Self-excitation push-pull type converter

Abstract

The invention discloses a self-excitation push-pull type converter, comprising a transformer. A closed magnetic core or iron core of the transformer is formed by a main part and a local part, wherein the local part achieves magnetic saturation earlier than the main part under excitation of the same increasing magnetic field. The converter disclosed by the invention can overcome the defects of the traditional self-excitation push-pull type converter, thus efficiency of the self-excitation push-pull type converter is obviously improved when the self-excitation push-pull type converter is in a light load state; when the self-excitation push-pull type converter is in a rated load state, the efficiency is further improved; number of windings of coils on a magnetic saturation transformer in the self-excitation push-pull type converter is reduced; working frequency of the self-excitation push-pull type converter is improved while loss is maintained to be lower; and probability that current peak is produced when the self-excitation push-pull type converter is conducted and closed is reduced, and the efficiency is further improved while output ripple is reduced.

Description

technical field [0001] The invention relates to a switching power supply, in particular to a self-excited push-pull converter type switching power supply. Background technique [0002] The existing self-excited push-pull converter, the circuit structure comes from the self-excited oscillating push-pull transistor single-transformer DC converter invented by G.H.Royer in 1955, also known as the Royer circuit, which is also a high-frequency conversion control circuit Part of the circuit comes from the self-excited push-pull double transformer circuit invented by Jen Sen in the United States in 1957, which was later called self-oscillating Jensen circuit or Jensen circuit; these two circuits , later generations are collectively referred to as self-excited push-pull converters. The relevant working principle of the self-excited push-pull converter is described on pages 67 to 70 of "The Principle and Design of Switching Power Supply" published by the Electronic Industry Press, an...

AI Technical Summary

Problems solved by technology

[0027] 2. At rated load, the efficiency cannot be further improved

Therefore, it is difficult to choose between these parameters when designing a self-excited push-pull converter

[0029] For the Jensen circuit, if you want to improve the conversion efficiency of the circuit, for the same reason, the effective cross-sectional area S of the magnetic core of the small transformer B1 is small, resulting in insufficient driving power, and the switching triode cannot enter a good saturated conduction, resulting in a large voltage drop loss. , the conversion efficiency of the converter is also low; the effective cross-sectional area S of the magnetic core of the small transformer B1 is larger, and the loss of the small transformer B1 itself also increases synchronously; of course, the problem of insufficient driving power can be solved by increasing the number of coil turns N, but It also brings the following technical problems, that is, the number of turns N increases, and since the small transformer B1 must work in a state of magnetic saturation, the air gap cannot be opened, which brings great difficulties to winding

[0030] 3. When the input voltage is relatively high, the number of turns on the transformer B1 is too many, making it difficult to process

[0031] Self-excited push-pull converter, taking the Royer circuit as an example, from the formula (1), we can see that under the premise of increasing the input voltage, if the operating frequency of the self-excited push-pull converter remains unchanged, then the formula ( The parameters corresponding to the denominator in 1) should be increased. For industrial-grade small module power supplies of the same series and power, magnetic cores of the same size are often used. At this time, the problem can only be solved by changing and increasing the number of coil turns N, such as Picture 1-1 The announced circuit parameters, if made into a 24V input product, the primary side coil N P1 and N P2 The number of turns will increase from 20 turns at 5V input to 96 turns each, because Picture 1-1 The medium transformer B1 must work in a state of magnetic saturation and cannot open an air gap, which brings great difficulties to winding. At present, so many turns of enameled wire are wound on a small magnetic ring with a diameter of less than 10mm. Whether it is made by hand or hand-wound, there are processing difficulties

Machine winding is used. When the first layer is wound and the second layer is wound, the second layer of wires is difficult to stack on the first layer, which will destroy the line sequence of the first layer, and the result will be worse and more chaotic; Manual winding, so many turns, all depend on the operator's careful memory, it is difficult to guarantee that there will be no more than one or two turns, or one or two less turns. Once the number of turns is changed, the output voltage will deviate. In serious cases, the transformer will be installed After that, the original function cannot be realized

[0032] If the effective cross-sectional area S of the magnetic core is doubled, the number of turns can be reduced to 48 turns, but at this time the effective cross-sectional area S of the magnetic core of transformer B1 is doubled, and at the same frequency, its own loss is also doubled , the conversion efficiency of the converter decreases

[0033] Therefore, it is difficult to see self-excited push-pull converter modules working at 48V and above in the industrial field and on the market. This is also the reason, and the efficiency can only be reduced in exchange for fewer turns.

[0034] 4. It is difficult to increase the working frequency

[0035] Since the self-excited push-pull converter circuit uses the magnetic core saturation characteristic to perform push-pull oscillation, each push-pull conversion is realized by the magnetic core approaching or entering magnetic saturation, so when the operating frequency is increased, the loss increases and the conversion efficiency decreases.

[0036] For the Jensen circuit, for the same reason, the effective cross-sectional area S of the magnetic core of the small transformer B1 is smaller. Under the input voltage of 24V, it is often necessary to wind the primary side of 60 turns. Winding in parallel, only winding 30 turns, and then connecting in series to get 60 turns of the primary side, but because the diameter of the small transformer B1 is smaller, there are processing difficulties whether it is wound by machine or by hand

For 48V input voltage, the small transformer B1 can hardly be processed

Similarly, if the effective cross-sectional area S of the magnetic core is doubled, the number of turns can be reduced. Under the same operating frequency, the loss of itself is also doubled, and the conversion efficiency of the converter is reduced.

[0037] 5. There will be current spikes when the circuit is turned on and off, so the efficiency of the converter is low

[0040] 1) When the load is light, the efficiency of the converter is low;

[0041] 2) At rated load, the efficiency cannot be further improved;

[0042] 3) When the input voltage is relatively high, the number of turns on the transformer B1 is too many, making it difficult to process;

[0043] 4) It is difficult to increase the working frequency;

[0044] 5) There will be current spikes when the circuit is turned on and off, so the efficiency of the converter is low

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