Brief introduction of switching power supply:
Our common power supply including power adapter and charger belongs to switching power supply. Switching power supply (SMPS) is a kind of power supply that uses the time ratio of switching on and off to maintain stable output DC voltage. SMPS is generally composed of pulse width modulation control IC and MOSFET field effect transistors. High-frequency switching power supply is the direction of its development. High-frequency makes switching power supply miniaturized, and makes switching power supply enter a wider application field, especially in the high-tech field, which promotes the miniaturization and portability of high-tech products. In addition, the development and application of switching power supply are of great significance in energy saving, resource saving and environmental protection.
The principle of switching power supply:
Switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit and protection circuit. Here are their roles: input grid filter: it is used to eliminate interference ripple from AC network, such as light switch, switch of household appliances, switch of air conditioner, lightning strike, etc. It also prevents high frequency noise from switching power supply from spreading to the grid; input rectifier filter: it is used to transfer electricity. The input voltage of the network is rectified and filtered to provide DC voltage for the converter. Inverter: It is the key part of the switching power supply. It converts DC voltage into high frequency AC voltage and isolates the output part from the input power grid; Output rectifier filter: It filters the high frequency AC voltage output from the converter to obtain the required DC voltage, while preventing the interference of high frequency noise to the load; Control circuit: Detecting the output DC current. Voltage is amplified by comparing it with the reference voltage. The pulse width of the oscillator is modulated to control the converter to maintain the stability of the output voltage. The protection circuit: When the switching power supply has over-voltage and over-current short circuit, the protection circuit makes the switching power supply stop working to protect the load and the power supply itself. Switching power supply is a kind of converting device that converts AC to DC first.
The advantages of switching power supply: small size, light weight, easy to carry, high efficiency, strong anti-interference, wide output voltage range, especially in Europe and the United States and other regions of the power supply efficiency and standby power consumption requirements, the switching power supply highlights its most advantages.
Introduction of Linear Power Supply:
Linear power supply first reduces the voltage amplitude by passing alternating current through transformer, then rectifies through internal rectifier circuit, so as to obtain pulsed direct current, and then filters to obtain a DC voltage power conversion device with small ripple voltage.
The working principle of linear power supply:
In fact, a linear power supply strings another high-power triode at the output end of the transformer. As long as the control circuit outputs a small current to the base of the triode, the output current of the triode can be controlled, so that the power supply system can stabilize the voltage once again on the basis of the transformer. Therefore, the stability performance of the linear regulated power supply is better than that of the open regulated power supply. Power off or transformer 1-3 orders of magnitude. However, power transistors (also known as regulators) generally occupy 10 volts of voltage, and each output ampere of current consumes 10 watts more power inside the power supply. For example, the loss of 500V 5A power supply on the power transistor is 50 watts, which accounts for 2% of the total output power. Therefore, the efficiency of linear power supply is slightly lower than that of transformer.
The advantages of linear power supply: stable performance, no high-frequency ripple and other interference. The disadvantage of linear power supply: heat generation and low energy utilization. There is no super power supply for choice.
The voltage feedback circuit of linear power supply works in linear (amplified) state, and the voltage of switching power supply works in saturated and cut-off area, i.e. switching state, where the voltage of switching power supply is regulated. Linear power supply is to sample the output voltage and send it to the comparative voltage amplifier with reference voltage. The output of this voltage amplifier is used as the input of the voltage regulator to control the regulator to change its junction voltage with the change of input, so as to adjust its output voltage. But the switching power supply adjusts the opening and closing of the regulator by changing the opening and closing of the regulator. Time is to change the duty cycle to change the output voltage. From its main characteristics: although the technology of linear power supply is mature, its production cost is not low. Compared with switching power supply, it has lost too much advantage in price, but linear power supply can achieve high stability, smaller ripple, less interference and noise, but because it works at 50Hz, it changes. Voltage transformer has large volume, low efficiency, large overall volume, and it is bulky. And the range of input voltage is demanded to be high. Switching power supply is working in high frequency state, the volume of transformer is relatively small and relatively portable, but the output ripple is larger than linear power supply, but because of its simple structure, low cost and high efficiency (switching power on the market). Source efficiency can also reach more than 90%.) In many cases, linear power supply has been replaced, which is the trend of power supply development in the future.
