The electronic transformer described below has an input of AC220V, an output of AC12V, and a power of up to 50W. It is primarily a transformer circuit developed based on the high-frequency electronic ballast circuit. Its performance is stable, compact in size, and capable of handling significant power, thus addressing the drawbacks of traditional silicon steel sheet transformers, such as their bulky size, heavy weight, and high cost.
The circuit operates similarly to a switching power supply. Diodes VD1 to VD4 form a rectifier bridge to convert the mains electricity into direct current. The high-frequency oscillating circuit comprising the oscillating transformer T1 and transistors VT1 and VT2 converts the pulsating DC into a high-frequency current, which is then stepped down by the iron-oxygen output transformer T2 to generate the desired voltage and power. Resistor R1 acts as a current limiter. Resistor R2, capacitor C1, and the bidirectional trigger diode VD5 form a start trigger circuit. Transistors VT1 and VT2 are selected as S13005, with a beta of 15 to 20 times. High-power transistors like C3093 or other BUceo ≥ 350V can also be used. The trigger diode VD5 selects DB3 or VR60 of approximately 32V. The oscillating transformer can be self-made and wound on an audio cable around the magnetic ring of H7X10X6. TIa and T1b should have around 3 turns each, while Tc should have about 1 turn. The ferrite output transformer T2 also requires self-making, using a ferrite core with a side length of 27 mm, width of 20 mm, and thickness of 10 mm. T2a is wound with a diameter of 0.45 mm and high-strength enameled wire around 100 turns, and T2b is wound with a diameter of 1.25 mm and high-strength enameled wire. Diodes VD1 to VD4 select the IN4007 type, bidirectional trigger diodes use the DB3 type, and capacitors C1 to C3 use polypropylene polyester capacitors with a withstand voltage of 250V.
During operation, the working voltage at point A is approximately 12V; at point B, about 25V; at point C, around 105V; and at point D, about 10V. If these voltages do not match the expected values or if the circuit does not oscillate, check the circuit for miswiring, missing connections, or poor soldering. Ensure that VT1 and VT2 are functioning correctly and verify the polarity of T1a and T1b. Once the entire circuit is successfully adjusted, it can be housed in a small metal box, which aids in shielding and heat dissipation, but it's crucial to maintain proper insulation between the circuit and the outer casing. Additionally, adjusting the number of turns in the T2a and T2b coils can modify the high-frequency voltage output.
This electronic transformer is a great solution for applications requiring compactness and efficiency. Its design allows for easy integration into various devices, ensuring reliable performance under varying load conditions. The use of high-quality components ensures longevity and stability, making it a cost-effective alternative to traditional transformers. Whether you're designing a lighting system or a power supply unit, this transformer offers flexibility and adaptability, making it a valuable asset in modern electronics. By carefully selecting and adjusting the components, users can optimize the performance of their circuits, achieving both energy efficiency and operational reliability.
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