JPH08294278A - Switching power supply device - Google Patents

Abstract

PURPOSE: To improve the power factor of the AC power inputted into a diode bridge with a simple circuit configuration. CONSTITUTION: The full wave of the AC voltage from an AC power source 1 is rectified by a diode bridge 2, and the rectified output is applied to the primary winding Np while a switching element 4 is on. The voltage induced to the secondary winding Ns is rectified and smoothed by a rectifier and smoothing circuit 16 to output DC output voltage Vout. When the switching element 2 is off, the energy accumulated in the inductor 13 of the rectifier and smoothing circuit 16 is taken out from the primary chalk winding NLp to change a capacitor C2 of large capacitance through a rectifier circuit (diode D1) and, when the voltage becomes a prescribed one, apply it to the primary winding Np of a transformer 3 through the second diode D2 together with the output of the diode bridge 2. As a result, the outputted current of the diode bridge 2 runs through the period of a valley in pulsating current, and AC current runs around zero of AC voltage, thus improving power factor.

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 used as a DC power supply for various electronic devices.

[0002]

2. Description of the Related Art In recent years, switching power supply devices (also called switching regulators) have been used as DC power supplies for electronic equipment.
Has become popular. FIG. 10 shows an example of a conventional circuit configuration of the switching power supply device. This is a capacitor input type, 1 is an AC power supply, 2 is a diode bridge for full-wave rectifying the AC voltage from the AC power supply 1, and C1 is a voltage smoothed between the output terminals a and b rectified by the diode bridge 2. It is a capacitor.

Reference numeral 3 is a transformer for converting the DC voltage smoothed by the capacitor C1, and has a primary winding Np and a secondary winding Ns. A switching element 4 is connected in series with the primary winding Np of the transformer 3, and its series circuit is connected between the output terminals a and b of the diode bridge 2.
Reference numeral 5 is a control circuit for controlling the switching element 4 on / off.

A rectifying / smoothing circuit 6 rectifies and smoothes the AC voltage generated in the secondary winding Ns of the transformer 3 and outputs the rectified diode 7, a choke coil 8 for smoothing.
And a capacitor 10 and a commutation diode 9. Output terminals 11 and 12 output the voltage across the capacitor 10 as a DC output voltage Vout, and this voltage Vout is also fed back to the control circuit 5.

According to this switching power supply device, the AC voltage from the AC power supply 1 is full-wave rectified by the diode bridge 2 and then converted into a DC voltage by smoothing the ripple component removed by the capacitor C1. . This DC voltage is applied to the series circuit of the primary winding Np of the transformer 3 and the switching element 4.

The switching element 4 is turned on / off by applying a rectangular wave drive signal from the control circuit 5 to the control terminal (base), so that the DC voltage applied to the primary winding Np of the transformer 3 is controlled. To switch. Due to this switching, an AC voltage is generated in the secondary winding Ns of the transformer 3, the AC voltage is converted into a DC voltage by the rectifying and smoothing circuit 6, and the DC output voltage Vout is output from the output terminals 11 and 12.
And is fed back to the control circuit 5.

In the rectifying / smoothing circuit 6, the switching element 4
When is on, current flows through the diode 7 and the choke coil 8 to charge the capacitor 10. Further, when the switching element 4 is on, the energy stored in the choke coil 8 is released through the capacitor 10 and the commutation diode 9 when the switching element 4 is off, and the charging current continues to flow through the capacitor 10.

Further, the control circuit 5 performs, for example, pulse width control, generates a drive signal having a duty ratio according to the voltage fed back, controls the on / off time ratio of the switching element 4, and outputs the output terminal. A predetermined DC output voltage Vout is obtained between 11 and 12.

FIG. 11 shows the voltage and current waveforms at various points in FIG. 10, where (a) is the AC voltage waveform applied from the AC power supply 1 to the diode bridge 2, and (b) is the output voltage waveform from the diode bridge 2. Contains a ripple component. (C) is the output current waveform of the diode bridge 2,
The pulsating current flows only during a period from when the absolute value of the voltage of (a) exceeds the voltage of (b) to when it reaches a peak.
(D) is the input current waveform of the diode bridge 2,
The current flows in the direction corresponding to the polarity of the voltage of (a) for the same period as the output current of (c).

In such a switching power supply device, a capacitor C1 for removing the ripple component of the rectified output of the diode bridge 2 is generally large in capacity. Therefore, the current flowing into the capacitor C1 becomes a pulsating current with a high peak value as shown in FIG. 9C, resulting in a reduction in the power factor of the circuit.

There is also a problem that the charging / discharging current of the capacitor C1 causes the internal loss of the capacitor C1 to generate heat, resulting in a decrease in its life. Further, since the input power is large, noise is increased due to the generation of the switching frequency and its harmonics, which adversely affects the switching power supply device or other devices sharing the AC power supply 1.
Therefore, a large capacity noise filter circuit is required.

Further, there is a choke input type in which the drawback is improved in order to prevent the decrease of the power factor due to the above-mentioned capacitor input type, but an inductance of several mH or more is required, and the choke coil becomes extremely large. Therefore, there has been a problem that the power supply device is increased in size and price. In order to solve such a problem, conventionally, for example, JP-A-3-65050, JP-A-3-273865, and JP-A-2-2
There is also a switching power supply device (switching regulator) as disclosed in Japanese Patent No. 66868.

The switching regulator disclosed in Japanese Patent Laid-Open No. 3-65050 is provided with a reset winding as a tertiary winding in a transformer and resets a current due to a flyback pulse generated in the transformer when a switching element is turned off. A capacitor different from the smoothing capacitor is charged through the winding, and the voltage of this capacitor and the voltage of the conventional smoothing capacitor (corresponding to the capacitor C1 in FIG. 8) are applied to the primary winding of the transformer. ing. Thereby, the current can be made to flow even in the valley portion of the pulsating current of the output current of the diode bridge, and the power factor can be improved.

The switching regulator disclosed in Japanese Patent Laid-Open No. 273865/1990 has two systems of a transformer and a switching element, one transformer is provided with a reset winding as a tertiary winding, and the other is provided. A capacitor is connected in parallel with the primary winding of the transformer, and the capacitor is charged with the current of the flyback pulse generated when the switching element on the one transformer side is turned off.
By applying the charging voltage and the voltage of the smoothing capacitor to the primary winding of the other transformer, the power factor is improved.

Further, in the one disclosed in Japanese Patent Laid-Open No. 2-266868, the voltage obtained by switching the DC voltage obtained by the diode bridge and the smoothing capacitor by four switching elements at a predetermined timing is passed through a transformer. After boosting by rectification and smoothing, the reference sine wave is amplitude-modulated with the DC output voltage, the modulated signal is phase-synchronized with the input AC voltage, and then the clock pulse is amplitude-modulated, and the modulated signal The waveform distortion is reduced by controlling the on / off timings of the four switching elements according to the above.

[0016]

However, the above-mentioned JP-A-3-65050 and JP-A-3-273865.
In the device disclosed in Japanese Patent Publication, the structure of the transformer is complicated because a tertiary winding is provided in the transformer, the transformer becomes large, and there are problems in terms of creepage distance and protection in terms of safety standards. Also, the energy of the flyback pulse changes greatly depending on the size of the load, and the charging voltage to the capacitor also changes greatly. Therefore, the ripple of the capacitor output becomes large. That is, there arises a problem that the power factor is deteriorated when the load is light or heavy. Also, the leakage magnetic flux is large, which adversely affects noise.

Further, in the case of the one disclosed in Japanese Patent Laid-Open No. 3-273865, two transformers are used to take out a small amount of electric power from two systems, and there is a problem that the structure becomes complicated and the cost becomes high. Occurs. Furthermore, JP-A-2-26
The device described in Japanese Patent No. 6868 also requires four switching elements and their respective control circuits, so that there is a problem that the circuit configuration becomes very complicated and the cost becomes high.

The present invention has been made in view of the above circumstances, and an object thereof is to improve the power factor, stability, and reliability which are simple in structure, inexpensive, and independent of load fluctuations. To do. Therefore, the current is made to flow in the period of the valley of the pulsating current in the output current waveform of the diode bridge,
An object of the present invention is to provide a switching power supply device capable of passing a current even when the AC voltage is near zero voltage.

[0019]

SUMMARY OF THE INVENTION According to the present invention, as described above, a diode bridge for full-wave rectifying an AC input and a primary winding connected in series with a switching element are provided between output terminals of the diode bridge. A transformer, a rectifying / smoothing circuit that rectifies and smoothes and outputs an AC voltage generated in the secondary winding of the transformer, and a control circuit that controls ON / OFF of the switching element according to the output voltage of the rectifying / smoothing circuit. In order to achieve the above-mentioned object, a switching power supply device including and is as follows.

The rectifying and smoothing circuit includes a diode that rectifies the voltage generated in the secondary winding of the transformer, a capacitor that charges the rectified voltage and smoothes the primary choke winding, and a secondary choke winding. The secondary choke winding is formed by an inductor having the secondary choke winding inserted in series with the capacitor charging circuit and a commutation diode forming a circuit for discharging the energy stored in the inductor through the capacitor.

A first diode having an anode connected to the negative output terminal of the diode bridge and a cathode connected to one end of the primary choke winding of the inductor, and the primary choke winding of the inductor The capacitor connected between the end and the negative side output terminal of the diode bridge, and the anode is connected to the other end of the primary choke winding, and the positive side output terminal of the diode bridge and the transformer 1 side.
A second diode having a cathode connected to a connection point with the next winding is provided.

Alternatively, one end of the primary choke winding NLp of the inductor 13 is directly connected to the negative side output terminal b of the diode bridge 2, and the cathode of the first diode is connected to the capacitor and the anode of the second diode. To the point
The anode may be connected to the other end of the primary choke winding of the inductor.

In the switching power supply device configured as described above, the energy stored in the inductor when the switching element is on can be taken out from the primary choke winding when the switching element is off and stored in the capacitor. When is turned on again, the voltage of the capacitor and the output of the diode bridge flow to the primary winding of the transformer.

Therefore, the current can be continued to flow even in the period between the pulsating currents in the output current waveform of the diode bridge, and the input AC current of the diode bridge also flows along with it, so that the power factor is reduced. Be improved. Moreover, since the inductor is used at a high switching frequency, a small size inductor can be used.

Further, by connecting a capacitor having a smaller capacity than the capacitor storing the electric energy generated in the primary choke winding of the inductor between the output terminals of the diode bridge, noise due to the switching frequency and its harmonics is reduced. can do. Also,
The following elements may be provided instead of the first and second diodes and the capacitors connected to the primary choke winding side of the inductor in the power supply device.

That is, the first capacitor connected between the negative output terminal of the diode bridge and one end of the primary choke winding of the inductor, and the anode connected to the negative output terminal of the diode bridge, A first diode in which a cathode is connected to the other end of the primary choke winding of the inductor, and one end is connected to one end of the primary choke winding of the inductor, and the other end is connected to the diode bridge via a second capacitor. A third capacitor connected to the negative side output terminal of, the anode is connected to the connection point between the second capacitor and the third capacitor, and the positive side output terminal of the diode bridge and the primary winding of the transformer A second diode having a cathode connected to the connection point of the second diode, and an anode connected to the cathode of the first diode, and an anode of the second diode. Providing a third diode connected to the cathode.

With this configuration, during the overcurrent protection operation, the control circuit is stable even if the ON time of the switching element is shortened, the saturation of the transformer and the damage of the transistor do not occur, and the small transformer and the inductor. The power factor can be improved with a simple and inexpensive configuration using the.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 shows the first of the present invention.
9 is a circuit configuration diagram of the switching power supply device showing the embodiment of the present invention, parts having substantially the same functions as in FIG.

The rectifying / smoothing circuit 16 in this embodiment.
Uses an inductor 13 having a primary choke winding NLp and a secondary choke winding NLs in place of the choke coil 8 in the rectifying / smoothing circuit 6 of the conventional switching power supply device shown in FIG. Choke winding NLs
It is inserted in series in the charging circuit between the cathode of the rectifying diode 7 and the positive terminal of the capacitor 10 that charges and smoothes the rectified voltage. The commutation diode 9 forms a circuit for discharging the energy stored in the inductor 13 when the switching element 4 is on through the capacitor 10 when the switching element 4 is off.

On the other hand, on the primary choke winding NLp side of the inductor 13 and the primary winding Np side of the transformer 3, a first diode D1, a second diode D2 and a large capacity capacitor C2 are provided. The anode of D1 is connected to the negative output terminal b of the diode bridge 2, and its cathode is connected to one end h of the primary choke winding NLp of the inductor 13.

Further, the capacitor C2 is connected to the inductor 13
Is connected between the other end g of the primary choke winding NLp and the negative output terminal b of the diode bridge 2, and the anode of the second diode D2 is also connected to the connection point f (inductor 1).
3 the same as the other end g of the primary choke winding NLp).
The cathode is connected to the positive output terminal a of the diode bridge 2.
And the primary winding Np of the transformer 3 are connected to each other.

Therefore, the diode D2 and the capacitor C2
And are connected in series, and this series circuit is a transformer 3
Are connected in parallel between the primary winding Np and the switching element 4 in series, and between the output terminals a and b of the diode bridge 2. A capacitor C5 having a smaller capacity than the capacitor C2 is connected between the output terminals a and b of the diode bridge 2. This capacitor C5 is shown in FIG.
It may have a much smaller capacity than the capacitor C1 in the conventional switching power supply device shown in FIG.

Next, the operation of the switching power supply device configured as described above will be described. When the switching element 4 is on, the charging voltage of the small-capacity capacitor C5 is immediately discharged to the primary winding Np of the transformer 3, so that the output voltage of the diode bridge 2 is almost always present in this primary winding Np. It is applied as it is and a current flows through the switching element 4. Then, when the switching element 4 is turned off, the charging current flows from the diode bridge 2 to the capacitor C5, but the peak value of the current is small because the charging current is small. At this time, since the charging current is blocked by the diode D2, the capacitor C2 is not charged.

When the switching element 4 is off, if the load is large enough, the inductor 13
The charging current continuously flows through the commutation diode 9 to the capacitor 10 by the energy stored in the secondary choke winding NLs. By this, the primary choke winding N
A current is also induced in Lp, and the current flows through the diode D1 and the capacitor C2 to charge the capacitor C2. When the charging pressure reaches a predetermined level, the diode D2
Are conducted, and the charging voltage is applied to the primary winding Np of the transformer 3.

As a result, when the switching element 4 is on, the capacitors C2 and C5 and the diode bridge 2 are
Will supply power to the primary winding Np of the transformer 3. In this case, the large-capacity capacitor C2 supplies electric power to the primary winding Np of the transformer 3 even during a valley period when the output of the diode bridge 2 is in a valley, so that the input AC voltage from the AC power supply 1 is zero. Power supply to the primary winding Np can be maintained even in the vicinity. That is, the input AC current flows in a wide range of the input AC voltage, and the power factor can be improved.

Although the capacitor C5 may be omitted, since noise due to the switching frequency and its harmonics may affect other peripheral equipment through the power line of the AC power source 1, this capacitor C5 should be provided. This is preferable because it can also have a function as a noise filter.

FIG. 2 shows the waveforms of the voltage and current of each part in FIG. 1, where (a) is the AC voltage waveform applied from the AC power supply 1 to the diode bridge 2, and (b) is the output voltage waveform of the diode bridge 2. , (C) is a diode bridge 2
Is an output current waveform of the diode bridge 2, and (d) is an input current waveform of the diode bridge 2. The output voltage waveform of the diode bridge 2 shown in (b) has a substantially pulsating flow because the smoothing action of the AC component is lower than that in the case of (b) of FIG.

However, the primary winding Np of the transformer 3
On the other hand, when the energy stored in the secondary side inductor 13 is released, the capacitor C2 is charged, and the voltage is applied through the diode D2. As a result, as for the output voltage waveform of the diode bridge 2, as shown by the solid line in (c) of FIG. Along with this, the input current waveform of the diode bridge 2 also has a continuous current flow as shown by the solid line in FIG. 3D, and the power factor of the AC power can be improved.

The dashed-dotted lines in FIGS. 2 (b), 2 (c) and 2 (d) show the waveforms when the inductance of the primary choke winding NLp of the inductor 13 is larger than that shown by the solid line. ing. From these figures, it can be seen that the larger the inductance, the greater the effect of improving the power factor. Moreover, since the inductor 13 is used at a high switching frequency, it can be miniaturized. On the other hand, if a tertiary winding is provided on the transformer 3 as in the conventional example, the transformer 3
Will be larger.

FIG. 3 is a circuit configuration diagram of a switching power supply device showing a second embodiment of the present invention, and the portions corresponding to those in FIGS. 1 and 8 are designated by the same reference numerals. This embodiment differs from the above-described embodiment shown in FIG. 1 only in the connection position of the first diode D1. That is, in the switching power supply device shown in FIG.
The anode of the diode of is the terminal g of the primary choke winding NLp of the inductor 13, and the cathode is the second diode D.
It is connected to a connection point f between the anode of No. 2 and the positive side of the capacitor C2. The terminal g of the primary choke winding NLp is directly connected to the negative output terminal b of the diode bridge 2.

Even if the connection position of the first diode D1 is changed as described above, the primary choke winding N of the inductor 13 is
The current induced in Lp can be rectified to form a circuit that charges capacitor C2. When the charging pressure of the capacitor C2 reaches a predetermined value, the diode D
2 becomes conductive, and its charging voltage is the primary winding Np of the transformer 3.
The same action and effect as in the above-described embodiment can be obtained. That is, the effect of improving the power factor can be obtained with an inexpensive structure.

FIG. 4 is a circuit configuration diagram of a switching power supply device showing a third embodiment of the present invention, and the portions corresponding to those in FIGS. 1 and 8 are designated by the same reference numerals. In this embodiment, the inductor 13 in the rectifying / smoothing circuit 16 is
The secondary choke winding NLs of the transformer 3 to the secondary winding Ns of the transformer 3.
And a connection point between the anode of the commutation diode 9 and the negative terminal of the capacitor 10 are inserted in the charging circuit.
Other configurations are the same as those in the first embodiment described above.

FIG. 5 is a circuit configuration diagram of a switching power supply device showing a fourth embodiment of the present invention, and the portions corresponding to those in FIG. 4 are designated by the same reference numerals. This embodiment is different from the above-described embodiment shown in FIG. 4 in that
The first diode D1 is connected to the terminal g of the primary choke winding NLp of the inductor 13 as in the case of the embodiment of FIG.
And the anode of the second diode D2 and the capacitor C2
It is only the point connected in the illustrated direction between the connection point f and the positive side of. The action and effect in this case are also the same as those in the above-described embodiments.

Here, when the current flowing through the inductor 13 becomes discontinuous, for example, when the load becomes light, or when the overcurrent protection operation operates when the load becomes too heavy, switching is performed. The control circuit 5 operates so as to shorten the ON time of the element 4. As a result, the current flowing through the primary choke winding NLp decreases and the voltage applied to the capacitor C2 also becomes insufficient, so that the output current waveform of the diode bridge 2 has a deep valley waveform.
As a result, the switching power supply has an extremely large fluctuation in the output voltage, which may cause saturation of the transformer 3, damage to the transistor 4, or instability of the circuit during the overcurrent protection operation, resulting in reduced reliability.

This will be described in more detail. G- generated in the primary choke winding NLp of the inductor 13 in the normal state
The voltage between h is shown in (a) of FIG. Here, the control circuit 5
Attempts to narrow the width of the ON pulse to the switching element 4 (“ON width” in FIG. 8) in the state of the overcurrent protection operation by the overcurrent protection circuit (not shown). If the inductance of the secondary choke winding NLs of the inductor 13 is insufficient, the gradient of the ripple current becomes steep, and when the load is lightened, the ripple current becomes discontinuous at some point. Even in such a case where the current flowing through the secondary choke winding NLs becomes discontinuous, the control circuit 5
Tries to narrow the width of the on-pulse.

The voltage between g and h in this state is shown in FIG.
The voltage across the capacitor C2 is shown in (c).
In the switching power supply device of FIG. 1 or FIG. 3 to FIG. 5, in such a state, the voltage applied to the capacitor C2 becomes insufficient, and the output current waveform of the diode bridge 2 becomes a waveform with deep valleys, which causes fluctuations in the output voltage. Also becomes very large, which causes problems such as unstable operation of the control circuit 5.

Although it is conceivable to increase the inductance with respect to the current discontinuity of the inductor 13, if this is done, the core becomes large and the cost becomes high. Further, even if the inductance of the inductor 13 is increased, the fluctuation of the output voltage during the overcurrent protection operation is not improved.

FIG. 6 is a circuit configuration diagram of a switching power supply device showing a fifth embodiment of the present invention in which such a problem is improved, and corresponds to FIG. 1 showing the first embodiment of the present invention. The same reference numerals are given to the parts to be marked. The switching power supply device shown in FIG. 6 is replaced with the first teode D1 in the switching power supply device shown in FIG.
The diode D4 and the third diode D3 are provided, the first capacitor C4 and the third capacitor C3 are further provided, and the capacitor C2 is used as the second capacitor.

A capacitor C4 is connected between the negative side output terminal b of the diode bridge 2 and one end h of the primary choke winding NLp of the inductor 13, and the negative side output terminal b of the diode bridge 2 is connected to the diode D4. The anode is connected, and the cathode is connected to the other end g of the primary choke winding NLp of the inductor 13. Third capacitor C3
Has one end of the inductor 13 primary choke winding NLp
, And the other end is connected to the negative side output terminal b of the diode bridge 2 via the second capacitor C2.

The second capacitor C2 and the third capacitor C2
The second diode D2 at the connection point with the capacitor C3 of
Of the diode bridge 2 is connected to the connection point between the positive side output terminal a of the diode bridge 2 and the primary winding Np of the transformer 3 as in the example of FIG. The third diode D3 has its anode connected to the cathode of the first diode D4 (connected to the other end g of the primary choke winding NLp of the inductor 13) and its cathode connected to the anode of the second diode D2 (capacitors C2 and C3). Are connected to the connection points f).

Next, the operation of the switching power supply device configured as described above will be described. When the switching element 4 is turned on by the on-pulse from the control circuit 5,
The current induced in the primary choke winding NLp of the inductor 13 is rectified by the diode D3 and the capacitor C3.
It is charged and charges the capacitor C2. Further, when the switching element 4 is turned off by the off pulse from the control circuit 5, the primary choke winding NLp of the inductor 13
Current induced in the diode D4 and capacitor C4
Is rectified and charged by and the capacitor C2 is charged with a voltage added to the charging voltage of the capacitor C4.

As described above, the primary choke winding NLp of the inductor 13 is connected to the voltage doubler rectifier circuit including the diodes D3 and D4 and the capacitors C3 and C4, and the output voltage thereof charges the capacitor C2. Will be done. When the charging voltage of the capacitor C2 reaches a predetermined value, the diode D2 becomes conductive and the charging voltage is applied to the primary winding Np of the transformer 3. Therefore, even if the number of turns of the primary choke winding NLp is reduced to 1/2, the capacitor C2 can be charged in the same manner as in the above-described embodiments.

As a result, when the switching element 4 is turned on, the outputs of the capacitor C2 and the diode bridge 2 supply power to the primary winding Np of the transformer 3, and the input AC voltage from the AC power supply 1 is supplied. Even when is close to zero, the power supply to the primary winding Np of the transformer 3 is maintained. The currents generated by these on-pulses and off-pulses may be exchanged for rectification.

Here, the operation of the overcurrent protection operation in this switching power supply will be described with reference to FIG. The gh voltage generated between the primary choke windings NLp in the normal operation state is shown in FIG. Further, the voltage between gh in the state where the load is suddenly reduced and the state where the overcurrent protection operation is being performed is shown in FIG. Even during the overcurrent protection operation, since the rectifier circuit connected to the primary choke winding NLp of the inductor 13 uses the half-wave voltage doubler method, the capacitor C2 in FIGS. The energy supplied to the
And Q '(hatched portion).

Therefore, the capacitor C2 in the state where the load is suddenly reduced and the state where the overcurrent protection operation is being performed.
The voltage between terminals (charging voltage) is as shown in FIG. Therefore, the supply of energy by the off pulse of the control circuit 5 does not cause the voltage across the terminals of the capacitor C2 to drop to 0 volt.

Further, as described in Japanese Patent Publication No. 5-86130, for example, during the overcurrent protection operation in such a power supply device, the ON width is narrowed as the load becomes heavier, and the ON pulse is generated. Although the supplied energy decreases, the energy Q ′ supplied between the terminals of the capacitor C2 increases as the OFF width increases. Therefore, unlike the case of the circuit configurations of the first and second embodiments, the terminal voltage of the capacitor C2 does not drop to 0 volt as shown in FIG.

The rectifier circuit connected to the primary choke winding NLp of the inductor 13 may be a diode bridge, but two more diodes are required and the capacitor C
The voltage drop between the two terminals and the circuit loss increase.

FIG. 7 is a circuit configuration diagram of a switching power supply device showing a sixth embodiment of the present invention, and the portions corresponding to those in FIG. 6 are designated by the same reference numerals. This switching power supply device includes an inductor 1 in a rectifying / smoothing circuit 16.
The secondary choke winding NLs of the transformer 3 to the secondary winding N of the transformer 3.
6 is different from the fifth embodiment shown in FIG. 6 only in that it is inserted in the charging circuit between the connection point between s and the anode side of the commutation diode 9 and the negative terminal of the capacitor 10. Since the configuration and the function and effect thereof are the same, the description thereof will be omitted.

[0059]

As described above, the switching power supply device according to the present invention uses a large transformer having a complicated structure having a tertiary winding as in the prior art, or two transformers and two systems. Without providing a switching circuit or using many switching elements,
With a simple structure using a small transformer and inductor, the power factor can be improved at low cost regardless of the size of the load.

If a small-capacity capacitor is provided between the output terminals of the diode bridge in series with the second diode and the large-capacity capacitor, noise due to the switching frequency and its harmonics is generated in the power line. Can be prevented from being transmitted to other peripheral devices.

Further, the voltage induced in the primary choke winding NLp of the inductor provided in the rectifying / smoothing circuit on the secondary side of the transformer is rectified by the voltage doubling rectifying circuit and a large capacity capacitor (second If the capacitor is charged, in addition to the above effects, during overcurrent protection operation,
Even if the ON time of the switching element is shortened, the control circuit operates stably, and there is no risk of saturation of the transformer or damage to the transistor. Also, the number of turns of the primary choke winding of the inductor can be halved.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram showing voltage and current waveforms of respective parts of FIG.

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

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

FIG. 5 is a circuit configuration diagram of a switching power supply device showing a fourth embodiment of the present invention.

FIG. 6 is a circuit configuration diagram of a switching power supply device showing a fifth embodiment of the present invention.

FIG. 7 is a circuit configuration diagram of a switching power supply device showing a sixth embodiment of the present invention.

8 is a waveform diagram showing the relationship between the ON width of the switching element 4 and the terminal voltage of the capacitor C2 in the switching power supply device shown in FIGS. 1 and 3 to 5. FIG.

9 is an ON width of a switching element 4 and a capacitor C2 in the switching power supply device shown in FIGS. 6 and 7.
FIG. 6 is a waveform diagram showing the relationship with the voltage between terminals.

FIG. 10 is a circuit configuration diagram showing an example of a conventional switching power supply device.

FIG. 11 is a waveform diagram showing voltage and current waveforms of respective parts of FIG.

[Explanation of symbols]

 1: AC power supply 2: Diode bridge 3: Transformer Np: Primary winding of transformer Ns: Secondary winding of transformer 4: Switching element 5: Control circuit 7: Diode for rectification 9: Diode for commutation 10: Smoothing Capacitors 12, 12: output terminal 13: inductor 16: rectifying and smoothing circuit NLp: primary choke winding of inductor NLs: secondary choke winding of inductor D1, D4: first diode D2: second diode D3: Third diode C2: Large-capacity capacitor (second capacitor) C3: Third capacitor C4: First capacitor C5: Small-capacity capacitor

Claims (5)

[Claims] 1. A diode bridge (2) for full-wave rectifying an AC input, and a primary winding (Np) connected in series with a switching element (4) between output terminals (a, b) of the diode bridge. A transformer (3), a rectifying and smoothing circuit (16) for rectifying and smoothing an AC voltage generated in the secondary winding (Ns) of the transformer, and outputting the rectifying and smoothing circuit according to the output voltage of the rectifying and smoothing circuit. A switching power supply device comprising a control circuit (5) for controlling on / off of an element (4), wherein the rectifying / smoothing circuit (16) is connected to the transformer (3).
A diode (7) that rectifies the voltage generated in the secondary winding (Ns), a capacitor (10) that charges and smoothes the rectified voltage, a primary choke winding (NLp), and a secondary choke winding (NLs). ), The secondary choke windings (NLs) of which are inserted in series with the charging circuit of the capacitor (10), and the energy stored in the inductor is discharged through the capacitor (10). A diode (9) for commutation forming a circuit for connecting the anode to the negative output terminal (b) of the diode bridge (2), and the primary choke winding (NLp) of the inductor (13). A first diode (D1) having a cathode connected to one end (h) of the diode, the other end (g) of the primary choke winding (NLp) of the inductor (13) and the negative of the diode bridge (2). An anode is connected to the capacitor (C2) connected between the output terminal (b) and the other end (g) of the primary choke winding (NLp) of the inductor (13) to connect the diode bridge (2). A switching power supply device comprising: a second diode (D2) having a cathode connected to a connection point between the positive output terminal (a) and the primary winding (Np) of the transformer (3). 2. A diode bridge (2) for full-wave rectifying an AC input, and a primary winding (Np) connected in series with a switching element (4) between output terminals (a, b) of the diode bridge. A transformer (3), a rectifying and smoothing circuit (16) for rectifying and smoothing an AC voltage generated in the secondary winding (Ns) of the transformer, and outputting the rectifying and smoothing circuit according to the output voltage of the rectifying and smoothing circuit. A switching power supply device comprising a control circuit (5) for controlling on / off of an element (4), wherein the rectifying / smoothing circuit (16) is connected to the transformer (3).
A diode (7) that rectifies the voltage generated in the secondary winding (Ns), a capacitor (10) that charges and smoothes the rectified voltage, a primary choke winding (NLp), and a secondary choke winding (NLs). ), The secondary choke windings (NLs) of which are inserted in series with the charging circuit of the capacitor (10), and the energy stored in the inductor is discharged through the capacitor (10). A negative side output terminal (b) of the diode bridge (2) and one end (h) of the primary choke winding (NLp) of the inductor (13). And a first diode (D1) having an anode connected to the other end (g) of the primary choke winding (NLp), a cathode of the first diode (D1) and the diode bridge ( 2) a capacitor (C2) connected between the negative side output terminal (b), the capacitor (C2) and the first diode (D1)
The anode is connected to the connection point (f) with the cathode of the diode bridge, and the cathode is connected to the connection point between the positive side output terminal (a) of the diode bridge (2) and the primary winding (Np) of the transformer (3). And a second diode (D2) which is provided, and a switching power supply device. 3. The switching power supply device according to claim 1, wherein a capacitor (C5) having a smaller capacity than that of the capacitor (C2) is connected between the output terminals (a, b) of the diode bridge (2). A switching power supply device characterized by the above. 4. A diode bridge (2) for full-wave rectifying an AC input, and a primary winding (Np) connected in series with a switching element (4) between output terminals (a, b) of the diode bridge. A transformer (3), a rectifying and smoothing circuit (16) for rectifying and smoothing an AC voltage generated in the secondary winding (Ns) of the transformer, and outputting the rectifying and smoothing circuit, and the switching according to the output voltage of the rectifying and smoothing circuit. A switching power supply device comprising a control circuit (5) for controlling on / off of an element (4), wherein the rectifying / smoothing circuit (16) is connected to the transformer (3).
A diode (7) that rectifies the voltage generated in the secondary winding (Ns), a capacitor (10) that charges and smoothes the rectified voltage, a primary choke winding (NLp), and a secondary choke winding (NLs). ), The secondary choke windings (NLs) of which are inserted in series with the charging circuit of the capacitor (10), and the energy stored in the inductor is discharged through the capacitor (10). A negative side output terminal (b) of the diode bridge (2) and one end (h) of the primary choke winding (NLp) of the inductor (13). The first capacitor (C4) connected between
And the anode is connected to the negative output terminal (b) of the diode bridge (2), and the cathode is connected to the other end (g) of the primary choke winding (NLp) of the inductor (13). One end is connected to the diode (D4) and one end (h) of the primary choke winding (NLp) of the inductor (13), and the other end is connected to the diode bridge (2) via the second capacitor (C2). Third capacitor (C3) connected to the negative output terminal (b) of
An anode is connected to a connection point between the second capacitor (C2) and the third capacitor (C3), and the positive side output terminal (a) of the diode bridge (2) and the transformer (3) are connected to each other. A second diode (D2) having a cathode connected to the connection point with the primary winding (Np), and an anode connected to the cathode of the first diode (D4) to connect the second diode (D2) A switching power supply device comprising: a third diode (3) having a cathode connected to an anode; 5. The switching power supply device according to claim 3, further comprising a capacitor (C5) having a smaller capacity than the second capacitor (C2) between the output terminals (a, b) of the diode bridge (2). A switching power supply device characterized by being connected.