【Repost】Detailed introduction of commonly used voltage regulators

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【Repost】Detailed introduction of commonly used voltage regulators [Copy link]

In our daily life, we often use transformers. We can see transformers in TV sets, radio recorders, air conditioners and other electrical appliances. So what are the common transformers in life and how are they used? After reading this article, we have more or less some understanding. The following is a detailed introduction to some commonly used transformers:

1. Intermediate frequency transformer

Open the back cover of the radio recorder, and you can see several silver-white cube metal shells on the circuit board. There is a "one" notch on the top, which can be gently rotated with a non-inductive screwdriver. There are red, white, green and other colors. This is the intermediate frequency transformer. The intermediate frequency transformer used in the transistor radio has two types: single-tuned circuit and double-tuned circuit. Its appearance and circuit symbol are shown in Figure 1.

Figure 1 Intermediate frequency transformer

Intermediate frequency transformers are mainly used for frequency selection and inter-stage coupling in radios. Frequency selection means selecting useful signal frequencies from many signals and transmitting the useful signals. In an AM radio, the useful signal of 465kHz is selected through an intermediate frequency transformer. And coupled to the next stage for amplification. At the same time, the signal outside 465kHz is suppressed so that it cannot be transmitted to the next stage.

2. Power transformer

In daily life, various household appliances use different voltages. Household appliances all use low-voltage DC power supply. A power transformer is needed to convert 220 V AC mains power into low-voltage AC power, which is then rectified by diodes and filtered by capacitors to form a DC power supply. Moreover, in this conversion process, the energy loss itself is small, thus achieving the purpose of convenience and economy. The TV picture tube requires a voltage of tens of thousands of volts to work, which is supplied by the "line output transformer".

In view of the wide variety of electronic equipment, the required voltage and power required to be transmitted are different, as well as the installation location and the size of the space inside the whole machine, the types and shapes of transformers are also different. The appearance of a common power transformer is shown in Figure 2.

Figure 2 Switching transformer

As can be seen from Figure 2, the power transformer has several shapes, such as "口" shape, "日" shape, and "C" shape. Even if the shape is the same, the size is not the same. For example, the power transformer in the radio is much smaller than the transformer in the TV or power amplifier.

3. Switching power transformer

The switching power transformer is an important component in the switching regulated power supply of the color TV. It is a pulse transformer. Its function is to transmit power, provide the required power supply voltage for the color TV set, and realize reliable electrical isolation between input and output. The shape and symbol of the common switching power transformer are shown in Figure 3.

Figure 3 Switching power supply transformer

4. Input and output transformers

The main functions of input and output transformers are: to achieve impedance matching; to transmit signal voltage and signal power without distortion; and to isolate DC. The appearance and symbols of common input and output transformers are shown in Figure 4.

Figure 4 Input and output transformers

The purpose of input and output transformers is: The output transformer couples the output power of the final power amplifier of the transistor radio to the speaker, so that the optimal load of the power amplifier tube matches the voice coil impedance of the speaker. In tape recorders and televisions, the pot coupling between power tubes and speakers is also inseparable from it. The input transformer is usually a coupling transformer between the final stage and the final stage in the low-frequency circuit.

5. Line output transformer

(1) Line output transformer for black and white TVs

The line output transformer is referred to as FBT, sometimes also referred to as line reverse transformer. There are mainly two types of line output transformers for black and white TVs: "separate" and "integrated". The separate type is rarely used now.

The integrated line output transformer is composed of high and low voltage coils, high voltage rectifier tubes, plastic skeletons, high voltage coils and shells packaged together with non-toxic, non-corrosive, high temperature resistant and highly insulating chemical materials. Figure 5 shows the appearance structure diagram of the integrated line output transformer.

Figure 5 Line output transformer

(2) Color TV line output transformer (FDT)

Color TVs all use a multi-stage primary step-up line output transformer. The high-voltage winding of this line output transformer is wound in multiple sections, and high-voltage rectifier diodes are connected between each section. The DC ultra-high voltage output is generated by multi-stage rectification and then connected in series. Therefore, it is called a multi-stage primary step-up method. Since the high-voltage winding, low-voltage winding and high-voltage rectifier diode of this line output transformer are all encapsulated in a shell, it is often called an integrated line output transformer. Figure 6 shows the structure and step-up ratio principle diagram of a practical four-stage step-up line output transformer.

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Collector-base coupling is a step-down coupling, using transformers for cascade coupling, which is equivalent to adding an extra stage of current amplification.

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Impedance matching is the main job of input and output transformers, but don't forget that speakers have rated power and amplifiers have voltage specifications. Transformers are still transformers, and the voltage transformation function always exists. Among the three links, only two can be dominant, and the remaining link is to adapt according to the two given parameters.