Fly-back type switch power supply

Abstract

The invention discloses a fly-back type switch power supply. On basis of an LCL fly-back converter, an NP1 dotted terminal of a transformer B is connected with a power supply, and a second primary winding NP2 dotted terminal is grounded, and NP1 and NP2 adopt bifilar winding arrangement. One end of a capacitor C1 is connected with an NP1 undotted terminal, and the other end is connected with an NP2 undotted terminal. The NP2 dotted terminal is connected with the power supply by a clamping network 400 formed by serially connecting a field effect transistor Q2 and a C3 together, and therefore when Q1 is in a saturation conduction state, NP1 and NP2 are excited, and when Q1 is shut off, a secondary side NS is used to output energy, and active clamping of energy of leakage inductance is realized by NP2 via the clamping network 400, and then ZVS, lossless absorption is realized after changing a control strategy, and a duty ratio is allowed to be greater than 0.5, and conversion efficiency is high.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a flyback switching power supply. Background technique [0002] At present, switching power supplies are widely used. For occasions where the input power is below 75W and the power factor (PF, PowerFactor, also known as power factor) is not required, the flyback (Fly-back) switching power supply has attractive advantages: circuit topology Simple, wide input voltage range. Due to the small number of components, the reliability of the circuit is relatively high, so it is widely used. For convenience, many documents are also called flyback switching power supply, flyback power supply, and flyback converter. Japan and Taiwan are also called flyback converters, flyback switching power supplies, and flyback power supplies. Common topologies for AC / DC converters such as figure 1 As shown, the prototype of the figure comes from page 60 of "Switching Power Converter Topology and...

AI Technical Summary

Problems solved by technology

[0004] The inductance of the primary winding is also low, and it often happens that the calculated number of turns cannot be evenly wound from the left to the right of the trunking of the skeleton, especially when the working voltage is high, the sandwich series winding method can be used. Because the two primary windings are not on the same layer, there is a leakage inductance between the two primary windings, and this leakage inductance will cause losses, thus making the efficiency of the switching power supply change. Low, the loss problem caused by the leakage inductance between the two parallel primary windings: this will exist during excitation and demagnetization; if the third winding is used for demagnetization, it is not good to choose the third winding to be connected in parallel with the two Which of the primary windings is wound in parallel, only two tertiary windings can be used, which are respectively wound in parallel with the two parallel primary windings, and then connected in parallel to form a "third winding". The process is complicated. There are also three windings that will induce unequal voltages, causing losses and greater electromagnetic interference

[0005] In fact, for the common demagnetization of the third winding, the advantage is lossless demagnetization and high efficiency, but the selection of the wire diameter of the third winding is also a problem: the selection is relatively thin, and it is troublesome to wind in parallel with the primary winding, and it is easy to The thin wire is broken; if the wire diameter is selected to be the same as that of the primary winding, the cost will be high

But in these two schemes, figure 2 This demagnetization method has strict requirements on the leakage inductance, otherwise, the excitation energy may be directly returned to the DC power supply U by D1 DC , does not appear in the secondary winding N S In the middle, there is no current in the secondary side D2, so that the output voltage is low or there is no output; and it is required that the reflected voltage generated when D2 is turned on cannot be greater than the DC power supply U DC , and if the duty cycle cannot be greater than 0.5, the power density cannot be further improved

for image 3 , the degaussing circuit itself is a more classic topology, the duty cycle can be greater than 0.5, but the energy of the leakage inductance has not been recycled

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