JPH0686546A - Switching power supply equipment - Google Patents

Abstract

PURPOSE:To realize a compact, high-efficiency switching power supply equipment by stabilizing a plurality of outputs, improving efficiency and suppressing the generation of noise in a switching power supply equipment used in various electronic equipment. CONSTITUTION:When a first switching element 4 is ON, a voltage induced in one of the secondary windings 3b of a transformer 3 is supplied to a first output 13a-13b through a first rectifying and smoothening circuit comprising a rectifying means, smoothening choke coil 11 and a smoothening capacitor 12; and when a second switching element 7 is ON, a voltage induced to another secondary winding 3c of the transformer 3 is supplied to a second output 18a-18b through a second rectifying circuit comprising rectifying means, a smoothening choke coil 16 and a smoothening capacitor 17. By doing this, a plurality of outputs are stabilized, the efficiency is improved and noise generation is suppressed thereby providing a compact, high efficiency switching power supply equipment.

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 supplies have been required to be smaller, more stable in output, and more efficient, as electronic devices have become lower in price, smaller in size, higher in performance, and more energy efficient. .

A conventional switching power supply device will be described below. FIG. 6 shows a conventional switching power supply device,
This is a so-called feedforward converter. In FIG. 6, reference numeral 1 denotes a rectifying and smoothing AC voltage with an input DC power source, or a battery or the like. The input voltage is supplied to the input terminals 2a-2b and a positive voltage is supplied to the input terminal 2a
, And a negative voltage is connected to the input terminal 2b. Reference numeral 3 denotes a transformer, one end of the primary winding 3a is connected to the input terminal 2a, the other end is connected to the input terminal 2b via the first switching element 4, and one end of the secondary winding 3b is connected to the rectifier diode 9 The other end is connected to the output terminal 13b. Reference numeral 4 denotes a first switching element, which is turned on / off by an on / off signal VG of the control circuit 20, and applies or cuts off the input voltage VIN to the primary winding 3a of the transformer 3.

A rectifying diode 9 has an anode connected to one end of the secondary winding 3b and a cathode connected to an output terminal 13a via a smoothing choke coil 11. 1
Reference numeral 0 is a rectifying diode, the anode of which is the secondary winding 3b.
Is connected to the connection point between the other end of the output terminal 13b and the output terminal 13b, and the cathode is connected to the connection point between the rectifying diode 9 and the smoothing choke coil 11. 12 is a smoothing capacitor, which is the output terminal 1
It is connected between 3a and 13b. 21 is a capacitor,
22 is a resistor, 23 is a diode, and the capacitor 21
And the parallel connection circuit of the resistor 22 via the diode 23,
The snubber circuit 24 is configured by being connected to both ends of the primary winding 3a. A control circuit 20 has an output terminal 13a-
The voltage between 13b is detected, and the on / off ratio of the first switching element 4 is changed so as to keep the output voltage constant.

The operation of the switching power supply device configured as described above will be described in detail with reference to FIG. 7A to 7F show the operation waveforms of each part of the conventional switching power supply device of FIG. 6, and FIG. 7A shows the ON / OFF signal waveform VG of the control circuit 20 applied to the first switching element 4. Where (b) is the current waveform IL flowing through the primary winding 3a of the transformer 3, (c) is the voltage waveform VDS across the first switching element 4, and (d) is the first switching element. 4 is a current waveform IQ flowing in 4, and (e)
Is the voltage waveform VD across the rectifier diode 10,
(F) is the current waveform ID flowing through the rectifying diode 9.

In order to show the temporal change of the operating state, t1, t
3, t5 are shown in the figure. When turned on by the on / off signal VG of the control circuit 20 at time t1, a spike current flows through the first switching element 4 due to a rapid voltage drop of VDS. This is the charge / discharge current to the distributed capacitance such as the line capacitance and the interlayer capacitance existing between the primary winding 3a and the secondary winding 3b of the transformer 3 or the discharge current or the recovery current of the parasitic capacitance of the rectifying diode. It is due to. This spike current causes an increase in noise, a decrease in reliability, and an increase in loss. First switching element 4
Turns on and VDS becomes sufficiently small, the primary winding 3a
The input voltage VIN is applied to the first switching element 4
Is a sum current of the current supplied from the secondary winding 3b of the transformer 3 to the output through the rectifying diode 9 and the smoothing choke coil 11 and the exciting current that is linearly determined by the inductance value of the primary winding 3a. IQ flows and the exciting current is stored in the transformer 3.

When the first switching element 4 is turned off at the time t2, the current IQ flowing in the first switching element 4 is suddenly cut off, so that the secondary winding 3b
The current that has been supplied to the output via the transformer disappears, and the back electromotive force (hereinafter referred to as the flyback voltage) is generated due to the exciting current already stored in the transformer 3 and the capacitor 2
The voltage VDS across the first switching element 4 rises rapidly until the diode 23 turns on, exceeding the voltage stored in 1, and the rectifying diode 9 also turns off. Due to this rapid change in current and voltage when the first switching element 4 is turned off, large turn-off loss and noise are generated in the first switching element 4. When the first switching element 4 is turned off and the exciting current of the transformer 3 is completely discharged to and absorbed by the capacitor 21 via the diode 23, the flyback voltage also disappears and the inter-winding voltage disappears. First
While the switching element 4 is off, the exciting current stored in the smoothing choke coil 11 causes the rectifying diode 1
The output current IO continues to be supplied via 0.

When the first switching element 4 is turned off at time t5, the first switching element 4 is turned on again and the first operation is repeated to supply a current to the output. On the other hand, the output voltage VO is calculated from the voltage applied to the smoothing choke coil 11 during the ON period of the first switching element 4 and the voltage applied during the OFF period from the reset condition of the smoothing choke coil 11 to (VIN × N−VO ) × TON = VO × TOFF, and VO = (TON / (TON + TOFF)) × VIN × N can be derived. Here, N is the number of windings NP of the primary winding 3a and 2
It is a winding number ratio (N = NS / NP) of the winding number NS of the next winding 3b. Therefore, it is understood that the output voltage VOUT can be controlled by changing the on / off ratio of the first switching element 4. Further, the voltage of the capacitor 21 is balanced by the current discharged by the resistor 22 and the exciting current charged.

FIG. 8 shows another conventional switching power supply device in which the polarity of the transformer of the feedforward converter described in FIG. 6 is inverted to apply a flyback voltage to the output as on-off transmission. Is. In FIG. 8, the same parts as those in FIG.

In FIG. 8, 1 is an input DC power source,
Reference numerals 2a-2b are input terminals, 3 is a transformer, which has a primary winding 3a and a secondary winding 3b, and 4 is a first switching element, which is on / off controlled by a control circuit 19, and 9 and 1
0 is a rectifying diode, 11 is a smoothing choke coil, 12 is a smoothing capacitor, 13a-13b
Is an output terminal. Reference numeral 5 denotes a diode, which has anodes at both ends of the first switching element 4 and the input terminal 2b.
Is connected to the connection point of the switching element 4 and the cathode is connected to the connection point of the primary winding 3a and the first switching element 4, and the current supplied to the output becomes smaller than the exciting current of the transformer 3. , Used when regenerating excess current to the input. A second switching element 7 is on / off controlled by the control circuit 19 and is connected to both ends of the primary winding 3b via the capacitor 30. Reference numeral 8 is a diode, which is connected to both ends of the second switching element 7. The capacitor 30 is the first switching element 4
Stores a part of the exciting current stored in the primary winding 3a during the ON period via the diode 8, and the stored current is returned to the primary winding 3a as an exciting current during the ON period of the second switching element 7. Be done. Reference numeral 19 is a control circuit, which has an output terminal 13a.
The voltage between −13b is detected, and the first switching element 4 and the second switching element 7 are alternately turned on and off so as to keep the output voltage constant, and the on / off ratio is changed.

The operation of the switching power supply device configured as described above will be described in detail with reference to FIG.
9A to 9I show the operation waveforms of each part of the conventional switching power supply device of FIG. 8, and FIG. 9A shows an ON / OFF signal VG1 of the control circuit 19 applied to the first switching element 4. Yes, (b) is an on-off signal VG2 of the control circuit 19 applied to the second switching element 7,
(C) is a current waveform I flowing through the primary winding 3 a of the transformer 3.
L, (d) is the voltage waveform VDS1 across the first switching element 4, (e) is the current waveform IQ1 flowing through the first switching element 4 and the diode 5, (f)
Is the voltage waveform VDS2 across the second switching element 7, and (g) is the second switching element 7 and the diode 8
Is a current waveform IQ2 flowing through the rectifying diode 10, (h) is a voltage waveform VD across the rectifying diode 10, and (i) is a current waveform ID flowing through the rectifying diode 9.

T1 to t5 for indicating the temporal change of the operating state
Is shown in the figure. When the first switching element 4 is turned on by the ON / OFF signal VG1 of the control circuit 19 at time t1, a spike current flows through the first switching element 4 with a rapid voltage drop of VDS1. This is the charge / discharge current to the distributed capacitance such as the line capacitance and the interlayer capacitance existing between each winding of the primary winding 3a and the secondary winding 3b of the transformer 3 or the discharge current or recovery of the parasitic capacitance of the rectifying diode. It is due to the electric current. This spike current causes an increase in noise, a decrease in reliability, and an increase in turn-on loss. The first switching element 4 turns on and VDS
Is sufficiently small, the input voltage VIN is applied to the primary winding 3a of the transformer 3, and at the same time the secondary winding 3a of the transformer 3 is
An induced voltage is generated in b, but at this time, since the diode 9 is connected so as to be off, the current IQ1 of only the exciting current that linearly increases depending on the inductance value of the primary winding 3a flows. During this period, the second switching element 7 is kept off by the on / off signal VG2 of the control circuit 19.

At time t2, the on / off signal VG of the control circuit 19 is
When the first switching element 4 is turned off by 1, the current IQ1 flowing in the first switching element 4 is suddenly cut off, so that the exciting current stored in the transformer 3 causes a fly current to fly to each winding of the transformer 3. When the back voltage is generated and exceeds the voltage stored in the capacitor 30, the first switching element 4 is abruptly increased until the diode 8 is turned on.
The voltage VDS1 between both ends of the voltage rises. Due to the sudden change in current and voltage applied to the first switching element 4, the first
A large turn-off loss and noise are generated in the switching element 4. The exciting current of the transformer 3 is supplied as the output current IO through the secondary winding 3b, the rectifying diode 9 and the smoothing choke coil 11, and the excessive exciting current that cannot be supplied to the output is absorbed by the capacitor 30. .

At time t3, the second switching element 7 is turned on by the ON / OFF signal VG2 of the control circuit 19, but the exciting current of the transformer 3 supplied during the ON period of the second switching element 7 decreases linearly, Output current IO
When it is further reduced, the exciting current absorbed in the capacitor 30 is absorbed by the second switching element 7 and the primary windings 3a, 2
The current that is supplied as a part of the output current IO through the secondary winding 3b and the smoothing choke coil 11 and is supplied to the output is secured.

When the second switching element 7 is turned off at time t4, the current supplied from the capacitor 30 to the output is cut off, so that the exciting current supplied from the transformer 3 to the output cannot maintain the output current I0. This time, the exciting current stored in the smoothing choke coil 11 is supplied to the output current IO through the rectifying diode 10 and the rectifying diode 9 via the secondary winding 3b. As a result, the flyback voltage generated at both ends of the secondary winding 3b is eliminated, so that the voltage between the windings of the transformer 3 is eliminated. During this period, the first switching element 4 is kept off by the on / off signal VG1 of the control circuit 19.

When the first switching element 4 is turned on at time t5, the operation shown at time t1 is repeated, but the input voltage VIN is applied to the primary winding 3a, so that the secondary winding 3
Since an induced voltage is generated in b so as to turn off the rectifying diode 9, the output current IO supplied from the smoothing choke coil 11 is supplied only via the rectifying diode 10.

On the other hand, the output voltage VO is calculated from the voltage applied to the smoothing choke coil 11 during the off period of the first switching element 4 and the voltage applied during the off period from the reset condition of the smoothing choke coil 11 (VC × N-VO) × TOFF = VO × TON, and VO = (TOFF / (TON + TOFF)) × VC × N can be derived. Further, from the reset condition of the transformer 3, the voltage VC across the capacitor 30 becomes VIN × TON = VC × TOFF, and VC = VIN × TON / TOFF can be derived. Now, by summarizing both relational expressions, VO = (TOFF / (TON + TOFF)) × VIN × N can be derived. Here, N is the number of windings NP of the primary winding 3a and 2
It is the winding number ratio of the number of windings NS of the next winding 3b (N = NS / NP), and in order to simplify the formula, the time t2-t3 and t4-t5 periods are sufficiently shorter than the TON and TOFF periods. I can ignore it. Therefore, the output voltage VOUT becomes the first and second
It can be seen that control is possible by changing the on / off ratio of the switching elements 4 and 7 of No. Further, the voltage VC of the capacitor 30 is balanced by the current discharged to the output through the second switching element 7 and the exciting current charged, and the flyback voltage shown by the above equation is held.

[0018]

However, in the configuration of the conventional switching power supply device described above, since the spike current at the time of turn-on of the first switching element 4 and the loss at the time of turn-on and turn-off occur, the conversion efficiency decreases. Or a large amount of noise is generated and reliability is reduced. In particular, in the feed-forward converter of on-on transmission, a loss for processing the exciting current of the transformer 3 and magnetically resetting occurs, and by inverting the polarity of the transformer 3 of the feed-forward converter,
In a converter that uses on-off transmission, all the current supplied to the output is covered by the exciting current. Therefore, the flyback voltage rises sharply when a large exciting current is cut off, and turn-off loss and noise deteriorate. Had.

It is an object of the present invention to eliminate the above-mentioned conventional drawbacks and to provide a switching power supply device which does not generate a spike current and has less noise.

[0020]

In order to solve this problem, a switching power supply device according to the present invention includes a transformer having at least a primary winding and two secondary windings, and an input voltage when an on / off operation is repeated. The first switching means applied to the primary winding of the transformer, the capacitor for holding the counter electromotive voltage generated by the excitation of the transformer, and the first switching means are repeatedly turned on and off to be turned on. There is a second switching means for applying the counter electromotive voltage held in the capacitor to the primary winding of the first transformer at a time, and when the first switching means is on, one of the secondary windings of the transformer is provided. The voltage induced in the winding is supplied to the first output through the first rectifying / smoothing circuit including the rectifying means, the smoothing choke coil, and the smoothing capacitor, and the second switch is supplied. There is a configuration in which the voltage induced in the other secondary winding of the transformer is supplied to the second output through the second rectifying / smoothing circuit including the rectifying means, the smoothing choke coil and the smoothing capacitor when the teaching means is on. is doing.

[0021]

With this configuration, the current supply to the output is on-
In addition to being supplied in the ON state, the exciting current of the transformer can also be used as the output current, which enables efficient power conversion. Furthermore, when the first and second switching means are turned on, the parasitic capacitors of the switching means and the distribution of the transformer are distributed. Since the energy stored in the capacitor is turned on and then turned on, no spike current is generated, and when the first and second switching means are turned off,
It is possible to prevent the generation of spike voltage due to the influence of the leakage inductance of the transformer.

[0022]

(Embodiment 1) 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, the same parts as those in FIG.

Reference numeral 1 is an input DC power source, 2a-2b are input terminals, 3 is a transformer, and a primary winding 3a and two 2
The secondary windings 3b and 3c are provided, and one end of the primary winding 3a is connected to the input terminal 2a and the other end is connected to the input terminal 2b via the first switching element 4, and the secondary winding 3b is rectified. Output terminal 13a via diode 9 and smoothing choke coil 11
-13b, the secondary winding 3c is a rectifier diode 1
4. Output terminal 18a-via smoothing choke coil 16
Connected to 18b. Reference numeral 4 denotes a first switching element, which is turned on / off by the control circuit 19. Reference numeral 5 denotes a diode, the cathode of which is connected to the connection point between the first switching element 4 and the primary winding 3a, and the anode of which is connected to the connection point between the input terminal 2b and the first switching element 4 so that the excitation current becomes excessive. Used when regenerating a large current to the input. Reference numeral 6 denotes a capacitor, which stores a part of the exciting current stored in the primary winding 3a by the first switching element 4 in the ON period via the diode 8 and stores the stored exciting current in the second switching element 7a. Is returned to the primary winding 3a as a reverse excitation current during the ON period. A second switching element 7 is on / off controlled by the control circuit 19 and is connected to both ends of the first switching element 4 via the capacitor 6.
Reference numeral 8 is a diode, which is connected to both ends of the second switching element 7.

Reference numerals 9 and 10 are rectifying diodes, and
Reference numeral 1 is a smoothing choke coil, 12 is a smoothing capacitor, and 13a-13b are output terminals. Reference numeral 14 is a rectifying diode, the anode of which is connected to one end of the secondary winding 3c, and the cathode of which is connected to the output terminal 18a via the smoothing choke coil 16. Reference numeral 15 is a rectifying diode, the anode of which is connected to the connection point of the other end of the secondary winding 3c and the output terminal 18b, and the cathode of which is connected to the connection point of the rectification diode 14 and the smoothing choke coil 16. A smoothing capacitor 17 is connected between the output terminals 18a and 18b. 18a-18b are second output terminals. 1
A control circuit 9 controls the on / off signals VG1 and VG2 that detect the voltage between the output terminals 18a and 18b and change the on / off ratio of the first switching element 4 and the second switching element 7 so that the output voltage becomes constant. To do.

The operation of the switching power supply device configured as described above will be described in detail with reference to FIG. 2A to 2K show the operation waveforms of each part of the switching power supply device of the first embodiment of FIG. 1, and FIG. 2A shows the ON / OFF signal waveform of the first switching element 4 of the control circuit 19. VG1 is shown, (b) shows an ON / OFF signal waveform VG2 of the second switching element 7 of the control circuit 19, and (c) shows a current waveform IL flowing in the primary winding 3a of the transformer 3. (D) shows the voltage waveform VDS1 across the first switching element 4, and (e) shows the current waveform I flowing through the first switching element 4 and the diode 5.
Q1 is shown, (f) shows the voltage waveform VDS2 across the second switching element 7, and (g) shows the current waveform IQ1 flowing through the second switching element 7 and the diode 8, ( h) is the voltage waveform VD1 across the rectifier diode 10, (i) shows the current waveform ID1 flowing through the rectifier diode 9, (j) is the voltage waveform VD2 across the rectifier diode 15, and (k) is Rectifier diode 14
3 shows a current waveform ID2 flowing through the.

T1 to t5 to indicate the temporal change of the operating state
Is shown in the figure. When the first switching element 4 is turned on by the ON / OFF signal VG1 of the control circuit 19 at time t1, the input voltage VIN is applied to the primary winding 3a of the transformer 3, and at the same time, both ends of the secondary windings 3b and 3c of the transformer 3 are applied. Although an induced voltage is generated in the secondary winding 3b, the rectifying diode 9 is connected so as to be blocked by the induced voltage at both ends of the secondary winding 3b, and the rectifying diode 14 is connected so as to be conducted by the induced voltage at both ends of the secondary winding 3c. Therefore, the primary winding 3a
From the secondary winding 3c, the rectifying diode 14, and the smoothing choke coil 16 to the output terminals 18a-18b, the output current IO2 is supplied. During the on period of the first switching element 4, the second switching element 7 continues to be off, so that no current flows through the capacitor 6 and the current flowing through the primary winding 3a increases linearly as determined by the inductance value. The sum current IQ1 of the current and the current supplied to the output flows, and the exciting current is stored in the transformer 3.

On / off signal VG of control circuit 19 at time t2
When the first switching element 4 is turned off at 1, the output current IQ1 flowing through the first switching element 4 is abruptly cut off, so that the exciting current stored in the transformer 3 causes the flywheel to fly to each winding of the transformer 3. The back voltage is generated and exceeds the voltage stored in the capacitor 6 and the diode 8
The voltage across the first switching element 4 rises sharply until the switch turns on, but at the same time a flyback voltage in the direction of turning on the rectifying diode 9 is also generated in the secondary winding 3b. Output terminal 13 through secondary winding 3b, rectifying diode 9, smoothing choke coil 11
The output current IO1 is supplied to a-13b, and an excessive exciting current that cannot be supplied to the output is absorbed by the capacitor 6. Further, since the flyback voltage generated in the secondary winding 3c turns off the rectifying diode 14, the exciting current stored in the smoothing choke coil 16 is output to the output terminals 18a-18b via the rectifying diode 15 at the output current IO2. To supply.

At time t3, the second switching element 7 is turned on by the on / off signal VG2 of the control circuit 19, but the exciting current supplied from the transformer 3 linearly decreases during the off period of the first switching element 4. , When the output current IO1 is reduced, the exciting current component absorbed by the capacitor 6 is already turned on via the second switching element 7, the primary winding 3a, the secondary winding 3b, and the smoothing choke coil 11. Is supplied as a shortage of the output current IO1, the output current IO1 supplied to the output is continuously secured.

When the second switching element 7 is turned off at time t4, the current supplied from the capacitor 6 is cut off, and the output current IO1 cannot be maintained only by the exciting current supplied from the transformer 3 to the output. The exciting current stored in the smooth choke coil 11 is supplied to the output current IO through the rectifying diode 10, the secondary winding 3b, and the rectifying diode 9. As a result, the secondary winding 3b
Since the flyback voltage generated at both ends of the transformer 3 disappears, the voltage between the windings of the transformer 3 disappears. During this period, the first switching element 4 is kept off by the on / off signal VG1 of the control circuit 19.

When the first switching element 4 is turned on at time t5, the operation shown at time t1 is repeated, but the input voltage VIN is applied to the primary winding 3a, so that the secondary winding 3
Since an induced voltage is generated in b so as to turn off the rectifying diode 9, the output current IO1 supplied from the smoothing choke coil 11 is supplied only through the rectifying diode 10.

On the other hand, the output voltage VO1 is already applied to the smoothing choke coil 11 and the transformer 3 during the off period of the first switching element 4 and during the off period, as shown in FIG. 8 of the conventional circuit example. Based on the voltage, the following is shown from the reset condition of the smooth choke coil 11 and the reset condition of the transformer 3.

VO1 = (TOFF / (TON + TOFF)) × VIN × N1 Further, the output voltage VO2 is shown below from the reset condition of the smoothing choke coil 16 as already shown in FIG. 6 of the conventional circuit.

VO2 = (TOFF / (TON + TOFF)) × VIN × N2 Here, N1 is the number of windings NP of the primary winding 3a and the secondary winding 3b.
Is the winding ratio of the number of windings NS1 (N1 = NS1 / NP), N2
Is a winding number ratio (N2 = NS2 / NP) of the number of windings NP of the primary winding number 3a and the number of windings NS2 of the secondary winding 3c. In order to simplify the equation, time t2 to t3, t4 to t5. The period is sufficiently short compared to the TON and TOFF periods and can be ignored. Therefore, it can be seen that the output voltages VO1 and VO2 can be controlled at the same time by changing the on / off ratio of the first and second switching elements 4 and 7.

With this configuration, the circuit system for supplying a current to the output by the on-on transmission and the circuit system for supplying a current to the output by the on-off transmission can be configured on the same transformer 3 and both Since both have the same input / output transfer characteristics, it is possible to stabilize both by controlling either one, and it is also possible to easily take out a plurality of different outputs. As for efficiency, in the case of the conventional on-on type forward converter, the transformer 3 is used.
If the flyback converter is an on-off type, the output current is supplied only by the exciting current of the transformer 3, so that there is a turn-off due to an increase in the switching current. Although there were problems such as an increase in loss, efficiency is improved in this configuration because the output current is supplied both on-on and on-off.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to FIG. FIG. 3 shows the configuration of the switching power supply device according to the second embodiment of the present invention. In FIG. 3, the same components as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted.

Reference numeral 1 is an input DC power source, 2a-2b are input terminals, and 3 is a transformer having a primary winding 3a and secondary windings 3b and 3c. Reference numeral 4 denotes a first switching element, which is turned on / off by the control circuit 19. Reference numeral 5 is a diode, 6 is a capacitor, and 7 is a second switching element, which is turned on / off by the control circuit 19.
8 is a diode, 9 and 10 are rectifying diodes, 11 is a smoothing choke coil, 12 is a smoothing capacitor, 13a-13b are output terminals,
Reference numerals 14 and 15 are rectifying diodes, 16 is a smoothing choke coil, and 17 is a smoothing capacitor. 1
A control circuit 9 detects the voltage between the output terminals 13a and 13b and generates ON / OFF signals VG1 and VG2 for changing the ON / OFF ratio of the first switching element 4 and the second switching element 7 so that the output voltage becomes constant. To do.

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

In FIG. 3, the operation waveforms of the respective parts are the same as those in FIG. 2, and the operation is also completely the same, but the difference from FIG. 1 is that the output circuits of the secondary winding 3b are connected to the output terminals 13a-13b and the output circuit of the secondary winding 3b. Both output circuits of the secondary winding 3c are connected.
In this case, the number of windings NS1 and NS2 of the secondary windings 3b and 3c
The same number of windings, the output current I from both windings
O is taken out, and the current balance between them becomes almost equal. With this configuration, it is possible to prevent a loss due to a circulating current when a plurality of secondary windings are connected in parallel, and to reduce the ripple voltage because the output ripple voltages are generated so as to cancel each other's voltage change. . Here, the smoothing capacitors 12 and 17 may be one. further,
In this example, the outputs are connected in parallel, but the output ripple characteristic can be achieved by configuring the outputs in series.

(Embodiment 3) A third 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 third embodiment of the present invention. 4, the same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

Reference numeral 1 is an input DC power source, 2a-2b are input terminals, and 3 is a transformer having a primary winding 3a and secondary windings 3b and 3c. Reference numeral 4 denotes a first switching element, which is turned on / off by the control circuit 19. Reference numeral 5 is a diode, 6 is a capacitor, and 7 is a second switching element, which is turned on / off by the control circuit 19.
8 is a diode, 9 and 10 are rectifying diodes, 11 is a smoothing choke coil, 12 is a smoothing capacitor, 13a-13b are output terminals,
14 and 15 are rectifying diodes, 16 is a smoothing choke coil, 17 is a smoothing capacitor, and 1
8a-18b are output terminals. Reference numeral 19 denotes a control circuit that detects the voltage between the output terminals 18a and 18b and changes the ON / OFF ratio of the first switching element 4 and the second switching element 7 so that the output voltage becomes constant.
Both G1 and VG2 are generated, and there is a period during which both are turned off.

The operation of the switching power supply device configured as described above will be described in detail with reference to FIG. 5A to 5K show the operation waveforms of each part of the switching power supply device of the third embodiment of FIG. 4, and FIG. 5A shows an ON / OFF signal of the first switching element 4 of the control circuit 19. The waveform VG1 is shown, (b) shows the on / off signal VG2 of the second switching element 7 of the control circuit 19,
(C) is a current waveform I flowing through the primary winding 3 a of the transformer 3.
L shows (L), (d) shows the voltage waveform VDS1 across the first switching element 4, (e) shows the current waveform IQ1 flowing through the first switching element 4 and the diode 5, ( f) shows the voltage waveform VDS2 across the second switching element 7, (g) shows the current waveform IQ2 flowing through the second switching element 7 and the diode 8, and (h) shows the rectifying diode 10 Voltage waveform V at both ends
D1 is shown, (i) shows the current waveform ID1 flowing through the rectifying diode 9, (j) shows the voltage waveform VD2 across the rectifying diode 15, and (k) shows the current waveform ID2 flowing through the rectifying diode 14. ing.

T1 to t5 for indicating the temporal change of the operating state
Is shown in the figure. When the first switching element 4 is turned on by the ON / OFF signal VG1 of the control circuit 19 at time t1, the input voltage VIN is applied to the primary winding 3a of the transformer 3, and at the same time, both ends of the secondary windings 3b and 3c of the transformer 3 are applied. Although an induced voltage is generated in the rectifier diode 9, the rectifier diode 9 connected to the secondary winding 3b is connected so as to cut off the rectifier diode 14 connected to the secondary winding 3c. Therefore, from the primary winding 3a to the secondary winding 3c, the rectifying diode 14, the smoothing choke coil 16
The output current IO2 is supplied to the output terminals 18a-18b via the. The ON period of the first switching element 4 is the second
Since the switching element 7 of continues to be off, the capacitor 6
Current does not flow in the primary winding 3a, and the sum current IQ1 of the linearly increasing exciting current determined by the inductance value and the current supplied to the output flows, and the exciting current is stored in the transformer 3.

At time t2, the on / off signal VG of the control circuit 19
When the first switching element 4 is turned off at 1, the output current IQ1 flowing through the first switching element 4 is suddenly cut off, but the exciting current stored in the transformer 3 is paralleled to the first switching element 4. Since the capacitor 41 connected to the capacitor absorbs and discharges the charge of the capacitor 40, the turn-off loss of the first switching element 4 is reduced by gently suppressing the increase in the flyback voltage. The flyback voltage of each winding of the transformer 3 increases, and the voltage across the first switching element 4 gradually increases until it exceeds the voltage stored in the capacitor 6 and the diode 8 turns on. At the same time, the secondary winding 3b Also, a flyback voltage in the direction of turning on the rectifying diode 9 is generated, and the exciting current of the transformer 3 passes through the secondary winding 3c, the rectifying diode 9, and the smoothing choke coil 11 to the output terminal 13
The output current IO1 is supplied to a-13b, and an excessive exciting current that cannot be supplied to the output is absorbed by the capacitor 6. Further, the flyback voltage generated in the secondary winding 3c is such that the exciting current stored in the smoothing choke coil 16 supplies the output current IO2 to the output terminals 18a-18b via the rectifying diode 15 to turn off the rectifying diode 14. To do.

At time t3, the second switching element 7 is turned on by the on / off signal VG2 of the control circuit 19, but since the diode 8 is turned on at this point, the zero cross turn is turned on, and during the on period of the second switching element 7. The supplied exciting current decreases linearly, and when it decreases from the output current IO1, the exciting current absorbed by the capacitor 6 is absorbed by the second switching element 7 and the primary winding 3
a is supplied as a part of the output current IO1 through the secondary winding 3b and the smoothing choke coil 11, and the current supplied to the output is secured, while the excessive excitation current that cannot be supplied to the output is primary. The transformer 3 is reversely excited via the winding 3a.

When the second switching element 7 is turned off at time t4, the current supplied from the capacitor 6 is suddenly cut off, but the capacitor 40 connected in parallel with the second switching element 7 is stored in the transformer 3. The generated reverse excitation current is absorbed and the electric charge of the capacitor 41 is discharged, and the generation and rise of a counter electromotive voltage (this voltage is a forward voltage because it is an electromotive voltage having a polarity opposite to that of the flyback voltage) are gradually generated. Suppress to. By gently suppressing the rise of the forward voltage, the turn-off loss of the second switching element 7 is reduced. When the forward voltage of each winding of the transformer 3 rises and the voltage generated at both ends of the secondary winding 3c tries to exceed zero, output is performed via the secondary winding 3c, the rectifying diode 14, and the smoothing choke coil 16. The reverse exciting current stored in the transformer 3 is supplied as the current I02. However, when the reverse exciting current is larger than the output current I02, the excess exciting current is used to further charge and discharge the capacitors 40 and 41, so that each winding of the transformer 3 is The forward voltage of the line further rises until the voltage across the primary winding 3a exceeds the input voltage, and the diode 5 turns on. During this time, the voltage generated across the secondary winding 3b is generated so as to turn off the rectifying diode 9, so that the exciting current stored in the smoothing choke coil 11 passes through the rectifying diode 10 and the secondary winding to output the output current 3b. Supplied to IO1. In addition, by the on / off signal VG1 of the control circuit 19, the first
The switching element 4 of is kept off during this period.

When the first switching element 4 is turned on while the diode 5 is on at time t5, zero cross turn-on is achieved, and this time the input voltage VIN is applied to the primary winding 3a. The operation indicated by t1 is repeated. In this way, by setting the time periods t2 to t3 and t4 to t5 at which both the first and second switching elements 4 and 7 are turned off, it is possible to significantly reduce the turn-on and turn-off losses. .

In this operation, the output voltage VO1 is applied to the smoothing choke coil 11 and the transformer 3 during the off period of the first switching element 4 and during the off period, as already shown in FIG. 8 of the conventional circuit example. Based on the applied voltage, the following is shown from the reset condition of the smooth choke coil 11 and the reset condition of the transformer 3.

VO1 = (TOFF / (TON + TOFF)) × VIN × N1 Further, the output voltage VO2 is shown below from the reset condition of the smoothing choke coil 16 as already shown in FIG. 6 of the conventional circuit.

VO2 = (TOFF / (TON + TOFF)) × VIN × N2 Here, N1 is the number of windings NP of the primary winding 3a and the secondary winding 3b.
Is the winding ratio of the number of windings NS1 (N1 = NS1 / NP), N2
Is the number of windings NP of the primary winding 3a and the number of windings NS of the secondary winding 3c
The turn ratio is 2 (N2 = NS2 / NP), and in order to simplify the formula, the time t2 to t3 and t4 to t5 period can be ignored in a sufficiently short period as compared with the TON and TOFF periods. Therefore, the output voltages VO1 and VO2 are changed by changing the on / off ratios of the first and second switching elements 4 and 7,
It can be seen that both output voltages can be controlled simultaneously.

With this configuration, the circuit system for supplying current to the output by on-on transmission and the circuit system for supplying current to the output by on-off transmission can be configured on the same transformer 3, and both Since both have the same input / output transfer characteristics, it is possible to stabilize both by controlling either one, and it is also possible to easily take out a plurality of different outputs. In terms of efficiency, in the case of the conventional on-on type forward converter, the excitation current of the transformer 3 is consumed to cause a loss for reset operation, and in the case of the on-off type flyback converter, the output current is reduced. Since there is a problem such as an increase in turn-off loss due to an increase in switching current, since it is supplied only by the exciting current of No. 3, in this configuration, the output current is supplied by both on-on and on-off. In addition, the loss of turn-on is eliminated by realizing the zero-cross turn-on of the first and second switching elements 4 and 7, and the turn-off loss is greatly reduced. Regarding the generated noise, abrupt changes in voltage and current at the time of turn-on and turn-off of the first and second switching elements 4 and 7 are suppressed and alleviated, so that the generation of noise is significantly reduced.

In the configuration of the third embodiment, it is possible to connect both the output circuit of the secondary winding 3b and the output circuit of the secondary winding 3b in a para connection. In this case, the number of turns NS of the secondary windings 3b and 3c is NS.
By setting 1 and NS2 to the same number of windings, the output currents I0 are taken out from both windings, and the current balances between them are almost equal. With this configuration, in addition to improving efficiency and reducing generated noise in the third embodiment, loss due to circulating current when a plurality of secondary windings are connected in parallel is generated, and output ripple voltages are generated so as to cancel each other's voltage changes. Therefore, there is a feature that a low ripple voltage can be achieved. Here, the smoothing capacitors 12 and 17 may be one. further,
In the third embodiment, the output is connected in series.
Can improve the efficiency, reduce the generated noise, and lower the output ripple voltage.

In this embodiment, diodes 5 and 8 connected in parallel with the first and second switching elements 4 and 7 are used.
If the switching element is an element such as a MOSFET in which a diode is built in parallel with the switching element in advance, the diodes 5 and 8 are unnecessary.

[0053]

As described above, according to the present invention, Example 1
Then, the circuit system that supplies current to the output by on-on transmission and the circuit system that supplies current to the output by on-off transmission can be configured on the same transformer, and both have the same input / output transfer characteristics. Therefore, it is possible to stabilize both by controlling either one, and it is also possible to easily take out a plurality of different outputs. In terms of efficiency, the conventional on-on type forward converter consumes the transformer's exciting current and causes a loss for reset operation, and the on-off type flyback converter has an output current. However, since there is a problem such as an increase in the turn-off loss due to an increase in the switching current, the present invention supplies the output current at both on-on and on-off. Efficiency is improved.

In the second embodiment, the loss due to the circulating current when a plurality of secondary windings are connected in parallel is prevented, and the output ripple voltage is generated so as to cancel the mutual voltage change, so that the ripple voltage can be reduced. In the third embodiment, the circuit system that supplies current to the output by on-on transmission and the circuit system that supplies current to the output by on-off transmission can be configured on the same transformer 3, and both are the same. Since it has an input / output transfer characteristic, it is possible to stabilize both by controlling either one, and it is also possible to easily take out a plurality of different outputs. In terms of efficiency, in the case of a conventional on-on type forward converter, a loss occurs for consuming the exciting current of the transformer 3 to perform a reset operation, and in the case of an on-off type flyback converter, the output current is a transformer. Since it is supplied only by the excitation current of No. 3, there are problems such as an increase in turn-off loss due to an increase in switching current. However, in the present invention, output current is supplied to both on-on and on-off, so that the efficiency is improved. Is improved, and lossless turn-on is realized by realizing zero cross turn-on of switching elements.
It is possible to greatly improve efficiency by greatly reducing turn-off loss. As for generated noise, a sharp change in voltage and current at turn-on and turn-off of the switching element is suppressed and alleviated, so that a switching power supply device in which the generation of noise is significantly reduced is realized.

[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 explanatory diagram showing operation waveforms of the circuit configuration diagram of FIG. 1 of the present invention.

FIG. 3 is a circuit configuration diagram showing a switching power supply device according to a second embodiment of the present invention.

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

FIG. 5 is an explanatory diagram showing operation waveforms of the circuit configuration diagram of FIG. 4 of the present invention.

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

7 is an explanatory diagram showing operation waveforms of the conventional circuit configuration diagram of FIG.

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

9 is an explanatory diagram showing operation waveforms of the conventional circuit configuration diagram of FIG.

[Explanation of symbols]

 1 input DC power supply 2a-2b input terminal 3 transformer 4,7 switching element 5,8 diode 9,10,14,15 rectifying diode 11,16 smoothing choke coil 12,17 smoothing capacitor 13a-13b output terminal 18a-18b output terminal 19 Control circuit

(72) Inventor Takaharu Murakami 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Toshinari Ueyama, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A transformer having at least a primary winding and two secondary windings, a first switching element for applying an input voltage to the primary winding of the transformer when it is repeatedly turned on and off, and the transformer. Is repeatedly turned on and off alternately with the capacitor for holding the counter electromotive voltage generated by the excitation of the first switching element, and the counter electromotive voltage held in the capacitor when turned on is the primary of the first transformer. Having a second switching element applied to the winding,
The voltage induced in one secondary winding of the transformer when the first switching element is on is supplied to the first output through the first rectifying / smoothing circuit including the rectifying means, the smoothing choke coil, and the smoothing capacitor. Then, when the second switching element is on, the voltage induced in the other secondary winding of the transformer is output through the second rectifying / smoothing circuit including the rectifying means, the smoothing choke coil and the smoothing capacitor to the second output. Switching power supply to supply to. 2. An output through the first rectifying and smoothing circuit, and a second
2. The switching power supply device according to claim 1, wherein the output through the rectifying / smoothing circuit is connected in parallel and is supplied to the output. 3. A transformer having at least a primary winding and two secondary windings, a first switching element for applying an input voltage to the primary winding of the transformer when it is repeatedly turned on and off, and the transformer. Is repeatedly turned on and off alternately with the capacitor for holding the counter electromotive voltage generated by the excitation of the first switching element, and the counter electromotive voltage held in the capacitor when turned on is the primary of the first transformer. Having a second switching element applied to the winding,
When a capacitor is connected to both ends of the first switching element or both ends of the second switching element, or both of them, and when on / off is repeated alternately, both the first switching element and the second switching element are turned off. A period of time, and a voltage induced in one of the secondary windings of the transformer when the first switching element is on is passed through a first rectifying / smoothing circuit including rectifying means, a smoothing choke coil, and a smoothing capacitor. Supply 1 output,
The voltage induced in the other secondary winding of the transformer when the second switching element is on is supplied to the second output through the second rectifying / smoothing circuit including the rectifying means, the smoothing choke coil, and the smoothing capacitor. Switching power supply.