The article presents a straightforward motor speed control circuit that eliminates the need for mechanical gear shifting, thereby improving the efficiency and performance of mechanical systems. This electronic circuit is specifically designed for single-phase motors operating on 220V AC power, with a rated current below 6.5A and a power rating around 1kW. It is ideal for household fans, ceiling fans, and similar applications. With minor modifications, the circuit can also be used for dimming lights, controlling electromagnetic vibrations, or managing fan temperature automatically.
The core of the circuit consists of silicon diodes VD1 to VD4, which form a full-wave bridge rectifier. The rectified voltage is then fed into a thyristor VS, which controls the motor's power. During the negative half-cycle, current flows through the motor, VD1, VS, R1, and VD3. On the positive half-cycle, the path changes to VD2, VS, R1, VD4, and back to the motor. The voltage across the motor depends largely on the conduction angle of the thyristor. By adjusting this angle, the voltage applied to the motor can be controlled, effectively regulating its speed.
The thyristor’s trigger pulse is generated by a simple unijunction transistor (UJT) circuit. A Zener diode DW provides a stable reference voltage, and capacitor C2 charges through resistors R4 and R5. When C2 reaches the UJT’s peak voltage, it triggers the thyristor. After the UJT turns off, the capacitor recharges based on the motor’s current, creating a feedback mechanism that helps maintain torque at lower speeds.
The feedback resistor R1 is determined experimentally to ensure proper charging of C2 during each cycle. As the motor’s current increases, so does the voltage on C2, reducing the time needed to trigger the UJT in the next cycle. This results in a smaller firing angle and higher voltage applied to the motor, increasing its effective torque. Diode VD5 and capacitor C1 prevent unwanted triggering during the thyristor’s conduction phase.
Resistor R2 acts as a current limiter, ensuring the Zener diode operates within its voltage regulation range. R4 sets the upper limit of the motor voltage, while R3 provides temperature compensation for the UJT. This circuit is also suitable for reversible motor control, offering a continuous voltage adjustment range from 35V to 215V. If the load is a motor or electromagnetic coil, no additional torque compensation is required, simplifying the design further.
For applications where high voltage isn't necessary, the full-wave bridge can be replaced with a half-wave rectifier, limiting the output voltage to 30–100V. The circuit can also be adapted for temperature-controlled fan speed using a thermistor. As the ambient temperature changes, the thermistor’s resistance alters the conduction angle of the thyristor, adjusting the fan speed accordingly.
Component selection is crucial for reliability. Diodes VD1–VD4 should have a breakdown voltage above 400V and a current rating over 0.4A. The thyristor must withstand over 500V and handle at least 1A. The UJT (BT35) should have an emitter-to-base ratio η greater than 0.5, and the transistor (3CG14) should have a current gain β above 80.
Once assembled, the circuit should be tested by connecting the fan and adjusting the potentiometer RP until the fan stops. Placing a soldering iron near the thermistor should increase the fan speed, while removing it should slow it down. Fine-tuning the potentiometer ensures optimal performance under varying conditions.
gsm high gain antenna,Good sale of Ultra Short Wave Antenna,G10 Aircraft Ash Ultra Short Wave Antenna
Mianyang Ouxun Information Industry Co., Ltd , https://www.ouxunantenna.com