What is the difference and relationship between switching power supply and linear power supply?


1. Introduction to switching power supply: Our common p […]

1. Introduction to switching power supply:
Our common power supplies, including power adapters and chargers, are all classified as switching power supplies. Switching power supply is a kind of power supply that uses the time ratio of switching on and off of the control switch tube to maintain a stable output of DC voltage. The switching power supply 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 allows switching power supply to enter a wider range of applications, especially in the high-tech field. It promotes the miniaturization and simplicity of high-tech products.化. The development and use of other switching power supplies have important implications in terms of saving power, saving resources and maintaining the environment.
Principle of switching power supply:
Switching power supplies mainly include input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, and maintenance circuit. Standard plug manufacturers will introduce their effects separately below: Input grid filter: It is used to eliminate disturbance ripples from light switches, household appliances, air conditioners, and lightning strikes in the communication grid. Avoid the spread of high-frequency noise generated by the switching power supply to the power grid; input rectifier filter: it is to rectify and filter the input voltage of the power grid to supply DC voltage to the converter; inverter: it is a key part of the switching power supply. It converts the DC voltage into high-frequency communication voltage, and has the effect of blocking the output part from the input power grid; output rectifier filter: it rectifies and filters the high-frequency communication voltage output by the converter to obtain the required DC voltage, while avoiding High-frequency noise disturbs the load; control circuit: detects the output DC voltage, compares it with the reference voltage, and amplifies it. Modulate the pulse width of the oscillator to control the converter to maintain the stability of the output voltage; Maintenance circuit: When the switching power supply has overvoltage or overcurrent short-circuit, the maintenance circuit stops the switching power supply to maintain the load and the power supply itself. Switching power supply is a conversion device that rectifies the communication power into direct current for power supply.
The advantages of switching power supply: small size, light weight, convenient carrying, high efficiency, strong anti-interference ability, wide output voltage scale, especially in Europe and the United States, after the power efficiency and standby power consumption requirements of the switching power supply are highlighted Most of its strengths

2. Introduction of linear power supply:
The linear power supply is a power conversion device that first passes the communication power through a transformer to reduce the voltage amplitude, and then rectifies it through an internal rectifier circuit to obtain pulsed direct current, and then filters to obtain a direct current voltage with a small ripple voltage.
Working principle of linear power supply:
The linear power supply is actually a high-power transistor connected to the output of the transformer. The control circuit only needs to output a small current to the base of the transistor to control the output of the transistor's large current, so that the power system is stabilized on the basis of the transformer. Once, so the voltage regulation performance of this kind of linear regulated power supply is better than switching power supply or transformer 1-3 orders of magnitude. However, the power transistor (also known as the regulator tube) generally takes up 10 volts, and every 1 ampere of output current will consume 10 watts of power inside the power supply. For example, the loss of a 500V 5A power supply on the power tube is 50 watts, accounting for the total output 2% of the power, so the efficiency of the linear power supply is slightly lower than that of the transformer.
The advantages of linear power supply: stable performance, no interference such as high-frequency ripple. Defects of linear power supply: heat generation and low power utilization. There is no super-powered power supply for selection
3. The voltage response circuit of the linear power supply is operating in the linear (amplified) condition, and the voltage of the switching power supply is the voltage adjustment tube operating in the saturation and cut-off region, that is, the switching condition. The linear power supply samples the output voltage and then sends the reference voltage to the comparison voltage amplifier. The output of this voltage amplifier is used as the input of the voltage regulator tube to control the junction voltage of the regulator tube to change with the input change, thereby adjusting its output voltage , But the switching power supply changes the output voltage by changing the time when the regulator tube is turned on and off, that is, by changing the duty cycle. Judging from its main characteristics: Although the linear power supply technology is mature, the production cost is not low. Compared with the switching power supply in terms of price, it has lost much advantage, but the linear power supply can reach a high degree of stability. , The ripple is small, the disturbance and noise of itself are relatively small, but because the operation is at the power frequency (50Hz), the transformer is relatively large in size, low in efficiency, and the overall volume is relatively large, which is relatively heavy. And the input voltage scale is required to be high; The switching power supply is the high-frequency condition of the operation. The volume of the transformer is relatively small and relatively simple, but the output ripple is larger than the linear power supply, but because of its simple structure, low cost and high efficiency, it has replaced the linear power supply in many occasions.