation range is limited by the circuit design
Solution Approach 1:
The patent applies dynamics by making the frequency control current adjustable through an external resistor connected to the frequency control terminal. This allows the oscillation frequency of the PFM signal to be dynamically varied over a wide range (e.g., 20 kHz to 100 kHz) without changing the internal circuit structure, thereby resolving the contradiction between frequency variation range and circuit design flexibility.
2Illumination intensity
If continuous power supply is used to maintain luminance, then stable light output is achieved, but power loss increases and audible noise is generated
Solution Approach 1:
The patent implements periodic action through burst mode operation, where the inverter alternates between on-periods and off-periods. During off-periods, power supply to the fluorescent lamp is interrupted, eliminating power loss and audible noise. The burst duty ratio is controlled to maintain average luminance at the desired level, thus resolving the contradiction between luminance stability and power loss reduction.
3Loss of energy
If burst dimming control is implemented with alternating on and off periods, then power loss is reduced, but precise control of luminance levels becomes more difficult
Solution Approach 1:
The patent employs feedback control by detecting the current through a current detection resistor and feeding back the detection signal to a error amplifier. The error amplifier compares this signal with a reference voltage and adjusts the drive signal accordingly, enabling precise control of the average luminance level during burst mode operation. This feedback mechanism resolves the contradiction between power loss reduction and luminance control precision.
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
The solution enables precise control of luminance levels, reduces power loss and audible noise, and allows for adjustable frequency range, improving the reliability and efficiency of the load driving circuit.
Implementation Method 1
an oscillator configured to alternately repeat a state in which a capacitor is charged using a charging current that corresponds to a frequency control current that flows through the current generating transistor and a state in which the capacitor is discharged
Implementation Method 2
a main transformer arranged such that the load is connected to a secondary winding side
Data Source
AI summary
A main transformer is arranged such that a load is connected to its secondary winding side. A first error amplifier generates a feedback signal that corresponds to the difference between a detection signal which indicates the electrical state of the load and a predetermined first reference voltage. A current generating resistor is arranged between a current generating transistor and a fixed voltage terminal. A second error amplifier is arranged such that the first input terminal receives the electric potential at a node that connects the current generating transistor and the current generating resistor, a predetermined second reference voltage is input to the second input terminal thereof, and the output terminal thereof is connected to the control terminal of the current generating transistor. An adjustment resistor is arranged between the output terminal of the first error amplifier and a node that connects the current generating transistor and the current generating resistor.