Principle of linear power supply and comparison with switching power supply
On linear power supply
Brief introduction of linear power supply:
Linear power supply is to transform alternating current through transformer, and then get unstable DC voltage through rectification and filtering of rectifier circuit. To achieve high-precision DC voltage, the output voltage must be adjusted through voltage feedback. From the main performance point of view, this power supply technology is very mature, can achieve high stability, ripple is also very small, and there is no interference and noise with switching power supply. The voltage feedback circuit works in a linear state, and there is a certain voltage drop on the regulator tube. When the output current is large, the power consumption of the regulator tube is too large and the conversion efficiency is low.
Linear power supply means that the tube used for voltage adjustment works in the linear region. Correspondingly, the switching power supply means that the tube used for voltage adjustment works in the saturation and cutoff region, that is, the switching state.
Generally, linear power supply samples the output voltage and sends it to a comparison 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 make its junction voltage change with the input, so as to adjust its output voltage. However, the switching power supply changes the output voltage by changing the on and off time of the regulating tube, that is, the duty ratio.
The tube used for voltage adjustment of linear power supply works in linear region. Correspondingly, the switching power supply means that the tube used for voltage adjustment works in the saturation and cutoff region, that is, the switching state.
Generally, linear power supply samples the output voltage and sends it to a comparison 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 make its junction voltage change with the input, so as to adjust its output voltage. However, the switching power supply changes the output voltage by changing the on and off time of the regulating tube, that is, the duty ratio.
Principle of linear power supply:
Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit and protection circuit. Linear power supply is to transform alternating current through transformer, and then get unstable DC voltage through rectification and filtering of rectifier circuit. To achieve high-precision DC voltage, the output voltage must be adjusted through voltage feedback. This power supply technology is very mature, which can achieve high stability, small ripple and no interference and noise with switching power supply. However, its disadvantages are that it needs a huge and bulky transformer, and the volume and weight of the filter capacitor are also quite large. Moreover, the voltage feedback circuit works in a linear state, and there is a certain voltage drop on the regulating tube. When outputting a large working current, the power consumption of the regulating tube is too large, the conversion efficiency is low, and a large heat sink is installed. This kind of power supply is not suitable for the needs of computers and other equipment, and will be gradually replaced by switching power supply. 3. Contrast switching power supply: Switching power supply mainly includes input power grid filter, input rectifier filter, inverter, output rectifier filter, control circuit and protection circuit. Their functions are:
1. Input power grid filter: eliminate the interference from the power grid, such as the start of the motor, the switch of electrical appliances, lightning strikes, etc., and also prevent the high-frequency noise generated by the switching power supply from spreading to the power grid.
2. Input rectifier filter: the input voltage of the power grid is rectified and filtered to provide DC voltage for the converter.
3. Inverter: It is the key part of switching power supply. It converts DC voltage into high-frequency AC voltage and isolates the output part from the input power grid.
4. Output rectifier filter: Rectify and filter the high-frequency AC voltage output by the converter to obtain the required DC voltage, and at the same time prevent the interference of high-frequency noise on the load.
5. Control circuit: detect the output DC voltage, compare it with the reference voltage and amplify it. The pulse width of the oscillator is modulated to control the converter to keep the output voltage stable.
6. Protection circuit: When the switching power supply is short-circuited by overvoltage and overcurrent, the protection circuit stops the switching power supply to protect the load and the power supply itself.
Switching power supply is to rectify alternating current into direct current, then reverse the direct current into alternating current, and then rectify and output into the required direct current voltage. In this way, the switching power supply saves the transformer in the lower linear power supply and the voltage feedback circuit. The inverter circuit in switching power supply is completely digital adjustment, which can also achieve very high adjustment accuracy.
