How to identify various transformers!

Transformers are a common component, with a wide variety of shapes and shapes. Commonly used in radio and electronic production are: power transformers, audio input transformers, output transformers, intermediate frequency transformers, high frequency transformers, pulse transformers, etc.

1. The text symbol of the transformer is “T”.

How to identify various transformers!

2. The transformer works by using the principle of mutual induction, and has the function of transmitting alternating current, direct current, voltage conversion, impedance transformation and phase transformation. The transformer consists of coils that are not connected to each other in the primary and secondary parts. The core or core is used as the coupling medium between them (Fig. 14). By changing the turns ratio between the primary and secondary, the voltage ratio and impedance ratio can be changed. Changing the connection of the transformer coil makes it easy to invert the signal voltage.

How to identify various transformers!

3. The power transformer is the most commonly used type of transformer. The main parameters of the power transformer are power and secondary voltage and current. The power is proportional to the square of the core section. As shown in Figure 15(a), the larger the core cross section, the greater the power of the transformer. The purpose of the power transformer is to change the power supply voltage and provide multiple power supply voltages to meet the needs of the electronic circuit, as shown in Figure 15(b). When manufacturing, you should use a transformer with the required secondary voltage and current as needed.

How to identify various transformers!

4. Another use of power transformers is power isolation. Due to the isolation of the transformer, even if the human body is exposed to the voltage U2, it will not form a circuit with the AC 220V mains, which ensures personal safety (Figure 16). This is the reason why the power supply isolation transformer must be used when repairing the hot floor appliance.

How to identify various transformers!

5. The audio transformer works in the audio range and has the functions of signal voltage transmission, distribution and impedance matching. Figure 17 shows the push-pull power amplifier circuit. The input transformer transmits and distributes the signal voltage to the transistors VT1 and VT2 (the signal sent to VT2 is also inverted), so that VT1 and VT2 alternately amplify the positive and negative half-cycle signals, and then The signal is synthesized and output by the output transformer. The output transformer also converts the 8Ω low resistance of the speaker to a high impedance of hundreds of ohms, matching the output impedance of the amplifier, so that the amplifier outputs the largest audio power with minimal distortion.

How to identify various transformers!

6. The intermediate frequency transformer is accustomed to being referred to as the middle week, and is applied to the intermediate frequency amplifying circuit of the superheterodyne radio and the television. The IF transformer has the function of frequency selection and coupling. Figure 18 (a) shows the partial circuit of the superheterodyne radio. The primary coils of the intermediate frequency transformers T1 and T2 resonate with C1 and C2 at 465 kHz, respectively, as the load of VT1 and VT2. Therefore, only the 465 kHz IF signal is amplified. Played a role in frequency selection. Figure 18 (b) shows the amplitude-frequency characteristic curve of the intermediate frequency transformer, f0 is the resonant frequency, and Δf is the passband.

How to identify various transformers!


7. High-frequency transformers usually refer to transformers that operate in the RF range. The magnetic antenna of the radio is a high-frequency transformer. The primary coil and the variable capacitor C form a frequency selective circuit. The selected station signal is transmitted to the high-level or variable-frequency stage VT1 through the coupling between the primary and secondary (Fig. 19).

How to identify various transformers!

8. The transformer can be tested with a multimeter (Figure 20). One is to detect the winding and breaking of the winding coil, the other is to detect the insulation resistance between the winding coils, and the third is to detect the insulation resistance between the winding coil and the iron core.

How to identify various transformers!How to identify various transformers!


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