AC Motor Phase Control Circuit Without Transformer
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Solution Overview
Problem
Existing electric tools using AC motors for phase or antiphase control with transistors face challenges in reducing electromagnetic noise, requiring costly and space-consuming components like transformers for gate power supply and experiencing instability in obtaining high DC voltage from commercial AC power supplies.
Innovation Solution
The implementation of a series circuit of a resistor and diode with a parallel circuit of a capacitor and Zener diode to generate a constant voltage from AC power, using two transistors connected in anti-series for phase or antiphase control, and employing a photocoupler for control signal switching to minimize electromagnetic noise without a transformer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a transformer is used for gate power supply in phase control using transistors, then sufficient gate driving voltage can be obtained, but the device complexity, cost, and space increase
Solution Approach 1:
The patent extracts and eliminates the transformer component from the gate power supply circuit, replacing it with a simplified voltage generation circuit using resistors, capacitors, and diodes. This removal of the transformer directly reduces device complexity, cost, and space while still providing sufficient gate driving voltage for transistor operation during phase control
Solution Approach 2:
The patent creates a functional equivalent of the transformer using a different circuit topology - a voltage division and rectification circuit using resistors (R1, R2), capacitors (C1, C2), and diodes (D1, D2). This copied function achieves the same gate driving voltage generation without requiring magnetic transformation, thereby simplifying the overall device structure
2Object-generated harmful factors
If the current flowing through the AC motor is decreased to reduce electromagnetic noise, then electromagnetic noise is reduced, but the power of the AC motor is reduced
Solution Approach 1:
The patent applies preliminary action by implementing phase control that anticipates and manages current flow timing. By controlling the conduction angle and timing of the transistors, the system regulates power delivery to the AC motor in advance, reducing peak currents that generate electromagnetic noise while maintaining sufficient average power for motor operation
Solution Approach 2:
The patent employs periodic action through phase-controlled switching of transistors that modulates current flow in periodic cycles. This periodic control allows the motor to receive pulsed power delivery with controlled current magnitudes, reducing electromagnetic noise from continuous high current while maintaining adequate average power through repeated cycling
3Object-generated harmful factors
If a snubber circuit is provided to reduce electromagnetic noise, then electromagnetic noise is reduced, but the space required and cost increase
Solution Approach 1:
The patent merges the noise reduction function into the existing phase control circuitry itself. The capacitors (C1, C2) and diodes (D1, D2) that are already part of the voltage generation circuit also serve to suppress voltage spikes and reduce electromagnetic noise, eliminating the need for separate snubber circuits and thereby saving space
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
This solution reduces electromagnetic noise, lowers costs, saves space, and simplifies the circuit structure while generating sufficient constant voltage for controlling large current transistors, enabling effective phase or antiphase control of AC motors with reduced electromagnetic interference.
Implementation Method 1
constant voltage generating means includes a series circuit of a first resistor and a diode and a parallel circuit of a capacitor and a Zener diode
Implementation Method 2
parallel circuit of a capacitor and a Zener diode
Implementation Method 3
employing a photocoupler for control signal switching to minimize electromagnetic noise
Data Source
Figure 1~2
Figure 3
AI summary
In an electric tool, in order to carry out a phase control or an antiphase control using a transistor with the cost lower and structure simpler, and to suppress an electromagnetic noise, constant voltage generating means of the electric tool includes a series circuit of a resistor 91 and a diode 93 and a parallel circuit of a capacitor 95 and a Zener diode 97, one end of the resistor 91 is connected to a node between an AC power supply 1 and an AC motor 3, a cathode of the diode 93 is connected to one end of the capacitor 95 and a cathode of the Zener diode 97, and the other end of the capacitor 95 and an anode of the Zener diode 97 are connected to sources of transistors 51, 52. One ends of resistors 53, 54 are connected to gates of the transistor 51, 52, and a voltage at the other ends of the resistor 53, 54 are switched between a voltage at a node between the series circuit and the parallel circuit and a voltage of the source of the transistors 51, 52 so that the transistors 51, 52 are turned ON or OFF.