JP3590153B2 - Switching power supply - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching power supply used as a DC power supply for various electronic devices.
[0002]
[Prior art]
In recent years, switching power supplies (also called switching regulators) have been frequently used as DC power supplies for electronic devices.
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 rectification of 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.
[0003]
Reference numeral 3 denotes a transformer for converting the DC voltage smoothed by the capacitor C1, which 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 a series circuit is connected between the output terminals a and b of the diode bridge 2. Reference numeral 5 denotes a control circuit for controlling the switching element 4 to turn on and off.
[0004]
Reference numeral 6 denotes a rectifying / smoothing circuit for rectifying and smoothing an AC voltage generated in the secondary winding Ns of the transformer 3 and outputting the rectified diode 7, a rectifying diode 7, a smoothing choke coil 8 and a capacitor 10, and a commutating diode 9 It is constituted by. Output terminals 11 and 12 output the voltage between both ends of the capacitor 10 as a DC output voltage Vout. This voltage Vout is also fed back to the control circuit 5.
[0005]
According to this switching power supply, the AC voltage from the AC power supply 1 is full-wave rectified by the diode bridge 2, and then the ripple component is removed by the capacitor C1 to be smoothed and converted to a DC voltage. This DC voltage is applied to a series circuit of the primary winding Np of the transformer 3 and the switching element 4.
[0006]
The switching element 4 switches a DC voltage applied to a primary winding Np of the transformer 3 by applying a rectangular wave drive signal from a control circuit 5 to a control terminal (base) and performing on / off control. . By this switching, an AC voltage is generated in the secondary winding Ns of the transformer 3, and this AC voltage is converted into a DC voltage by the rectifying and smoothing circuit 6, and supplied to the load from the output terminals 11 and 12 as a DC output voltage Vout. , To the control circuit 5.
[0007]
In the rectifying and smoothing circuit 6, when the switching element 4 is turned on, a current flows through the diode 7 and the choke coil 8 to charge the capacitor 10. In addition, 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, so that the charging current continues to flow through the capacitor 10.
[0008]
The control circuit 5 performs, for example, pulse width control. The control circuit 5 generates a drive signal having a duty ratio according to the fed-back voltage to control the on / off time ratio of the switching element 4, and outputs the output terminals 11 and 12. A predetermined DC output voltage Vout is obtained in the meantime.
[0009]
11A and 11B show waveforms of voltages and currents at various parts in FIG. 10. FIG. 11A shows an AC voltage waveform applied from the AC power supply 1 to the diode bridge 2, and FIG. 11B shows an output voltage waveform of the diode bridge 2 and a ripple component. Contains. (C) is an output current waveform of the diode bridge 2 and has a pulsating flow that flows only during a period from when the absolute value of the voltage (a) exceeds the voltage (b) to when it reaches a peak. (D) is an input current waveform of the diode bridge 2 and flows in a direction corresponding to the voltage polarity of (a) for the same period as the output current of (c).
[0010]
In such a switching power supply, a capacitor C1 for removing a ripple component of a rectified output of the diode bridge 2 generally has a large capacity. Therefore, the current flowing into the capacitor C1 becomes a pulsating current having a high peak value as shown in FIG. 9C, resulting in a reduction in the power factor of the circuit.
[0011]
Further, there is also a problem that the capacitor C1 generates heat due to internal loss due to the charging / discharging current of the capacitor C1, and its life is shortened. Furthermore, since the input power is large, the noise due to the generation of the switching frequency and its harmonics increases, which adversely affects the switching power supply device or other devices that share the AC power supply 1. Therefore, a large-capacity noise filter circuit is required.
[0012]
Further, in order to prevent the power factor from being reduced by the above-mentioned capacitor input type, there is a choke input type in which the disadvantage is improved. However, an inductance of several mH or more is required, and the choke coil becomes extremely large. Therefore, there is a problem that the power supply device is increased in size and cost.
In order to solve such a problem, for example, a switching power supply device disclosed in, for example, JP-A-3-65050, JP-A-3-273865, and JP-A-2-266868 has been proposed. Switching regulator).
[0013]
In the switching regulator disclosed in Japanese Patent Application Laid-Open No. 3-65050, a transformer is provided with a reset winding as a tertiary winding, and a current generated by a flyback pulse generated in the transformer when the switching element is turned off passes through the reset winding. A capacitor other than the smoothing capacitor is charged, and the voltage of this capacitor and the voltage of a conventional smoothing capacitor (corresponding to the capacitor C1 in FIG. 8) are applied to the primary winding of the transformer. As a result, the current can also flow through the valley of the pulsating flow of the output current of the diode bridge, and the power factor can be improved.
[0014]
The switching regulator disclosed in Japanese Patent Application Laid-Open No. 3-273865 is provided with two systems of a transformer and a switching element. One of the transformers is provided with a reset winding as a tertiary winding. A capacitor is connected in parallel to the next winding, the flyback pulse current generated when the switching element on the one transformer side is turned off is charged in the capacitor, and the charging voltage and the voltage of the smoothing capacitor are transferred to the other transformer. To improve the power factor.
[0015]
Further, the one disclosed in Japanese Patent Application Laid-Open No. Hei 2-266868 raises a voltage obtained by switching a DC voltage obtained by a diode bridge and a smoothing capacitor at a predetermined timing by four switching elements via a transformer. After rectifying and smoothing, amplitude-modulating the reference sine wave with the DC output voltage, synchronizing the modulated signal with the input AC voltage, and further amplitude-modulating the clock pulse, and according to the modulated signal. The waveform distortion is reduced by controlling the on / off timing of the four switching elements.
[0016]
[Problems to be solved by the invention]
However, those disclosed in the above-mentioned JP-A-3-65050 and JP-A-3-273865 complicate the structure of the transformer because a tertiary winding is provided in the transformer, and increase the size of the transformer and increase the safety. Problems also arise in terms of creepage distance and protection in the standard. Also, the energy of the flyback pulse greatly changes depending on the size of the load, and the charging voltage to the capacitor greatly changes.
Therefore, the ripple of the capacitor output increases. That is, there is a problem that the power factor is deteriorated under a light load or a heavy load.further,Leakage magnetic flux is large and adversely affects noise.
[0017]
In the case of Japanese Patent Application Laid-Open No. 3-273865, two transformers are used to extract two systems of small electric power, which causes a problem that the configuration becomes complicated and the price becomes high.
Furthermore, the device described in Japanese Patent Application Laid-Open No. 2-266868 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 price becomes high.
[0018]
The present invention has been made in view of such circumstances,Switching power supplySimple configuration and low costSo,And depend on load fluctuationsNotPower factor, stability,andThe purpose is to improve reliability.
Therefore, an object of the present invention is to provide a switching power supply device that allows a current to flow even in a period between valleys of a pulsating flow in an output current waveform of a diode bridge and allows a current to flow even near zero voltage of an AC voltage.
[0019]
[Means for Solving the Problems]
The present invention provides a diode bridge for performing full-wave rectification of an AC input, a transformer having a primary winding connected in series with a switching element between output terminals of the diode bridge, and a secondary winding of the transformer. A switching power supply device comprising: a rectifying and smoothing circuit that rectifies and smoothes an AC voltage generated in a line and outputs the rectified and smoothed voltage; and a control circuit that controls on / off of the switching element according to an output voltage of the rectified and smoothing circuit. The following is achieved to achieve the above object.
[0020]
The rectifying and smoothing circuit includes a diode for rectifying a voltage generated in a secondary winding of the transformer, a capacitor for charging and smoothing the rectified voltage, a primary choke winding and a secondary choke winding, The secondary choke winding is constituted by an inductor inserted in series with a charging circuit of the capacitor, and a commutation diode forming a circuit for discharging the energy stored in the inductor through the capacitor.
[0021]
And the negative output terminal of the diode bridgeA first capacitor connected between the inductor and one end of a primary choke winding of the inductor; an anode connected to a negative output terminal of the diode bridge; and a cathode connected to the other end of the primary choke winding of the inductor. A connected first diode, a third capacitor having one end connected to one end of a primary choke winding of the inductor, and the other end connected to a negative output terminal of the diode bridge via a second capacitor; A second diode having an anode connected to a connection point between the second capacitor and the third capacitor and a cathode connected to a connection point between the positive output terminal of the diode bridge and the primary winding of the transformer; A third diode having an anode connected to the cathode of the first diode and a cathode connected to the anode of the second diode;And a diode.
[0022]
[0023]
The switching power supply device configured as described above includes a switching element, The current induced in the primary choke winding of the inductor is rectified by the voltage doubler rectifier circuit comprising the third and first diodes and the third and first capacitors. 2 can be charged. When the charging voltage of the second capacitor reaches a predetermined level, the second diode conducts, and the charging voltage is applied to the primary winding of the transformer.
[0024]
As a result, when the switching element is turned on, the output of the second capacitor and the diode bridge will supply power to the primary winding of the transformer,The current can continue to flow even during the valley of the pulsating flow in the output current waveform of the diode bridge,From AC power supplyInput AC voltageIs zero, Power supply to the primary winding of the transformer is maintained, so that the power factor is improved.
In addition, since the inductor is used at a high switching frequency, a small inductor can be used.
Further, in the overcurrent protection operation, even if the ON time of the switching element is shortened, the current induced in the primary choke winding of the inductor is rectified by the rectifier circuit of the voltage doubler type as described above, and the second Since the capacitor is charged, the voltage across its terminals does not drop to 0 volts, so the control circuit is stable, there is no transformer saturation or transistor damage, etc. The power factor can be improved with an inexpensive configuration.
[0025]
Further, by connecting a capacitor having a smaller capacity than a capacitor for storing electric energy generated in the primary choke winding of the inductor between output terminals of the diode bridge, it is possible to reduce noise due to a switching frequency and its harmonics.it can.
[0026]
[0027]
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.Prior to this, an example of a switching power supply device on which the present invention is based will be described.
Figure 1,Of the present inventionUnderlyingSwitching power supplyShow the first exampleIt is a circuit configuration diagram,FIG.Parts having substantially the same functions as those described above are denoted by the same reference numerals, and redundant description will be omitted.
[0029]
thisSwitching power supplyThe rectifying / smoothing circuit 16 in FIG. 1 uses an inductor 13 having a primary choke winding NLp and a secondary choke winding NLs instead of the choke coil 8 in the rectifying / smoothing circuit 6 of the conventional switching power supply device shown in FIG. The secondary choke winding NLs is inserted in series in a charging circuit between the cathode of the rectifying diode 7 and the positive terminal of the capacitor 10 which charges and smoothes the rectified voltage. The commutation diode 9 forms a circuit that releases 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.
[0030]
On the other hand, a first diode D1, a second diode D2, and a large-capacity capacitor C2 are provided on the primary choke winding NLp side of the inductor 13 and the primary winding Np side of the transformer 3, and the anode of the diode D1 is provided. 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.
[0031]
Further, the capacitor C2 is connected between the other end g of the primary choke winding NLp of the inductor 13 and the negative output terminal b of the diode bridge 2, and the anode of the second diode D2 is connected to the connection point f (inductor 13 is the same as the other end g of the primary choke winding NLp), and its cathode is connected to the connection point between the positive output terminal a of the diode bridge 2 and the primary winding Np of the transformer 3.
[0032]
Accordingly, the diode D2 and the capacitor C2 are connected in series, and this series circuit is connected in parallel between the series circuit of the primary winding Np of the transformer 3 and the switching element 4 and the output terminals a and b of the diode bridge 2. It is connected to the.
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 may have a much smaller capacity than the capacitor C1 in the conventional switching power supply device shown in FIG.
[0033]
Next, the operation of the thus configured switching power supply device will be described.
When the switching element 4 is turned 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 mostly supplied to the primary winding Np. The current is applied as it is and a current flows through the switching element 4.
When the switching element 4 is turned off, a charging current flows from the diode bridge 2 to the capacitor C5. However, since the charging capacity is small, the peak value of the current is small. At this time, since the charging current is blocked by the diode D2, the capacitor C2 is not charged.
[0034]
Also, when the switching element 4 is off, if the load is of a certain magnitude, the charging current is continuously supplied to the capacitor 10 through the commutation diode 9 by the energy stored in the secondary choke winding NLs of the inductor 13. Flows.
As a result, a current is also induced in the primary choke winding NLp, 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 conducts, and the charging voltage is applied to the primary winding Np of the transformer 3.
[0035]
As a result, when the switching element 4 is on, the outputs of the capacitors C2 and C5 and the diode bridge 2 supply power to the primary winding Np of the transformer 3. In this case, since the large-capacity capacitor C2 supplies power to the primary winding Np of the transformer 3 even during the period when the pulsating current output from the diode bridge 2 is in the valley, the input AC voltage from the AC power supply 1 becomes zero. Even in the vicinity, the supply of power to the primary winding Np can be maintained. That is, the input AC current flows in a wide range of the input AC voltage, and the power factor can be improved.
[0036]
Although the capacitor C5 can be omitted, noise due to the switching frequency and its harmonics may affect other peripheral devices through the power supply line of the AC power supply 1. Therefore, providing the capacitor C5 provides a noise filter. It is preferable because it can also have the function of
[0037]
2A and 2B show waveforms of voltages and currents at various parts in FIG. 1. FIG. 2A shows an AC voltage waveform applied from an AC power supply 1 to a diode bridge 2, FIG. 2B shows an output voltage waveform of the diode bridge 2, and FIG. () Shows the output current waveform of the diode bridge 2, and (d) shows the input current waveform of the diode bridge 2.
The output voltage waveform of the diode bridge 2 shown in FIG. 11B has a substantially pulsating flow because the smoothing action of the AC component is lower than in the case of FIG.
[0038]
However, when the energy stored in the secondary-side inductor 13 is released to the primary winding Np of the transformer 3, the capacitor C2 is charged, and the voltage is applied through the diode D2. As a result, as shown by the solid line in FIG. 2C, the output voltage waveform of the diode bridge 2 allows the current to flow even during the period between the valleys of the pulsating flow. Accordingly, the input current waveform of the diode bridge 2 also flows continuously as shown by the solid line in FIG. 4D, and the power factor of the AC power can be improved.
[0039]
2 (b), 2 (c), and 2 (d) show waveforms when the inductance of the primary choke winding NLp of the inductor 13 is larger than the case indicated by the solid line. It can be seen from these figures that the greater the inductance, the greater the effect of improving the power factor.
In addition, since the inductor 13 is used at a high switching frequency, the size can be reduced. On the other hand, if a tertiary winding is provided in the transformer 3 as in the conventional example, the transformer 3 becomes large.
[0040]
FIG.UnderlyingSwitching power supplyShow a second exampleFIG. 1 is a circuit configuration diagram,FIG.The parts corresponding to are denoted by the same reference numerals.
thisSwitching power supplyIn FIG.Switching power supplyThe only difference is that the connection position of the first diode D1.
That is, in the switching power supply device shown in FIG. 3, the anode of the first diode is connected to the terminal g of the primary choke winding NLp of the inductor 13, and the cathode is connected to the anode of the second diode D2 and the positive side of the capacitor C2. Connected to connection point f. The terminal g of the primary choke winding NLp is directly connected to the negative output terminal b of the diode bridge 2.
[0041]
Thus, even if the connection position of the first diode D1 is changed, a circuit for rectifying the current induced in the primary choke winding NLp of the inductor 13 and charging the capacitor C2 can be formed. When the charging pressure of the capacitor C2 reaches a predetermined level, the diode D2 conducts, and the charging voltage is applied to the primary winding Np of the transformer 3, andFirst exampleThe same operation and effect as in the case of can be obtained. That is, the effect of improving the power factor can be obtained with an inexpensive configuration.
[0042]
FIG.UnderlyingSwitching power supplyShow a third exampleFIG. 1 is a circuit configuration diagram,FIG.The parts corresponding to are denoted by the same reference numerals.
thisSwitching power supplyThen, in the rectifying and smoothing circuit 16, the secondary choke winding NLs of the inductor 13 is charged between the connection point between the secondary winding Ns of the transformer 3 and the anode side of the commutation diode 9 and the negative terminal of the capacitor 10. Inserted in the circuit. Other configurations are described above.First exampleIs the same as
[0043]
FIG. 5 shows the structure of the present invention.UnderlyingSwitching power supplyShow a fourth exampleFIG. 5 is a circuit configuration diagram, and portions corresponding to FIG. 4 are denoted by the same reference numerals.
thisSwitching power supplyIn FIG.Third example3 is different from the first diode D1 in FIG.The second example shown inAs in the case of the above, a point connected in the illustrated direction between the terminal g of the primary choke winding NLp of the inductor 13 and the connection point f between the anode of the second diode D2 and the positive side of the capacitor C2. Only.
The operation and effect in this case are the same as those in the above-described embodiments.
[0044]
Here, when the current flowing through the inductor 13 becomes discontinuous, for example, when the load becomes light, or when the overcurrent protection operation is activated when the load becomes too heavy, the switching element 4 The control circuit 5 operates so as to shorten the on-time. As a result, the current flowing through the primary choke winding NLp decreases, and the voltage applied to the capacitor C2 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 a very large fluctuation in output voltage, and the saturation of the transformer 3, the damage of the transistor 4, or the instability of the circuit during the overcurrent protection operation may occur, and the reliability may be reduced.
[0045]
This will be described in more detail. FIG. 8A shows the gh voltage generated in the primary choke winding NLp of the inductor 13 in the normal state. Here, when the control circuit 5 is in the state of the overcurrent protection operation by the overcurrent protection circuit (not shown), the control circuit 5 tries to narrow the width of the ON pulse to the switching element 4 (“ON width” in FIG. 8). In addition, if the inductance of the secondary choke winding NLs of the inductor 13 is insufficient, the slope of the ripple current becomes steep, and when the load is reduced, the ripple current is interrupted at a certain point.in this wayWhen the current flowing through the secondary choke winding NLs is discontinuousLikeAlso in this case, the control circuit 5 tries to reduce the width of the on-pulse.
[0046]
FIG. 8B shows the voltage between g and h in this state, and FIG. 8C shows the voltage between the capacitors C2. 1 or 3 to 5Each shownIn such a state in the switching power supply device, the voltage applied to the capacitor C2 becomes insufficient, the output current waveform of the diode bridge 2 becomes a deep valley waveform, and the fluctuation of the output voltage becomes very large. Problems such as instability of the operation of No. 5 occur.
[0047]
In addition, it is conceivable to increase the inductance for the discontinuity of the current of the inductor 13, but doing so increases the size of the core and increases the cost. Even if the inductance of the inductor 13 is increased, the fluctuation of the output voltage during the overcurrent protection operation is not improved.
[0048]
The switching power supply according to the present invention improves such a problem, and an embodiment thereof will be described below.
FIG.thisInventionFirstIt is a circuit configuration diagram of a switching power supply device showing an embodiment of the present invention,FIG.The parts corresponding to are denoted by the same reference numerals.
The switching power supply device shown in FIG. 6 includes a first diode D4 and a third diode D3 in place of the first diode D1 in the switching power supply device shown in FIG. 1, and further includes a first capacitor C4 and a third diode D3. Is provided, and the capacitor C2 is used as a second capacitor.
[0049]
The capacitor C4 is connected between the negative output terminal b of the diode bridge 2 and one end h of the primary choke winding NLp of the inductor 13, and the anode of the diode D4 is connected to the negative output terminal b of the diode bridge 2. The cathode is connected to the other end g of the primary choke winding NLp of the inductor 13.
The third capacitor C3 has one end connected to one end h of the primary choke winding NLp of the inductor 13, and the other end connected to the negative output terminal b of the diode bridge 2 via the second capacitor C2. I have.
[0050]
Then, an anode of a second diode D2 is connected to a connection point between the second capacitor C2 and the third capacitor C3, and the cathode thereof is connected to the node shown in FIG.Pointing out toungueAs in the example, it is connected to the connection point between the positive output terminal a of the diode bridge 2 and the primary winding Np of the transformer 3.
The third diode D3 has an 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 a cathode connected to the anode (capacitors C2 and C3) of the second diode D2. To the connection point f).
[0051]
Next, the operation of the thus configured switching power supply device 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:ThirdWith diode D3ThirdRectified and charged by the capacitor C3,SecondThe capacitor C2 is charged.
When the switching element 4 is turned off by the off pulse from the control circuit 5, the current induced in the primary choke winding NLp of the inductor 13 is:FirstWith diode D4FirstRectified and charged by the capacitor C4,ThirdCapacitorC3The voltage added to the charging voltage ofSecondThe capacitor C2 is charged.
[0052]
Thus, the primary choke winding NLp of the inductor 13 has:Third, firstWith diodes D3 and D4Third and firstA voltage doubler rectifier circuit with capacitors C3 and C4 is connected.SecondThe capacitor C2 will be charged.SecondWhen the charging voltage of the capacitor C2 reaches a predetermined value,SecondThe diode D2 conducts, 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 halved,Switching power supplyAs inSecondThe capacitor C2 can be charged.
[0053]
As a result, when the switching element 4 is turned on,SecondThe output of the capacitor C2 and the diode bridge 2 supplies power to the primary winding Np of the transformer 3, and even if the input AC voltage from the AC power supply 1 is near zero, the primary winding of the transformer 3 The supply of power to Np is maintained.
The rectification may be performed by exchanging the currents generated by the ON pulse and the OFF pulse.
[0054]
Here, the operation of the overcurrent protection operation in this switching power supply device will be described with reference to FIG.
The voltage between g and h generated between the primary choke windings NLp in the normal operation state is shown in FIG. FIG. 3B shows the voltage between g and h in the state where the load is suddenly reduced and the state where the overcurrent protection operation is being performed.
Even during the overcurrent protection operation, since the rectifier circuit connected to the primary choke winding NLp of the inductor 13 is of the half-wave multiple voltage type, the capacitor C2 shown in FIGS. Are supplied as Q and Q '(hatched portions) in each state.
[0055]
Therefore, the voltage between the terminals of the capacitor C2 (charging voltage) in the state where the load is suddenly reduced and the state where the overcurrent protection operation is being performed is as shown in FIG. 9C. Therefore, the supply of energy by the off-pulse of the control circuit 5 does not cause the voltage across the capacitor C2 to drop to 0 volts.
[0056]
Further, as described in Japanese Patent Publication No. 5-86130, for example, during an overcurrent protection operation in such a power supply device, the ON width becomes narrower as the load becomes heavier, and the energy supplied by the ON pulse becomes smaller. Although it decreases, the energy Q 'supplied between the terminals of the capacitor C2 increases as the off-width increases.
for that reason,Switching power supply device shown in FIGS. 1 and 36, the voltage across the capacitor C2 does not drop to 0 volts as shown in FIG.
[0057]
The rectifier circuit connected to the primary choke winding NLp of the inductor 13 may be a diode bridge, but requires two more diodes, and the voltage drop between the terminals of the capacitor C2 and the circuit loss increase.
[0058]
FIG.Second7 is a circuit configuration diagram of the switching power supply device according to the embodiment, and portions corresponding to FIG. 6 are denoted by the same reference numerals.
In this switching power supply, the secondary choke winding NLs of the inductor 13 in the rectifying and smoothing circuit 16 is connected to the connection point between the secondary winding Ns of the transformer 3 and the anode side of the commutation diode 9 and the negative terminal of the capacitor 10. Only the point interposed in the charging circuit during is shown in FIG.FirstSince the present embodiment is different from the above-described embodiment and the other configuration and the operation and effect are the same, the description thereof is omitted.
[0059]
【The invention's effect】
As described above, the switching power supply according to the present invention uses a large-sized transformer having a complicated structure provided with a tertiary winding as in the related art, or includes two transformers and two switching circuits. Alternatively, the power factor can be improved irrespective of the size of the load with a simple configuration using a small transformer and an inductor without using a large number of switching elements.
[0060]
If a small-capacitance 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 may be transmitted from the power supply line to another line. Transmission to peripheral devices can be prevented.
[0061]
Further, the voltage induced in the primary choke winding NLp of the inductor provided in the rectifying and smoothing circuit on the secondary side of the transformer is rectified by the rectifying circuit of the voltage doubler type to form a large-capacity capacitor (second capacitor). To chargeBecauseIn the overcurrent protection operation, even if the ON time of the switching element is shortened, the control circuit operates stably, and there is no possibility that the saturation of the transformer, the damage of the transistor, or the like occurs. Further, the number of turns of the primary choke winding of the inductor can be reduced to half.
[Brief description of the drawings]
FIG. 1 of the present invention.UnderlyingSwitching power supplyShow the first exampleIt is a circuit block diagram.
FIG. 2 is a waveform chart showing voltage and current waveforms of respective parts in FIG.
FIG. 3 of the present invention.UnderlyingSwitching power supplyShow a second exampleIt is a circuit block diagram.
FIG. 4 of the present invention.UnderlyingSwitching power supplyShow a third exampleIt is a circuit block diagram.
FIG. 5 of the present invention.UnderlyingSwitching power supplyShow a fourth exampleIt is a circuit block diagram.
[FIG. 6] The present inventionbySwitching power supply1 shows a first embodiment.It is a circuit block diagram.
[FIG. 7] The present inventionbySwitching power supplyShows a second embodimentIt is a circuit block diagram.
FIG. 8 is a waveform diagram showing a relationship between an ON width of the switching element 4 and a voltage between terminals of the capacitor C2 in the switching power supply device shown in FIGS. 1 and 3 to 5;
9 is a waveform diagram showing a relationship between an ON width of a switching element 4 and a voltage between terminals of a capacitor C2 in the switching power supply device shown in FIGS. 6 and 7. FIG.
FIG. 10 is a circuit diagram showing an example of a conventional switching power supply device.
FIG. 11 is a waveform chart showing voltage and current waveforms of respective parts in FIG.
[Explanation of symbols]
1: AC power supply 2: Diode bridge
3: Transformer Np: Transformer primary winding
Ns: secondary winding of transformer
4: Switching element 5: Control circuit
7: Diode for rectification 9: Diode for commutation
10: capacitor for smoothing 11, 12: output terminal
13: Inductor 16: Rectifying 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 (2)

A diode bridge (2) for full-wave rectification of an AC input, and a transformer (3) having a primary winding (Np) connected in series with a switching element (4) between output terminals (a, b) of the diode bridge. A rectifying and smoothing circuit (16) for rectifying and smoothing an AC voltage generated in a secondary winding (Ns) of the transformer, and outputting the rectified and smoothed voltage; A switching power supply device comprising a control circuit (5) for controlling on / off;
A diode (7) for rectifying a voltage generated in a secondary winding (Ns) of the transformer (3), a capacitor (10) for charging and smoothing the rectified voltage, An inductor (13) having a primary choke winding (NLp) and a secondary choke winding (NLs), wherein the secondary choke winding (NLs) is inserted in series in a charging circuit of the capacitor (10); A commutation diode (9) forming a circuit for discharging the energy stored in the inductor through the capacitor (10),
A first capacitor (C4) connected between a negative output terminal (b) of the diode bridge (2) and one end (h) of a primary choke winding (NLp) of the inductor (13);
A first diode (A) having an anode connected to the negative output terminal (b) of the diode bridge (2) and a cathode connected to the other end (g) of the primary choke winding (NLp) of the inductor (13). D4),
One end is connected to one end (h) of a primary choke winding (NLp) of the inductor (13), and the other end is connected to a negative output terminal () of the diode bridge (2) via a second capacitor (C2). a third capacitor (C3) connected to b);
An anode is connected to a connection point between the second capacitor (C2) and the third capacitor (C3), and a positive output terminal (a) of the diode bridge (2) and a primary of the transformer (3) are connected. A second diode (D2) having a cathode connected to a connection point with the winding (Np);
A third diode ( D3 ) having an anode connected to the cathode of the first diode (D4) and a cathode connected to the anode of the second diode (D2);
A switching power supply device comprising: 2. The switching power supply according to claim 1 , wherein a capacitor (C5) having a smaller capacity than the second capacitor (C2) is connected between the output terminals (a, b) of the diode bridge (2). Switching power supply device.

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