JPH02285963A - Switching power supply - Google Patents

Abstract

PURPOSE:To suppress fluctuation of output voltage by regulating coupling between the primary and secondary windings of an insulating transformer thereby suppressing fluctuation of output voltage due to fluctuation of load and reducing the amount of heat to be produced. CONSTITUTION:Primary winding N1 of an insulating transformer and first secondary winding N2 for main load are coupled sparsely while the primary winding N1 and second secondary winding N'3 for voice load are coupled tightly. When the first secondary winding N2 and the second secondary winding N'3 are coupled sparsely, amount of heat to be produced is low even for maximum voice load and variation of output voltage for the main load due to variation of voice load and variation of output voltage for the voice load due to variation of the main load can be suppressed. Such a power supply can be employed easily as the switching power supply for a heavy load, large voice output large color television receiver or a projector.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply device for obtaining a stable output voltage.

[Summary of the invention]

The present invention is a switching power supply device in which the coupling relationship between the primary winding and the secondary winding of an isolation transformer is adjusted to suppress fluctuations in output voltage due to load fluctuations.

[Conventional technology]

2. Description of the Related Art Conventionally, there has been a switching power supply device that performs switching control on a DC input power source and obtains a constant voltage output via an orthogonal transformer, a power transformer, or the like.

For example, as described in Japanese Unexamined Patent Publication No. 62-64266, an orthogonal transformer for controlling the oscillation frequency of the oscillation drive circuit by controlling the switching of the DC input power source by a switching element of the oscillation drive circuit is used. It is supplied to the primary side of the power transformer via the Then, a control circuit controls the inductance of the orthogonal transformer according to the output voltage from the secondary side of the power transformer, controls the oscillation frequency of the oscillation drive circuit, and stabilizes the secondary side output voltage of the power transformer. It is something.

FIG. 7 is an example of the above-mentioned switching power supply device.

In the figure, PS is a DC power supply, and OD is an oscillation drive circuit. The DC power supply PS is connected to the collector of a switching transistor Q of the oscillation drive circuit OD, and is connected to the collector stop base of this transistor Q1 via a resistor R2. The emitter and base are connected via a diode D. The connection midpoint between the emitter of the transistor Q and the diode D1 is connected to the transistor Q through the secondary winding N B + of the orthogonal transformer PRT, the resistor R1, and the capacitor CI of the drive circuit OD.
connected to the base of Further, the connection midpoint between the collector of the transistor Q and the resistor R1 is connected to the base of the switching transistor Q2 via the resistor R2. The emitter of this transistor Q2 is grounded,
The collector is connected to the midpoint between the diode DI and the secondary winding N1. Further, the connection midpoint between the base of the transistor Q2 and the resistor R2 is grounded via the diode D2, and the capacitor C2 and the orthogonal transformer P
It is grounded via the resistor RB□ of RT and the secondary winding N12. Also, the emitter of transistor Q+ is connected to the isolation transformer P via the primary winding NA of the orthogonal transformer PRT.
IT0) Connected to one end of the primary winding N, . and,
The other end of this primary winding N is a resonance capacitor CI O
grounded through.

Further, one end of the first secondary winding N2 of the isolation transformer PIT is connected to an output terminal T for an output voltage of 135 V via a diode D21 of an output rectifier circuit OR. The other end of the first secondary winding N2 is a diode D24.
via diode D2. and terminal T.

Connected to the midpoint of the connection. Also, this secondary winding N2
is connected to the output terminal T2 for the output voltage 15V via the diode D22, and the diode [)2f
Similarly, it is connected to the output terminal T2 via f.

Also, the second secondary winding N of the isolation transformer PIT.

One end of is diode D! + to the output terminal T3 for the output voltage 45V, the secondary winding N, and the other end is connected to the diode D31 and the output terminal T3 via the diode D22.
Connected to the midpoint of the connection. Also, this secondary winding N3
The midpoint of is connected to terminal T.

The midpoint of the connection between the diode D2 and the output terminal T1 of the output rectifier circuit OR, and the midpoint of the connection between the diode D2□ and the output terminal T2 are connected to the control circuit CC.

The control signal from this control circuit CC is applied to the control winding N of the orthogonal transformer PRT.

The inductance of the orthogonal transformer PRT is controlled, and the oscillation frequency of the oscillation drive circuit OD is controlled. That is, the on/off timing of the switching transistors Q and Q2 of the oscillation drive circuit OD is controlled, and the oscillation frequency is controlled.

Now, the primary winding Nl, the secondary windings N2 and N of the isolation transformer PIT of the switching power supply shown in FIG.
, are conventionally wound around the core of the transformer PIT as shown in FIG.

That is, in FIG. 8, CR is the core of the isolation transformer PIT, B'b is a bobbin, and this bobbin B'b is arranged around the periphery of the core CR, and the primary winding N.

The primary winding part FW is wound with the secondary windings N2 and N
3 is wound around the secondary winding part SW. The secondary winding section SW includes first and second secondary windings N2.
and N are stacked and wound, the second secondary winding N3 and the primary winding N1 are loosely coupled, and the second
The secondary winding N and the first secondary winding N2 are tightly coupled.

[Problem to be solved by the invention]

By the way, when the above-mentioned conventional switching power supply device is applied to, for example, a large television receiver, output terminals T1 and T2 are connected to a main load such as a video signal processing circuit, and output terminal T3 is connected to an audio load. good.

However, in the conventional switching power supply device described above, the first and second secondary windings N2 of the isolation transformer PIT
Since N3 and N3 are tightly coupled, the following disadvantages occur.

(1) When the audio load is maximum, for example, 45V x 2.0A
=90W, a large current of, for example, 10Ap-p flows through the primary winding N+ of the isolation transformer PIT and the resonance capacitor CIG, resulting in a large amount of heat generation.

(11) The audio load generally fluctuates easily, with a maximum value of, for example, 45 V N2. OA = 90W to minimum value e.g. 45
If it changes to V×0.1Δ−4.5W, the output to the main load will fluctuate, and the brightness of the television screen will fluctuate.

(iii) Contrary to the above-mentioned (11), the output to the audio load fluctuates due to fluctuations in, for example, brightness of the main load, causing the audio to become unnecessarily low or loud.

[Means to solve the problem]

Therefore, in the present invention, the primary winding of the isolation transformer PIT and the first secondary winding for the main load are loosely coupled, and the primary winding and the second secondary winding for the audio load are connected to each other. The first secondary winding and the second secondary winding are loosely coupled.

Further, according to the present invention, the isolation transformer PIT can be divided into two transformers: a main load transformer and an audio load transformer.

[Effect]

Even when the audio load is maximum, the amount of heat generated is small, and it is possible to suppress fluctuations in the output voltage to the main load due to fluctuations in the audio load and fluctuations in the output voltage to the audio load due to fluctuations in the main load.

〔Example〕

FIG. 1 is an embodiment of the present invention, and is a sectional view of a main part of an isolation transformer PIT of a switching power supply device.

In the figure, a bobbin Bl] is arranged around the periphery of the core CR of the isolation transformer PIT. The bobbin Bb has a primary winding section PW around which the primary winding N is wound, and a first secondary winding section SW1 around which the first secondary winding N2 is wound.
and a second secondary winding 15w2 around which the second secondary winding N' is wound. The second secondary winding section SW2 is connected to the primary winding section FW and the first secondary winding section SW.
+ and the second secondary winding N'
s and the primary winding N are tightly coupled, and the secondary windings N' and N2 are loosely coupled. Furthermore, the primary winding N1 and the secondary winding N2 are loosely coupled.

The primary winding N1 is the primary winding NA of the orthogonal transformer PRT and the resonant capacitor CI as in the example in FIG.
Connected to O. Further, the first secondary winding N2 is connected to the output rectifier circuit OR3, and the second secondary winding N'3 is connected to the output rectifier circuit OR2.

When the isolation transformer PIT is configured as shown in the example in Fig. 1, the current 11 flowing from the orthogonal transformer PRT to the primary winding N1 of the isolation transformer PIT and the resonance capacitor C1° is The second secondary winding N'3 is activated at a faster timing than the secondary winding N2.
An induced electromotive force is generated in this secondary winding N'3.

Therefore, when the audio load is at its maximum, a current 1 flows through the collector of the switching transistor Q1 of the oscillation drive circuit OD.
c and the second secondary winding N'3 of the isolation transformer PIT
The current I flowing through the current I, and the primary winding N of the isolation transformer PIT
The current ■1 flowing through 1 has waveforms as shown in FIG. 2 A, C, and D. That is, for example, if the audio load is 45
When VX2, 0A = 90W and maximum, current ■. is Figure 2A
The current 3 has a waveform with two peak points at 5A and 4A as shown in Figure 2C, and the current I has a waveform with the peak to 8 as shown in Figure 2C, and the current I has a waveform as shown in Figure 2C. The waveform has two peak points, the size of the first peak point and the peak point is 10A, and the size of the second peak point and the peak point is 8A.

On the other hand, if the isolation transformer of the switching power supply has the conventional configuration as shown in Figure 8, when the audio load is at its maximum of 90 W, the current I'c flowing through the collector of the switching transistor Q1 is , the current 1/ flowing in the second secondary winding N3 of the isolation transformer, and the current I11 flowing in the primary winding N1 of the isolation transformer have waveforms as shown in FIGS. 9A, C, and D, These are different from those in FIG. In other words, the current I'c
becomes a waveform with a peak of 5A as shown in Figure 9A,
The current 1/ has a waveform with a peak of 3.5 A as shown in FIG. 9C, and the current 1/1 has a peak-to-peak waveform of IOA as shown in FIG.

Since the collector current IC has a waveform as shown in FIG. 2, the switching transistor Q1
The switching loss that occurs during the falling time when the collector current turns from on to off is the waveform 1 of the collector current shown in Figure 9.
The switching loss is reduced compared to the case where the angle is 1°.

In addition, because the primary winding N and the second secondary winding N' of the isolation transformer PIT are more closely coupled than in the conventional case, the number of turns required for the second secondary winding can be reduced. is possible,
It is possible to reduce the winding area. For example, whereas conventionally the number of turns of the second secondary winding N was required to be 36 turns, the number of turns of the secondary winding N'3 in the example shown in FIG. 1 can be changed to 20 turns. Furthermore, the primary winding N, and the first two
Since the coupling with the next winding N2 is looser than in the conventional case, the leakage inductance is increased and the control sensitivity is improved compared to the conventional case. Therefore, the control range of the operating frequency due to changes in the audio load is, for example, 5Qk in the conventional system.
Hz ~ 66.6kt (Z's 16.6kHz is 50k) lz ~ 55.5k) Iz's 5.5ktl
z, which can be reduced to about 173 from the conventional method.

In addition, since the first secondary winding N2 and the second secondary winding N's are more loosely coupled than conventional ones, fluctuations in the output voltage to the main load due to fluctuations in the audio load and Fluctuations in the output voltage to the audio load due to fluctuations in the main load can be suppressed.

In addition, the maximum value of the main load is 135V x 1.2A + 15
V xl, 5A ~ 184.5w, minimum value 135VX
O,5A+15VX1,5Δ=90W, and the maximum audio load is 45V N2. OA = 90W, minimum value 45
V xO, 1A = 4.5W, the core of the isolation transformer is E-50, the primary winding N1 is 33 turns, the first 2
Next winding N2 is 108 turns, resonance capacitor C+
When the capacitance value of a is 0.1 μF, according to experiments, the second secondary winding N3 in the conventional device needs 36 turns in order to cope with the fluctuation of the input terminal from 90V to 120V. In one embodiment of the invention, the second
It was sufficient for the next winding N' to have 20 turns.

Furthermore, the heat generation of the switching transistors Q and Q2 when the audio load is the maximum is about 10°C lower in this embodiment than the conventional example, and the heat generation of the switching transistors Q1 and Q2 when the audio load is the minimum. The heat generation in this example was about 3°C lower.

Further, the variation in the output voltage to the audio load due to the variation in the main load was ±10V in the conventional system, but it was ±5V in this embodiment. The variation in the output voltage to the main load due to audio load variation is 150% in the conventional case.
mV, but in this example it was 80 mV.

FIG. 3 is a circuit diagram of another embodiment of the present invention, and FIG.
Components equivalent to those in the illustrated example are given the same reference numerals. In the case of this example in Figure 3, the isolation transformers are the main load transformer PIT, and the audio load transformer PI.
It is divided into two transformers with T2.

In other words, one end of the primary winding N'l of the main load transformer PIT is the resonance capacitor C'l. is connected to the primary winding NA of the orthogonal transformer PRT through 1
The other end of the next winding N'1 is grounded. Then, the leakage inductance of the primary winding N'1 and the capacitor C'IO
A series resonant circuit is formed. Also, transformer P
The secondary winding N'2 of IT, is connected to the output rectifier circuit OR,.

And the primary winding N of the transformer PITz for audio load
One end of '1 is a resonance capacitor C'l. The other end of the primary winding N'1 is grounded. And the primary winding N'
A series resonant circuit is formed by the leakage inductance of , and the capacitor C' IO. Also, transformer PIT
2's secondary winding N'3 is connected to the output rectifier circuit OR2. Note that the primary winding N'+ and the secondary winding N'x are tightly coupled with a coupling coefficient of approximately 0.85.

The output voltage to the main load when the main load is the maximum changes as shown in curve (2) in Fig. 4 depending on the frequency f, and the output voltage to the main load when the main load is the minimum changes according to the frequency f. It changes as shown in curve (1) in the figure. Therefore, in order to make the output voltage of the main load 135 V, the frequency f is controlled to be fO when the main load is maximum, and the frequency f is controlled to be fO + Δf when the main load is minimum.
It may be set to 1.

As shown in curves (3) and (4) in Figure 4, when the audio load is maximum, the output voltage to the audio load is 45V at frequency fO, and when the audio load is minimum, the output voltage is 45V at frequency fO.
The transformer PIT2 may be adjusted so that the output voltage to the audio load is 45V at +Δ.

In other words, as described above, the resonance capacitor C'l. What is necessary is to adjust the capacitance value of , the cross-sectional area of the core of the transformer PIT2, and the number of turns of the primary winding N' l .

In addition, in the example in Figure 3, the maximum value of the main load is 184
．． 5 W, the minimum value is 90 W, the maximum value of the audio load is 90 W, the minimum value is 4.5 W, and in order to cope with the fluctuation of the input terminal from 90 V to 120 V, according to experiments, the core of the isolation transformer PIT is In EE-40, the number of turns of the primary winding N' is 50 turns, and the number of turns of the secondary winding N'2 is 1.
08 turn, resonance capacitor C'l. The capacitance value of is 0
．． 033μF, and the core of isolation transformer PIT2 is U-
18, the number of turns of the primary winding N'l is 120 turns, the number of turns of the secondary winding N'3 is 50 turns, and the capacitor C'l for resonance. The capacitance value was 0.01 μF. At this time, the waveform of the current I/1 flowing through the primary winding N'l of the transformer PIT is shown in Figure 5A.
The waveform of the current 1810 flowing through the primary winding N'l of T2 is shown in FIG. 5N8, and the collector current rc of the switching transistor Q1 of the oscillation drive circuit OD is shown in FIG. 5C. Also, Figure 6 shows the output voltage to the audio load and the output current to the main load when the audio load is maximum! +
35 is shown in the solid curve (6), and the case where the audio load is minimum is shown in the solid curve (5). In this case, the fluctuation in the output voltage to the audio load is approximately ±4V. In addition, in the case of the example in Figure 3, when the input terminal is 100 V and the total load of the audio load and main load is the maximum of 274.5 W, the required human power is 304 W, and the loss is 29.5 W.
The power conversion efficiency was approximately 90% at W.

In contrast, in the case of the conventional example, experiments showed that the core of the isolation transformer PIT was E-50 and the number of turns of the primary winding N was 3.
The number of turns of the first secondary winding N2 was 108 turns, the number of turns of the second secondary winding N3 was 36 turns, and the capacitance value of the resonance capacitor C2 was 0.1 μF. At this time, the current (1
The waveform of 1 is as shown in Figure 9, and the resonance drive circuit O
The collector current of the switching transistor Q of D is 1/
The waveform of c is now shown in FIG. 9A. Also, the 6th
In the figure, the broken line curve (8) shows the relationship between the output voltage to the audio load and the output current IIS to the main load when the audio load is maximum in the case of the conventional example, and the broken line shows the relationship when the audio load is the minimum. This is shown in curve (7). In this case, the variation in the output voltage to the audio load is approximately ±IOV. In addition, in the case of the conventional example, when the input terminal is 100V and the total load of the audio load and main load is the maximum 274.5W, the required human power is 308.5W, the loss is 34W, and the power conversion efficiency is was about 89%.

Therefore, compared to the conventional example, the device of the example in FIG. 3 suppresses fluctuations in the output voltage to the main load due to changes in the audio load and fluctuations in the output voltage to the audio load due to changes in the main load, and Power conversion efficiency is improved.

〔Effect of the invention〕

Thus, according to the present invention, one of the isolation transformers PIT
The primary winding N1 and the first secondary winding N2 for the main load are loosely coupled, and the primary winding N1 and the second secondary winding N'j for the audio load are tightly coupled. In addition, since the first secondary winding N2 and the second secondary winding N' are configured to be loosely coupled, the amount of heat generated is small even when the audio load is maximum. , fluctuations in the output voltage to the main load due to changes in the audio load and fluctuations in the output voltage to the audio load due to changes in the main load are suppressed, so it is possible to suppress changes in the output voltage to the audio load due to changes in the audio load. It can be easily applied as a switching power supply.

In addition, the isolation transformer PIT is used as the main load transformer P
Even if the transformer is separated into two transformers: IT, and voice load transformer PIT2, the above-mentioned effects can be achieved.

[Brief explanation of drawings]

Fig. 1 is a sectional view of essential parts of an isolation transformer according to an embodiment of the present invention, Fig. 2 is a signal waveform diagram, Fig. 3 is a circuit diagram of another embodiment of the invention, and Fig. 4 is an output voltage Fig. 5 is a signal waveform diagram, Fig. 6 is a diagram showing voltage fluctuation, Fig. 7 is an explanatory diagram of a conventional example, and Fig. 8 is a cross section of the main part of a conventional isolation transformer. 9 are waveform diagrams of a conventional example. PS is a DC power supply, OD is an oscillation drive circuit, PRT is an orthogonal transformer, PIT is an isolation transformer, and PIT. is the first isolation transformer, PIT2 is the second isolation transformer, N l+ N'l, N'+ is the primary winding, N2
is the first secondary winding, N'j is the second secondary winding, OR,
, OR2 is an output rectifier circuit, and CC is a control circuit. Deputy Hitomatsu Hide Kuma Moriichi Bunryoku ← Bamboo 1 No Takashi - # Dankuko 1st figure? - Refusal of drink, Figure 8 - ¥Tora example of dark form country

Claims (1)

[Claims] 1. The second secondary winding has a primary winding, a first secondary winding, and a second secondary winding. is wound between the primary winding and the first secondary winding, tightly coupling the primary winding and the second secondary winding, and
A switching power supply device comprising an isolation transformer in which a secondary winding and the first secondary winding are loosely coupled. 2. A DC power supply, an oscillation drive circuit connected to the DC power supply, an oscillation frequency control transformer that controls the oscillation frequency of the oscillation drive circuit, and a first output rectifier circuit connected to the first load. a second output rectifier circuit connected to a second load; a primary winding connected to the primary winding of the oscillation frequency control transformer; and a primary winding connected to the first output rectifier circuit. Ru2
a first insulation transformer having a primary winding connected to the primary winding of the oscillation frequency control transformer, and a second insulation transformer connected to the second output rectifier circuit;
a second isolation transformer having a secondary winding; and controlling the inductance of the oscillation frequency control transformer according to the output signal from the first output rectifier circuit to control the oscillation frequency of the oscillation drive circuit. A switching power supply device equipped with a control circuit.