Definition
Forward switching power supply refers to the switching power supply that uses a forward high-frequency transformer to isolate the coupling energy, and the corresponding flyback switching power supply.
Positive excitation specifically refers to when the switching tube is switched on, the output transformer acts as a medium to directly couple the magnetic field energy, the electrical energy is converted into magnetic energy, and the magnetic energy is converted into electrical energy, and the input and output are carried out at the same time.
The structure of the forward switching power supply is slightly complex, but the output power is much larger than the flyback switching power supply, so it is widely used.
Advantages: larger power than flyback switching power supply, high output transformer utilization, suitable for 100W-300W switching power supply.
Disadvantages: need to increase the back electromotive force winding, or topological drive, secondary add 1 rectifying inductor, high cost.
Forward switching power supply has two kinds of single tube forward excitation and double tube forward excitation in switching applications. For single tube forward excitation, because the transformer needs to add additional magnetic reset winding, when the main switch Mosfet is turned off, the Mosfet will bear twice the stress of the input voltage, so we recommend high BV Mosfet in this type of topology application to cope with the impact of voltage changes.
For the double-tube forward excitation, it is a very stable topology, the operating frequency is not high, there will be no excessive impact current, the requirements for MOS tubes are relatively loose, usually with PFC used in 200W~800W adapters, industrial power supplies, computer power supplies or the environment is relatively harsh and high stability requirements. In the application, we recommend MOS with lower thermal resistance and better switching characteristics as the first choice.
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