Electronic Load Testing and Working Principle of Switching Power Supplies
1, The entire process of the main circuit from AC grid input to DC output, including: 1. Input filter: Its function is to filter out the clutter existing in the grid, while also hindering the feedback of the clutter generated by the machine to the public grid. 2. Rectification and filtering: Directly rectify the AC power supply of the power grid into smoother DC power for down conversion. 3. Inverter: converts rectified DC power into high-frequency AC power, which is the core part of high-frequency switching power supplies. The higher the frequency, the better the ratio of volume, weight, and output power. 4. Output rectification and filtering: provides stable and reliable DC power according to load needs.
2, On the one hand, the control circuit samples from the output terminal, compares it with the set standard, and then controls the inverter to change its frequency or pulse width to achieve stable output. On the other hand, based on the data provided by the test circuit, the protection circuit identifies and provides various protection measures for the entire machine through the control circuit.
3, In addition to providing various parameters that are currently running in the protection circuit, the detection circuit also provides various display instrument data.
4, The auxiliary power supply provides different power requirements for all individual circuits. The principle of switch controlled voltage regulation is that switch K is repeatedly turned on and off at certain time intervals. When switch K is turned on, input power E is provided to load RL through switch K and filtering circuit. During the entire switch on period, power E provides energy to the load; When switch K is disconnected, input power source E interrupts the supply of energy. It can be seen that the input power supply provides energy to the load intermittently. In order for the load to receive continuous energy supply, the switch stabilized power supply must have an energy storage device that stores a portion of the energy when the switch is turned on and releases it to the load when the switch is turned off. In the diagram, the circuit composed of inductor L, capacitor C2, and diode D has this function. Inductance L is used to store energy. When the switch is turned off, the energy stored in inductance L is released to the load through diode D, allowing the load to receive continuous and stable energy. Because diode D keeps the load current continuous, it is called a freewheeling diode. The average voltage EAB between AB can be represented by the following equation: TON is the time the switch is turned on each time, and T is the duty cycle of the switch (i.e. the sum of the switch on time TON and off time TOFF). As can be seen from the equation, changing the ratio of switch on-time to duty cycle also changes the average voltage between AB, therefore, automatically adjusting the ratio of TON and T with changes in load and input power supply voltage can maintain the output voltage V0 unchanged. Changing the on-time TON and duty cycle ratio, that is, changing the pulse duty cycle, is a method called "Time Ratio Control" (TRC).
