JP2696956B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply for supplying large power, and more particularly to a switching power supply of a current resonance type magnetic flux control system.

[Summary of the Invention]

According to the present invention, a primary winding of a saturable reactor transformer for controlling an oscillation frequency is connected to a primary side of an insulating converter transformer, and a secondary winding of the saturable reactor transformer is a control terminal of a switching element of an oscillation drive circuit. And a switching power supply device that controls the inductance of the saturable reactor transformer according to the secondary voltage of the insulating converter transformer, controls the switching frequency on the primary side, and controls the output voltage on the secondary side constant. By providing a current branch in parallel with the primary winding of the saturable reactor transformer and, if necessary, dividing the primary winding of the insulating converter transformer into two or more sets, control of the switching element of the oscillation drive circuit The current flowing through the terminal is set to an appropriate value even under a large power load, thereby realizing a configuration suitable for large power supply.

[Conventional technology]

Various types of switching power supply devices that perform switching control of a DC input power supply and obtain a desired constant voltage output via a power transformer or the like are known. As an example of such a switching power supply, the applicant of the present application has previously described:
In JP-A-62-64266 and JP-A-62-71382, a saturable reactor transformer is used to control a primary side series resonance impedance according to an output voltage from a secondary side of a power transformer, A switching power supply device that stabilizes an output voltage by controlling an exciting current has been proposed.

FIG. 7 shows an example of such a switching power supply device. As a DC input power supply to the power supply device, for example, a commercial AC input power supply 101 is rectified and smoothed by a diode bridge type full-wave rectifier 102 and a smoothing capacitor 103. It is gained by doing. The DC input power source is supplied to the primary winding via the N _A, the series resonant circuit consisting of the primary winding N ₁ and the capacitor 113 of the insulating converter transformer 112 of the saturable reactor transformer 111. Current of the DC input power source, a secondary winding N _B1 and the switching transistors Q ₁ and secondary coil serial resonance circuit of the capacitor C _B1 is connected to the base N _B2 and capacitor C _B2 of the saturable reactor transformers 111 It has turned, to be Ofusu'ichingu controlled by two stone structure of the self-excited oscillation drive circuit 114 using a switching transistor Q ₂ to which the series resonant circuit is connected to the base of the.

For example, as shown in FIG. 8, the saturable reactor transformer 111 has a control winding N _C wound in a direction orthogonal to the windings N _A , N _B1 and N _B2 . by inductance of the windings N _B1 and N _B2 is controlled in accordance with the current flowing through the line N _C, oscillation frequency of the oscillation drive circuit 114 are controlled.

The secondary side of the insulating converter transformer 112 is provided with a winding N ₂ and N _3, respectively rectifying and smoothing circuit 115 and 116 in relation to these windings N ₂ and N ₃ are provided. From the rectifying / smoothing circuit 115, a DC high-voltage power supply of 135V1.2A and a DC power supply of 15V1.5A or 7V1A used for a television video deflection system and the like are taken out. A 30V2A DC power supply is taken out of the system. The DC high voltage output from the rectifying and smoothing circuit 115 is converted into a control current by the control circuit 118 is sent to the control winding N _C of the saturable reactor transformer 111.

Therefore, the inductance of the saturable reactor transformer 111 changes in accordance with the fluctuation of the DC output voltage, and the primary side series resonance impedance of the insulating converter transformer 112 changes to change the exciting current, thereby making the DC output voltage constant. Can be controlled.

[Problems to be solved by the invention]

In the case of applying such a switching power supply device for high power, for example, when the load power is above 200W, the peak of the sine wave current I _A flowing through the primary winding N _A of the saturable transformer 111 - Since the peak value reaches 8 A and the base current of the switching transistors Q ₁ and Q ₂ of the oscillation drive circuit 114 connected to the secondary windings N _B1 and N _B2 increases,
It is necessary to insert and connect drive damping resistors R _B1 and R _B2 in series with the secondary windings N _B1 and N _B2 , respectively. This is to supply a base current that satisfies the optimum drive condition that minimizes the switching loss of the switching transistors Q ₁ and Q ₂ .

However, such a base current limiting resistor R
_The oscillation drive circuit configuration using _B1 and _RB2 has the following disadvantages. That is, for example, when a transistor of model number 2SC4054 (500 V, 5 A) is used as the switching transistors Q ₁ and Q ₂ , three resistors of 4.7 Ω / 3 W are used as the resistors R _B1 and R _B2 , respectively, for a total of six resistors. Is required, and the power loss is 3 W at each combined resistance, for a total of 6 W. For this reason, the 6 W heat generated in the resistors R _B1 and R _B2 on the power supply board is applied to the secondary windings N _B1 and N _{B2 of} the transformer 111 and the film capacitors C _B1 and C _B2 via the board copper foil. Conduct,
The temperature of these peripheral components is increased, which is not preferable.

The present invention has been made in view of such a conventional situation. Even when the load power increases to, for example, 200 W or more, the load is supplied from the secondary winding of the saturable reactor transformer to the switching element of the oscillation drive circuit. It is an object of the present invention to provide a switching power supply device capable of effectively preventing a current (base current of a transistor) from being excessively large and improving a maximum load power and a power conversion efficiency.

[Means for solving the problem]

In order to solve the above-mentioned problems, a switching power supply according to the present invention provides an excitation of a primary winding of an insulating converter transformer via a primary winding of a saturable reactor transformer on a primary side of the insulating converter transformer. An oscillation drive circuit for switching the current is connected, an output from a secondary winding of the saturable reactor transformer is supplied to a control terminal of a switching element of the oscillation drive circuit, and a secondary output voltage of the insulation converter transformer is provided. A switching power supply that controls the inductance of the saturable reactor transformer and controls the switching frequency to control the secondary output voltage to a constant voltage in accordance with the following equation: A current shunting channel having a parallel relationship with the primary winding of the saturable reactor transformer is provided; It is characterized by diverting a primary excitation current of the insulating converter transformer. In this case, it is preferable that the current shunt channel does not include the resistance component but shunts the current by inductance or capacitance.

Another feature of the present invention is that, in a switching power supply having such a feature, the primary winding of the above-mentioned insulated converter transformer is divided into two or more sets, and the current flowing through each of the sets of the primary windings is divided. Is diverted to the primary winding of the saturable reactor transformer.

(Operation)

By shunting the primary excitation current of the insulating converter transformer between the primary winding of the saturable reactor transformer and the above-mentioned shunt path, the primary winding of the saturable reactor transformer flows at a large load power of, for example, 200 W or more. The current is suppressed, and the current supplied from the secondary winding of the saturable reactor transformer to the control terminal of the switching element is optimized without inserting a resistor or the like.

〔Example〕

FIG. 1 is a circuit diagram showing a switching power supply device according to a first embodiment of the present invention.

In FIG. 1, the DC input power to the power supply device is obtained, for example, by rectifying and smoothing the above-described commercial AC input power. The DC input power source, a current on the oscillation drive circuit 24 to be described later, is off switching control, the primary winding N ₁ of an insulating converter transformer 22 via the primary winding N _A of the saturable reactor transformers 21
And although not supplied to become more series resonant circuit with capacitor 23, in the present invention, there is provided a current shunt path has a parallel relationship with respect to the primary winding N _A. Particularly, in the first embodiment, the primary winding N _A of the saturable reactor transformer 21 and the inductor 31 are connected in series between the oscillation driving circuit 24 and the primary winding N ₁ of the insulating converter transformer 22. Insertion connection is performed, and an inductor 32 is connected in parallel with the series connection circuit to form a current branch channel. As these inductors 31 and 32, for example, a so-called micro inductor or a small drum type choke coil can be used.

Next, as described with reference to FIG. 8, the saturable reactor transformer 21 includes a primary winding N _A , two secondary windings N _B1 , N
_B2 and a control winding N _C, and turning the winding N _A, N _B1, winding the control winding N _C in a direction perpendicular to the winding direction of the N _B2. The secondary winding N of such a saturable reactor transformer 21
_In connection with _B1 and _NB2 , an oscillation drive circuit 24 for controlling ON / OFF switching of the current of the DC input power supply is provided. The oscillation drive circuit 24, connected to a pair of switching transistors Q ₁ and diode D _B1 connected between the emitter and base of the transistor Q _1, another set of transistors Q ₂ and the diode D _B2 set and is in series is, the transistor Q ₁ is connected so as to be inserted between the primary winding N _a of the DC input power source and the saturable reactor transformer 21, a transistor Q ₂ is a ground primary winding N _a of the saturable reactor transformers 21 It is inserted and connected between. Between the emitter and base of the transistor Q ₁ is, in parallel with the diode D _B1, the series resonant circuit with the secondary winding N _B1 and capacitor C _B1 of the saturable reactor transformer 21 are connected, emitter-base of the transistor Q ₂ between the series resonant circuit with the secondary winding N _B2 and capacitor C _B2 of the saturable reactor transformer 21 in parallel with the diode D _B2 is connected. Further, starting resistors R _S1 and R _S2 are inserted and connected between the DC input power supply and the bases of the switching transistors Q ₁ and Q ₂ , respectively.

Next, on the secondary side of the insulation converter transformer, the winding N ₂
And N ₃ are provided, each rectifying and smoothing circuit 25 and 26 in relation to these windings N ₂ and N ₃ are provided. Here, for example, a 135 V 1.2 A DC high-voltage power supply used for a television video deflection system and a DC power supply such as a 15 V 1.5 A and 7 V 1 A signal processing circuit system are taken out from the rectification / smoothing circuit 25, and the rectification / smoothing circuit 26 is used. From the 30V2A DC power supply of the audio signal system. Rectifier smoothing circuit
The DC high voltage output from 25 is converted into a control current by the control circuit 28 are sent to the control winding N _C of the saturable reactor transformer 21, the control circuit 28 of the 7V or 15V as a circuit supply DC power is supplied.

The oscillation drive circuit 24 of the switching power supply having such a configuration is provided with a secondary winding N of the saturable reactor transformer 21.
The switching transistor Q ₁ is driven by a sine wave alternating current flowing through the series resonant circuit between the _B1 and the capacitor C _B1, also sinusoidal, which flows through the series resonant circuit with the secondary winding N _B2 and capacitor C _B2 of the saturable reactor transformers 21 the switching transistor Q ₂ is driven by the wave alternating current, the transistors Q _1, Q ₂ is adapted to continue a switching operation by turning on repeated alternately.

The control winding N _C of the saturable reactor transformer 21 is supplied with a DC control current from a control circuit 28 obtained by detecting the output voltage of the insulating converter transformer 22. DC output voltage from 22 so that always constant, control the current flowing through the control winding N _C of the saturable reactor ton lance 21 is controlled by the control circuit 28, the inductance of the secondary winding N _B1, N _B2 is Under the control, the oscillation frequency of the oscillation drive circuit 24 is controlled.

If large as where the load power, for example, 200W or more, is supplied to the primary winding N _A of diverted saturable reactor ton lance 21 by the primary side excitation current I ₁ the inductors 31 and 32 of the insulating converter transformer 22 This satisfies the optimum drive conditions for the base currents of the switching transistors Q ₁ and Q ₂ of the oscillation drive circuit 24. That is, the inductor
When 31 and 32 of the inductor chest and L _P1, L _P1 respectively, current I _P1 flowing through the primary winding N _A of the saturable reactor transformer 21 (inductance L _NA) is Becomes As an example, L _NA = 3 μH, L _P1 = 6.8 μH, L _P2
= If _{3.3μH, I P1 ≒ I 1/} 4 , and the first approximately 1/4 of the primary excitation current I ₁ of the insulating converter transformer 22 as shown in FIG. 2 is a saturable reactor transformer 21 primary It will flow windings N _a. That is, when the primary excitation current I ₁ flows 4A peak value, whereas in prior art the excitation current I ₁ has been flowing in the primary winding of all saturable reactor transformer, the present invention embodiment According to this, the current is reduced to about 1A (peak value) of about 1/4, and the base current of the switching transistors Q ₁ and Q ₂ of the oscillation drive circuit 24 can be optimized.
Here, when the current amplification factor h _FE of the transistors Q ₁ and Q ₂ increases, the inductance L _{P1 of the} inductor 31 increases, and when the h _FE decreases, the inductance L _{P of the} inductor 31 decreases.
The drive condition can be satisfied by reducing _P1 . Note that the second figure corresponds to the current I _P1 flowing through the primary winding N _A of the reduction saturation reactor transformer,
Shows current I _NB1 flowing through each secondary winding N _B1, N _B2 of the saturable reactor transformer 21, I _NB2, and the base current I _B1, I _B2 of the switching transistors Q _1, Q ₂ of the oscillation drive circuit 24, respectively ing.

According to the experiment, when the maximum load power is 240 W, in the case of the embodiment of the present invention, the conventional base current limiting resistor of FIG.
The power loss can be reduced by about 6 W as compared with the case of using R _B1 and R _B2 . Further, by flowing current I _P1 to the primary winding N _A of the saturable reactor transformer 21, for example, it decreased to about 1/4, conduction and radiation heat by heat generation from the resistor is eliminated, the saturable reactor transformers 21 The temperature of the winding was reduced by about 15 ° C, and the time constants of the capacitors C _B1 and C _B2 were reduced by about 10 ° C.

The saturable reactor transformer 21 is used as a current branch channel.
It is conceivable to connect in parallel to the resistor to the primary winding N _A of this as the partial diversion resistance, for example, cement large resistance 2.2 ohms / 20W is required, large mount area of the substrate, temperature rise Is relatively large, it is preferable to shunt the current using an inductor or the like that does not include a resistance component as in the above embodiment.

Incidentally, FIG. 3 the inductor 32 provided to divert the primary excitation current, may be additionally provided to the primary winding N ₁ of an insulating converter transformer 22, this as a second embodiment Shown in

That, in this third second embodiment illustrating a main part in FIG., One turn to the primary winding N ₁ of an insulating converter transformer 22 windings 22P provided, the winding portion 22P the first used as an inductor 32 in the embodiment, the inductor 33 is serially connected to the primary winding N _a of the saturable reactor transformer 21. Then, for the inductance of the winding part 22P, the inductor 3
The drive condition can be satisfied by appropriately adjusting the inductance of (3).

Next, FIG. 4 shows a main part of a third embodiment of the present invention, in which the primary windings of the insulating converter transformer 22 are N _1a , N _1b
When divided into two, these units windings N _1a, in parallel the N _1b each other, i.e. between one of the windings _1a and shunt current adjustment of the inductor 34 and primary winding N _A of the saturable reactor transformers 21 The other winding _N1b is connected in parallel with the series connection circuit. Here, when the winding N _1b is wound inside the coil bobbin of the insulating converter transformer 22 and the winding N _1a is wound outside thereof with an interlayer sheet (insulating film) interposed therebetween, When the windings are short-circuited, the leakage inductances L _1a and L _1b of the respective windings N _1a and N _1b satisfy L _1a <L _1b , and a large amount of current is slightly shunted to the winding N _1a , but the switching transistor Q ₁ , the current the shunt so that the base current of the optimum drive condition adapted to the Q ₂ of h _FE may do it restricts the inductance of the inductor 34.

Adjustment of the ratio of the shunt currents flowing through the two sets of primary windings N _1a and N _1b is performed as in the fourth embodiment shown in FIG.
It can also be realized by using capacitors 36 and 37 instead of inductors. In the fifth fourth embodiment shown in FIG, for example when it is desired to the current flowing through the primary winding N _A of the saturable reactor transformer 21 and 1/4 of the primary excitation total current, the capacitor 36 and 37 The ratio of the capacitance values C _P1 and C _P2 of (1/4) :( 3 /
4), ie 1: 3.

It is also possible to divide the primary winding of the insulating converter transformer 22 into three or more, for example as in the fifth embodiment shown in FIG. 6, N _1a and 3 dividing the primary winding, N _1b , N _1c ,
Winding N _1a of primary winding N _A of the saturable reactor transformer 21 connected in series, the winding N _1b in parallel with the series connection circuit, N
_1c are connected respectively. In this case, without using the inductor 34 and capacitors 36 and 37, be the primary winding N _A substantially 1/3 of the primary exciting total current the current flowing through the saturable reactor transformers 21 it can.

According to these third to fifth embodiments, not only effects similar to those of the first and second embodiments can be obtained, but also
Primary winding of insulation converter transformer 22
N _1a, since the divided into N _1b such divert primary excitation current I _1, the DC resistance loss of the winding, can both reduce high frequency loss, can improve the reliability of the transformer. In particular, when the load power is extremely large, such as 200 W or more, a single set of primary windings requires a bundle of litz wires of, for example, about 60 μm in a bundle of about 200 μm to reduce the temperature rise. In contrast to the custom-made product, which is expensive and the space factor at the time of winding is reduced, the size of the coil bobbin must be increased. On the other hand, according to the third to fifth embodiments, For example, by connecting two or more pairs of litz wires of 60 μm108 bundle in parallel, it is possible to suppress the temperature rise, and furthermore, the space factor is improved, and the required number of turns (for example, 42 turns) is realized with a coil bobbin of a normal size. Becomes possible. In addition, depending on the load power, the primary winding of the insulating converter transformer 22 may be connected to a small-diameter litz wire (for example,
m80 bundle), and the transformers can be easily manufactured and assembled by using the same wire including the secondary side, which is advantageous in terms of mass productivity and cost reduction.

The other components in each of the embodiments shown in FIGS. 4 to 6 are the same as those in the first embodiment described above, and the description thereof will be omitted.

〔The invention's effect〕

According to the switching power supply of the present invention, the primary current of the insulating converter transformer is shunted and supplied to the primary winding of the saturable reactor transformer. The current supplied to the switching element of the drive circuit can be optimized, and the switching drive can be performed under optimal drive conditions. Further, there is no need to perform resistance damping or shunting by resistance, and heat generation is reduced, so that downsizing of the printed circuit board, cost reduction, and improvement in serviceability can be realized at the same time.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the first embodiment, and FIG. 3 is a diagram showing a main part of the second embodiment of the present invention. FIG. 4 is a circuit diagram showing a main part of the third embodiment of the present invention, FIG. 5 is a circuit diagram showing a main part of the fourth embodiment of the present invention, and FIG. FIG. 7 is a circuit diagram showing an example of a conventional switching power supply device, and FIG. 8 is a schematic perspective view showing an example of a saturable reactor transformer according to a fifth embodiment of the present invention. 21 ...... saturable reactor transformer 22 ...... insulating converter transformer 23 ...... resonant capacitor 24 ...... oscillation drive circuit 25, 26 ...... rectifying and smoothing circuit 28 ...... controller _{N 1a, N 1b, N 1c} ...... 1 Tsugimaki Each part of the wire 31, 32, 33, 34 …… Inductor 36, 37 …… Capacitor

Claims (2)

(57) [Claims] An oscillation drive circuit for switching-controlling an exciting current on a primary side of the insulating converter transformer is connected to a primary winding of the insulating converter transformer via a primary winding of a saturable reactor transformer. An output from a secondary winding of the saturable reactor transformer is supplied to a control terminal of a switching element of the oscillation drive circuit, and controls an inductance of the saturable reactor transformer according to a secondary output voltage of the insulating converter transformer. In a switching power supply device for controlling the switching frequency to control the secondary side output voltage to a constant voltage, the switching power supply device controls a primary winding of the saturable reactor transformer connected to a primary winding of the insulating converter transformer. A current shunting channel is provided in parallel to shunt the primary excitation current of the insulating converter transformer. Switching power supply. 2. The primary winding of said insulated converter transformer is divided into two or more sets, and only a part of the current flowing through each set of said primary windings is divided into one set of said saturable reactor transformer.
2. The switching power supply according to claim 1, wherein the current is divided into the secondary winding.