The reason why the switching power supply is rectified into DC
Why is the switching power supply rectified into DC?
The switching power supply first converts the alternating current into direct current through rectification at the input end, which is a prerequisite for reducing the size of the power supply and realizing automatic control of output characteristics (constant voltage or constant current).
In the past power transformers, since the operating frequency was only 50-60Hz, in order to obtain sufficient inductive reactance, it was necessary to use heavy silicon steel sheet iron cores and thick coils. The volume of a 100ⅤA transformer was almost equivalent to half a brick. The weight is 2 ~ 3Kg.
Therefore, reducing the size of the transformer has become the key to the miniaturization of the power supply.
According to the inductive reactance formula XL=2πfL, it can be seen that increasing the frequency can also increase the inductive reactance. After increasing the frequency, the volume of the transformer can be made very small, and the number of turns of the coil is also greatly reduced.
Therefore, the switching power supply must convert the alternating current into direct current, and turn it into a high-frequency current of several tens of kHz through a high-power tube and an oscillation circuit, and then become the required voltage through a transformer.
When the load of the power supply changes, the information at the output end will be fed back (the optical corner in the switching power supply undertakes this task) to the oscillator circuit to adjust the ratio of the on-off and off-state of the switch.
The on-time is long and the off-time is short when the load is heavy, and the on-time is shortened when the load is light. This realizes the stability of the output voltage or current of the switching power supply.
All transistors responsible for these oscillation and automatic control functions require DC power supply and establish a proper DC operating point in order to maintain the normal operation of the power supply. Therefore, when designing a switching power supply, first convert the alternating current into direct current.
In the switching power supply circuit, there are electrolytic capacitors, triodes, and diodes. The first condition for them to work properly: the positive and negative polarities of each component must be guaranteed to be consistent (extended to positive or negative).
Therefore, when designing the circuit, there are three groups: positive, negative, and ground. When grounding, it can be connected to the positive pole or the negative pole.
After the overall circuit is finally merged, there are positive and negative poles. Therefore, the switching power supply is 220V AC from the mains, and is converted into DC by diode rectification to supply power to the circuit.
The switching power supply is a power supply that supplies power to the load, and the load that uses electricity basically needs a DC power supply. For example, a mobile phone is a 4.2-volt DC power supply. Commonly used electric vehicles require 24-volt, 36-volt, and 48-volt DC power. Computers generally A 5V, 12V DC power supply is required.
Since these loads all require direct current, the switching power supply that supplies power naturally needs to output direct current.
The above is the reason why the switching power supply needs to be rectified into DC. I hope it will be helpful to everyone.
