The difference between a switch mode power supply and a linear power supply
What is switching power supply
Switching power supply is the abbreviation of switching regulated power supply. It generally refers to an AC (alternating current)-DC (direct current) converter whose input is AC voltage and whose output is DC voltage. The power switch tube inside the switching power supply works in a high-frequency switching state, and consumes very low energy. The power efficiency can reach 75% to 90%, which is twice that of ordinary linear regulated power supplies.
1. Working principle of switching power supply
The switching power supply is a power supply that uses modern power technology to control the turn-on and turn-off time ratio of the switching transistor to maintain a stable output voltage. The switching power supply is composed of pulse width modulation (PWM) control (metal oxide semi-field effect transistor).
The switching power supply is composed of four parts: main circuit, control circuit, detection circuit and auxiliary circuit. Switching power supply, as the name suggests, is equivalent to having a door here, one door allows current to pass through, and the other door stops current from passing through. So what is a door?
Some switching power supplies use thyristors, and some use switching tubes. These rely on pulse signals to be added to the base, (switching tube) control electrode (thyristor) to complete the conduction and cutoff, making the electronic switch continuously The ground is 'on' and 'off', allowing the electronic switching device to pulse modulate the input voltage, thereby achieving DC/AC, DC/DC voltage conversion, as well as adjustable output voltage and automatic voltage stabilization.
The difference between switching power supply and linear power supply
Simply put, the voltage regulation of a linear power supply can be regarded as a resistance value, which is equivalent to changing the voltage by adjusting a sliding rheostat, while a switching power supply changes the voltage by adjusting the frequency of the switch. At the same time, compared with linear power supplies, the cost of both switching power supplies increases with the increase in output power, but the growth rates are different.
1. The cost of linear power supply is higher than that of switching power supply at a certain output power point.
Therefore, with the development and innovation of power electronics technology, switching power supply technology continues to make breakthroughs and innovations. This cost issue has instead moved switching power supply technology to the low-output power end, providing a wide range of development space for switching power supplies.
2. Power electronic equipment is increasingly closely related to people's work and life, and electronic equipment is inseparable from a reliable power supply. After entering the 1980s, computers fully realized switching power supplies. By the 1990s, switching power supplies successively entered various electronic and electrical appliances. field.
In just ten years, switching power supply technology has rapidly occupied the core position of power electronic equipment. Is this just because of the small size of switching power supply?
3. In fact, it can be understood from the schematic diagram of the switching power supply: it does not use a bulky power frequency transformer, and at the same time, because the power dissipation on the adjustment tube is greatly reduced, a larger heat sink is omitted. This makes the switching power supply smaller and lighter. However, the biggest advantage of switching power supply is-low power consumption and high efficiency. In the switching power supply circuit, the transistor is stimulated by the excitation signal, and it continuously repeats the switching state of 'on' and 'off'. The conversion speed is extremely fast, and the frequency is only 50HZ, which greatly improves the power supply efficiency.
4. The switching power supply has a wide voltage stabilizing range. The output voltage from the switching power supply is adjusted by the duty cycle of the excitation signal, and changes in the input signal voltage can be compensated through frequency modulation or width modulation. In this way, it can still ensure a relatively stable output voltage when the power frequency grid voltage changes greatly.
5. The working frequency of the switching power supply is currently basically 50kHz, which is 1000 times that of the linear regulated power supply. This increases the filtering efficiency after rectification by almost 1000 times; even if half-wave rectification is used and capacitor filtering is used, the efficiency is still low. Improved 500 times. Under the same ripple output voltage, when using a switching power supply, the capacity of the filter capacitor is only 1/500~1/1000 of the filter capacitor in a linear regulated power supply.
