Thyristor Switched LED Driver Circuit
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Solution Overview
Problem
Existing LED driver circuits fail to maintain constant current over power supply voltage and ambient temperature variations, leading to reduced LED lifespan, thermal issues, and poor illumination, often requiring bulky and expensive capacitors for power factor correction.
Innovation Solution
A thyristor switched current source circuit that uses a triggered thyristor, driven from an unsmoothed rectified AC voltage source, eliminating the need for high-quality capacitors and power factor correction hardware, and employing a zener diode or component with temperature coefficient to maintain constant current through shifts in the thyristor trigger angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a resistor is used in series connection with LED load to stabilize current, then the LED current is somewhat stabilized, but the power dissipation on the resistor becomes excessive at high temperatures or high supply voltages, limiting the number of LEDs that can be driven
Solution Approach 1:
The patent uses a thyristor switch that changes its conduction state based on the instantaneous voltage level. At lower voltages, the thyristor conducts more, providing higher current; at higher voltages, it conducts less, providing lower current. This dynamic parameter adjustment maintains constant LED current while minimizing power dissipation compared to a fixed resistor.
Solution Approach 2:
The circuit transitions from a static resistor-based current control to a dynamic thyristor-based control that automatically adjusts its conduction characteristics in response to voltage variations. The thyristor's gating mechanism enables real-time adaptation to changing operating conditions, maintaining optimal current control across different voltage and temperature scenarios.
2Stability of the object's composition
If high quality smoothing capacitors are used to eliminate rectifier bridge ripple voltage, then a pure DC voltage is obtained, but the capacitors are bulky, expensive and have a short lifetime
Solution Approach 1:
The patent extracts and eliminates the need for large smoothing capacitors from the circuit by using a thyristor-based current control mechanism that functions effectively with unsmoothed rectified voltage. The thyristor's voltage-dependent conduction characteristics allow it to regulate LED current despite the presence of voltage ripple, removing the requirement for bulky electrolytic capacitors.
Solution Approach 2:
The patent replaces expensive, bulky, and short-lived electrolytic capacitors with a thyristor switch and simple rectifier circuit. The thyristor-based approach uses smaller, more reliable components that can be easily replaced if needed, eliminating the need for high-cost smoothing capacitors while maintaining effective LED current control.
3Stability of the object's composition
If linear regulators or switched type regulators are used to provide constant current over wide DC power supply voltage range, then constant current is achieved, but the circuit complexity and cost increase
Solution Approach 1:
The patent utilizes the periodic nature of the AC voltage waveform and the thyristor's triggering mechanism to achieve constant current control. By timing the thyristor's conduction based on the instantaneous voltage level within each AC cycle, the circuit automatically regulates LED current without requiring complex feedback control circuits or additional regulatory hardware.
Solution Approach 2:
The thyristor-based circuit is self-regulating, automatically adjusting its conduction state in response to voltage variations without requiring external control signals or complex feedback mechanisms. The voltage-dependent gating characteristic of the thyristor provides inherent current regulation, eliminating the need for additional regulators or control circuits.
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 provides a durable, cost-effective, and flicker-free constant current to LEDs, extending their lifespan by maintaining current within safe limits across voltage and temperature fluctuations without the need for expensive capacitors or complex hardware, while minimizing electromagnetic interference.
Implementation Method 1
The thyristor switch can be an SCR or a TRIAC or an equivalent circuit for an SCR or a TRIAC. This circuit, by utilizing a triggered thyristor, is driven from an unsmoothed rectified AC voltage source.
Implementation Method 2
employing a zener diode or component with temperature coefficient to maintain constant current through shifts in the thyristor trigger angle
Implementation Method 3
driven from an unsmoothed rectified AC voltage source. Without a high quality smoothing electrolytic capacitor the LED load voltage is a 120 Hz rectified AC voltage waveform.
Data Source
AI summary
A circuit for controlling power to a load from a rectified AC supply is disclosed. The load like an LED or another type is driven by a power device such as a MOSFET or a transistor. The power device is biased from a resistive string which also includes a thyristor switch in series combination. At a specific trigger or conduction angle of the thyristor switch the proper bias for the power device is obtained to enable the load current to remains fairly constant with AC supply voltage fluctuations or loading. Furthermore the trigger circuit of the thyristor switch is properly configured in order for the load current to stay constant or even change with ambient temperature variations as well.