The electronic transformer described here has an input of AC220V, an output of AC12V, and a power capacity of up to 50W. It is primarily a transformer circuit developed based on a high-frequency electronic ballast circuit. This design offers several advantages, including stable performance, compact size, and high power density. These features effectively address the drawbacks of traditional silicon steel sheet transformers, which tend to be bulky, heavy, and expensive.
The circuit operates similarly to a switching power supply. The diodes VD1 through VD4 form a rectifier bridge to convert alternating current from the mains into direct current. The high-frequency oscillating circuit, comprising the oscillating transformer T1 and transistors VT1 and VT2, transforms the pulsating DC into high-frequency current. Subsequently, the ferrite output transformer T2 steps down the high frequency and high voltage pulses to produce the desired voltage and power. Resistor R1 serves as a current-limiting resistor. The resistor R2, capacitor C1, and bidirectional trigger diode VD5 together form a startup trigger circuit. Transistors VT1 and VT2 are selected as S13005 types with a gain (B) of 15 to 20 times. High-power transistors like C3093 and other BUceo ≥ 350V can also be used. The trigger diode VD5 is chosen as DB3 or VR60, approximately 32V. The oscillating transformer can be self-made by winding an audio cable on an H7X10X6 magnetic core. Winding T1a and T1b around 3 turns each, and T1c around 1 turn. The ferrite output transformer T2 also needs to be custom-made, using an EI-type ferrite core with dimensions of 27mm x 20mm x 10mm. T2a is wound with a 0.45mm diameter high-strength enamel wire for approximately 100 turns, while T2b is wound with a 1.25mm diameter high-strength enamel wire. Diodes VD1 to VD4 are selected as IN4007 types, bidirectional trigger diodes use DB3 types, and capacitors C1 to C3 are polypropylene polyester capacitors with a voltage rating of 250V.
During operation, the voltage at point A is about 12V; point B is about 25V; point C is about 105V; and point D is about 10V. If these voltages do not match the expected values, or if the circuit fails to oscillate, check for miswiring, missing connections, or poor soldering. Ensure that transistors VT1 and VT2 are functioning properly and verify the phase alignment of T1a and T1b. Once the circuit is fully adjusted, it can be housed in a small metal enclosure, which provides excellent shielding and heat dissipation. However, it's crucial to maintain proper insulation between the circuit and the external housing. Additionally, adjusting the number of turns on the T2a and T2b windings can modify the output high-frequency voltage.
In conclusion, this electronic transformer represents a significant advancement in transformer technology, combining efficiency, reliability, and cost-effectiveness. Its compact design and ability to handle high power make it ideal for various applications, from household appliances to industrial equipment. By addressing the limitations of traditional transformers, this design sets a new standard in modern electronics. Whether you're an engineer or hobbyist, this circuit offers a versatile solution for your power conversion needs.
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