Forward switching power supply

Abstract

The invention discloses a forward switching power supply. On the basis of a common three-winding absorption forward switching converter, the like terminal of a first primary winding NP1 in a transformer B is connected with a power supply, the like terminal of a second primary winding NP2 in a transformer B is grounded, and NP1 and NP2 are wound in a bifilar manner. A capacitor C1 is added, one end of C1 is connected with the unlike terminal of NP1, and the other end of C1 is connected with the unlike terminal of NP2, so in case of saturation conduction of Q1, both NP1 and NP2 are excited magnetically, and a secondary winding outputs energy; in case of turn-off of Q1, the energy of primary exciting current is losslessly absorbed by NP2 through D1. The forward switching power supply is suitable for working under a low voltage, and the utilization rate and the current density of the primary windings are improved, so the power density is large, large leakage inductance between primary and secondary sides is allowed, and the conversion efficiency is high.

Description

technical field [0001] The invention relates to the field of switching power supplies, in particular to a single-end forward switching power supply. Background technique [0002] At present, switching power supplies are widely used. In the industry, they are often called converters. The basic forward converter in the forward switching power supply is an ideal isolated version of the Buck converter. Common topologies include single-ended forward converters, Symmetrically drive half-bridge converters, full-bridge converters, push-pull converters, symmetrical push-pull forward converters, etc. What needs to be mentioned is the symmetrical push-pull forward converter, as shown in Figure 0-1. This figure is quoted from "Switching Power Converter Topology" written by Dr. Zhang Xingzhu, ISBN978-7-5083-9015-4 and Design, Figure 5-14 on page 91, which is referred to in this article as: Reference 1. [0003] Symmetrical push-pull forward converters are known in the patent literature...

AI Technical Summary

Problems solved by technology

Since the demagnetization energy of the three windings can be recovered, the efficiency is high, but due to the low voltage, the same power is converted, and the working current of the primary winding has to increase. In order to reduce the current skin effect at high frequencies, the primary winding must use multiple strands The wires are wound in parallel; the inductance of the primary winding is also low, and it often occurs that the calculated number of turns cannot be tiled from the left to the right of the wire slot that is completely wound around the skeleton, especially the sandwich series winding method, which is forced to use a sandwich parallel connection For the winding method, since the two primary windings are not on the same layer, there is a leakage inductance between the two primary windings. This leakage inductance will generate losses, thereby reducing the efficiency of the switching power supply. Two parallel primary windings Problems caused by leakage inductance between windings:

[0013] 1) During excitation, due to the existence of leakage inductance, the induced voltage difference has a pressure difference on the leakage inductance, causing a non-negligible loss. This is easier to understand: if the number of turns of two parallel primary windings is one turn, it is equivalent to existence The turn-to-turn short circuit in this turn is just a short circuit through the DC internal resistance of the two parallel primary windings. Relatively speaking, the loss is not as large as the real turn-to-turn short circuit.

[0014] 2) If the third winding is used to demagnetize, which of the two parallel primary windings is the third winding? Only two tertiary windings can be used, which are respectively wound in parallel with the two primary windings connected in parallel, and then connected in parallel to form a "third winding". voltage, causing loss and large electromagnetic interference

[0015] 3) The common demagnetization of the third winding has the advantages of 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 put the thin wire Pulled off; if the wire diameter is selected to be the same as that of the primary winding, the cost will be high

Because the winding does not participate in the excitation, the current density of the primary side is low, the window utilization rate of the magnetic core is low, and the transformer volume is large

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