The distinction between a linear power supply and a switching power supply
1. About the development of power supply technology
The development direction of modern power electronics technology is changing from traditional power electronics, which focuses on low-frequency technology to deal with problems, to modern power electronics, which focuses on high-frequency technology to deal with problems. In the application of power electronics technology and various power supply systems, switching power supply technology is at the core.
From the self-excited oscillating push-pull transistor single-transformer DC converter invented by GH. Roger in 1955, which was the beginning of realizing high-frequency conversion control circuit, to today's switching power supply technology has become indispensable in the rapid development of the electronic information industry. Power mode.
2. What is a switching power supply
Switching power supply is the abbreviation of switching regulated power supply, which generally refers to an AC (alternating current)-DC (direct current) converter whose input is AC voltage and output is DC voltage. The power switching tube inside the switching power supply works in a high-frequency switching state, and its energy consumption is very low. The power supply efficiency can reach 75% to 90%, which is double that of ordinary linear regulated power supplies.
1. Working principle of switching power supply
Switching power supply is a kind of power supply that uses modern power technology to control the time ratio of switching transistor on and off to maintain a stable output voltage. Switching power supply is composed of pulse width modulation (PWM) control (metal oxide half 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 silicon controlled rectifiers, and some use switching tubes. These all rely on the base, (switching tube) control pole (silicon controlled silicon) to add pulse signals to complete the conduction and cut-off, so that the electronic switch continues to switch on and off. The ground is 'on' and 'off', allowing the electronic switching device to pulse-modulate the input voltage, thereby realizing DC/AC, DC/DC voltage conversion, and output voltage adjustment and automatic voltage stabilization.
3. The difference between switching power supply and linear power supply
In simple terms, the voltage regulation of a linear power supply can be regarded as adjusting the resistance value, which is equivalent to changing the voltage by adjusting the sliding rheostat, while the switching power supply changes the voltage by adjusting the frequency of the switch. At the same time, compared with the linear power supply, the cost of the switching power supply increases with the increase of the output power, but the growth rate of the two is 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, the switching power supply technology continues to break through and innovate. This cost problem has instead moved the switching power supply technology to the low output power end, providing a wide range of development space for switching power supplies.
2. The relationship between power electronic equipment and people's work and life is getting closer and closer, and electronic equipment is inseparable from a reliable power supply. After entering the 1980s, computers fully realized the switching power supply, and in the 1990s, switching power supplies entered various electronic and electrical appliances field.
In just ten years, switching power supply technology has quickly 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 learned from the schematic diagram of the switching power supply: it does not use a heavy 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, under the excitation of the excitation signal, the transistor continuously repeats the switching state of "on" and "off". The switching 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 range of voltage regulation. The output voltage of the switching power supply is adjusted by the duty cycle of the excitation signal, and the change of the input signal signal voltage can be compensated by frequency modulation or width modulation. In this way, when the power frequency grid voltage changes greatly, it can still guarantee a relatively stable output voltage.
5. The operating frequency of the switching power supply is basically 50kHz at present, which is 1000 times that of the linear regulated power supply, which increases the filtering efficiency after rectification by almost 1000 times; Improvement by 500 times. Under the same ripple output voltage, when a switching power supply is used, the capacity of the filter capacitor is only 1/500~1/1000 of the filter capacitor in a linear regulated power supply.
