JPH02188904A - Offset-magnetism preventing transformer - Google Patents

Abstract

PURPOSE:To prevent an offset magnetism from being generated by means of a simple constitution and to efficiently reduce a loss of a transformer in a region of a high-frequency and large electricpower load by a method wherein the transformer is constituted of a magnetic core containing no gap in a magnetic path and a winding which has been wound independently on another magnetic core is connected in parallel with a primary winding of the transformer. CONSTITUTION:A transformer T is constituted of a magnetic core I1 in which no gap is formed in a magnetic path; a winding which has been wound independently on another magnetic core 12 separately from the magnetic core I1 is connected in parallel with a primary winding N1 of the transformer T; the transformer T is excited. Through this constitution, a means to prevent an offset magnetism from being generated in the transformer T is installed. For example, one end of a battery with a voltage Vi is connected to the center of a primary winding N1 of said offset-magnetism preventing transformer T1 the other end of the battery is connected to both ends of the primary winding N1 via parallel connections Q1 and D1 as well as Q2 and D2 of FET switches and diodes; diodes D3, D4 connected to both ends of a secondary winding N2 are connected electrically to a load resistance RL via a smoothing circuit composed of a reactor L and a capacity C; thereby, a push-pull converter is constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to the prevention of biased magnetism in power transformers, especially power transformers suitable for the configuration of small, highly efficient, large capacity power supplies such as push-pull converters. Regarding transformers that prevent the occurrence of unbalanced magnetism, in particular, those that prevent the occurrence of unbalanced magnetism with an extremely smooth configuration and can effectively reduce transformer losses in areas of high frequency and large power loads. It is.

(Prior art) -a. As various information processing devices, including microcomputers, become widespread and are used in advanced ways, small and
There is an increasing demand for high efficiency, large capacity power supplies. On the other hand, push-pull converters and bridge-type multi-system converters, which transform the AC voltage generated by switching battery voltage and convert it into the required DC power supply voltage, are based on the polarity of the voltage applied to the primary winding of the transformer used. Since the polarity is reversed every half cycle, there is no need for a magnetic flux reset circuit, and the utilization rate of the magnetic core is high, so it has been widely used as a large-capacity power supply circuit system.

Although this type of power supply circuit is symmetrically constructed, asymmetry in the circuit due to slight differences in characteristics that become noticeable in the high frequency range of semiconductor switch elements that are arranged and connected symmetrically cannot be avoided. Therefore, it was essential to use a transformer with countermeasures against unbalanced magnetism to absorb circuit imbalance to some extent.

(Problems to be Solved by the Invention) Conventionally used methods for preventing unbalanced magnetization in transformers have fallen into one of two categories.

(a) Lower the magnetic flux density of the transformer to provide some margin before the saturation magnetic flux density.

(b) Create a gap in the transformer's magnetic core to reduce magnetic permeability.

(C) Adjust the on-time in switching the battery voltage.

In addition, (a) and (b) are those in which the magnetic circuit itself is configured so that biased magnetization is unlikely to occur, and (C) is one in which biased magnetism generated in the magnetic circuit is removed by an external circuit. Methods (a) and (b) to prevent unbalanced magnetism applied to the magnetic circuit itself are often used together, but as a result of setting the maximum operating magnetic flux density low, a large magnetic core is used, which reduces the size of the transformer. There were some difficulties.

In addition, the method (b) for preventing biased magnetization is widely used because it is simple and easy to implement. There was a problem with the temperature rising. Furthermore, increased iron loss due to magnetic flux imbalance also became a problem. Particularly for high-frequency, large-capacity converters, these losses in transformers become a serious problem. In addition, there was a problem in that a magnetic material with low loss in the high frequency range could not be effectively used as the magnetic core due to the machining problem of cutting the magnetic core to provide the gap.

On the other hand, the unbiased magnetization prevention method (C) requires a control circuit with a complicated configuration that detects the DC value of the primary current in the transformer, provides negative feedback, and converts it into the pulse width of the control pulse.
The number of circuit components increases, reducing the reliability of the power supply.
There was a problem.

As mentioned above, converter type power supplies such as push-pull type originally have a high utilization rate of the transformer magnetic core, but by preventing unbalanced magnetization, the magnetic core becomes larger and the excitation current increases. The magnetic core temperature rises due to increased loss due to magnetism, proximity effects, and magnetic flux imbalance, and the control circuit becomes complicated, making the original advantages not fully utilized.

Therefore, with the increasing demand for smaller and cheaper power supply devices, it has become a challenge to realize a compact, highly efficient, high reliability power transformer that has a simple structure and prevents biased magnetism.

(Means for Solving the Problems) An object of the present invention is to solve the above-mentioned conventional problems, and to generate biased magnetism without special work on the magnetic core or without the need for a complicated external control circuit. An object of the present invention is to provide an anti-biased magnetic transformer which prevents the occurrence of problems and takes advantage of the inherent advantages of a converter type power supply device.

In other words, the unbiased magnetization prevention transformer of the present invention is equivalent to a conventional transformer with a gap in the magnetic core, because it has a magnetic core without a gap and a reactor with a separate magnetic core connected in parallel to the windings attached to the magnetic core. The transformer is designed to achieve the same or better effect of preventing biased magnetism, and the transformer is constructed using a magnetic core with no air gap in the magnetic path, and the transformer is constructed using a magnetic core that is independent of the magnetic core and is separate from the magnetic core. The transformer is configured such that a winding wound around the transformer is connected in parallel to the primary winding of the transformer to excite the transformer, and means is provided for preventing the occurrence of biased magnetization in the transformer. It is something to do.

(Function) Therefore, according to the present invention, due to the extremely simple configuration with a small number of components, it can be applied to converter type power supply devices such as push-pull type, where eccentric magnetization of the transformer core is a serious problem. It is possible to realize an anti-biased magnetic transformer that can effectively reduce loss in high frequency/high power load areas.

(Example) The present invention will be described in detail below with reference to the drawings.

The unbalanced magnetization prevention transformer of the present invention has a structure in which the transformer part and the excitation inductance part of the conventional gapped transformer are separated and connected in parallel, and the unbalanced magnetization prevention is the same as in the conventional gapped transformer. Operate. The basic structure is the first
The simplified equivalent circuit is shown in Figure 1 (b).
). In the basic configuration shown in the figure, the primary winding N1 of the transformer T is formed by a gap-free magnetic core 1, and a reactor 3 is connected to both ends of the primary winding N1 of the transformer T, which is formed by a magnetic core I2 having a winding that allows the reactor current iL to flow. . Note that the gapless magnetic core 1. Therefore, the excitation inductance of the transformer T and the axle inductance L
It can be considered to have a sufficiently large value compared to pj, and the winding resistances in the transformer T and reactor Lp3 can be ignored as being sufficiently small.

Here, it is assumed that the switch S is turned on in a no-load state with the secondary side open as shown in the figure, the battery voltage ■i is applied to the polarity shown in the figure, and the current i flowing from the battery and the exciting current is
, 'The basic circuit configuration shown in the figure is simply analyzed by selecting J-acdle current iL and interlinkage magnetic flux Φ as variables,' and the following circuit equation is obtained.

KiiL+. ,-0,Φ,. , = 0, the flux linkage increases to the value obtained by integrating the battery voltage V, over the switch-on period. Now, assuming that the flux linkage is excited to Φ, the entire current i supplied from the battery becomes the exciting current 11 in the absence of the reactor Lp1.

On the other hand, when the reactor Lpj is connected, the current i supplied from the battery is as follows from equation (3).

i=i, +i.

When the switch S is turned on at time 1=0, a much larger value of battery current l is required in the reactor current to reach the saturation magnetic flux Φ than when the reactor Lp3 is not connected, and the transformer T is saturated by that much. Under no-load conditions, the current i supplied by the battery is the excitation current i,
Therefore, the battery current i according to equation (5) is the reactor L
, 3 are connected to the transformer T. The relationship between such currents is illustrated in FIG. 2.

Furthermore, from equation (5), the equivalent circuit of a transformer T with reactors p and I connected as shown in FIG. 1 can be derived in a simplified manner.゛The equivalent circuit shown in the figure consists of a parallel connection of transformer excitation inductance L2, reactor inductance Lp3, and ideal transformer T due to a gapless magnetic core 1, and the transformer section and excitation in a transformer with a gap in the magnetic core. It can be considered that the inductance section is separated from each other.

In the unbiased magnetic transformer of the present invention as described above, even if a toroidal core with a large magnetic permeability μ is used, the effective magnetic permeability can be reduced without cutting, which makes it possible to reduce the effective magnetic permeability of the transformer with a conventional gap. It is possible to achieve prevention of biased magnetism equivalent to that of the transformer T due to the magnetic core l, which is responsible for power transmission.
It becomes possible to independently optimally design the reactor with the magnetic core (2) and the magnetic core (2) connected in parallel to prevent biased magnetization.

FIG. 3 shows an example of the circuit configuration of a push-pull converter to which the present invention is applied. In the illustrated configuration example, the transformer T uses a magnetic core of 1° without a gap, and the −th order winding N1
With a separate magnetic core I2 across the reactor current i,
This is done by configuring it to flow or by connecting the accelerator Lp3. As a push-pull converter, one end of a battery with a voltage v1 is connected to the center of the primary winding N+ of the unbalanced magnetic transformer having such a configuration, and the other end of the battery is connected in parallel with an FET switch and a diode Q. DI and Q! and D
! are connected to both ends of the primary winding N, respectively, and are connected to both ends of the secondary winding N2. Connect to resistor RL and output voltage ■. It is configured so that it can be taken out.

This push-pull converter is used in an operation mode in which the reactor current iL is continuous, and the inductance of the smoothing reactor L is sufficiently large to operate as a constant current circuit with respect to the load resistance RL. Note that the winding resistance of the transformer T and the reactor Lp3 for preventing unbalanced magnetism is sufficiently small, and the loss is caused by the switch Q consisting of a MOS FET,
It is sufficient to consider only the on-resistance R, ,7 of ,Q. Furthermore, by using a sufficiently high-speed operating semiconductor element for the switches Q, , Q, the switching transient state can be ignored compared to the state during other periods.

An analysis of the biased magnetism of the transformer T in the main states (1) to (2) shown in Table 1 of this push-pull converter results in the following.

Table 1 Push-pull converter operating mode In state I, when diode D4 is on and PUT switch Q2 and diode D are off, current flows through the solid line in the equivalent circuit shown in FIG. 4(a). The reactor L1 includes two series excitation inductances L 111 + L in the primary winding of the transformer T.
Since it is connected across Dt, a voltage approximately twice as high as the voltage applied to the excitation inductance pl is induced. Here, assuming that the reactor LP3 is connected to both ends of the excitation inductance Lpl that shares half of the voltage applied to the transformer, the same reactor current iL as in the circuit shown in Fig. 4(a) will flow. When each component is converted, a simplified equivalent circuit shown in FIG. 4(b) is obtained.

(1) State I In the equivalent circuit shown in Figure 4 ('b), the exciting current 1
11. If reactor current iL and interlinkage flux Φ are selected as variables and winding resistance is ignored, the circuit equation becomes as follows.

The FET switches Q and t and the reactor current ILI in the configuration shown in Figure 3 are each expressed by the following (13)
and (14).

The excitation current i and the reactor current iL are transformed, and the initial value of each current is . Solving the above circuit equation as ILO and ILO yields the following.

Here, V+=Vt Ro, (nlo+Ito), then t
= T, excitation current 11 (2) state after elapsed ■ During the period when both FET switches Q1 and Q2 in the configuration shown in the third figure are off, the diodes D,
, D4 are both turned on, and voltages with opposite polarities are generated in the secondary winding N2. Therefore, the transformer T
The secondary winding side of is almost short-circuited, no interlinkage flux Φ is generated, and the exciting current 17 continues to flow through the diodes D, , D, on the secondary winding side, resulting in the above-mentioned state. Maintain the final current value at ■. Therefore, the condition ■
The equivalent circuit in is shown in FIG. 5, and the final values of the exciting current 11 and the reactor current iL are respectively Iv
Assuming at and Ill, each final current value in state (2) is given by the following equations (15) and (16), respectively.

■,, = ■,t (ts)
I L2= I tt (1
6) (3) State ■ In state ■, as shown in Fig. 6, Fig. 4 (a)
Using an equivalent circuit similar to the equivalent circuit for state I shown in , the circuit equation becomes as follows.

2 dt dt Φ Here, V3= Vt Ro, +(n I o I c
z) Next, the excitation current L2 and reactor IL3 after t = T are given by the following equations (24) and (25), respectively.

When the above circuit equation is solved by modifying the excitation current i and the reactor current it and setting the initial values of each current to 11 and ILz, the following is obtained.

p2 (4) State ■ The equivalent circuit in state ■ is as shown in FIG. 7, similar to the equivalent circuit in state ■ shown in FIG.
, and the final value of reactor current LL, respectively, rs<
and IL4, each final current value in state (2) is given by equations (26) and (27), respectively.

! ,,=1. :+ (26
)I L−=Ill (
27) In the steady state, the initial current value and final current value in one cycle of the operation mode shown in Table 1 are equal as shown below.

1, o=1. a (2B) Also, the operating voltage and current waveforms in the one-cycle operating mode shown in Table 1, especially the reactor Lp in the steady state.
The applied voltage waveform and excitation current waveform of No. 3 are as shown in FIG. 8, respectively.

Therefore, the DC component Δ11 of the exciting current 11, which causes biased magnetization in the transformer, can be calculated using the above-mentioned equations (13), (
15), (24), and (26) over − periods, calculations can be made according to the following equation (29).

As can be seen from the detailed description above, if the present invention is applied, a bias-preventing transformer can be created that exhibits the same magnetic characteristics as a conventional push-pull converter transformer in which a gap is provided in the magnetic core to prevent bias. This can be reliably and easily realized by using an extremely simple configuration in which a separate magnetic core is used in parallel with the primary winding of a transformer without a gap in the magnetic core, or an axle is connected to the primary winding.

Next, Table 2 shows the specifications of a prototype push-pull converter in which the present invention is applied to prevent unbalanced magnetization of the transformer used as described above.

Nao, Table 2 shows Figures 9 (a), (b) and Figure 10 (a).

The specifications of prototype converters #1 and #2, which will be described later, are shown for the following examples. Since there is no gap-forming spacer sandwiched between the EL core that makes up the transformer, there is little magnetic flux leaking from the EI core joint.Also, regarding the winding method, the degree of coupling between the -order winding and the secondary winding is small. In order to improve the magnetic flux, bifilar windings are used, and they are connected in parallel or in series to reduce leakage magnetic flux. On the other hand, the reactor for preventing unbalanced magnetization is the same size as that used for the transformer [■ The core is wound with twice the number of turns as the next winding of the transformer, and each turn transforms. This is done so that the same magnetic flux change as in the container occurs. The inductance value of the reactor for preventing biased magnetism was adjusted by changing the gap length of the El core joint.

In addition, in practical use, it is possible to manufacture using a magnetic core smaller than the size shown in the table.

Prototype push-pull converter #1 with specifications shown in Table 2
Examples of output power/current-efficiency characteristics obtained for
These are shown in Figures (a) and (b), respectively. In the illustrated characteristic curve, the solid line shows the characteristics of a circuit using a transformer with a reactor added by applying the present invention, and the broken line shows the characteristics of a circuit using a transformer with a gap in the magnetic core without adding a reactor. The characteristics of the conventional circuit are shown. The switching frequency is 9th
50KHz in figure (a), 100K in figure 9(b)
)Iz, and the input voltage ■ is set to 50v1 so that the operating magnetic flux density is almost constant between the circuit of the present invention and the conventional circuit at 14T (terrace) even in the worst case.
In FIG. 9(b), "i?" was adjusted to 100 V and the characteristics were measured.

Therefore, the switching frequency 5 shown in FIG. 9(a)
In the case of 0KIIz, as the gap length in the conventional circuit is increased, the efficiency of the corresponding circuit of the present invention exceeds the efficiency of the conventional circuit.

This tendency becomes even more pronounced when the switching frequency is 100 KHz as shown in Figure 9(b), and when the output current exceeds IA, the conventional transformer with no gap in the magnetic core, which had the lowest loss, It even exceeds the efficiency of the circuit. The reason for this is that when only a transformer with no gap in the magnetic core is used, biased magnetization occurs in the transformer due to unbalance in switching times, etc., which was not a problem in low frequency ranges because there is no gap in the magnetic core. This is because losses increase.

For ferrite cores, it is known that the operating magnetic flux density has a large effect on transformer loss. Considering this point, the input voltage V is set to 100V, and the output voltage is set to ■. Figure 10 (a) shows an example of the output power/current-efficiency characteristics when the operating magnetic flux density is varied in the prototype converter #2 shown in Table 2 when 5 ■.
), shown in (b).

In this case, since the output voltage v0 is low, the characteristics were measured by changing the switching and rectifying diodes from fast recovery diodes to Schottky barrier diodes as shown in Table 2. There is. In addition, the switching frequency and the operating magnetic flux density B at the worst time are each 25 KHz in Fig. 10(a).
and 0.257 (terrace), respectively 100 KHz and 0.06 T (terrace) in Figure 1O(b).

Also in FIGS. 10(a) and (b), FIG. 9(a),
Similarly to FIG. 10(b), the corresponding characteristic curves of the circuit of the present invention and the conventional circuit are shown by solid lines and broken lines, respectively. In FIG. 10(b), where the operating magnetic flux density B is extremely small, There is almost no difference between the characteristic curves of the circuit of the present invention and the conventional circuit as seen in other cases, and as shown in FIG. 10(a),
As the operating magnetic flux density B is increased, the efficiency improvement of the converter according to the present invention becomes noticeable.

Next, for the case where there is a 1% on-time difference in battery voltage switching in a push-pull converter, excitation current (■) in the transient state and steady state. The excitation current i when the power switch of the push-pull converter is turned on. is the initial value I,. The calculation results under the conditions shown in the figure for the mode of change from =0 to reaching the steady value are shown in FIGS. 11(a) and 11(b), respectively, for the circuit of the present invention and the conventional bypass.

As can be seen from the illustrated changes in the excitation current, the circuit of the present invention is superior to the conventional circuit in terms of transient response and steady-state value of the amount of biased magnetism.

As can be seen from the prototype measurement results and calculation results mentioned above,
In conventional transformers that have a gap in the magnetic core to prevent magnetic bias, the efficiency decreases due to the large proximity effect due to leakage magnetic flux and the unbalanced magnetic flux, and increasing the gap in the magnetic core increases loss. This tendency becomes more pronounced as the output current becomes larger, the operating magnetic flux density becomes higher, and the switching frequency becomes higher. However, in a transformer in which a reactor is added to prevent unbalanced magnetization according to the present invention, the effective magnetic permeability of the transformer is It can be lowered to provide an anti-biasing function, and a high operating magnetic flux density can be obtained in a large current range.In addition, the efficiency of the transformer can be improved as the switching frequency increases, making it excellent for high-frequency, large-capacity applications. Therefore, it exhibits certain characteristics.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, a transformer used in a converter type power supply device can be The device can have an anti-biased magnetic function,
Moreover, since no load current flows through the excitation inductance, it is possible to reduce transformer loss, and when applied to push-pull converters, it suppresses the occurrence of biased magnetization, and is suitable for high frequencies, high magnetic flux densities, and large currents. It is possible to reduce the loss of the transformer with respect to the load. Therefore, according to the present invention, the following remarkable effects can be achieved.

(1) By simply connecting a reactor in parallel to a transformer with no gap in the magnetic core, it is possible to provide the same anti-biasing function as a conventional transformer with a gap in the magnetic core.

(2) The power transmission transformer and the unbiased magnetization prevention reactor can be optimally designed independently of each other.

(3) Since no gap is provided in the transformer's magnetic core, a metal ribbon or amorphous magnetic core can be used, and a ferrite cut core can be used in the reactor's magnetic core.

(4) Since there is no gap in the magnetic core of the transformer, leakage and deviation of magnetic flux are suppressed, and the transformer can be applied as a highly efficient transformer to high-frequency, large-capacity converter-type power supplies.

(5) High reliability can be obtained because no control electronic circuit is required and the device can be constructed using only a simple magnetic circuit.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are circuit diagrams showing the basic configuration and simplified equivalent circuit of the bias-preventing transformer of the present invention, respectively. Figure 2 is a line showing the operating principle of the bias-preventing transformer of the present invention. 3 is a circuit diagram showing a configuration example of a push-pull converter to which the present invention is applied, and FIG. 4(a) and Φ) are equivalent circuits and simplified equivalent circuits of the push-pull converter in state 1. Figure 5 is a circuit diagram showing the equivalent circuit of the push-pull converter in state ■, and Figure 6 is a circuit diagram showing the equivalent circuit of the push-pull converter in state ■. Figure 7 is a circuit diagram showing the equivalent circuit of the push-pull converter in state ■, and Figure 8 is the equivalent circuit of the push-pull converter.
Waveform diagrams showing the operating voltage and current waveforms of the converter; Figures 9(a) and (b) are characteristic curve diagrams respectively showing examples of the output power and current-efficiency characteristics of the push-pull converter; Figure 10 ( a) and (b) are the same push-pull and
Characteristic curve diagrams showing other examples of the output power/current-efficiency characteristics of the converter, FIGS. 11(a) and 11(b) also show the excitation current waveforms of the push-pull converter and the conventional push-pull converter. It is a diagram showing examples respectively. Q, , Q, . . . semiconductor switch (MOS FET) D
,~D4...Diode ■,...Battery voltage S・
...Switch T, T, ...Transformer It
,It...Magnetic core N,,N! ...Winding,
2...Reactor C...Smoothing capacitor L...Smoothing inductance RL...Load resistance Figure 2 Figure 3 ) Simplified bribe circuit <a> State If) Zero circuit <bz 4 dog sum iIt> Mg zero i a circuit R,,f Figure 5 Cane!!■ Bank circuit Figure 6 1H Electrical value circuit of the blind working circuit No. 7 diagram L!■ ↓V9+9 -.- ■ 4;

Claims (1)

[Claims] 1. A transformer is configured using a magnetic core with no air gap in the magnetic path, and a winding independently wound on another magnetic core separate from the magnetic core is connected in parallel to the primary winding of the transformer. A transformer for preventing biased magnetism, characterized in that the transformer is configured to be energized, and is provided with means for preventing occurrence of biased magnetism in the transformer.