Electronic transformer

The electronic transformer introduced in this article has an input of AC220V, an output of AC12V, and a power of up to 50W. It is mainly a transformer circuit developed on the basis of high-frequency electronic ballast circuit. It has stable performance, small size and high power, thus overcoming the shortcomings of traditional silicon steel sheet transformers such as large body, bulkiness and high price. The circuit is shown in the figure. Its working principle is similar to that of a switching power supply. The diodes VD1~VD4 form a rectifier bridge to convert the mains power into DC power. The high-frequency oscillation circuit composed of the oscillation transformer T1 and transistors VT1 and VT2 converts the pulsating DC into high-frequency current, and then the iron The oxygen body output transformer T2 steps down the high-frequency and high-voltage pulses to obtain the required voltage and power. R1 is the current limiting resistor. Resistor R2, capacitor C1 and bidirectional trigger diode VD5 constitute the start trigger circuit. Transistors VT1 and VT2 are S13005, and their B is 15 to 20 times. High-power transistors with BUceo>=35OV such as C3093 can also be used. The trigger diode VD5 should be DB3 or VR60 with around 32V. The oscillation transformer can be made by yourself, and the audio wire is wound around the H7 X 10 X 6 magnetic ring. TIa and T1b are wound with 3 turns, and Tc is wound with 1 turn. The ferrite output transformer T2 also needs to be homemade, and the magnetic core is made of EI type ferrite with a side length of 27mm, a width of 20mm, and a thickness of 10mm. T2a is wound with 100 turns of high-strength enameled wire with a diameter of 0.45mm, and T2b is wound with 8 turns of high-strength enameled wire with a diameter of 1.25mm. The diodes VD1~VD4 are of the IN4007 type, the bidirectional trigger diodes are of the DB3 type, and the capacitors C1~C3 are polypropylene polyester polyester capacitors with a withstand voltage of 250V. When the circuit is working, the working voltage of point A is about 12V; point B is about 25V; point C is about 105V; point D is about 10V. If the voltage does not meet the above values, or the circuit does not oscillate, you should check whether there are mis-soldering, missing soldering or weak soldering in the circuit. Then check whether VT1 and VT2 are in good condition, and whether the phases of T1a and T1b are correct. After the entire circuit is successfully installed, it can be placed in a small box made of metal material to facilitate shielding and heat dissipation, but attention must be paid to the insulation between the circuit and the casing. By changing the number of turns of the two coils a and b of T2, the output high-frequency voltage can be changed.