Structure and characteristics of linear power supply

The switching power supply is different from the linear power supply, the switching power supply regulating tube works in the on and off state, and the linear power supply adjustment tube works in a linear state. The power adapter achieves regulation by controlling the on and off times of the regulation tube. The advantages of the power adapter are small size, light weight, low power consumption, wide voltage regulation range, and efficiency up to 80% to 90%. The adjustment tube power loss is small and the heat sink is also reduced. The power adapter operates at a frequency of several tens of kilohertz or even hundreds of kilohertz. The filter inductor and capacitor components can be used with a small capacity, and the allowable ambient temperature can be greatly improved. It is widely used in various electronic devices.

Comparison of regulated power adapters

Electronic devices are inseparable from the power adapter. The energy required by the power adapter to supply the electronic device. The performance and quality of the power adapter directly affect the safe and reliable operation of the electronic device. Therefore, the requirements for the performance and quality of the power adapter of the electronic device are also increasing. There are two main types of existing power adapters: a series linear regulated power adapter ( linear power supply) and a switching regulator power adapter (power adapter). These two types of power adapters are widely used.

Linear power supply are usually supplied by the AC power provided by the power grid through voltage transformation, rectification, filtering and voltage regulation. The function of each part of the circuit is as follows:

1 power adapter transformer – convert 220V/110V grid voltage into the AC voltage value required by the rectifier circuit, while a small number of circuits use capacitor step-down, such as remote control fan circuit.

2 rectifier circuit – converts the AC voltage into a pulsating DC voltage. Commonly used rectifier circuits include a half-wave rectifier circuit, a full-wave rectifier circuit, and a bridge rectifier circuit.

3 filter circuit – converts the pulsating DC voltage into a smoother DC voltage. Filter circuits commonly used in linear power supply include inductive filtering, capacitive filtering, and RC filtering. The most common one is capacitive filtering.

4 voltage regulator circuit – stabilizes the output voltage of the DC power adapter, basically independent of the grid voltage or load. The regulator circuits commonly used in linear power supply are diode regulated and series regulated. Among them, the series regulator has ready-made integrated circuits, such as integrated circuits with fixed voltage output, such as LM78××, LM79××, etc. The integrated circuits with adjustable voltage output include LM317 and LM337.

Linear power supply have the advantages of good stability, fast transient response, high reliability, high output voltage accuracy, and low output ripple voltage. The disadvantage is that the operating frequency is low, and the power frequency transformer and filter used have a large volume and weight. The adjustment tube works in a linear state, and the power consumption is large and the efficiency is low, and a heat sink needs to be installed.