LED Driver Voltage Limiting Circuit Reduces MOSFET Heat
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Solution Overview
Problem
Existing apparatuses for driving light emitting elements, such as LEDs, generate excessive heat due to the increased drain-source voltage of MOS transistors, especially when using high power LEDs, which affects the reliability and lifespan of the devices.
Innovation Solution
Incorporating a voltage limiting circuit unit that divides the total voltage applied to the constant-current circuit, using a second MOS transistor and a voltage dividing resistor to control the voltage applied to the constant-current circuit, and employing a voltage division controller to regulate the second tuning voltage, thereby limiting the voltage below a predetermined level and reducing heat generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving voltage is increased to supply sufficient power to high power LEDs, then the light output is improved, but the drain-source voltage of the MOS transistor increases and causes excessive heat generation
Solution Approach 1:
The patent divides the voltage control function into two separate stages: a voltage limiting circuit that divides the total voltage to limit the maximum voltage applied to the constant-current circuit, and a constant-current circuit that maintains stable current flow. This segmentation allows the system to handle high power LED requirements while controlling heat generation in the MOS transistor by preventing excessive voltage accumulation in a single circuit stage.
2Device complexity
If a simple current source circuit is used to drive LEDs, then the circuit complexity is reduced and switching noise is minimized, but heat generation from the MOS transistor becomes a serious problem
Solution Approach 1:
The patent introduces a voltage limiting circuit as an intermediary component between the power supply and the constant-current circuit. This intermediary circuit divides the total voltage before it reaches the MOS transistor, thereby reducing the voltage stress and heat generation in the transistor while maintaining the simplicity and low noise characteristics of the current source configuration.
3Adaptability or versatility
If the voltage applied to the constant-current circuit is not limited, then the circuit can accommodate voltage variations, but the MOS transistor experiences excessive heat generation and reliability decreases
Solution Approach 1:
The patent implements preliminary voltage limitation through the voltage limiting circuit that divides the total voltage before it reaches the constant-current circuit and MOS transistor. This preliminary action prevents excessive voltage from ever reaching the transistor, thereby protecting the device and ensuring long-term reliability while still allowing the circuit to adapt to normal voltage variations within the limited range.
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 effectively reduces heat generation in the MOS transistors, improving the reliability and lifespan of light emitting element drivers by maintaining a constant current while controlling voltage and current flow, and enhancing operational stability through precise feedback control.
Implementation Method 1
a voltage limiting circuit unit connected between the cathode terminal of the light emitting element array and the constant-current circuit unit, and dividing a total voltage applied between the cathode terminal of the light emitting element array and a ground according to a second tuning voltage to limit a voltage applied to the constant-current circuit unit below a predetermined voltage
Implementation Method 2
a constant-current circuit unit maintaining a constant current flowing through the light emitting element array according to a first tuning voltage; a comparator comparing a detection voltage detected by the sensing resistor with a predetermined reference voltage to supply a tuning voltage determined by a difference between the two voltages to the gate of the MOS transistor
Implementation Method 3
a sensing resistor connected between the source of the MOS transistor and the ground, and comparing a detection voltage detected by the sensing resistor with a predetermined reference voltage
Data Source
AI summary
Provided is an apparatus for driving a light emitting element. The apparatus includes a power unit, a light emitting element array, a constant-current circuit unit, and a voltage limiting circuit unit. The power unit supplies driving power. The light emitting element array includes a plurality of light emitting elements connected in series between an anode terminal connected to the power unit and a cathode terminal. The constant-current circuit unit maintains a constant current flowing through the light emitting element array according to a first tuning voltage. The voltage limiting circuit unit is connected between the cathode terminal of the light emitting element array and the constant-current circuit unit, and divides a total voltage applied between the cathode terminal of the light emitting element array and a ground according to a second tuning voltage to limit a voltage applied to the constant-current circuit unit below a predetermined voltage.