Switching power supply chip classification
There are also many varieties of control chips for switching power supplies, which are mainly divided into two categories: current control type and voltage control type. The voltage control type only samples the output voltage, stops closed-loop control as a response signal, and uses PWM technology to adjust the output voltage. From the perspective of control theory, this is a single-loop control system. The current control type is based on the voltage control type, adding a current negative reaction link, making it a double-loop control system, thereby improving the performance of the power supply.
First of all, from the input side comparison, AC/DC is far more difficult to do than DC/DC. Because the AC/DC is directly connected to the public network, some mains are directly small hydropower, and can be as high as 350VAC at night; some are connected to the wrong phase line, and the direct voltage is 380VAC, and the low voltage can also reach below 130V. In addition, there are many devices with different input characteristics in the public network connection, there are rational loads, capacitive loads, there are many spike noises on the power grid, and repeated harmonic components, thunderstorms and other factors. The combined effects make the public network more complex. The input voltage of DC/DC usually comes from a rectifier or a battery. The commonly used voltages are 12V/24V/48V/60V, etc. 4 types, the rectifier is AC/DC, which has been isolated once.
Secondly, in terms of device selection and reliability, AC/DC design is more difficult than DC/DC. It can be seen that AC/DC is directly faced with high voltage. The selection of input devices, especially power MOSFETs, the higher the voltage, the greater the conduction voltage drop and switching loss, and the more difficult it is to meet the thermal design of the power supply. Other diodes and triodes also exist. The problem of high pressure is difficult to choose, and low pressure is easy to choose. At the same time, the safety level of AC/DC power supply requirements is much higher than that of DC/DC. From the perspective of circuit structure, AC/DC generally requires two-stage conversion, while DC/DC only needs one-stage conversion, and the main power conversion circuit used by DC/DC is relatively simple.
