JPS61207169A - Switching regulator - Google Patents

Abstract

PURPOSE:To organize a simplified circuit and prevent the circuit from being polarized and saturated, by providing a polarization correcting circuit to a section on the main transformer output side, and by obtaining voltage for correcting polarization using exciting current. CONSTITUTION:Switching sections are formed with a pair of switch elements Q1, Q2. A transformer 12 is provided with the primary and secondary windings of intermediate tap type. A rectifying circuit 6 and an output smoothing circuit 7 are connected to the secondary winding, and the switching regulator of push/ pull type is organized, and specified power for output is generated. Then, a polarization correcting circuit 5 is organized with a saturable reactor ML, to be added. The reactor ML is provided with windings W51, W52, wound up on the same core, and the windings are respectively connected to the diodes D1, D2 of the rectifying circuit 6 in series. As the result, by the polarization correcting circuit 5, voltage is generated only for a time according to the scale of exciting current during the OFF-period of the switch elements Q1, Q2, and the voltage is applied to windings on the transformer output side, and polarization is autonomously corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a switching regulator, and more particularly, to a switching regulator suitable for a push-pull type, a half-bridge type, or the like.

[Background of the invention]

Switching regulators are characterized by the magnetization characteristics of the transformer.
It is roughly divided into flyback history, forward type, and push-pull type.

Among these, the push-pull type has a high utilization rate of the transformer core and requires less current in the switch element.
Widely used for models with medium capacity or higher. In addition, demand for power supplies, mainly for computer-related equipment, is increasing year by year.

However, as is well known, in the push-pull type, the main transformer is biased in magnetism, so there are many accidents such as destruction of the switch elements. For this reason, as described in Japanese Patent Laid-Open No. 59-6773, measures to prevent biased magnetization have become an important issue. However, this technology requires a resistor for current detection in the main circuit.
There is a problem of increased circuit loss.

In addition, the time constant of the current detection circuit needs to be sufficiently large compared to the operating frequency of the main switch element, which slows down the response speed to biased magnetism, and there is a risk that biased magnetism cannot be suppressed in the event of a sudden change in input. .

Generally, the excitation current of the main transformer is detected during the ON period of the switch element, and the switch element is controlled so as to correct the irregularity of the yt product. These are, for example,
As shown in No. 2-74828, the circuit becomes complicated. Furthermore, the most severe conditions for biased magnetization occur at maximum output, but at this time, sufficient detection sensitivity cannot be obtained because the excitation current is extremely small relative to the load current.

Further, since the switch element is driven by the feedback signal on the output side so as to stabilize the output, the accuracy of output stabilization is inhibited when the bias detection signal of the main transformer is added.

For this reason, the 'Asymmetric Op Switching Impulse Width Modulated Power
Subrise # (Electron; No. 167 p33-34
, GB 几, 1979) [Asymmetry o
f 3w -itching in Pulse -W
idth-Modulatedpower 5upp
lies (Electron; A 167,
Pages 33-34. GB 几, 1979] and special feature: New generation power supply - SW regulator (Transistor technology i, 1
As described in the document entitled "February 1979, pages 208-209), there are many examples in which half-bridge m+ is adopted as full-bridge m+.

These have a compensation capacitor in series with the input winding of the main transformer. Therefore, it is necessary to use an expensive and large capacitor that has a capacity and high voltage resistance sufficient to cover the converted power.

In addition, for the purpose of controlling the output to a constant level, JP-A-57-11
As shown in Japanese Patent No. 1713, a main transformer equipped with a saturable reactor on the output side is known. In this case, a free wheel diode is provided to regenerate the energy stored in the choke coil during the off period of the switch element, so that this current does not flow through the saturable reactor.

This is so as not to adversely affect the reset of the saturable reactor. Also shown is the use of a saturable reactor with a main winding on one tripod core and a reset winding biased by an external DC power source. In this circuit configuration, the saturable reactor is biased in only one direction, and the main transformer is always magnetized in one direction via the main transformer winding. However, the main transformer core is the first of the B-H curves.
Since the magnetic flux density changes in both positive and negative directions from the quadrant to the third quadrant and operates, if a saturable reactor is magnetized in only one direction, apart from the output control function, the polarized magnetization will increase and saturation will occur. It reaches . Therefore, the present technology further requires means for preventing biased magnetization of the main transformer.

[Purpose of the invention]

An object of the present invention is to provide a switching regulator that can prevent biased magnetization and saturation of a main transformer with a simple circuit configuration without sacrificing output accuracy.

[Summary of the invention]

The present invention focuses on the fact that the excitation current of the main transformer during the OFF period of the switch element is released to the output side thereof, and a bias correction circuit is provided in a part of the circuit configuration on the output side of the main transformer. It is in. This bias correction circuit is configured so that a full voltage is generated for a time corresponding to the magnitude of the excitation current during the switch element off period, and this voltage is applied to the winding on the output side of the main transformer.

At this time, since the iron core of the main transformer can be magnetized to the opposite polarity to the previous on-period, biased magnetization can be corrected autonomously without an external circuit.

[Embodiments of the invention]

An embodiment of the present invention will be functionally explained in FIG. l
is the input DC power supply, 2 is the main transformer, 3 is the switching section,
4 is a drive circuit, and 8 is a control circuit. The unbalanced magnetic correction circuit 5 and the rectifier circuit 6 and the output smoothing circuit 7 are both provided on the output side of the main transformer.

A voltage is generated and applied to the main transformer 2 for a period of time according to your needs. This voltage is generated in such a way that the main transformer 2 is of opposite polarity to the polarity with which it was magnetized during the on-period of the switch element.

Next, a specific embodiment of the present invention will be explained with reference to FIG.

Ql and Qz are a pair of switching elements such as transistors, which are the main components of the switching section 3. The transformer 2 is
Center tap type primary and secondary windings are provided, and a bias correction circuit 5, a rectifier circuit 6, and an output smoothing circuit 7 are connected to the secondary windings. The overall configuration consists of a push-pull type switching regulator, switch element Q1. A predetermined power can be supplied during the on period of Qz.

The biased magnetism correction circuit 5 can be configured with a saturable reactor ML. Windings WSI and WS2 wound on the same core
are connected in series with the diodes D1+D2 of the rectifier circuit 6, and thus become a path through which the current of the secondary winding of the main transformer 2 flows.

The operation of the embodiment of this configuration will be explained in the following four modes. However, the drive circuit 4 for the switch elements Q=, Qz and the control circuit 8 shown in FIG. 1 are conventional techniques, and detailed explanations thereof will be omitted.

(1) The period in which Qr is on and Q2 is off is defined as mode 1.

During this period, from the secondary winding W21 of the main transformer 2 to WIL
1% DI and choke coil Ly and capacitor Crt
- Power is supplied to the load from the output terminals 9a and 9b through the output terminals 9a and 9b. At the same time, magnetic energy is accumulated in the choke coil Lr.

To explain the operation of saturable reactor ML during this period,
Since the voltage of the secondary winding W22 of the main transformer 2 is blocked by the diode D2, no voltage is applied to the winding WS2.

Immediately after the switch element Q1 is turned on, Wsl induces a voltage with positive polarity indicated by the black circle in the figure, but immediately reaches the magnetic saturation region and exhibits low impedance, making it possible to supply power as described above. At this time, the magnetization direction of the saturable reactor Mx is set to be the positive direction.

(2) Ql ; off + Q4 i The off period is defined as mode 2.

During this period, the stored energy of the choke coil LP is Cv
This current is divided into two paths: Wz1°Wsl, D, and Wz 2 , W2 z , D B . At this time, the exciting current that was flowing through the main transformer 2 in mode 1 is no longer able to flow to the input side, and is therefore discharged to the secondary winding. This current flows in the direction opposite to the implied black circle with positive polarity, so the winding W2!
Wsi+D2+LP, flows to the intermediate tap via -CF.

Therefore, if the current flowing through LP in mode 1 is 2Io, then iz = Io + leg in diode D2.
...... (1) Also, the diode D1 has 11 = Io 1 @II..."'
・A current expressed by (2) flows. As a result, the saturable reactor ML is relatively magnetized by the following current.

d 1 =': l 2 11 = 21 @ II
(3) Here, 1jll is the excitation current converted to the output side of the main transformer 2. Equation (3) is M
The difference in the current flowing through both windings of L is 210. As a result, a voltage is induced in the winding Mt, with the polarity opposite to the black circle shown in the figure being positive.

This voltage is applied to Wz] of the main transformer 2 via DI, LF, and Ctt-, and its polarity is positive on the side opposite to the black circle in the figure. Well, since D2 is activated, W
A voltage is similarly applied to W22 from S2.

Therefore, the main transformer 2, which was magnetized in the positive direction by applying a positive polarity voltage to the black circle shown in the figure in mode 1, is now magnetized in the opposite direction depending on the magnitude of the excitation current. In other words, correction for biased magnetism has been applied.

(3) The period in which Ql is off and Ql is on is defined as mode 3.

During this period, a voltage is induced in the secondary winding W22 of the main transformer 2, with the polarity opposite to the black circle shown in the figure being positive, and the magnetic flux density of the main transformer 2 changes in the negative direction, contrary to mode 1. . The saturable reactor ML similarly changes in the negative direction and becomes saturated, and Ws
Power is supplied via z + Di.

(4) Qs; Off 1Q2; The off period is mode 4.

During this period, the exciting current of the main transformer 2 is discharged from W21 with the black circle shown as positive polarity, so 11" Ig +
Igyo ・・・・・・・・・(4)12=
IO-i, 8 (5). At this time, the saturable reactor ML is magnetized at %214m in the opposite direction to mode 2, so a voltage with positive polarity indicated by the black circle in the figure is induced in the winding W51, and this voltage is applied to the main transformer w.
21. It is applied to w22 with the black circle side shown as positive polarity.

In mode 3, the main transformer is magnetized in the negative direction with a voltage whose polarity is opposite to the black circle in the figure, so during the period when both switch elements are off, magnetization is magnetized in the positive direction depending on the magnitude of the excitation current. It will become magnetized.

As explained above, in this embodiment, biased magnetization can be corrected in response only to the excitation current, regardless of the load current.

In addition, since biased magnetization of the main transformer occurs due to a slight unbalance of the yt product, in this embodiment, the Vt of the saturable reactor Mt
The product can be designed to be small.

Therefore, as described in modes 1 and 3 above, the saturable reactor Mt immediately after the main switch element is turned on
The non-conducting period of , can be made extremely short.

Here, the saturable reactor M1. of FIG. The operation will be explained in more detail.

First, mode 1 is the ON period of Ql; h t), Wx
A voltage with positive polarity at the O mark shown in the figure is induced at x, and power is supplied to a load (not shown) via the diode D1.

At this time, the magnetic flux density of the iron core of the main transformer 2 changes to point A in the B-H curve of FIG. 3(a), as indicated by the upward arrow in the diagram.

Next, in mode 2, it is the off period of both transistors,
Choke coil L? The current 2Io flowing in the winding WZ
Since the current flows separately into t and Wt2, their magnetic flux densities cancel each other out, and no voltage is generated in each winding of the main transformer 2.

That is, when viewed on the magnetization curve, it stops at point A.

Mode 3 is an on-period of the switch element Q2, in which a voltage is applied to Wt with a polarity opposite to the circle shown in the figure, and power is supplied from Wt2 via the diode D2. At this time, the magnetization of the main transformer 2 has progressed to point B as indicated by the downward arrow in FIG. 3(a).

Next, in mode 4, during the period when both transistors Q1 and Q2 are turned off again, the current in the choke coil Lr is divided into W21 and W2H and flows as in the previous mode 2.
It stops at point B on the magnetization curve and completes one cycle.

When the main transformer operates with the Vt products of the primary windings Wt1 and Wtz ideally balanced, the main transformer is magnetized to ±B and no biased magnetization occurs.

On the other hand, saturable reactor ML normally operates as a mere mechanical switch. That is, when a positive polarity voltage is applied to the ○n number of windings WSI shown in the figure in mode 1,
When it reaches magnetic saturation, it enters an on state and allows the current of Wit to flow to the load side.

Next, in mode 2, switch element Q! is turned off, and at this time, the excitation inductance of the main transformer 2 emits excitation energy whose polarity is positive and opposite to the O mark shown in the figure.

The 215th ahead! As can be seen from Q, this excitation energy cannot flow to the primary winding side, and ends up flowing superimposed on the current of the choke coil LF.

Since the current 2Io of the choke coil Lν remains unchanged, Wi
The current i1 flowing through t is expressed by equation (2), and the current 12 of WS2 is expressed by equation α).

Therefore, the saturable reactor ML is relatively 12 1
Since it is magnetized with the opposite polarity to the O mark shown in the figure by the current of 1=2fax, if the number of turns of the windings Wsl and Wsz of the saturable reactor ML is the same and is set to n, then 21.8 Ho= □・n ・・・・・・・・・・・・
(6) is magnetized in the opposite direction, and as shown in Figure 3(b), Q
The point changes to point P. At this time, the iron core magnetic path length t of the saturable reactor ML and the winding W, so that the magnetic flux density does not change,
, , W, , no voltage is induced in the winding of the saturable reactor ML.

Next, in the process of mode 3 and mode 4, the magnet is symmetrically magnetized in the opposite direction to the above, and one cycle ends after passing through points Q and R.

The present invention will now be described in detail for the case where biased magnetism occurs in mode 10. In this case, in the magnetization curve of Fig. 3(a), the operating point A increases and becomes closer to B, H, so naturally the excitation current emitted in mode 2 also becomes larger.
Saturable reactor M1. is reversely excited even more deeply than in the normal state, and reaches the Ho point in FIG. 3(b). At this time, the winding of the saturable reactor ML has a polarity opposite to the ○ mark in the diagram, V = n-8-ΔB / t-(7)
This voltage is induced across the diode DI,
Main transformer 2 W21 via Dz and output smoothing circuit 7
．． Wz 2 is applied, the magnetic flux density decreases toward point A in FIG. 3(a), and biased magnetization is prevented.

Even if biased magnetization occurs in mode 3, the biased magnetization of main transformer 20 can be suppressed by the voltage induced in saturable reactor ML based on the same principle.

The biased magnetism of the main transformer 2 is caused by a slight unbalance of the yt product, so by using a saturable reactor with high magnetic permeability, as shown in Figure 3 (0), it can be corrected with sufficient detection sensitivity. can do.

In another embodiment of the invention, the ML core can be implemented with a regular glue axle without square characteristics. Various core shapes can be used, but as mentioned earlier, a small core is sufficient.

Although the ML using this type of iron core has a voltage even when the main transformer 2 is operating normally, the purpose can be achieved by designing the operating point during unbalanced magnetization to a place on the B-H curve where the change is large. .

In this embodiment, the iron core can be obtained at a lower cost than that of a saturable reactor, and the coercive force is small, so the histleresis loss is small. Therefore, it has the advantage of being applicable to high frequency drive.

Up to now, the biased magnetism correction circuit 5 has mainly been shown in the embodiment of the saturable reactor ML, but other passive elements such as the fourth
It can be configured with a resistor as shown in the figure.

The operation of this embodiment is exactly the same as that of the saturable reactor ML described above. For example, if it is explained using the period of mode 2,
A voltage drop appears across resistors R1 and R2 with the polarity shown, WZt and W!, respectively. As a result, this difference numerator 21ax becomes WZt and the main transformer 2 is magnetized. Since this voltage has positive polarity on the side opposite to the black circle shown in the figure, even if biased magnetization occurs in mode I, it is quickly returned. child\
where r is the resistance value of resistor R1*R2.

Resistors R1 and R1 are the most easily available among passive elements and are stable, so the circuit configuration is simple and high reliability can be obtained.

Further, since the resistor exhibits a high impedance with respect to high frequencies, it has the advantage of effectively reducing output noise.

Next, as another embodiment, as shown in FIG. 5, an unbalanced magnetic correction circuit 5' can be constructed of a semiconductor element such as a t-diode. The operating principle is the same as in the case of the resistor, and the difference in the forward voltage drop of the semiconductor elements S1 and 82 during both switch-off periods, that is, the voltage Δ shown in mode 2 in FIG.
Unbalanced magnetic correction is applied with F.

In FIG. 5, each semiconductor element Sl, 82 is constructed, but it is also possible to construct a plurality of series-parallel circuits. As the semiconductor elements 81 and 82, diodes, transistors, etc. can be used.

In this embodiment, the diode DI of the rectifier circuit.

Since the reverse breakdown voltage of D2 can be shared, a diode with a low breakdown voltage can be used. For example, a Schottky barrier diode with excellent recovery characteristics can be used in a wider range of applications.

The above Fig. 4 and jlEs diagram have been explained using partial diagrams with the primary side of the push-pull type shown in Fig. 2 omitted, but
The present invention can also be implemented for an output that does not have a secondary winding 1fs''f and an intermediate tap type as shown in FIG.

In Figure 7, W2゜1 and W2゜2 are each independent two
The next winding has the same number of turns. In this embodiment, the common electrode of the diode of the rectifier circuit 6 can be connected to the output end 9b. Although the biased magnetism correction circuit 5 is shown as a saturable reactor, it may have other circuit configurations as shown in FIGS. 4 and 5.

The operating principle is exactly the same as described in Figure 2 above,
In mode 2 (or mode 4), the current in the choke coil Ly is divided into il and 12, so that the bias correction circuit 5 obtains a voltage for correcting bias magnetization based on the difference in excitation current.

Since the diodes Ds and Da are usually attached to the cooling fin with the common electrode side, the capacitance Cst with respect to the virtual ground
It is known to have In this embodiment, since the potential is fixed at one end of the DC output, there is an advantage that noise is not generated due to charging and discharging of Cs.

Next, another embodiment of a two-terminal output main transformer shown in FIG. 8 will be explained.

Since the voltage of the secondary winding Who is alternately inverted by turning on and off Qt s Qz, four rectifier diodes are required as shown in FIG.

In this example, first, Q! In the on-period of , that is, in mode 1, D t 1 + L t + CF + react k
Mt.

Power is supplied through the windings Wss and Ihzt.

At this time, ML is magnetized with a voltage whose polarity is positive as indicated by the black circle in the figure, and is saturated in the positive direction.

Next, in mode 2, where both switches Q,,Q, are turned off, the choke coil L? The current of D21. D22 or Dll
r can flow along the path of Dll, but Dzt
Since there are resistors WS2 and W114 in series on the tIhz side, the current flows through Dll and Ihzt''.

In addition, in this mode 2, the main transformer 20 winding W2.

An excitation current tax is emitted from the positive polarity on the side opposite to the black circle shown in the figure.

This current can flow through path (2) since Dll is activated. Since the saturable reactor Mt is magnetized in the opposite direction to mode 1 by this exciting current tax, a voltage with positive polarity on the side opposite to the black circle shown in the figure appears and is applied to the winding W20 of the main transformer 2.

In mode 3 and mode 4, similar operations are performed symmetrically to this, making it possible to prevent biased magnetization of the main transformer 2.

Although the embodiment has been described using the saturable reactor ML as the unbalanced magnetism correction circuit 5, the same effect can be obtained even if it is configured with a resistor as shown in FIG.

In this embodiment, since power conversion can be achieved with one output winding of the main transformer 2, there is an advantage that the winding configuration of the main transformer 20 can be simplified.

All of the above embodiments have been described in terms of push-pull type, but they can also be implemented in a full bridge type as shown in FIG. The output side of the main transformer 2 has the configuration shown in FIG. 2 and below as an output circuit 10. In this embodiment, since biased magnetism can be corrected on the output side, there is no need for an expensive compensation capacitor Co.
It is possible to fully utilize the advantages of the full bridge type, such as not requiring an intermediate tap in the primary winding.

Further, FIG. 10 shows an embodiment of a half bridge shop. In this case as well, Co is not required, and the split capacitors C1 and C
Even if there is a capacitance irregularity or a difference in leakage current between the two, the biased magnetization can be corrected on the output side, so the original advantages can be fully utilized.

Furthermore, there are many switching regulators of so-called multi-output type that obtain a plurality of independent outputs from one main transformer. These K can be provided in a system in which a bias correction circuit is provided only for the main output with large power, or for each output. Considering the relationship between the impedances of the respective outputs, the bias correction circuit 5 may be provided at the output through which the largest excitation current flows during the OFF period of the switch element.

In the embodiments described so far, the output smoothing circuit 7 is
Although the circuit is configured with a C circuit, for example, if the purpose is to output a constant current, it may be configured with only the choke coil Lr. In this case, in mode 2t7'C, the excitation current in mode 4 flows through the load, so that the same operation as in the above embodiment can be obtained.

〔Effect of the invention〕

According to the present invention, the excitation current discharged to the output side of the main transformer can be used to obtain a voltage that corrects biased magnetization, so that biased magnetization and saturation of the main transformer can be prevented with a simple circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of the present invention, FIG. 2 is an embodiment, and FIG. 3 is a main transformer 2 and saturable reactor ML.
4 and 5 are circuit diagrams of other embodiments of the present invention, and FIG. 6 is a graph of current-forward voltage characteristics of a semiconductor.
7 to 10 are circuit diagrams showing other embodiments of the present invention. l... Input DC power supply, 2... Main transformer, 3... Switching section, 5... Unbalanced magnetic correction circuit, 6... Rectifier circuit, 7... Output smoothing circuit.

Claims (1)

[Claims] 1. The main transformer is driven with alternating current by on/off control of at least one pair of switch elements provided on the input side of the main transformer, and a full-wave rectifier circuit is provided on the output side of the main transformer. An output smoothing circuit is provided to obtain a predetermined output from the input DC power supply on the input side of the main transformer, wherein a voltage is applied to the output side of the main transformer according to the magnitude of the excitation current of the transformer. A switching regulator characterized in that the switching regulator is equipped with an unbalanced magnetic correction circuit that applies the following to the output side winding of the transformer. 2. The switching regulator according to claim 1, wherein the bias correction circuit is formed in a path through which the excitation current of the main transformer flows during an off period of at least one of the switching elements. . 3. In claim 1 or 2,
The biased magnetic correction circuit is composed of two windings wound around the same core and magnetically coupled to each other, and the diode of the full-wave rectifier circuit and the winding are connected in series to form a pair, and one end of each is connected to the output winding of the main transformer configured in the form of an intermediate tap. 4. The switching regulator according to claim 1 or 2, wherein the biased magnetism correction circuit includes a reactor. 5. The switching regulator according to claim 4, wherein the reactor is a saturable reactor.