Main components and functions of switching power supply
A linear power supply generally samples the output voltage and sends it to a comparison voltage amplifier with a reference voltage. The output of this voltage amplifier is used as the input of a voltage regulator to control the regulator so that its junction voltage changes with the input, thereby adjusting its output voltage. But the switching power supply changes the output voltage by adjusting the on and off time of the regulating tube, that is, the duty cycle.
2, The principle of linear power supply: Linear power supply mainly includes power frequency transformer, output rectifier filter, control circuit, protection circuit, etc. A linear power supply first transforms AC power through a transformer, and then rectifies and filters it through a rectifier circuit to obtain an unstable DC voltage. To achieve high-precision DC voltage, the output voltage must be adjusted through voltage feedback. This power supply technology is very mature and can achieve high stability with minimal ripple and no interference or noise from switching power supplies. But its disadvantage is that it requires a large and bulky transformer, and the volume and weight of the required filtering capacitors are also quite large. In addition, the voltage feedback circuit works in a linear state, and there is a certain voltage drop on the adjustment tube. When outputting a large working current, the power consumption of the adjustment tube is too high, the conversion efficiency is low, and a large heat sink needs to be installed. This type of power supply is not suitable for the needs of computers and other devices, and will gradually be replaced by switch mode power supplies.
3, Comparison of Switching Power Supply: Switching power supply mainly includes input grid filter, input rectifier filter, inverter, output rectifier filter, control circuit, and protection circuit. Their functions are:
1. Input grid filter: eliminates interference from the grid, such as motor start-up, electrical switches, lightning strikes, etc., while also preventing high-frequency noise generated by switching power supplies from spreading to the grid.
2. Input rectifier filter: Rectify and filter the input voltage of the power grid to provide DC voltage for the converter.
3. Inverter: It is a crucial component of a switching power supply. It converts DC voltage into high-frequency AC voltage and serves to isolate 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, while also preventing high-frequency noise from interfering with the load.
5. 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 and maintain stable output voltage.
6. Protection circuit: When the switching power supply experiences overvoltage or overcurrent short circuit, the protection circuit stops the switching power supply from working to protect the load and the power supply itself.
Switching power supply rectifies alternating current into direct current, then inverts the direct current into alternating current, and finally rectifies and outputs the required direct current voltage. This way, the switching power supply eliminates the transformer and voltage feedback circuit in the linear power supply. The inverter circuit in the switching power supply is completely digitally adjusted, which can also achieve very high adjustment accuracy.
