Thyristor Power Control Circuit With Damping Resistor And Diode
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Solution Overview
Problem
Thyristor dimmer circuits used with power converters, such as those driving LEDs, face issues with electromagnetic interference (EMI) and lack of resistive damping, leading to erratic performance and flickering due to insufficient holding current.
Innovation Solution
A thyristor power control circuit is designed with a damping circuit including a series resistor and capacitor, and a diode in parallel to the resistor, which maintains a holding current and suppresses EMI by filtering high-frequency pulsed currents, preventing flickering at the LED load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a power converter is used to replace the incandescent lamp in the thyristor dimmer circuit, then energy efficiency is improved, but the holding current is insufficient causing the thyristor to turn off erratically
Solution Approach 1:
A damping circuit is introduced as an intermediary component between the power converter and the thyristor. This damping circuit includes a resistor and capacitor that work together to provide the necessary holding current to the thyristor during its conduction period, while the power converter maintains its energy efficiency benefits. The damping circuit acts as a mediator that bridges the gap between the low-holding-current power converter and the thyristor's holding current requirements.
2Ease of operation
If the thyristor switches at phase angle near 90 degrees to control power delivery, then power control capability is improved, but EMI is generated due to rapid voltage transitions
Solution Approach 1:
An input filter is introduced as an intermediary component between the AC voltage source and the thyristor circuit. This filter includes inductors and capacitors that suppress the high-frequency EMI generated by the rapid voltage transitions when the thyristor switches at phase angle near 90 degrees. The filter allows the power control capability to be maintained while attenuating the harmful electromagnetic interference before it propagates into the AC mains.
3Productivity
If the power converter draws pulsed current to achieve controlled DC output, then power conversion efficiency is improved, but ringing current is generated causing thyristor turn-off
Solution Approach 1:
A damping circuit is implemented to provide beforehand cushioning against the ringing current generated by the power converter's pulsed current draw. The damping circuit, consisting of a resistor and capacitor, is configured to absorb and dampen the high-frequency ringing oscillations that occur when the power converter switches. This cushioning effect prevents the ringing current from dropping the thyristor current below its holding current threshold, thereby maintaining stable thyristor conduction while allowing the power converter to operate efficiently with pulsed current.
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 effectively suppresses EMI and maintains a holding current through the thyristor, preventing flickering and ensuring stable operation of the LED load by using a damping resistor and capacitor configuration.
Implementation Method 1
A damping circuit coupled to an output terminal of the rectifier suppresses electromagnetic interference (EMI) by filtering high-frequency pulsed currents
Implementation Method 2
The damping circuit includes a damping resistor for maintaining a holding current in the thyristor during an ON period of the thyristor
Implementation Method 3
The damping circuit includes a first capacitor coupled in series to the damping resistor and a diode coupled in parallel to the damping resistor. The diode enables the first capacitor to discharge without causing power loss at the damping resistor
Data Source
AI summary
A thyristor power control circuit reduces EMI and maintains a holding current in the thyristor to prevent flickering at a load. The power control circuit includes a thyristor configured to receive an input AC voltage, and responsive to a gate pulse generates a modified AC voltage. A rectifier receives the modified AC voltage and generates a rectified DC voltage. A power converter coupled to the rectifier receives the rectified DC voltage and generates a controlled output current. A damping circuit coupled to an output terminal of the rectifier includes a damping resistor for maintaining the holding current in the thyristor during an ON period of the thyristor. The damping circuit includes a first capacitor coupled in series to the damping resistor and a diode coupled in parallel to the damping resistor. The diode enables the first capacitor to discharge without causing power loss at the damping resistor.