JPH05328719A - Switching power supply - Google Patents

Abstract

PURPOSE:To provide a high-efficiency switching power supply for supplying electronic equipment for industrial and consumer purposes with DC regulated voltage, in which low-voltage switching elements can be used. CONSTITUTION:This apparatus is a switching power supply of current resonance primary side regeneration system, in which the primary winding 3a of a transformer 3 is connected with an input DC power supply 1 via a capacitor 13 and leakage inductance or an inductor.

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.

Conventionally, as this type of switching power supply device, a self-excited flyback type switching power supply device has been widely used because it has few constituent parts and can be manufactured at low cost. However, it is known that there are problems that the switching frequency greatly changes depending on the output current, interference with electronic devices and the size of the rectifying / smoothing circuit increase.

As a method of solving such a conventional problem, a switching power supply of a current resonance primary side regenerative system having a configuration as shown in FIG. 5 has already been constructed. In FIG. 5, reference numeral 1 denotes an input DC power source for rectifying and smoothing an AC voltage, or a battery or the like. The input voltage is supplied to an input terminal 2-2 ′ and a positive voltage is connected to the input terminal 2. Then, a negative voltage is connected to the input terminal 2 '.

Reference numeral 3 denotes a transformer, one end of the primary winding 3a being connected to the input terminal 2 via the leakage inductance or the inductance element 14 and the other end being connected to the input terminal 2'through the switching element 4 and 2 One end of the secondary winding 3c is connected to the output terminal 10 'and the other end is connected to the output terminal 1 via the diode 7.
0, one end of the bias winding 3b is connected to the input terminal 2 ', and the other end is connected to the synchronous oscillation circuit 6.

Reference numeral 4 denotes a switching element, which is turned on / off by an on / off signal of the synchronous oscillation circuit 6 applied to the control terminal to apply or cut off the input voltage to the primary winding 3a. Reference numeral 6 denotes a synchronous oscillating circuit, which turns on the switching element 4 for a predetermined on-period and turns off the switching element 4 so that the off-period continues until the polarity of the induced voltage of the bias winding 3b is reversed. ,
Oscillation is continued by repeating this on / off.

Reference numeral 5 denotes a diode, the anode of which is connected to the connection point of the primary winding 3a and the switching element 4 and the cathode of which is connected to the input terminal 2'to regenerate the energy stored in the transformer 3 to the input. Reference numeral 7 denotes a rectifying diode, the anode side of which is connected to one end of the secondary winding 3c and the cathode side of which is connected to the output terminal 10.

A smoothing capacitor 8 has an output terminal 10
-10 ', the induced voltage of the secondary winding 3c is rectified via the rectifier diode 7 and smoothed by the smoothing capacitor 8 to obtain the output voltage. 12 is a rectifying diode, 1
Reference numeral 6 denotes a smoothing capacitor, and the rectifying diode 12 has an anode connected to the connection point between the primary winding 3a and the switching element 4 and a cathode connected to one end of the smoothing capacitor 16 to rectify the primary winding 3a. The diode 12, the smoothing capacitor 16, and the leakage inductance or the inductance element 14 are configured to form a closed circuit.

A second switching element 11 is connected in parallel with the rectifying diode 12 and is turned on / off by the control circuit 9. 9 is a control circuit, and the control circuit 9
It is assumed that the portion connected to the output terminals 10-10 'and the portion driving the switching element 11 are insulated inside.

Reference numeral 14 denotes the primary windings 3a and 2 of the transformer 3.
It is a leakage inductance between the secondary windings 3c or an external inductance element. The smoothing capacitor 16 and the leakage inductance or the inductance element 14 resonate, and are set so that the current waveform of the rectifying diode 7 becomes sinusoidal.

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. 6, (a) shows the switching element 4
2B shows a voltage waveform V _DS across both ends of the primary current I _D flowing in the switching element 4 or the diode 5.
(C) shows the drive pulse waveform V _G1 of the switching element 4 of the synchronous oscillation circuit 6, and (d) shows the primary current I _c flowing through the switching element 11 or the rectifying diode 12. , (E) shows the drive pulse waveform V _G2 to the switching element 11, (f)
Shows the secondary current I _o flowing through the secondary winding 3c, and (g) shows the change of the magnetic flux φ of the transformer 3.

A magnetic flux is generated in the transformer 3 by the primary current I _D flowing through the primary winding 3a during the ON period of the switching element 4 operating in the ON period determined by the synchronous oscillation circuit 6, and energy is accumulated. It At this time, an induced voltage is generated in the secondary winding 3c of the transformer 3, but the voltage is applied in a direction to reverse-bias the rectifying diode 7, and the rectifying diode 12 on the primary side is also reverse-biased and switching is performed. The element 11 is configured to be off.

When the switching element 4 is turned off by the off signal of the synchronous oscillation circuit 6, a flyback voltage is generated in the primary winding 3a, the rectifier diode 12 is forward biased, and at the same time, the secondary winding 3c is also generated. Since the flyback voltage is generated and the voltage is applied in the direction of forward biasing the rectifier diode 7, the energy accumulated in the transformer 3 is converted into the primary current I _c via the primary winding 3 a and the rectifier diode 12. It is discharged, smoothed by the smoothing capacitor 16 and supplied as a DC voltage V _c , and is discharged as a secondary current I _o via the secondary winding 3 c and smoothed by a smoothing capacitor 8 as an output voltage V _OUT. It is supplied to the output terminals 10-10 '.

At this time, the switching element 11 is the control circuit 9
The primary current I _c flows through either the rectifying diode 12 or the switching element 11, but there is no particular change in operation. If the capacitance component such as parasitic capacitance is not considered, the switching element 4 is turned off and the transformer 3
When the voltage of each winding is inverted, the energy stored in the transformer 3 is first discharged from the primary winding 3a due to the influence of the leakage inductance of the transformer 3. That is, the primary current I _c
Flows out with the final value I _P of the primary current I _D as the initial value, 2
The next current I _o rises from zero.

At this time, since the rectifying diode 7 and the rectifying diode 12 are turned on, the current flowing through each winding is equal to the smoothing capacitor 16 connected by the primary winding 3a and the secondary winding 3c of the transformer 3 and the leakage inductance or It becomes a transient current of a closed circuit composed of the inductance element 14 and the smoothing capacitor 8. This current is a sinusoidal resonance current because the resonance frequency of the capacitor 16 and the leakage inductance or the inductance element 14 is set sufficiently small.

At this time, the magnetic flux φ of the transformer 3 is equal to the primary winding 3
Since the stored energy is released when the DC voltage V _c is applied to a, it linearly decreases. Secondary winding current I _o
Is the sum of the exciting current that induces the magnetic flux φ and the primary winding current that is the resonance current.

Since the resonance current is set to have a sufficiently small resonance period, the secondary winding current I _o will eventually decrease to 0 A.
And the rectifying diode 7 is turned off. As the primary winding current I _{c, a} sinusoidal resonant current flows when the rectifying diode 7 is on, but when the rectifying diode 7 is off, the resonant current becomes zero and only the exciting current flows.

In this process, the primary winding current I _c becomes negative, but since the switching element 11 is turned on, the resonance phenomenon is maintained, and conversely, the discharge current from the smoothing capacitor 16 causes the switching element 11 to turn on. Through the primary winding 3a
To flow to. Even after the energy stored in the transformer 3 is released during the ON period of the switching element 4, the transformer 3 is reversely excited and the energy is stored in the reverse direction by applying the DC voltage V _c by the switching element 11. ..

The switching element 11 is controlled by the control circuit 9.
Is turned off, each winding voltage of the transformer 3 is inverted, and the induced voltage generated in the primary winding 3a is generated in a direction in which the connection end of the switching element 4 is set to a negative voltage and the connection end of the input terminal 2 is set to a positive voltage. Therefore, input DC power supply 1 via diode 5
The primary current I _D flows in the direction to charge the DC power, and the energy of the transformer 3 accumulated during the off period is regenerated to the input DC power supply 1.

At this time, the synchronous oscillating circuit 6 turns on the switching element 4, but there is no particular change in operation no matter which one of the primary currents I _D flows. When all the energy accumulated in the transformer 3 is released during the off period and the primary current becomes zero, the primary current is charged from the input DC power supply 1 in the opposite direction via the switching element 4 which is already on. A current I _D flows and a magnetic flux is generated in the transformer 3 to accumulate energy.

In this state, the polarity of the induced voltage generated in each winding of the transformer 3 does not change, and the synchronous oscillation circuit 6 keeps the switching element 4 on. Switching element 4 that operates in the ON period determined by the synchronous oscillation circuit 6
When is turned off, the energy stored in the transformer 3 passes through the primary winding 3a and the smoothing capacitor 13 and the 2
The secondary current I _o is discharged to the output through the secondary winding 3c. By repeating these operations, the output voltage is continuously supplied from the output terminals 10-10 '.

Further, the operation of stably controlling the output voltage will be described in detail. Each operation waveform is shown in FIG. 6, and the OFF period (t _{1 to} t ₃ ) of the drive pulse waveform V _G1 of the synchronous oscillation circuit 6 is set to T _OFF, and the reverse excitation period (t _{2 to} t) of the transformer 3 is included therein. the ₃₎ T 'and _{oF F,} whereas on period (t ₃ ~t ₅₎ and T _oN, of which the primary current I regeneration period of _D to (t ₃ ~t ₄₎ T' is _{turned oN.} During stable operation of the conventional switching power supply, the DC voltage V _c is the sum of the DC component and the resonance voltage of the smoothing capacitor 16 and the leakage inductance or the inductance element 14, but the voltage fluctuation can be sufficiently small.

On the other hand, the primary current I _c during the off period, which is the ripple current of the smoothing capacitor 13, has the same charge / discharge current,
Since the average current is 0 A, the energy discharged from the secondary winding 3c and supplied from the output terminal 10-10 'is from the energy stored in the transformer 3 during the _ON period, during the _T'ON period. It becomes equal to the difference in energy regenerated to the input DC power supply 1. On the other hand the average value V _c of the DC voltage is represented by a transformer reset condition _{V c = (T ON / T} OFF) × V IN = (T 'ON / T' OFF) × V IN. However, V _IN is an input voltage. Further, the output voltage V _OUT of the conventional switching power supply device is the secondary winding 3
obtained by rectifying the flyback voltage of c, a _{V OUT ≒ (N S / N} P) × V c because it can reduce the voltage variation width of the well V _c, by adjusting the DC voltage V _c, It can be seen that the output voltage V _OUT can also be adjusted. However, N _P is the number of turns of the primary winding 3a, and N _S is the number of turns of the secondary winding 3c.

Even if the fluctuation range of V _c is large, V _OUT can be controlled by controlling the average value of V _c . For example, when the output current I _OUT decreases and the output voltage V _OUT increases, the control circuit 9 controls the ON period of the switching element 11 (that is,
The OFF period T _OFF of the switching element 4 becomes large,
The smoothing capacitor 13 has a larger amount of discharged charge than charged charge, and the average value of the DC voltage V _c decreases.

When the DC voltage V _c decreases, the output voltage V _OUT also decreases, and the V _c generated / applied to the winding of the transformer 3 during the off period decreases, so that the inclination of the primary current I _c is also reduced. Eventually, the output voltage V _OUT settles down to the DC voltage V _{c at} which it becomes a predetermined voltage.

That is, the output voltage V _OUT can be stabilized by adjusting the ON period of the switching element 11.
Originally, the fluctuation amount of the DC voltage V _c for compensating the fluctuation (load regulation) of the output voltage V _OUT accompanying the fluctuation of the output current I _OUT is small, and therefore, if the _ON period T _ON is constant, the OFF period T _OFF is almost constant. It does not fluctuate, and the switching frequency and the magnetic flux change width ΔB are almost constant. This state is represented by the broken line in FIG.

Further, in this circuit configuration, the smoothing capacitor 1
6 and the rectifying diode 12 constitute a clamp circuit, and there is also an effect that no surge voltage is generated due to the turn-off of the switching element 4 shown in the first conventional example.

[0029]

[SUMMARY OF THE INVENTION However, the switching element 4 and switching element 11, the input sum voltage V _IN + V _c voltage V _IN and the DC voltage V _c is applied, it is necessary to high voltage switching element In addition, since the input voltage is directly applied to the primary winding 3a of the transformer 3 in the ON state of the switching element 4, there is a problem that the number of primary windings increases.

The present invention solves the above-mentioned problems of the prior art by suppressing changes in the switching frequency due to changes in the load and, at the same time, suppressing the occurrence of diode recovery and reducing noise and high efficiency current resonance primary side regeneration. An object of the present invention is to provide a high-efficiency switching power supply device that enables use of a low breakdown voltage switching element without impairing the effectiveness of the control type switching power supply device and further reduces the number of primary windings of a transformer. It is a thing.

[0031]

In order to achieve this object, a switching power supply device according to the present invention comprises a first switching means which repeats on / off, at least a primary winding and one or more secondary windings. , A capacitor for holding a DC voltage, and an input voltage when the first switching means is on, applied to the series circuit of the primary winding of the transformer and the capacitor to apply energy to the transformer. A rectifying / smoothing means for storing and obtaining an output from the energy emitted from the secondary winding of the transformer when the first switching means is off, and a second rectifying / smoothing means for alternately repeating on / off with the first switching means. The DC voltage is applied to the primary winding of the transformer via switching means to store energy in the transformer, and the second switching means When off, the energy stored in the transformer is regenerated from the primary winding of the transformer to the input voltage, and the output voltage is controlled by changing the on / off ratio of the first and second switching means. And a leakage inductance between the primary winding and the secondary winding of the transformer or an external inductance element in a closed circuit composed of the rectifying and smoothing means coupled by the transformer and the capacitor. Resonance is caused by the first rectifying / smoothing means, the capacitor, or both, and the resonance phenomenon causes the current in the secondary winding to become a resonance current.

[0032]

With this configuration, when the first switching means is off, the second switching means is on and only the input voltage is applied to the first switching means. Similarly, when the second switching means is off, the first switching means is on and only the input voltage is applied to the second switching means. Furthermore, in order to hold the flyback voltage of the transformer, a DC voltage opposite to the input voltage is generated in the capacitor,
When the first switching means is ON, the difference voltage between the input voltage and the DC voltage is applied to the primary winding of the transformer, so that the number of primary windings can be reduced.

[0033]

(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 according to the first embodiment of the present invention. In FIG. 1, the same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. 1 is a DC power supply, 2-2 '
Is an input terminal, 3 is a transformer having a primary winding 3a, a secondary winding 3c, and a bias winding 3b, and 4 is a switching element as a first switching means.
Is a diode, 6 is a synchronous oscillating circuit, 7 is a rectifying diode, 8 is a smoothing capacitor, and the rectifying diode 7 and the smoothing capacitor 8 constitute a rectifying and smoothing means. Reference numeral 9 is a control circuit, and 10-10 'is an output terminal.

A switching element 11 serves as a second switching means and is turned on / off by the control circuit 9. The control circuit 9 internally has an output terminal 10-1.
It is assumed that the portion connected to 0'and the portion driving the switching element 11 are insulated. 12 is a rectifying diode and 13 is a capacitor. Reference numeral 14 is a leakage inductance between the primary winding 3a and the secondary winding 3c of the transformer 3 or an external inductance element. The capacitor 13 and the leakage inductance or the inductance element 14 resonate with each other, and are set so that the current waveform of the rectifying diode 7 becomes sinusoidal.

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) shows the switching element 4
2B shows a voltage waveform V _DS across both ends of the primary current I _D flowing in the switching element 4 or the diode 5.
(C) shows the drive pulse waveform V _G1 of the switching element 4 of the synchronous oscillation circuit 6, and (d) shows the primary current I _c flowing through the switching element 11 or the rectifying diode 12. (E) shows the drive pulse waveform V _G2 to the switching element 11, (f)
Shows the secondary current I _o flowing through the secondary winding 3c, and (g) shows the change of the magnetic flux φ of the transformer 3.

During the ON period of the switching element 4 which operates in the ON period determined by the synchronous oscillation circuit 6, the input voltage V _IN and the DC voltage held by the capacitor 13 are passed through the capacitor 11 to the primary winding 3a of the transformer 3. the difference V _iN -V _c voltage between V _c is applied, the magnetic flux in the transformer 3 is generated energy by the primary current I _D flows through the primary winding 3a is accumulated. At this time, an induced voltage is generated in the secondary winding 3c of the transformer 3, but the voltage is applied in a direction to reverse-bias the rectifying diode 7, and the rectifying diode 12 on the primary side is also reverse-biased, and switching is performed. The element 11 is configured to be off.

At this time, only the input voltage V _IN is applied to the switching element 11. When the switching element 4 is turned off by the off signal of the synchronous oscillation circuit 6, a flyback voltage is generated in the primary winding 3a, and the rectifier diode 12 is forward biased, and at the same time, the flyback voltage is also applied to the secondary winding 3c. Is generated and a voltage is applied in the direction of forward biasing the rectifying diode 7, the energy accumulated in the transformer 3 is released as a primary current I _c through the primary winding 3a and the rectifying diode 12. It is smoothed by the capacitor 13 and supplied as a DC voltage V _c , and is discharged as a secondary current I _o through the secondary winding 3 c,
The output voltage V _OUT is smoothed by the smoothing capacitor 8 and supplied to the output terminals 10-10 '.

At this time, the switching element 11 is the control circuit 9
The primary current I _c flows through either the rectifying diode 12 or the switching element 11, but there is no particular change in operation. The DC voltage V _c is V _c = [T _ON / (T _ON + T _OFF )] × V _IN from the reset condition of the transformer 3. At this time, it is obvious that only the input voltage V _IN is applied to the switching element 4. If the capacitance component such as the parasitic capacitance is not considered, when the switching element 4 is turned off and the voltage of each winding of the transformer 3 is inverted, the energy stored in the transformer 3 is firstly affected by the leakage inductance of the transformer 3. It is discharged from the winding 3a. That is, the primary current I _c flows with the final value I _P of the primary current I _D as an initial value, and the secondary current I _o rises from zero.

At this time, since the rectifying diode 7 and the rectifying diode 12 are turned on, the current flowing through each winding is leakage inductance or inductance with the capacitor 13 coupled by the primary winding 3a and the secondary winding 3c of the transformer 3. It becomes a transient current of a closed circuit composed of the element 14 and the smoothing capacitor 8. This current is a sinusoidal resonance current because the resonance frequency of the capacitor 13 and the leakage inductance or the inductance element 14 is set sufficiently small.

At this time, the magnetic flux φ of the transformer 3 is equal to the primary winding 3
Since the stored energy is released when the DC voltage V _c is applied to a, it linearly decreases. Secondary winding current I _o
Is the sum of the exciting current that induces the magnetic flux φ and the primary winding current that is the resonance current. Since the resonance current is set to have a sufficiently small resonance period, I _o will eventually decrease to 0 A,
The rectifying diode 7 is turned off.

As for the primary winding current I _{c, a} sinusoidal resonant current flows when the rectifying diode 7 is on, but when the rectifying diode 7 is off, the resonant current becomes zero and only the exciting current flows.

In this process, the primary winding current I _c becomes negative, but since the switching element 11 is turned on, the resonance phenomenon is maintained, and conversely, the discharge current from the capacitor 13 passes through the switching element 11. Flow to the primary winding 3a. Even after the energy stored in the transformer 3 is released during the ON period of the switching element 4, the transformer 3 is reversely excited and the energy is stored in the reverse direction by applying the DC voltage V _c by the switching element 11. ..

The switching element 11 is controlled by the control circuit 9.
Is turned off, each winding voltage of the transformer 3 is inverted, and the induced voltage generated in the primary winding 3a is generated in a direction in which the connection end of the switching element 4 is set to a negative voltage and the connection end of the input terminal 2 is set to a positive voltage. Therefore, input DC power supply 1 via diode 5
The primary current I _D flows in the direction to charge the DC power, and the energy of the transformer 3 accumulated during the off period is regenerated to the input DC power supply 1.

At this time, the synchronous oscillating circuit 6 turns on the switching element 4, but there is no particular change in operation no matter which one of the primary currents I _D flows. When all the energy accumulated in the transformer 3 is released during the off period and the primary current becomes zero, the primary current is charged from the input DC power supply 1 in the opposite direction via the switching element 4 which is already on. A current I _D flows and a magnetic flux is generated in the transformer 3 to accumulate energy.

In this state, the polarity of the induced voltage generated in each winding of the transformer 3 does not change, and the synchronous oscillation circuit 6 keeps the switching element 4 on. Switching element 4 that operates in the ON period determined by the synchronous oscillation circuit 6
There is turned off, the energy stored in the transformer 3 and the capacitor 13 through the primary winding 3a, it is discharged to the output through the secondary winding 3c as the secondary current I _o. By repeating these operations, the output voltage is continuously supplied from the output terminals 10-10 '.

Further, the operation of stably controlling the output voltage will be described in detail. Each operation waveform is shown in FIG. 2. The OFF period (t _{1 to} t ₃ ) of the drive pulse waveform V _G1 of the synchronous oscillation circuit 6 is set to T _OFF, and the reverse excitation period (t _{2 to} t) of the transformer 3 is included therein. the ₃₎ T 'and _{oF F,} whereas on period (t ₃ ~t ₅₎ and T _oN, of which the primary current I regeneration period of _D to (t ₃ ~t ₄₎ T' is _{turned oN.}

During stable operation of the switching power supply according to the present invention, the DC voltage V _c is equal to the DC component and the capacitor 13
Is the sum of the resonance voltage of the leakage inductance or the inductance element 14, but the voltage fluctuation can be suppressed sufficiently small. Meanwhile primary current I _c during the off period is a ripple current of the capacitor 13 is equal charge and discharge current, because the average current is 0A, is released from the secondary winding 3c, supplied from the output terminal 10-10 ' The generated energy is equal to the difference between the energy stored in the transformer 3 during the _ON period and the energy regenerated to the input DC power supply 1 during the _T'ON period.

Further, the output voltage V _OUT of the switching power supply device according to the present invention is obtained by rectifying the flyback voltage of the secondary winding 3c, and the voltage fluctuation width of V _c can be sufficiently reduced, so V _OUT ≈ (N _S / N _P ) × V _c , and it can be seen that the output voltage V _OUT can also be adjusted by adjusting the DC voltage V _c . However, N _P is the number of turns of the primary winding 3a, and N _S is the number of turns of the secondary winding 3c. V _c
V by even significant width of variation to control the average value of V _c
OUT is controllable.

For example, when the output current I _OUT decreases and the output voltage V _OUT increases, the control circuit 9 increases the ON period of the switching element 11 (that is, the OFF period T _OFF of the switching element 4) and the capacitor 13 The amount of discharged electric charge becomes larger than the amount of charged electric charge, and the average value of the DC voltage V _c decreases.

When the DC voltage V _c decreases, the output voltage V _OUT also decreases, and the V _c generated / applied to the winding of the transformer 3 during the off period decreases, so that the slope of the primary current I _c also relaxes. Eventually, the output voltage V _OUT settles down to the DC voltage V _{c at} which it becomes a predetermined voltage. That is, the output voltage V
_OUT can be stabilized by adjusting the ON period of the switching element 11. Originally, the variation of the DC voltage V _c for compensating the variation (load regulation) of the output voltage V _OUT due to the variation of the output current I _OUT is small,
Therefore, if the ON period T _ON is constant, the OFF period T _OFF hardly changes, and the switching frequency and the magnetic flux change width ΔB
Is almost constant.

This state is represented by the broken line in FIG. Further, in this circuit configuration, the capacitor 13 and the diode 12 are
The clamp circuit is configured by, and there is also an effect that no surge voltage is generated due to the turn-off of the switching element 4 shown in the first conventional example.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows the configuration of the switching power supply according to the second embodiment of the present invention. In FIG. 3, the same parts as those in FIG. 1 is a DC power supply, and 2-
2'is an input terminal, 3 is a transformer, a primary winding 3a,
It has a secondary winding 3c and a bias winding 3b, 4 is a switching element as a first switching means, 5 is a diode, 6 is a synchronous oscillation circuit,
Reference numeral 7 is a rectifying diode, 8 is a smoothing capacitor, and the rectifying diode 7 and the smoothing capacitor 8 constitute a first rectifying and smoothing circuit. 9 is a control circuit, 10-1
0'is an output terminal.

A switching element 11 as a second switching means is turned on / off by the control circuit 9. The control circuit 9 internally has an output terminal 10-1.
It is assumed that the portion connected to 0'and the portion driving the switching element 11 are insulated. 12 is a rectifying diode and 13 is a capacitor. Reference numeral 14 is a leakage inductance between the primary winding 3a and the secondary winding 3c of the transformer or an external inductance element. The capacitor 13 and the leakage inductance or the inductance element 14 resonate and are set so that the current waveform of the rectifying diode 7 is sinusoidal.

Reference numeral 15 denotes a capacitor, which is connected to both ends of the switching element 4 and suppresses a sharp change in the voltage applied to the switching element 4 and the switching element 11. The switching element 4 and the switching element 1
1 turns on the control circuit 9 so that it has an off period at the same time.
The off signal and the on / off signal of the synchronous oscillation circuit 6 are set.

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. 4, (a) shows the switching element 4
2B shows a voltage waveform V _DS across both ends of the primary current I _D flowing in the switching element 4 or the diode 5.
(C) shows the drive pulse waveform V _G1 of the switching element 4 of the synchronous oscillation circuit 6, and (d) shows the primary current I _c flowing through the switching element 11 or the rectifying diode 12. , (E) shows the drive pulse waveform V _G2 to the switching element 11, (f)
Shows the secondary current I _o flowing through the secondary winding 3c, and (g) shows the change of the magnetic flux φ of the transformer 3.

The basic operation is the same as that of the circuit configuration of the first embodiment, but the switching element 4 and the switching element 11 have an off period at the same time, and the switching element 4 and the switching element 11 are applied during that period. Voltage is set to change. Since the capacitor 15 is connected to both ends of the switching element 4, the turn-off of the switching element 4 and the steep rise and fall of the voltage waveform at the time of turn-off are alleviated, and the electric charge stored in the capacitor 15 is supplied to the input DC power supply. Since the switching element 4 can be turned on after regeneration, there is no turn-on loss of the switching element 4. A similar effect also exists in the switching 11.

The operation other than the transition is similar to that of the embodiment described with reference to FIG. When these capacitors are added, the output impedance of each winding of the transformer 3 changes at the time of transition, and especially the initial current value of each winding current when the switching element 4 is turned off changes, but this does not affect the control operation itself. In addition to the effect of using the secondary winding current waveform as the resonance current, the voltage waveforms applied to the switching element 4 and the switching element 11 are not steep, so that the generation of noise is suppressed and the switching element 4 and the switching element 11 are suppressed. There is also an effect that the occurrence of switching loss 11 is suppressed. Furthermore, in this circuit configuration,
The clamp circuit is composed of the capacitor 13 and the diode 12, and there is also an effect that no surge voltage is generated due to the turn-off of the switching element 4 shown in the first conventional example.

[0060]

As described above, according to the present invention, the switching frequency and the variation width of the magnetic flux of the conventional current resonance primary side regeneration type switching power supply device hardly change due to the load, and the zero cross turn-on can be realized. At the same time, the turn-off current of the rectifying / smoothing means connected to the secondary side can be reduced to zero or small, and the withstand voltage of the switching element can be lowered without impairing the characteristics that loss and noise can be effectively suppressed. Since the excitation voltage of the transformer is small, the number of primary windings can be reduced and the loss can be reduced, and a small size, high efficiency, and low noise switching power supply device 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 operating 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 an explanatory diagram showing operating waveforms of the circuit configuration diagram of FIG. 2 of the present invention.

FIG. 5 is a circuit configuration diagram of a switching power supply device in a conventional example.

FIG. 6 is an explanatory diagram showing operating waveforms of the conventional circuit configuration diagram of FIG. 5;

[Explanation of symbols]

 1 Input DC power supply 2-2 'Input terminal 3 Transformer 4 Switching element 5 Diode 6 Synchronous oscillation circuit 7 Rectifying diode 8 Smoothing capacitor 9 Control circuit 10-10' Output terminal 11 Switching element 12 Rectifying diode 13 Capacitor 14 Leakage inductance or inductance element 15 capacitor 16 smoothing capacitor

Claims (2)

[Claims] 1. A first switching means for repeating on / off, a transformer having at least a primary winding and one or more secondary windings, a capacitor for holding a DC voltage, and the first switching means. When the switching means is on, the input voltage is applied to the series circuit of the primary winding of the transformer and the capacitor to store energy in the transformer,
Through a rectifying and smoothing means for obtaining an output from the energy emitted from the secondary winding of the transformer when the switching means is off, and a second switching means for alternately turning on and off with the first switching means. The DC voltage is applied to the primary winding of the transformer to store energy in the transformer, and when the second switching means is off, the energy stored in the transformer is input from the primary winding of the transformer to the input voltage. Is configured to perform voltage control of the output by changing the ON / OFF ratio of the first and second switching means, and is configured by the rectifying / smoothing means and the capacitor coupled by the transformer. In the closed circuit, the leakage inductance between the primary winding and the secondary winding of the transformer or an external inductance element The first rectifying and smoothing means or said resonates capacitor, or both, switching power supply and resonant current current of the secondary winding by the resonance phenomenon. 2. Both ends of the first switching means or the second
2. A capacitor is connected to both ends or both of the switching means of 1), and both the first switching means and the second switching means have a period in which they are turned off, so that they are alternately turned on and off. Switching power supply.