Transformer is a device that converts a certain level of AC voltage and current into another level of voltage and current of the same frequency according to the principle of electromagnetic induction. According to the purpose of transformer, it can be divided into power transformer, audio input transformer, output transformer, intermediate frequency transformer, high-frequency transformer, pulse transformer, etc. 1. Text symbol of transformer is "T". 2. The transformer works on the principle of mutual inductance, and has the functions of transmitting AC and isolating DC, voltage transformation, impedance transformation and phase transformation. The transformer is composed of primary and secondary coils which are not connected with each other, and the iron core or magnetic core is used as the coupling medium between them. The voltage ratio and impedance ratio can be changed by changing the ratio of turns between primary and secondary. By changing the connection of the transformer coil, the signal voltage can be easily inverted. 3. Power transformer is a kind of soft magnetic electromagnetic component, whose functions are power transmission, voltage transformation and insulation isolation. It is widely used in power supply technology and power electronics technology. The main parameters of power transformer are power, secondary voltage and current. The power is proportional to the square of the core section. The larger the iron core section is, the greater the transformer power is. The purpose of the power transformer is to transform the power supply voltage, and can simultaneously provide multiple power supply voltages to meet the needs of electronic circuits. During fabrication, transformers with satisfactory secondary voltage and current shall be selected as required. 4. Another use of power transformers is power isolation. Due to the isolation effect of the transformer, even if the human body contacts the voltage U2, it will not form a loop with the AC 220V mains power, ensuring personal safety. This is the reason why the power Isolation Transformer must be used when repairing the hot floor appliances. 5. Audio transformer is a transformer working in the audio range, also known as low-frequency transformer. The operating frequency range is generally from 10 to 20000 Hz. It is commonly used to convert the impedance of power supply or load. The figure shows a push-pull power amplifier circuit. The input transformer transmits and distributes the signal voltage to transistors VT1 and VT2 (the signal to VT2 is also inverted), so that VT1 and VT2 alternately amplify positive and negative half cycle signals, and then the output transformer synthesizes the signals for output. At the same time, the output transformer transforms the 8 Ω low resistance of the speaker into hundreds of ohms high resistance, matching with the output impedance of the amplifier, making the output audio power of the amplifier maximum and distortion minimum. 6. The intermediate frequency transformer is commonly referred to as the medium frequency transformer, which is a special component of superheterodyne radio. It is used in IF amplifier circuit of superheterodyne radio and TV. The intermediate frequency transformer has the function of frequency selection and coupling. In the middle amplifier circuit of superheterodyne radio, the primary coils of intermediate frequency transformers T1 and T2 resonate with C1 and C2 at 465kHz, respectively, as the load of VT1 and VT2. Therefore, only the 465kHz intermediate frequency signal is amplified, playing a role in frequency selection. Is the amplitude frequency characteristic curve of intermediate frequency transformer, f0 is the resonant frequency, Δ F is the passband. 7. High frequency transformer is usually a power transformer whose working frequency exceeds medium frequency (10kHz). It is mainly used as high-frequency switching power transformer in high-frequency switching power supply, and also used as high-frequency inverter power transformer in high-frequency inverter power supply and high-frequency inverter welding machine. The magnetic antenna of the radio is a high-frequency transformer. The primary coil and variable capacitor C form a frequency selection loop. The selected radio signal is transmitted to the high amplifier or variable frequency stage VT1 through the coupling between the primary and secondary. 8. The transformer can be tested with a multimeter. The first is to detect the on-off of winding coils, the second is to detect the insulation resistance between winding coils, and the third is to detect the insulation resistance between winding coils and iron core.
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