Power Shifter Circuit Using Segmented Thyristor Control
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Solution Overview
Problem
Existing power variators using triacs face issues such as abrupt switchings causing current and voltage gradients, leading to parasitic oscillations and acoustic noise, and are not suitable for low power consumption loads due to high microcontroller supply currents.
Innovation Solution
A power variation control circuit employing a first and second thyristor, diodes in antiparallel, and an insulated-gate transistor, with a control unit that turns on the transistor before the thyristor, reducing switching abruptness and using high-sensitivity thyristors to minimize microcontroller current draw.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a triac is used for power control, then power regulation is achieved, but abrupt switchings cause current and voltage gradients leading to parasitic oscillations and acoustic noise
Solution Approach 1:
The power control function is segmented into two distinct stages: a transistor handles the initial current rise with gradual switching, while a thyristor takes over for sustained conduction. This segmentation allows each component to operate in its optimal regime, eliminating the abrupt switching characteristics of triacs while maintaining power regulation capability.
Solution Approach 2:
The transistor performs preliminary action by initiating current flow and establishing a controlled current rise before the thyristor is triggered. This preliminary current establishment prevents the abrupt voltage gradients that occur with direct triac switching, thereby reducing parasitic oscillations and acoustic noise.
2Object-generated harmful factors
If an LC filter is added to reduce current and voltage gradients, then parasitic oscillations are attenuated, but the drive size and cost increase
Solution Approach 1:
The harmful current and voltage gradients are extracted and eliminated at their source through the controlled switching sequence of the transistor-thyristor combination, rather than attempting to filter them afterward with an LC circuit. This eliminates the need for bulky and expensive filter components.
Solution Approach 2:
The transistor acts as an intermediary device between the power source and the thyristor, providing controlled current rise and preventing the formation of harmful gradients that would otherwise require LC filtering. This intermediary approach solves the problem without adding filter complexity.
3Reliability
If the microcontroller supply circuit is sized to handle high trigger currents, then reliable triac triggering is achieved, but low power loads are inadvertently switched on
Solution Approach 1:
The triggering parameter is changed from high current (as required by triacs) to low current or voltage triggering (as required by thyristors with cathode gate). This parameter change allows the microcontroller supply circuit to be sized for low power operation while maintaining reliable switching capability.
Solution Approach 2:
The invention uses a control strategy that consumes minimal energy from the microcontroller supply, effectively treating the control signal as a low-energy event rather than a high-current demand. This allows accurate control of very low power loads without false activation.
Data Source
Figure 1~3
Figure 2A~2E
AI summary
The invention relates to a control circuit for varying the power of a load powered by an alternating voltage (V^Q), comprising: a first thyristor (Tl) and a first diode (Dl) connected in antiparallel between first (A) and second (R) nodes, the cathode of the first diode (Dl) being on the side of the first node (A); a second thyristor (T2) and a second diode (D2) connected in antiparallel between the second node (R) and a third node (B), the cathode of the second diode (D2) being on the side of the third node (B); third (D3) and fourth (D4) diodes connected in antiserial between the first (A) and third (B) nodes, the cathodes of the third (D3) and fourth (D4) diodes being connected to a fourth node (J); a transistor (Ml) between the second (R) and fourth (J) nodes; and a control unit (MCU) for controlling the first (Tl) and second (T2) thyristors and the transistor (Ml).