JPH0974753A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a stable voltage for outputting by supplying the voltages on both ends of a first rectifying diode and both ends of first and second smoothing capacitors connecting with a second secondary winding of a transformer. SOLUTION: An inductance element 9 and a first smoothing capacitor 10 are serially connected with each other and are respectively connected to both ends of a first rectifying diode, and a second secondary winding 6c is connected with a serial circuit consisting of a second rectifying diode 14 and a smoothing capacitor 15, further both ends of the capacitor 15 are connected with second output terminals 16a and 16b, respectively. The voltages on both ends of the capacitor 15 are divided by resistors 20 and 21, and the voltages generating on both ends of the resistor 21 and a reference voltage 22 are compared with each other by an error amplifier 23, then a pulse width control circuit 24 controls a first switching element 31 for on-off operation so that the error may become zero, thereby setting the voltages on both ends stably to the set value according to the voltage dividing ratio against the reference voltage 22. As a result, stabilized DC current can be supplied for outputting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device for supplying a regulated DC voltage to industrial and consumer electronic devices.

[0002]

2. Description of the Related Art In recent years, switching power supply devices have been strongly required to have high output stability and high efficiency, as electronic equipments have higher performance and higher efficiency.

Next, a conventional switching power supply device will be described. FIG. 6 shows a circuit configuration of a switching power supply device which is a first conventional example. In FIG. 6, reference numeral 1 is an input DC power supply, and the input voltage is V _IN . 2a-2b
Is an input terminal and is connected to the input DC power supply 1. 31
Is a first switching element, 32 is a first diode, and the first switching element 31 and the first diode 32 constitute the first switching means 3. Four
Reference numeral 1 is a second switching element, 42 is a second diode, and the second switching element 41 and the second diode 42 constitute the second switching means 4.
First switching means 3 and second switching means 4
Are connected in series and are connected to the input terminals 2a-2b. The first capacitor 5 holds the DC voltage V _C1 . 6
Is a transformer having a primary winding 6a and a first secondary winding 6b, and the winding ratio of the primary winding 6a and the first secondary winding 6b is 1:
n, the primary winding 6a is connected to both ends of the second switching means 4 via the first capacitor 5. 7 is the second
And holds the DC voltage V _C2 . Reference numeral 8 denotes a first rectifying diode, the anode of which is connected to one end of the first secondary winding 6b of the transformer 6 and the cathode of which is connected to the first secondary winding 6b of the transformer 6 via the second capacitor 7. Connected to the other end. 9 is an inductance element, and 10
Is a first smoothing capacitor. Inductance element 9
And the first smoothing capacitor 10 are connected in series, and are connected to both ends of the first rectifying diode 8. Reference numerals 12a-12b are first output terminals, 20 is a resistor, one end of which is connected to the first output terminal 12a and the other end of which is connected to the resistor 21. Reference numeral 21 is a resistor, one end of which is connected to the resistor 20 and the other end of which is connected to the first output terminal 12b. 22
Is a reference voltage, the positive side of which is connected to the non-inverting input terminal of the error amplifier 23 and the negative side of which is connected to the first output terminal 12b. An error amplifier 23 has a non-inverting input terminal connected to the positive side of the reference voltage 22, an inverting input terminal connected to a connection point between the resistor 20 and the resistor 21, and an output terminal input to the pulse width control circuit 24. Connected to. Resistor 20 and resistor 21
Reference voltage 22, error amplifier 23, pulse width control circuit 2
4, the control means 17 is constituted, and the first output terminal 12a-
The output voltage V _{O1 of} 12b is detected, and a control signal for changing the on / off ratio of the first switching element 31 and the second switching element 41 is generated so that the output voltage becomes constant.

The operation of the switching power supply device configured as described above will be described below with reference to the operation waveforms of the respective parts of FIG.

In FIG. 7, (a) shows the first of the control means 17.
Drive pulse waveform V _G1 of the switching element 31 of FIG. ₁ , (b) shows the drive pulse waveform V _G2 of the second switching element 41 of the control means 17, and (c) shows the primary winding of the transformer 6. shows a current waveform I _P line 6a,
(D) shows the voltage waveform V _D applied to the first switching means 3, and (e) shows the first rectifying diode 8
Shows a current waveform I _S1 flowing through the inductor, (f) shows a voltage waveform V _S1 applied to the first rectifying diode 8, and (g) shows a current waveform I S flowing through the inductance element 9.
_L is shown.

[0006] In order to show the temporal change of the operating state, t₀~ T_Four
Is shown in the figure. Time t₁To turn on the control means 17
Signal causes the first switching element 31 to turn on and
When the switching element 41 of No. 2 is turned off, the transformer 6
The voltage V is applied to the primary winding 6a._IN-V _C1Is applied. At this time
The first secondary winding 6b of the lance 6 has a voltage (V_IN-V_C1) ×
n is generated to turn off the first rectifying diode 8.
The voltage (V_IN-V_C1) × n +
V_C2-V_O1Is applied and flows through the inductance element 9.
The current increases linearly. Of the primary winding 6a of the transformer 6
Current I_PIs the exciting current of the transformer 6 and the first secondary winding 6b
Is linear because it is the sum of the primary side converted currents flowing through the
To the transformer 6 and the inductance element 9
Magnetic energy is stored.

At time t ₂ , the first off signal of the control means 17
When the switching element 31 of the first switching element 31 is turned off, the current flowing through the first switching element 31 becomes the second diode 42.
Turn on. At the same time, the second switching element 41 is turned on by the ON signal of the control means 17, but there is no change in the operation regardless of whether the on-current flows through the second diode 42 or the second switching element 41. When the second diode 42 or the second switching element 41 is turned on, the DC voltage V _C1 held by the first capacitor 5 is applied to the primary winding 6a of the transformer 6, and at the same time, the first voltage of the transformer 6 is reduced. A voltage V _C1 × n is generated in the next winding 6b, and the first rectifying diode 8 is forward biased and turned on. The current I _S1 of the first rectifying diode 8 increases from zero due to the influence of the leakage inductance of the transformer, and the current of the first secondary winding 6b gradually decreases. The current of the primary winding 6a gradually decreases from a positive value to a negative current as the exciting current of the transformer 6 decreases and the current of the first secondary winding 6b decreases. Since the first rectifying diode 10 is on, the output voltage V _O1 is applied to the inductance element 9 in the opposite direction. When a negative current is flowing in the second switching element 41, the second switching element 41 is turned off by the off signal of the control means 17.
When is turned off, the negative current becomes continuous due to the action of the leakage inductance of the transformer 6, so that the first diode 32 is turned on. At the same time, the first switching element 31 is turned on by the ON signal of the control means 17,
There is no change in the operation even if the current flowing through the switching means 3 flows through the first switching element 31 or the first diode 32. When the first switching element 31 is turned on and the second switching element 41 is turned off at the same time, the voltage V _IN -V _C1 is applied to the primary winding 6a of the transformer 6. A current for turning on the first rectifying diode 8 is flowing through the first secondary winding 6b of the transformer 6, but the current suddenly decreases to zero and the first rectifying diode 8 is turned off. The current of the primary winding 6a is the first secondary winding 6b.
Increases with increasing current. First rectifier diode 8
Is turned off, the voltage (V _IN −
V _C1 ) × n + V _C2 −V _O1 is applied, and excitation energy is accumulated in the transformer 6 and the inductance element 9. This operation is repeated.

The ON period of the first switching means 3 is T
_{When the ON} and OFF periods are T _OFF , (V _IN −V _C1 ) × T _ON = V _C1 × T _OFF is established depending on the reset condition of the transformer 6, and from the reset condition of the inductance element 9,
Since the period of t _{3 to} t ₄ (t _{0 to} t ₁ ) is short, it can be disregarded as follows: {(V _IN −V _C1 ) × n + V _C2 −V _O1 } × T _ON = V _O1 × T
_{It turns off} . Since the relationship between the voltage V _C1 and the voltage V _C2 is V _C1 × n = V _C2 , the voltage V _C1 and the voltage V _C2 are _calculated as follows: V _C1 = δ × V _IN V _C2 = δ × V _IN × n V _O1 = δ × V _IN × n, and the first output terminal 1 becomes the ON / OFF ratio of the first switching element 31 and the second switching element 41.
The output voltage V _O1 of 2a-12b can be controlled. t _{3 to} t
Considering ₄ (t _{0 to} t ₁ ), the output voltage V _O1 becomes low, but a predetermined voltage can be obtained by increasing δ accordingly.

In this configuration, the first switching element 31
Since the parasitic capacitance of the switching element and the distributed capacitance of the transformer 6 are discharged immediately before the second switching element 41 is turned on and then turned on, the generation of spike-like short-circuit current can be reduced, the efficiency is improved, and noise is generated. Can be suppressed. In addition, the first switching element 31 and the second switching element 31 caused by the leakage inductance of the transformer 6
The spike voltage at the time of turning off the switching element 41 is effectively absorbed by the first capacitor 5 and the input DC power supply 1 by turning on the first diode 32 and the second diode 42, and no spike voltage is generated. .

FIG. 8 shows a circuit configuration of a switching power supply device which is a second conventional example. In FIG. 8, 1
Is an input DC power supply. Input terminals 2a-2b are connected to the input DC power supply 1. Reference numeral 31 is a first switching element, which is repeatedly turned on and off by the control means 17 to form the first switching means 3. A transformer 6 has a primary winding 6a, a first secondary winding 6b, and a second secondary winding 6c. One end of the primary winding 6a is connected to the input terminal 2a and the other end is the first winding. Is connected to the input terminal 2b via the switching means 3 of FIG.

A series circuit of a first rectifying diode 8 and a first smoothing capacitor 10 is connected to the first secondary winding 6b, and a reference numeral 11 is a three-terminal regulator, which is an influence of a voltage fluctuation of the first smoothing capacitor 10. Is provided to eliminate
Both ends of the first smoothing capacitor 10 are connected to the first output terminals 12a-12b via the three-terminal regulator 11.

The second secondary winding 6c is connected to a series circuit of the output changeover switch means 13, the second rectifying diode 14 and the second smoothing capacitor 15, and both ends of the second smoothing capacitor 15 are connected to the second secondary winding 6c. It is connected to the output terminals 16a-16b. The output changeover switch means 13 is turned on / off by an external signal, and when it is on, the second output terminal 16a-1
The output voltage is supplied to 6b, and when it is off, the second output terminal 1
No output voltage is supplied to 6a-16b.

A resistor 19 has one end connected to the second output terminal 16a and the other end connected to the resistor 20. Two
Reference numeral 0 is a resistor, one end of which is connected to the resistor 19 and the other end of which is connected to the resistor 21. Reference numeral 21 denotes a resistor, one end of which is connected to the resistor 20 and the other end of which is connected to the second output terminal 16b. Reference numeral 18 denotes a switch means, which is turned on / off by an external signal, has one end connected to the connection point of the first rectifying diode 8 and the first smoothing capacitor 10 and the other end a resistor 19
And the resistor 20 are connected to each other. Reference numeral 22 is a reference voltage, the positive side of which is connected to the non-inverting input terminal of the error amplifier 23 and the negative side of which is connected to the second output terminal 16b. An error amplifier 23 has a non-inverting input terminal connected to the positive side of the reference voltage 22, an inverting input terminal connected to a connection point between the resistor 20 and the resistor 21, and an output terminal input to the pulse width control circuit 24. Connected to. The first output terminal 12b and the second output terminal 16b are connected to the ground. When the output changeover switch means 13 is on, the switch means 18 is off and the voltage across the second smoothing capacitor 15 is divided by the resistor 19, the resistor 20 and the resistor 21, and the voltage is applied across the resistor 21. The generated voltage and the reference voltage 22 are compared by the error amplifier 23, and the ON / OFF control of the first switching element 31 is performed by the pulse width control circuit 24 so that the error becomes zero, and both ends of the second smoothing capacitor 15 are controlled. The voltage is stabilized at a set value determined by the voltage division ratio with respect to the reference voltage 22.
When the output changeover switch means 13 is off, the switch means 18 is on and the voltage across the first smoothing capacitor 10 is divided by the resistors 20 and 21 to obtain the resistor 21.
Error amplifier 23 and the reference voltage 22 generated at both ends of the
And the ON / OFF control of the first switching element 31 is performed by the pulse width control circuit 24 so that the error becomes zero, and the voltage across the first smoothing capacitor 10 is set by the voltage division ratio with respect to the reference voltage 22. Stabilized to a value. Resistor 19, resistor 20, resistor 21 and reference voltage 2
2, the error amplifier 23, the pulse width control circuit 24, and the switch means 18 constitute the control means 17.

In the conventional switching power supply device configured as above, the operation when the output changeover switch means 13 is in the ON state will be described with reference to FIG.

FIG. 9 shows the output changeover switch means 1 of FIG.
3 shows the operation waveforms of each part when 3 is in the on state.
Is a control means 1 applied to the first switching element 31
7 shows the drive pulse waveform V _G , (b) shows the voltage waveform V _DS applied to the first switching means 3, and (c) shows the current waveform I flowing through the first switching means 3. _D is shown, and (d) is the first 2 of the transformer 6.
The voltage waveform V _S3 generated in the next winding 6b is shown,
(E) shows the voltage waveform V _S4 generated in the second secondary winding 6c of the transformer 6.

In order to show the temporal change of the operating state, t ₁ ~
t ₃ is shown in the figure. When the first switching means 3 is turned on by the ON signal of the control means 17 at time t ₁ , a spike current flows through the first switching means 3 in accordance with the voltage fluctuation of V _DS . This is due to the charging / discharging current to the distributed capacitance such as the line capacitance and the interlayer capacitance existing between the windings of the transformer 6 and the charging current of the parasitic capacitance related to the first switching means 3. This spike current causes an increase in noise, a decrease in reliability, and an increase in loss. When the first switching means 3 is turned on and V _DS becomes sufficiently small, the input voltage V _IN is applied to the primary winding 6a of the transformer 6, and V 1 is applied to the first secondary winding 6b of the transformer 6.
_IN × n, V _IN × m in the second secondary winding (where n and m are turn ratios of the primary winding and the first and second secondary windings, and the primary winding: the first winding (Secondary winding: second secondary winding = 1: n: m), the first and second rectifying diodes 8 and 14 are reverse-biased and turned off. Therefore, the exciting current of the transformer 6 flows through the primary winding 6a and increases linearly.

At time t ₂ , when the first switching means 3 is turned off by the off signal of the control means 17, a spike voltage is generated due to the leakage inductance of the transformer 6. The generation of this spike voltage causes noise and loss.

Further, the first and second secondary of the transformer 6
Flyback voltage is generated in the windings 6b and 6c,
The flyback voltage of is rectified and smoothed to obtain the output voltage. Time
Tick t _ThreeIn response to the ON signal of the control means 17, the first switch
When the switching means 3 is turned on, the transformer 1 becomes 1
An input voltage is applied to the next winding 6a. Repeat this.

Next, the operation when the state of the output changeover switch means 13 changes from OFF to ON will be described with reference to FIG.

FIG. 10 shows operation waveforms of each part when the state of the output changeover switch means 13 of FIG. 8 changes from OFF to ON, and FIG. 10A shows the output changeover switch means 13.
The state of the switch means 18 is shown in (b), and the second output terminals 16a-16b are shown in (c).
Voltage waveform V _O2 of the first smoothing capacitor 10, (d) shows the voltage waveform V _C3 across the first smoothing capacitor 10, and (e) shows the voltage waveform V _O1 of the first output terminals 12a-12b. ing. In order to show the change over time in the operating state, t ₁ to t ₅ are shown in the figure.

Time t₁Output changeover switch means 13
Is turned on, the second smoothing capacitor 15 is discharged.
Because of the maximum power that can be output from the converter, the second smoothing
The charging of the capacitor 15 is started, and the second output terminal 1
6a-16b terminal voltage V_O2Begins to rise. Trance
Flyback voltage output to the first secondary winding 6b of
Is V_O2Determined by the
You. When the flyback voltage is small, the first smoothing capacitor
The charge to the server 10 is cut off, and the three-terminal regulator 11 is connected.
Of the voltage V across the first smoothing capacitor 10_C3Is descending
Start dropping. Time t ₂And both of the first smoothing capacitor 10
Terminal voltage V_C3Is the minimum input voltage of the three-terminal regulator 11
When they are equal, time t₂After that, the first output terminal 12a-
12b terminal voltage V_O1Will start to fall, and for a given output voltage
It will be difficult to secure. Time t_ThreeAnd the first smoothing capacitor 1
When the charging to 0 is started, the first smoothing capacitor 10
Voltage V across_C3And of the first output terminals 12a-12b
Output voltage V_O1Begins to rise. Time t_FourAnd the first smooth
Voltage V across capacitor 10_C3Is a three-terminal regulator 11
Becomes equal to the minimum input voltage of_FourAfter that the first
The terminal voltage V of the output terminals 12a-12b_O1Is the specified output voltage
Continue to maintain pressure. Time t_FiveSwitch means 18 off
Then, the voltage V across the first smoothing capacitor 10_C3Voltage control
Output voltage V of the second output terminals 16a-16b_O2of
When switching to voltage control, the second output terminals 16a-16
b output voltage V_O2Stabilization is started.

[0022]

However, in the above-mentioned structure, due to the spike voltage caused by the leakage inductance of the transformer generated when the first switching means is turned off, the peak value of the spike voltage is 2 when the output is lightly loaded. Since the smoothing capacitor on the secondary side is charged, the regulation characteristic deteriorates. Further, when the state of the output changeover switch means 13 transits from OFF to ON, the output voltage V _{O1 of} the first output terminals 12a-12b drops and a predetermined voltage cannot be obtained. Therefore, as shown by the broken line in FIG. 10D, the voltage V _C3 across the first smoothing capacitor 10 does not fall below the minimum input voltage of the three-terminal regulator 11, and the voltage V _C across the first smoothing capacitor 10 is set in advance. _Although it is necessary to set _C3 to a high value, steady power loss and heat generation in the three-terminal regulator 11 are increased, and the conversion efficiency is reduced. Moreover, in such a configuration,
Since all the energy is stored in the transformer, the stress of the transformer becomes large, so that the size of the transformer becomes large and the conversion efficiency deteriorates.

It is an object of the present invention to eliminate the above-mentioned conventional drawbacks and provide a switching power supply device capable of supplying a stable DC voltage to the output without lowering the conversion efficiency. .

[0024]

In order to solve the above-mentioned problems, a series circuit of at least a first switching means for repeating ON / OFF and a second switching means for repeating ON / OFF alternately with the first switching means is input. A direct current power supply, and in parallel with the second switching means, a primary winding of a transformer having a primary winding and two or more secondary windings, and a series circuit of a first capacitor are connected, A first capacitor and a second capacitor are provided on the first secondary winding of the transformer.
Connecting a series circuit of the rectifying diode, a series circuit of an inductance element and a first smoothing capacitor is connected to both ends of the first rectifying diode, and a second rectifier is connected to a second secondary winding of the transformer. A series circuit of a diode and a second smoothing capacitor is connected, and the voltage across the first and second smoothing capacitors is supplied to the output.

[0025]

With this configuration, the spike voltage at the time of turning off the first switching element and the second switching element due to the leakage inductance of the transformer is effectively turned on by turning on the first diode and the second diode. It is absorbed by the No. 1 capacitor and the input DC power supply, and no spike voltage is generated. Therefore, it is possible to improve the regulation characteristic and efficiency when the output is lightly loaded, and suppress the generation of noise. Furthermore, energy corresponding to the output (flyback output) obtained from both ends of the second smoothing capacitor is accumulated in the transformer.
Since the output (forward output) from the smoothing capacitor is not accumulated, the stress of the transformer is reduced, and the transformer can be downsized and the loss can be reduced. Therefore, in the multi-output specification, the circuit supplied from the flyback output is used for the high voltage small current output, and the circuit supplied from the forward output is used for the low voltage large current output. be able to.

When the output changeover switch means makes a transition from off to on and the first switching means turns off, the output voltage of the first secondary winding becomes small for the same reason as in the conventional switching power supply device, The charging of the second capacitor is cut off, and the voltage V across the second capacitor V
_C2 begins to descend. The voltage of the first capacitor temporarily decreases due to the charging of the second smoothing capacitor when the second switching means is on, and the voltage generated in the first secondary winding of the transformer increases. The second capacitor is
It is discharged by the inductance element and gradually decreases because there is no charge from the first secondary winding.
Since the amount of increase in the voltage generated in the secondary winding is large, the voltage applied to the inductance element when the first switching means is ON is always larger than in the steady state.
Even if the control means changes the on / off ratio of the first switching means and the second switching means, the voltage applied to the inductance element does not become zero, so that the decrease in the current of the inductance element is small, and as a result, The voltage fluctuation of the first smoothing capacitor is smaller than that of the conventional switching power supply device, and the voltage across the first smoothing capacitor can be set small, so that the loss of the three-terminal regulator can be small.

Further, the leakage inductance of each winding or the second capacitor or the second smoothing capacitor is adjusted so that the current waveforms flowing through the first rectifying diode and the second secondary winding are substantially similar. The regulation characteristics can be improved by.

[0028]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a switching power supply device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 is an input DC power supply, and the input voltage is V _IN . 2a-2b are input terminals, to which the input DC power supply 1 is connected. Reference numeral 31 is a first switching element, 41 is a second switching element, and the first switching element 31 and the second switching element 41 are alternately turned on and off repeatedly and are connected in series to the input terminals 2a-2b. It Reference numeral 32 denotes a first diode, and the first switching element 31 and the first diode 32 constitute the first switching means 3. 42 is a second diode, and the second switching element 41 and the second diode 42 constitute the second switching means 4. 5 is the first
And holds the DC voltage V _C1 . Reference numeral 6 denotes a transformer, which includes a primary winding 6a, a first secondary winding 6b and a second winding 6a.
And the winding ratio of the primary winding 6a and the first secondary winding 6b is 1: n, and the winding ratio of the primary winding 6a and the second secondary winding 6c. Is set to 1: m, the primary winding 6a of the transformer is connected to the second switching means 4 via the capacitor 5.
Connected to both ends of. The second capacitor 7 holds the DC voltage V _C2 . Reference numeral 8 denotes a first rectifying diode, the anode of which is connected to one end of the first secondary winding 6b of the transformer 6 and the cathode of which is connected to the first secondary winding 6b of the transformer 6 via the second capacitor 7. Connected to the other end. Reference numeral 9 is an inductance element, and 10 is a first smoothing capacitor. The inductance element 9 and the first smoothing capacitor 10 are connected in series and are connected to both ends of the first rectifying diode 8. Both ends of the first smoothing capacitor 10 are connected to the first output terminals 12a-12b.

The second secondary winding 6c is connected to a series circuit of the second rectifying diode 14 and the second smoothing capacitor 15, and both ends of the second smoothing capacitor 15 are connected to the second output terminals 16a-16b. Connected.

Reference numeral 20 denotes a resistor, one end of which is an output terminal 16
It is connected to a and the other end is connected to the resistor 21. Reference numeral 21 denotes a resistor, one end of which is connected to the resistor 20 and the other end of which is connected to the output terminal 16b. Reference numeral 22 is a reference voltage, the positive side of which is connected to the non-inverting input terminal of the error amplifier 23 and the negative side of which is connected to the output terminal 16b. An error amplifier 23 has a non-inverting input terminal connected to the positive side of the reference voltage 22, an inverting input terminal connected to a connection point between the resistor 20 and the resistor 21, and an output terminal input to the pulse width control circuit 24. Connected to. The output terminal 12b and the output terminal 16b are connected to the ground. The voltage across the second smoothing capacitor 15 is applied to the resistor 20.
The voltage is divided by the resistor 21 and the voltage generated across the resistor 21 is compared with the reference voltage 22 by the error amplifier 23. The ON / OFF control of the first switching element 31 is pulse width control so that the error becomes zero. The voltage across the second smoothing capacitor 15 is stabilized by the circuit 24 to a set value determined by the voltage division ratio with respect to the reference voltage 22. The resistor 20, the resistor 21, the reference voltage 22, the error amplifier 23, and the pulse width control circuit 24 constitute the control means 17.

The operation of the switching power supply device configured as described above will be described below with reference to the operation waveforms of the respective parts of FIG.

In FIG. 2, (a) is the first of the control means 17.
Drive pulse waveform V _G1 of the switching element 31 of FIG. ₁ , (b) shows the drive pulse waveform V _G2 of the second switching element 41 of the control means 17, and (c) shows the primary winding of the transformer 6. shows a current waveform I _P line 6a,
(D) shows the voltage waveform V _D applied to the first switching means 3, and (e) shows the first rectifying diode 8
Shows a current waveform I _S1 flowing through the first rectifying diode 8, (f) shows a voltage waveform V _S1 applied to the first rectifying diode 8, and (g) shows a current waveform I _S2 flowing through the second rectifying diode 14. (H) shows the second rectifier diode 1
4 shows a voltage waveform V _S2 applied to No. 4.

T is used to indicate the change over time in the operating state.₀~ T_Four
Is shown in the figure. Time t₁To turn on the control means 17
Signal causes the first switching element 31 to turn on and
When the switching element 41 of No. 2 is turned off, the transformer 6
The voltage V is applied to the primary winding 6a._IN-V _C1Is applied. At this time
The first secondary winding 6b of the lance 6 has a voltage (V_IN-V_C1) ×
n is generated to turn off the first rectifying diode 8.
The voltage (V_IN-V_C1) × n +
V_C2-V_C3Is applied and flows through the inductance element 9.
The current increases linearly. At the same time the second 2 of the transformer 6
On the next winding 6c (V_IN-V_C1) × m occurs and the second rectifier
Turn off Iodo 14. Primary winding of transformer 6
6a current i_PIs the exciting current of the transformer 6 and the first secondary winding
To be the sum of the primary side converted currents of the current flowing through the line 6b
Increasing linearly, transformer 6 and inductance element
Excitation energy is stored in 9.

At time t ₂ , the first off signal is output from the control means 17.
When the switching element 31 of the first switching element 31 is turned off, the current flowing through the first switching element 31 becomes the second diode 42.
Turn on. At the same time, the second switching element 41 is turned on by the ON signal of the control means 17, but there is no change in the operation regardless of whether the on-current flows through the second diode 42 or the second switching element 41. When the second diode 42 or the second switching element 41 is turned on, the DC voltage V _C1 held by the first capacitor 5 is applied to the primary winding 6a of the transformer 6, and at the same time, the first voltage of the transformer 6 is reduced. A voltage V _C1 × n is generated in the next winding 6b, and the first rectifying diode 8 is forward biased and turned on. The current I _S1 of the first rectifying diode 8 increases from zero due to the influence of the leakage inductance of the transformer, and the current of the first secondary winding 6b gradually decreases. At the same time, a voltage V _C1 × m is generated in the second secondary winding 6c of the transformer 6, and the second rectifier diode 14 is forward biased and turned on. The current in the primary winding 6a gradually decreases from a positive value to a negative value as the exciting current of the transformer 6 decreases, the current in the first secondary winding 6b decreases, and the current in the second secondary winding 6c increases. It becomes an electric current. Since the first rectifying diode 10 is on, the voltage V _C3 across the first smoothing capacitor 10 is applied to the inductance element 9 in the opposite direction. When the second switching element 41 is turned off by the OFF signal of the control means 17 when a negative current is flowing in the second switching element 41, the negative current becomes continuous due to the action of the leakage inductance of the transformer 6. , The first diode 32 is turned on. At the same time, the first switching element 31 is turned on by the ON signal of the control means 17.
However, the operation does not change regardless of whether the current flowing through the first switching means 3 flows through the first switching element 31 or the first diode 32. When the first switching element 31 is turned on and the second switching element 41 is turned off at the same time, the voltage V _IN -V _C1 is applied to the primary winding 6a of the transformer 6. A current for turning on the first rectifying diode 8 is flowing through the first secondary winding 6b of the transformer 6, but the current suddenly decreases to zero and the first rectifying diode 8 is turned off. Second rectifier diode 1
4 is also turned off. The current in the primary winding 6a increases as the current in the first secondary winding 6b increases and the current in the second secondary winding 6c decreases. When the first rectifying diode 8 is turned off,
The voltage (V _IN −V _C1 ) × n + V is applied to the inductance element 9.
_C2- V _C3 is applied, and exciting energy is accumulated in the transformer 6 and the inductance element 9. This operation is repeated.

The ON period of the first switching means 3 is set to T
_{When the ON} and OFF periods are T _OFF , (V _IN −V _C1 ) × T _ON = V _C1 × T _OFF is established depending on the reset condition of the transformer 6, and from the reset condition of the inductance element 9,
Since the period of t _{3 to} t ₄ (t _{0 to} t ₁ ) is short, it is ignored. {(V _IN −V _C1 ) × n + V _C2 −V _C3 } × T _ON = V _C3 × T
_{It turns off} . Voltage V _C1 and voltage V _C2 and voltage V _C1 and voltage V _O2
The relationship is V _C1 × n = V _C2 V _C1 × m = V _O2 , and when the voltage V _C1 and the voltage V _C2 are calculated, V _C1 = δ × V _IN V _C2 = δ × V _IN × n The voltages V _C3 and V _O2 are V _C3 = δ × V _IN × n V _O2 = δ × V _IN × m, and the first smoothing capacitor 10 depends on the on / off ratio of the first switching element 31 and the second switching element 41. The voltage V _C3 across the terminal and the terminal voltage V _O2 of the second output terminal can be controlled. Considering t _{3 to} t ₄ (t _{0 to} t ₁ ), the voltages V _C3 and V _O2 become low, but a predetermined voltage can be obtained by increasing δ accordingly.

Also in this configuration, the characteristics of the first conventional example that prevent the generation of spike-like short-circuit current and spike voltage, improve the efficiency, and suppress the generation of noise are not lost.
Therefore, in the multi-output specification, the secondary side smoothing capacitor is not charged at the peak value of the spike voltage at the time of light output load, and the regulation characteristic is improved. FIG.
(A) is the terminal current I of the first output terminals 12a-12b.
Regarding the change of the terminal voltage V _O2 of the second output terminal due to the change of _O1, a comparison is made between the case of the switching power supply device in the second conventional example and the case of the switching power supply device in the first embodiment of the present invention. (B) shows the change of the terminal voltage V _O2 of the second output terminal due to the change of the terminal current I _O2 of the second output terminals 16a-16b, as compared with the case of the switching power supply device in the second conventional example. Compared with the case of the switching power supply device in the first embodiment of the invention, the switching power supply device in the first embodiment of the present invention is compared with the switching power supply device in the second conventional example (a). In both cases (b) and (b), the regulation characteristics at light output load are improved. Also, energy corresponding to the output (flyback output) obtained from both ends of the second smoothing capacitor is accumulated in the transformer,
Since the output (forward output) from the first smoothing capacitor is not accumulated, the stress of the transformer is reduced, and the size and loss of the transformer can be reduced. Therefore, in the multi-output specification, the circuit supplied from the flyback output is used for the high voltage small current output, and the circuit supplied from the forward output is used for the low voltage large current output. be able to.

The discharge of the parasitic capacitance of the first and second switching means 3 and 4 and the distributed capacitance of the transformer 6 just before the turn-on of the first switching means 3 is caused by the leakage inductance of the transformer 6. It goes without saying that the discharge energy can be increased by connecting an inductance element in series to the primary winding 6a or the first secondary winding 6b. Further, by reducing the inductance value of the transformer 6 and reversely exciting the transformer 6, it is possible to assist the discharge of the parasitic capacitance of the first and second switching means 3 and 4 and the distributed capacitance of the transformer 6. Further, the voltage applied to the switching means is the input voltage V _IN , the DC excitation component of the transformer 6 is due only to the output from the second output terminal, and the DC excitation component is the second component.
It is possible to realize a switching power supply device that is smaller than that of the conventional example, has high efficiency, low noise, and can be operated at a high frequency. In this method, the first rectifier diode and the second rectifier diode
The regulation characteristic can be improved by adjusting the leakage inductance of each winding or the second capacitor or the second smoothing capacitor so that the waveforms of the currents flowing through the subsequent windings are almost similar. In addition, the current of the rectifying diode is made sinusoidal by adjusting the first capacitor or the second capacitor, the leakage inductance of the transformer, the capacitance of the second smoothing capacitor, and the inductance, and it is exactly the same as when turning off the zero current. The effect is obtained.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows the configuration of a switching power supply device according to the second embodiment of the present invention. 4, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 4, reference numeral 1 is an input DC power supply.
2a-2b are input terminals, to which the input DC power supply 1 is connected. Reference numeral 31 is a first switching element and 41 is a second switching element, which are connected in series to the input terminals 2a-2b. 32 is a first diode,
The switching element 31 and the first diode 32 constitute the first switching means 3. 42 is a second diode, and the second switching element 41 and the second diode 42 constitute the second switching means 4. Reference numeral 5 is a first capacitor. 6 is a transformer, which is a primary winding 6a, a first secondary winding 6b, and a second secondary winding 6
c, the primary winding 6a and the first secondary winding 6b
Of the primary winding 6a and the second secondary winding 6c is 1: m, the primary winding 6a of the transformer is switched to the second switching via the capacitor 5. Means 4
Connected to both ends of. 7 is a second capacitor. 8
Is the first rectifier diode, the anode of which is the transformer 6
Is connected to one end of the first secondary winding 6b, and the cathode is connected to the other end of the first secondary winding 6b of the transformer 6 via the second capacitor 7. Reference numeral 9 is an inductance element, and 10 is a first smoothing capacitor. The inductance element 9 and the first smoothing capacitor 10 are connected in series,
It is connected to both ends of the first rectifying diode 8. A three-terminal regulator 11 is provided to eliminate the influence of the voltage drop of the first smoothing capacitor 10 that occurs when the output changeover switch unit 13 is turned on. Both ends of the first smoothing capacitor 10 are the three-terminal regulator. 11 is connected to the first output terminals 12a-12b.

The second secondary winding 6c is connected to the series circuit of the second rectifying diode 14 and the second smoothing capacitor 15, and both ends of the second smoothing capacitor 15 are connected to the second output terminals 16a-16b. Connected. The output changeover switch means 13 is turned on / off by an external signal, and when it is on, the second
The output voltage is supplied to the output terminals 16a-16b of the above, and when it is off, the output voltage is not supplied to the second output terminals 16a-16b.

Reference numeral 19 is a resistor, one end of which is an output terminal 16
It is connected to a and the other end is connected to the resistor 20. 20 is a resistor, one end of which is connected to the resistor 19 and the other end of which is the resistor 2
Connected to 1. Reference numeral 21 denotes a resistor, one end of which is connected to the resistor 20 and the other end of which is connected to the output terminal 16b. 1
Reference numeral 8 denotes a switch means, which is turned on / off by an external signal, has one end connected to the connection point of the first rectifying diode 8 and the first smoothing capacitor 10 and the other end of the resistor 19 and the resistor 2.
It is connected to the connection point of 0. Reference numeral 22 is a reference voltage, the positive side of which is connected to the non-inverting input terminal of the error amplifier 23 and the negative side of which is connected to the output terminal 16b. An error amplifier 23 has a non-inverting input terminal connected to the positive side of the reference voltage 22, an inverting input terminal connected to a connection point between the resistor 20 and the resistor 21, and an output terminal input to the pulse width control circuit 24. Connected to. The output terminal 12b and the output terminal 16b are connected to the ground. When the output changeover switch means 13 is on, the switch means 18 is off and the voltage across the second smoothing capacitor 15 is divided by the resistor 19, the resistor 20 and the resistor 21, and the voltage is applied across the resistor 21. The generated voltage and the reference voltage 22 are compared by the error amplifier 23, and the ON / OFF control of the first switching element 31 is performed by the pulse width control circuit 24 so that the error becomes zero, and both ends of the second smoothing capacitor 15 are controlled. The voltage is stabilized at a set value determined by the voltage division ratio with respect to the reference voltage 22. When the output changeover switch means 13 is off, the switch means 18 is on and the voltage V _C3 across the first smoothing capacitor 10 is _divided by the resistors 20 and 21 to be generated across the resistor 21. The voltage and the reference voltage 22 are compared by the error amplifier 23, and the ON / OFF control of the first switching element 31 is performed by the pulse width control circuit 24 so that the error becomes zero, and the voltage V across the first smoothing capacitor 10 is increased. _C3 is stabilized at a set value determined by the voltage division ratio with respect to the reference voltage 22. Resistor 19, resistor 20, resistor 21, reference voltage 22, error amplifier 23
The pulse width control circuit 24 and the switch means 18 constitute the control means 17.

The operation of the switching power supply device configured as described above will be described below.

Regarding the switching power supply device of the present invention,
When the output changeover switch 13 is on, it is equal to that of the first embodiment, and when the output changeover switch 13 is off, it is equivalent to that of the first conventional example.

Next, the operation when the state of the output changeover switch means 13 changes from OFF to ON will be described with reference to FIG.

FIG. 5 shows the output changeover switch means 1 of FIG.
3 shows operation waveforms of respective parts when the state of 3 changes from off to on, (a) shows the state of the output changeover switch means 13, and (b) shows the state of the switch means 18. (C) shows the voltage waveform V _O2 of the second output terminals 16a-16b, (d) shows the voltage waveform V _C2 across the second capacitor, and (e) shows the first smoothing capacitor. 10 shows a voltage waveform V _C3 at both ends of 10,
(F) is the voltage waveform V _O1 of the first output terminals 12a-12b
Is shown. T ₁ to t ₅ to show the change over time in the operating state
Is shown in the figure.

At time t ₁ , the output changeover switch means 13
Changes from off to on, and the first switching element 31
Is turned off and the second switching element 41 is turned on, the charging of the second smoothing capacitor 15 is started. However, since the second smoothing capacitor 15 has no electric charge, the voltage of the first capacitor 5 changes. Is charged via the primary winding 6a and the second secondary winding 6c of the transformer. Similarly, since no voltage is generated in the first secondary winding 6b, the second capacitor 7 is not charged and the inductance element 9
The applied voltage V _C2 gradually decreases because it is discharged by the current.

At time t ₂ , the voltage of the second smoothing capacitor 15 rises, the voltage of the second capacitor 7 decreases, and when the values become equal, the charging of the second capacitor 7 is started, so that the second capacitor 7 is charged. The voltage of the capacitor 7 starts to rise and gradually reaches a steady state.

At time t ₃ , the switch means 18 is turned off to switch from the voltage control of the voltage V _C3 across the first smoothing capacitor 10 to the voltage control of the output voltage V _O2 of the second output terminals 16a-16b. The stabilization of the output voltage V _O2 of the second output terminals 16a-16b is started.

The voltage applied to the inductance element 9 becomes larger than that in the stable state before the charging of the second capacitor 7 is started. In the normal control, the duty ratio is changed by the operation of the protection circuit so that the charging current of the second smoothing capacitor 15 is limited, so that the fluctuation of the current of the inductance element 9 is small. Therefore, the voltage fluctuation of the first smoothing capacitor 10 is small.

Therefore, in the switching power supply device of the present invention, the first smoothing capacitor 10 is continuously charged as compared with the conventional switching power supply device, so that the voltage across the first smoothing capacitor 10 fluctuates. Less is. Therefore, the input voltage of the three-terminal regulator 11 can be set small, and the loss of the three-terminal regulator 11 can be small.

In this embodiment, only the case of two outputs is shown, but it goes without saying that the same applies to the case of two outputs or more.

[0052]

As described above, in the first aspect of the present invention, the spike voltage at the turn-off of the first switching element and the second switching element due to the leakage inductance of the transformer has a spike voltage of the first diode and the second diode. Is turned on, it is effectively absorbed by the first capacitor and the input DC power supply, and no spike voltage is generated. Therefore, in the multi-output specification, charging of the smoothing capacitor on the secondary side at the peak value of the spike voltage at the time of light output load is also eliminated, so that it is possible to improve regulation characteristics and efficiency and suppress noise generation. Furthermore, the energy corresponding to the output (flyback output) obtained from both ends of the second smoothing capacitor is accumulated in the transformer, but the output (forward output) from the first smoothing capacitor is not accumulated. The stress is reduced and the transformer can be downsized and the loss can be reduced. Therefore,
In multi-output specifications, the efficiency can be improved by using the circuit that supplies from the flyback output for the high voltage and small current output and the circuit that supplies from the forward output for the low voltage and large current output. .

Further, in the second aspect of the present invention, when the output changeover switch means makes a transition from off to on and the first switching means turns off, the first secondary winding for the same reason as the conventional switching power supply device. Output voltage decreases, charging of the second capacitor is interrupted, and the voltage V _C2 across the second capacitor begins to drop. The voltage of the first capacitor temporarily decreases due to the charging of the second smoothing capacitor when the second switching means is on, and the voltage generated in the first secondary winding of the transformer increases. The second capacitor is discharged by the inductance element and gradually decreases because there is no charge from the first secondary winding, but the increase in the voltage generated in the first secondary winding of the transformer is large. The voltage applied to the inductance element when the first switching means is on is always higher than in the steady state. Even if the control means changes the on / off ratio of the first switching means and the second switching means, the voltage applied to the inductance element does not become zero, so that the decrease in the current of the inductance element is small, and as a result, The voltage fluctuation of the first smoothing capacitor is smaller than that of the conventional switching power supply device, and the voltage across the first smoothing capacitor can be set small, so that the loss of the three-terminal regulator can be small.

Further, the leakage inductance of each winding or the second capacitor or the second smoothing capacitor is adjusted so that the current waveforms flowing through the first rectifying diode and the second secondary winding are substantially similar. The regulation characteristics can be improved by.

[Brief description of drawings]

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

FIG. 2 is an operation explanatory diagram in the first embodiment of the present invention.

FIG. 3 is an operation explanatory diagram in the first embodiment of the present invention.

FIG. 4 is a circuit configuration diagram showing a switching power supply device according to a second embodiment of the present invention.

FIG. 5 is an operation explanatory diagram in the second embodiment of the present invention.

FIG. 6 is a circuit configuration diagram showing a switching power supply device in a first conventional example.

FIG. 7 is an operation explanatory view of the switching power supply device in the first conventional example.

FIG. 8 is a circuit configuration diagram showing a switching power supply device in a second conventional example.

FIG. 9 is an operation explanatory diagram of a switching power supply device in a second conventional example.

FIG. 10 is an operation explanatory view of the switching power supply device in the second conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input DC power supply 2a-2b Input terminal 3 1st switching means 31 1st switching element 32 1st diode 4 2nd switching means 41 2nd switching element 42 2nd diode 5 1st capacitor 6 Transformer 7 Second Capacitor 8 First Rectifier Diode 9 Inductance Element 10 First Smoothing Capacitor 11 Three-Terminal Regulator 12a-12b First Output Terminal 13 Output Changeover Switch Means 14 Second Rectifier Diode 15 Second Smoothing Capacitor 16a -16b Second output terminal 17 Control means 18 Switch means 19 Resistor 20 Resistor 21 Resistor 22 Reference voltage 23 Error amplifier 24 Pulse width control circuit

Claims (2)

[Claims] 1. A series circuit of at least a first switching means for repeating ON / OFF and a second switching means for repeating ON / OFF alternately with the first switching means, is connected to an input DC power supply, and the second switching means is connected. In parallel with a primary winding of a transformer having a primary winding and two or more secondary windings, and a series circuit of a first capacitor are connected, and a first secondary winding of the transformer is connected to the first winding. The series circuit of the second capacitor and the first rectifying diode is connected to
The rectifying diode of the
Connecting a series circuit of a smoothing capacitor, a series circuit of a second rectifying diode and a second smoothing capacitor to the second secondary winding of the transformer, and connecting at least the first and second smoothing capacitors A switching power supply that supplies the voltage at both ends to the output. 2. A series circuit of at least a first switching means for repeating on / off and a second switching means for repeating on / off alternately with the first switching means is connected to an input DC power source, and the second switching means is connected. In parallel with a primary winding of a transformer having a primary winding and two or more secondary windings, and a series circuit of a first capacitor are connected, and a first secondary winding of the transformer is connected to the first winding. The series circuit of the second capacitor and the first rectifying diode is connected to
The rectifying diode of the
Connecting a series circuit of a smoothing capacitor, a series circuit of a second rectifying diode and a second smoothing capacitor to a second secondary winding of the transformer, and connecting a second circuit of the transformer.
A switching power supply device, wherein switching means is provided between the secondary winding and the second rectifying diode, and supplies at least the voltage across the first and second smoothing capacitors to the output.