Overview of the working principle of high frequency switching power supply
The working principle of high-frequency switching power supply is power conversion. the
When the switch S is closed, current flows through the inductor L, and an output voltage is generated across the load RL. Due to the polarity relationship of the input voltage, the diode VD1 is in the reverse configuration, and L stores energy at this time. When the switch S is turned on, the polarity of the magnetic field of the inductor L changes, the energy stored in L is released through the load RL, the diode VD1 conducts forward, and the polarity of the voltage across the load remains unchanged. The diode VD1 is called a freewheeling diode because of its function in the circuit.
When the switch S is closed, the input circuit has current input, and when the switch is opened, the current is suddenly terminated. However, due to the effect of the inductance L and the freewheeling diode VD1, the output current is continuous. The inductance L and the capacitance C also play the role of filtering at the same time, so that the voltage on RL is smoother.
In practical applications, switching transistors are used as switches. At the same time, in the circuit shown in Figure 1, there is a lack of safety isolation measures between the input and output circuits, so high-frequency transformers are generally used as isolation devices.
VT1 is a switching transistor whose base is controlled by a square wave S1. When S1 is at a high level, VT1 is turned on, and power is generated at the primary stage of the transformer T and energy is stored. Since the secondary of the transformer is in phase with the primary, all quantities are also passed to the secondary of the transformer. The current flows through the forward-biased diode VD2 and the inductor L, the energy is transferred to the load RL, and the capacity is stored in the inductor L. At this time, the diode VD1 is in reverse bias.
When S1 is at a low level, VT1 is cut off, the voltage in the winding of the transformer T is reversed, the diode VD2 is cut off, the freewheeling diode VD1 is turned on, and the energy stored in the inductor L continues to be transmitted to the load RL.
Obviously, the output voltage VRL=V2×Ton/T=V2×X where X=Ton/T is the duty ratio; Ton is the conduction time of VT1, changing the pulse duty ratio δ can change the output voltage (or current) .
It can be seen that the switching power supply is a power conversion device.
The above briefly introduces the working principle of high-frequency switching power supply. It is not difficult for readers to see that it is a high-tech product integrating power transfer technology and pulse width modulation technology. It is the latest embodiment of the development of contemporary power electronics theory. Once it comes out, That is, it has received widespread attention and achieved unprecedented rapid development. Internationally, high-frequency switching power supplies have undisputedly occupied the leading position in the field of DC power supplies. In China, the HY series of high-frequency switching power supplies represented by Beijing Haoyuan Power Equipment Co., Ltd. Switching power supply has also emerged suddenly, dancing with various international famous brands on the stage of market economy with excellent performance, reliable quality and perfect service.
The grid power supply is filtered by EMI. Then it is rectified by a silicon bridge and filtered by a filter circuit to become direct current. Here, the filter circuit is represented by only one circuit C1. The auxiliary power supply converts the alternating current into a low-voltage direct current through rectification and filtering, and supplies power to the control circuit. Power MOS tubes V1 and V2 are used as switching elements. The control circuit generates a square wave (PWM) with a fixed frequency and adjustable pulse width. The square wave controls the on and off of V1 and V2.
