Thyristor Load Switching Circuit for Zero-Voltage AC Control
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Solution Overview
Problem
Existing load switching solutions using power triacs face issues with untimely restarting due to charge accumulation, require multiple control signals, and suffer from bulkiness, high cost, electromagnetic interference, and low control accuracy, especially when controlling inductive loads.
Innovation Solution
A load switching device comprising two power thyristors coupled head-to-tail and a control thyristor, with a single control input for both power thyristors, and optional galvanic isolation using a transformer with a voltage clamping circuit, eliminating the need for separate control signals and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a power triac is used to control load switching, then the device structure is simple, but untimely restarting occurs due to charge accumulation and high dV/dt and di/dt variations
Solution Approach 1:
The patent divides the single triac into two separate thyristors connected in inverse parallel configuration. Each thyristor handles one polarity of the AC cycle independently, preventing charge accumulation issues that cause untimely restarting in triacs. The segmentation allows each component to operate within its optimal characteristics without the harmful interactions present in integrated triac structures.
2Reliability
If two thyristors are used instead of a triac, then restarting problems are avoided, but two distinct control signals with different references are required
Solution Approach 1:
The patent introduces a control transformer as an intermediary device that receives a single control signal and generates the two required gate control signals for the two thyristors. The transformer provides galvanic isolation between the control circuit and the power circuit, while automatically generating the appropriate control signals with correct references, eliminating the need for two separate control signal sources.
3Reliability
If a pulse transformer with two secondaries is used for galvanic isolation, then two control signals can be obtained, but the transformer becomes bulky and expensive
Solution Approach 1:
The patent makes a single transformer secondary serve multiple functions by connecting it to both thyristor gates through appropriate circuitry. The same isolated control signal derived from one secondary is used to control both thyristors in sequence, eliminating the need for two separate secondaries. This multi-functional use reduces the transformer size, weight, and cost while maintaining galvanic isolation.
4Reliability
If opto-triac with opto-coupler is used for galvanic isolation, then control signals can be generated, but the solution requires buffer and rectifying diodes and offers low control accuracy
Solution Approach 1:
The patent replaces the opto-electronic control mechanism (opto-triac with opto-coupler) with a direct electromagnetic transformation approach using a control transformer. This substitution eliminates the need for opto-couplers, buffers, and rectifying diodes, simplifying the circuit while providing superior control accuracy for zero-voltage switching through direct voltage transformation and isolation.
Data Source
AI summary
The present description concerns a device for switching a load, comprising two power thyristors coupled head-to-tail to each other, and a control thyristor having its anode coupled to the gate of a first one of the two power thyristors and having its cathode coupled to the anode of the first one of the two power thyristors.