Detailed Explanation of Basic Knowledge of Main Components in Switching Power Supply Circuits

In the teaching of electronic circuits, power supply is an important component that we cannot avoid. Sometimes, faults occur in the power supply, especially in the switching power supply. The switch power supply circuit is generally composed of fuses, thermistors, mutual inductance filters, bridge rectifier circuits, filter capacitors, switch impulse integrated circuits, switch transformers, optocouplers, three-way terminal regulators, etc. To help you gain a comprehensive understanding, this article will summarize the basic knowledge of key components in switching power supply circuits.

1. The fuse in the power circuit of the fuse is generally installed around the AC 220V input terminal, ensuring the safe operation of the circuit is crucial. In circuits, fuses are usually cylindrical glass tubes. When there is a short circuit or other fault in the circuit, the current will abnormally rise. At this point, the fuse will disconnect the power supply when the current abnormally rises to a certain level, thereby protecting the safety of the circuit.

2. Thermistor

Thermistors have an impact resistance effect in circuits. Generally speaking, when the device is started, 220V AC current is charged through fuses, thermistors, and bridge rectifier stacks. According to the characteristics of capacitors, large instantaneous currents may generate surge currents, which can affect the bridge rectifier stack and fuses in the front circuit and cause damage. To avoid power shock, a thermistor is usually added behind the fuse to limit the current.

Generally speaking, when the resistance value of a thermistor is large, the current limiting effect is good, but the resistance also consumes a large amount of electrical energy. After the power circuit works, it consumes electricity. In order to achieve better current limiting effect and energy saving, Negative temperature coefficient thermistors are usually used for current limiting applications in power circuits.

Negative temperature coefficient thermistor (NTC) has the following characteristics: the higher the temperature, the lower the resistance. At room temperature, the resistance value is large, usually 8-10 Ω; When starting, it can have a better current limiting effect; When the power is turned on, the working current is heated by the thermistor, and the thermistor value significantly decreases (about 1-2 Ω). When the power is turned on, the electrical energy consumption of the thermistor is minimized.

The positive temperature coefficient (PTC) of thermistors is characterized by the higher the temperature, the greater the resistance, and is generally used in the starting circuit of refrigerator compressors.

3. Mutual inductance filter

The mutual inductance filter is composed of two sets of symmetrical coils, and its function is to eliminate the influence of external circuits on the pulse entering the circuit, so that the pulse signal in the circuit will not interfere with the power grid.

4. Bridge rectifier circuit

The key to the bridge rectifier circuit is the rectification of AC 220V voltage and 300V voltage output, which is composed of four rectifier diodes combined according to a certain connection relationship.

In addition, the bridge rectifier stack, as a rectifier device in some circuits, is actually a rectifier device that integrates four rectifier diodes together. It has four guide pins externally, two of which input AC current, and the other two pins export DC voltage. Its circuit function and principle are the same as the bridge rectifier circuit.

5. Filter capacitor

Filter capacitors are mainly used to filter the 300V DC voltage provided by bridge rectifier circuits, filter out the pulse components in the voltage, and convert the derived voltage into a stable DC voltage.

Filter capacitors are one of the most easily recognizable devices in power circuits, usually the largest capacitor in the circuit. The negative sign is usually marked on the shell of the capacitor to facilitate the determination of pin polarity.

6. Switching Impulse Integrated Circuit

When the power circuit is working, the switch oscillation integrated circuit mainly provides driving pulse signals for the switch transformer.

The actual structure of switch oscillation integrated circuits varies depending on the model. For example, some switch oscillation integrated circuits are internally integrated with switch transistors and resonant circuits; Some mainly include resonant circuits, actively cooperating with external switching transistors.

7. Switching transformer

A switching transformer is a pulse transformer with high output power (1k~50kHz). The primary winding of the transformer and the switching field-effect transistor (some installed separately and some integrated in the switching oscillation integrated circuit) form a resonant circuit, and the secondary and primary windings are protected. The key function is to convert high-frequency and high-voltage pulses into multiple high-frequency and low-voltage pulses.

8. Optocoupler and three-terminal voltage regulator

The main function of the optocoupler is to feedback the error signal of the switching power supply voltage of the variable frequency refrigerator to the switching impulse integrated circuit, which stabilizes the voltage based on the signal.

A three terminal voltage regulator is a DC voltage regulator integrated circuit with three pins, and different models of three terminal voltage regulators have different voltage regulation values.

If you have any purchasing needs for electronic components, please feel free to contact Chengyexing

Shenzhen electronic component IC chip supplier, one-stop BOM distribution company;

Can provide various electronic components (resistors, capacitors, inductors, switch connectors) for integrated circuit IC chips

If you cannot find the model you need, please contact us Chengyexing Company directly. The 50+purchasing team will be responsible for your needs and let us know the rest.

Service hotline: 134-3440-1267, 155-2178-1275