Thyristor Load Switching Circuit for Zero-Voltage Trigger Control
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Solution Overview
Problem
Existing load switching devices in electrical circuits face issues with untimely re-triggering due to charge accumulation and require separate control signals for thyristors, leading to bulkiness, high cost, electromagnetic interference, and low control accuracy.
Innovation Solution
A load switching device comprising two power thyristors coupled head-to-tail and a control thyristor, with a transformer for galvanic isolation and voltage clipping circuit, allowing a single control signal and improved control precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a triac is used for load switching, then the circuit can be simplified with a single component, but untimely re-triggering 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 head-to-tail. Each thyristor handles one polarity of the AC cycle independently, preventing charge accumulation issues that cause re-triggering in triacs. The segmentation allows each component to operate within its optimal parameters without interference from the other polarity.
Solution Approach 2:
The patent introduces a control thyristor as an intermediary component to manage the triggering of the two power thyristors. This control thyristor receives the control signal and generates the appropriate trigger pulses for both power thyristors, enabling reliable switching while maintaining circuit simplicity. The intermediary resolves the conflict between using simple components and achieving reliable switching.
2Reliability
If two thyristors are used instead of a triac, then re-triggering problems are eliminated, but two separate control signals are required which increases complexity
Solution Approach 1:
The patent merges the control functions for both thyristors into a single control thyristor. Instead of requiring two separate control signals, the control thyristor receives one control signal and internally generates the necessary trigger pulses for both power thyristors. This combining approach maintains the reliability benefits of two thyristors while eliminating the complexity of dual control signals.
Solution Approach 2:
The control thyristor performs multiple functions: it receives the control signal, generates trigger pulses for both power thyristors, and ensures proper timing and sequencing. This multi-functional component eliminates the need for separate control circuits for each thyristor, reducing overall system complexity while maintaining reliable switching operation.
3Measurement precision
If galvanic isolation is implemented using a pulse transformer with two secondaries, then control signals with distinct references are obtained, but the transformer becomes bulky and expensive
Solution Approach 1:
The patent extracts the galvanic isolation function from a bulky two-secondary pulse transformer and implements it through the inherent isolation capabilities of the control thyristor and associated circuitry. By removing the heavy transformer component while maintaining the necessary electrical isolation and control precision, the system achieves the same control signal reference precision without the weight and cost penalty.
Solution Approach 2:
Instead of using a physical transformer to provide galvanic isolation and control signal generation, the patent uses the control thyristor circuit to create equivalent isolated control signals. The control thyristor circuit copies the necessary isolation and signal generation functions in a more compact form, eliminating the need for a large transformer while maintaining control precision.
4Object-affected harmful factors
If an opto-triac is used for galvanic isolation, then isolation is achieved, but control precision for zero-voltage switching is reduced and additional components are required
Solution Approach 1:
The patent replaces the opto-triac's optical isolation mechanism with an electrical isolation approach using the control thyristor and associated circuitry. This substitution maintains electromagnetic isolation to prevent interference while providing superior control precision for zero-voltage switching. The electrical approach allows for more accurate timing and detection compared to the optical method.
Solution Approach 2:
The patent changes the isolation mechanism from optical (opto-triac) to electrical (control thyristor circuit), which fundamentally alters how galvanic isolation is achieved. This parameter change enables more precise control of the switching timing and voltage detection, improving zero-voltage switching precision while still providing the necessary electromagnetic isolation to prevent interference.
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
Eliminates untimely re-triggering, reduces power consumption, and enhances control accuracy for zero-voltage switching while minimizing bulkiness and cost.
Implementation Method 1
This galvanic isolation is, for example, formed by using a pulse transformer with a primary to which a single control signal is applied, and two separate secondaries on which the control signals applied to the gates of the two thyristors are obtained.
Implementation Method 2
the load switching device further comprises a voltage clipping circuit coupled to the terminals of the primary of the transformer
Data Source
Figure 1~2
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Figure 5~6
AI summary
The present description relates to a device (100) for switching a load (1006), comprising two power thyristors (102, 104) coupled head-to-tail to each other, and a control thyristor (106) whose anode is coupled to the gate of a first of the two power thyristors (102) and whose cathode is coupled to the anode of the first of the two power thyristors (102); and in which: - the trigger of a second of the two power thyristors (104) is coupled to a first control input (114) of the device, and the trigger of the control thyristor is coupled to a second control input (116) of the device, distinct from the first control input, or - the trigger of the control thyristor and the trigger of the second of the two power thyristors are coupled to the same control input of the device.