JPH07298611A - Switching power source - Google Patents

Abstract

PURPOSE:To provide a switching power source having a high power factor and a high efficiency by avoiding an increase in size and loss of an element even under the condition of a wide input voltage range. CONSTITUTION:When an input voltage is low, terminal voltages of first and second smoothing capacitors 45, 46 are applied to a primary winding 47 of a transformer 52. A doubled voltage is applied as compared with a power source having one smoothing capacitor and no switching element 44 which becomes ON for a period in which an output voltage of an AC power source is low. Thus, numbers of turns of a secondary winding 48 and a control winding 50 of the transformer can be reduced to 1/2. As a result, a current flowing to a switching element 34 is reduced to 1/2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type DC stabilized power supply device which inputs AC.

[0002]

2. Description of the Related Art FIG. 7 shows the configuration of a switching power supply proposed by the present inventors in Japanese Patent Application No. 5-177379. This switching power supply has a simple configuration including a switching element 34 and a control circuit 41, and simultaneously realizes a high power factor of an input current waveform and a constant voltage of an output.

The configuration of FIG. 7 has a commercial AC power source 20, a full-wave rectifier 21 composed of diodes 22, 23, 24, 25, an inductor 26, a primary winding 28, and a secondary winding 2.
9, a transformer 27 having a tertiary winding 30 and a control winding 31
A rectifying / smoothing circuit 35 including a smoothing capacitor 32, a diode 33, a switching element 34, diodes 36 and 37, an inductor 38, and a capacitor 39.
And a control circuit 41. 40 is a load.

This operation is as follows. Transformer 27
The primary winding 28 is N ₁ , the secondary winding 29 is N ₂ , the tertiary winding 30 is N ₃ , and the control winding 31 is N ₄ , respectively. , And the electric potentials at points c are V _a , V _b , and V _c , respectively. If N ₁ = N ₄ is set here, the transformer 27 is turned on when the switching element 34 is on.
The voltage of the smoothing capacitor 32, that is, V _b is applied to the primary winding 28. At this time, a voltage of (V _b · N ₄ ) / N ₁ is generated in the control winding 31 of the transformer 27, but since it has been set that N ₁ = N ₄ , this is almost V
is equal to _b . Therefore the voltage V _a of a point subtract generated voltage V _b of the control winding 31 of the transformer 27 from the voltage V _b of the smoothing capacitor 32 becomes zero volts. That is,
When the switching element 34 is on, the potential at the point a is always 0 volt.

When the switching element 34 is turned on,
The flow of current in the path is primarily the smoothing capacitor 32 →
 Primary winding 28 of transformer 27 → Secondary winding 29 →
 Rectifying and smoothing circuit 35 → Transformer via load 40
Returning to the primary winding 28, flowing through the switching element 34,
This causes the energy of the smoothing capacitor 32 to
Sending to 0. In addition, the switching element 34 is turned on.
Sometimes the voltage V at point a _a Is always zero volts, so
Input voltage V to the inductor 26_{in (3)} Is applied,
The inductance of the₂₆Flowing through the inductor 26
Current I_{L (on )} , Turn on the switching element 34
Let's say that time is t

[0006]

[Equation 1]

The current determined by is flowing through the inductor 26. This current flows through the control winding 31 of the transformer 27, and consequently the primary winding 28 of the transformer 27 and the switching element 34. Due to such a current flow, the energy of the commercial AC power supply 20 is transferred to the inductor 2
Stored in 6.

Next, when the switching element 34 is off, a counter electromotive force is generated in the tertiary winding 30 of the transformer 27 to reset the transformer, and a current flows into the smoothing capacitor 32 via the diode 33. At this time, the voltage between the terminals of the tertiary winding 30 is clamped by the voltage V _b of the smoothing capacitor 32, so the voltage V _{N4 (off )} generated in the control winding 31.
Is

[0009]

[Equation 2]

[0010] Therefore, the voltage V _{a (off) at} point a is

[0011]

[Equation 3]

Therefore, the input voltage V
_The voltage difference from _{in (3)} , that is,

[0013]

[Equation 4]

The current flowing through the inductor 26 is reduced by the application of the voltage Further, when the switching element 34 is off, there is a current flow in the circuit in which the current for resetting the transformer 27 flows into the smoothing capacitor 32 from the tertiary winding 30 through the diode 33. While the switching element 34 is off, the current of the inductor 26 flows into the smoothing capacitor 32 through the control winding 31, and at the same time, the current of the inductor 27 flows through the control winding 31 of the transformer 27.
From the tertiary winding 30 through the diode 33 into the smoothing capacitor 32. That is, due to such a current flow, the transformer 27 is turned off during the off period of the switching element 34.
The exciting energy of the transformer 27 is sent to the smoothing capacitor 32 for resetting the
The energy stored in is transmitted to the smoothing capacitor 32. Simultaneously with the above operation, the control circuit 41 controls the on / off period of the switching element 34 so that the output voltage of the rectifying / smoothing circuit 35 becomes a specified voltage.

8 (a), (b) and (c) show the operation waveforms of the respective parts of FIG. 7, and as described above, the input voltage V is maintained between the terminals of the inductor 26 while the switching element 34 is on.
_{When in (3 )} is applied and the switching element 34 is off,

[0016]

[Equation 5]

Since the voltage is applied, the current of the inductor 26 when the switching element 34 is turned on is represented by the above equation. Where V _{in (3)} is the commercial input voltage, L
₂₆ is the inductance of the inductor 26, and t is the time after the switching element 34 is turned on. Further, the current of the inductor 26 is set to zero ampere just before the switching element 34 is turned on. When this switching power supply is operating normally, the switching element 3
4 ON width t _on, so it is considered substantially constant at commercial AC cycle, on the switching element 34 at a high frequency - the peak value of the current of the inductor 26 in one cycle of turning off I
_{If L (Peek)} ,

[0018]

[Equation 6]

It becomes So V _{in (3)} is a sine wave,
From the above equation, it can be seen that the line connecting the peak current I _{L (Peek)} of the inductor 26 also has a sine wave. Next, when the switching element 34 is turned off, as described above, the inductor 26
Then

[0020]

[Equation 7]

[0021] Where V_{in (3)} Is the commercial input voltage,
V_b Is the voltage of the smoothing capacitor 32, N ₃ Is transformer 27
Number of turns of the tertiary winding 30 of N_Four Is the control winding of the transformer 27
There are 31 turns.

Therefore, the time t _off-1 from when the switching element 34 is turned off to when the current of the inductor 26 becomes zero amperes is expressed by the following equation.

[0023]

[Equation 8]

Therefore, the sum of t _on and t _off-1 is

[0025]

[Equation 9]

[0026] The current waveform at this time is as shown in FIG. Therefore, if the current of the inductor 26 is set so that it is always reset to zero amperes in the cycle of high frequency switching, the average value _{IL (Ave)} of the current of the inductor 26 in one cycle of high frequency switching is t ₀ at high frequency switching. When the period is, the following equation is obtained.

[0027]

[Equation 10]

Here, since V _{in (3)} is a sine wave at the commercial input voltage, if V _b is made 1.5 to 2 times or more larger than V _{in (3)} , it becomes a commercial cycle. I _{L (Ave)}
Is approximately a sine wave.

That is, a commercial input current waveform is approximated by using a low-pass filter for high-frequency ripple removal immediately before or after the full-wave rectifier 21 with respect to the current of the inductor 26 that increases and decreases at high frequencies. A sine wave can be used to increase the power factor.

[0030]

However, the above configuration has a problem when the fluctuation range of the AC input voltage is large. That is, since the switching element 34 and the diodes 36 and 37 must withstand the applied voltage at the maximum input voltage and the passing current at the minimum input voltage, a high withstand voltage inevitably occurs when the variation range of the input voltage is large. This is the point that a large current element is required. This is cost,
Not only does this lead to an increase in size, but generally, a switching element having a high breakdown voltage has a larger loss when passing a current than a switching element having a high breakdown voltage, so that the overall efficiency also decreases.

Therefore, it is conceivable to use a voltage doubler rectifier circuit as shown in FIG. 8 is a transformer, 15 is a switching element, 16 is a rectifying / smoothing circuit, 21 is a load, 2
2 is a control circuit. When the voltage of the AC power supply 1 is low, the switch element 44 is turned on. Then, in the positive half cycle of the AC power supply 1, the AC power supply 1 → diode 3 → capacitor 45 → switch element 44 → AC power supply 1
Current flows through the route of, and AC power supply 1 in the negative half cycle
→ Switch element 44 → Capacitor 46 → Diode 4 → Current flows in the route of AC power supply 1.
Since the capacitors 45 and 46 are charged at the peak value of the AC input voltage, a voltage twice as high as that in the case of full-wave rectification can be obtained between a and b in the figure. AC power supply 1
When the voltage is high, the switch element 44 is turned off to form a simple full-wave rectifier circuit. Thus, by switching the switch element 44 according to the voltage of the AC power supply 1,
The circuit in FIG. 9 can reduce the voltage fluctuation between a and b. Operation waveforms when the switch element 44 is off are shown in FIGS.

However, since this circuit is a capacitor input, as can be seen from FIG. 10, the input current I
_The power factor is extremely low due to surge _in . For this reason, simply adding the voltage doubler rectifier circuit shown in FIG. 9 in the preceding stage of the switching power supply device shown in FIG. 7 makes it possible to increase the power factor of the input current waveform of the switching power supply device shown in FIG. There is a problem of losing.

It is an object of the present invention to provide a switching power supply device having a high power factor and a high efficiency, which avoids an increase in size of an element and an increase in loss even under a wide input voltage range condition.

[0034]

In the switching power supply device of the present invention, a smoothing capacitor is connected between the output terminals of a full-wave rectifier connected to an AC power source, and a primary winding of a transformer is connected between the terminals of the smoothing capacitor. A series circuit of switching elements is connected, a rectifying / smoothing circuit is connected to the secondary winding of the transformer, and power is supplied to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, an output of the rectifying / smoothing circuit. In a switching power supply device including a control circuit that controls the switching element so that the voltage becomes a specified voltage, an inductor and a transformer control winding are respectively provided between an output terminal of the full-wave rectifier and each terminal of the smoothing capacitor. Connecting a series circuit of wires, and configuring the smoothing capacitor by series connection of first and second smoothing capacitors,
A switch element is interposed between a connection point between the first smoothing capacitor and the second smoothing capacitor and one end of the AC power supply, and the switch element is turned on while the output voltage of the AC power supply is low. It is characterized in that it is turned off during a period when the output voltage of the AC power supply is high.

[0035]

According to this structure, when the input voltage is low,
The terminal voltages of the first and second smoothing capacitors are applied to the primary winding of the transformer, the number of smoothing capacitors is one, and there is no switch element that is turned on when the output voltage of the AC power supply is low. A voltage twice as high as that of the device is applied, and the number of turns of the secondary winding and the control winding of the transformer can be halved, and as a result, the current flowing through the switching element is halved.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each embodiment of the present invention will be described below based on the equivalent circuits shown in FIGS. 1 to 6 and 11 to 13.

FIG. 1 shows a first embodiment of the present invention. This switching power supply device is a full-wave rectifier 2 composed of a commercial AC power supply 20 and diodes 22, 23, 24, 25.
1, the inductor 42, the primary winding 47, the secondary winding 4
8, a transformer 52 having a tertiary winding 49, control windings 50 and 51, smoothing capacitors 45 and 46, and a diode 3
3, switching element 34, diodes 36, 3
The control circuit 41 includes a rectifying / smoothing circuit 35 including an inductor 7, an inductor 38, and a smoothing capacitor 39. Reference numeral 40 is a load, and the basic configuration is the same as that of the circuit shown in FIG.

In the first embodiment, the smoothing capacitor 32 shown in FIG. 7 is changed to a series circuit of smoothing capacitors 45 and 46, and the connection point between the smoothing capacitor 45 and the smoothing capacitor 46 and the connection between the diode 24 and the diode 25. The switch element 44 is interposed between the point and the point. In addition, the series circuit of the inductor 43 and the control winding 51 of the transformer 52 forms a connection point between the diode 33, the smoothing capacitor 46, and the switching element 34, the diode 23, and the diode 2.
5 is connected to the connection point. Switch element 44
ON / OFF is controlled according to the voltage of the commercial AC power supply 20 as follows.

First, consider the case where the input voltage from the commercial AC power source 20 is low. As explained in the voltage doubler rectifier circuit shown in FIG. 9, the switch element 44 is turned on when the input voltage is low.

Then, when the switching element 34 is turned on, in the positive half cycle of the commercial AC power source 20, the commercial AC power source 20 → diode 22 → inductor 42.
→ Control winding 50 → Smoothing capacitor 45 → Switch element 44 → Current flows through the route of the commercial AC power supply 20.

In the negative half cycle, the commercial AC power source 20
→ switch element 44 → smoothing capacitor 46 →
Control winding 51 → inductor 43 → diode 2
3 → Current flows through the route of the commercial AC power supply 20.

Equivalent circuits at this time are shown in FIGS. 11 and 12, respectively. Therefore, in this loop, the operation of this circuit is equivalent to that of FIG. 7, which is the source of this circuit. Next, when the input voltage is high, the switch element 44 is turned off. Then, when the switching element 34 is turned on, the commercial AC power source 20 → the diode 22
→ inductor 42 → control winding 50 → smoothing capacitor 45 → smoothing capacitor 46 → control winding 5
1 → inductor 43 → current flows through the route of diode 25, or commercial AC power supply 20 → diode 24 → inductor 42 → control winding 50
→ Smoothing capacitor 45 → Smoothing capacitor 46 →
Control winding 51 → inductor 43 → diode 2
Electric current flows through route 3. This is because only the two blocks A and B shown in FIG. 1 are connected in series, so that the equivalent circuit is as shown in FIG. Therefore,
The operation is equivalent to that of FIG. 7 which is the basis of this circuit. As described above, the operation is equivalent to the original circuit.

Next, the operation after the smoothing capacitor will be considered. First, when the input voltage is low, the terminal voltage of the smoothing capacitors 45 and 46 is applied to the primary winding 47 of the transformer 52, and the applied voltage is twice that in the case of the device shown in FIG. Therefore, as compared with FIG.
The number of turns of the control windings 50 and 51 can be halved, and as a result, the current flowing through the switching element 34 becomes ½ of that in the case of FIG. 7.

Next, when the input voltage is high, the transformer 5
The voltage applied to the second primary winding 47 is the same as in the case of FIG. However, since the number of turns of the secondary winding 48 and the control windings 50 and 51 is halved, the voltage-time product of the transformer 52 is insufficient as it is. You can make up for it by doubling. The passing current of the switching element 34 at this time is shown in FIG.
Compared with the case of, the secondary winding 48 and the control windings 50, 5
Since the number of turns of 1 is 1/2, the passing current is 1
It becomes / 2, and it turns out that the ON time is doubled.
Ignoring the exciting current of the transformer 52, the passing current of the switching element 34 can be regarded as a rectangular wave, so that its effective value is "1 / √2" as compared with the circuit of FIG.

FIG. 2 shows a second embodiment. The same components as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted.

The difference from the configuration of FIG. 1 is that in FIG. 1 showing the first embodiment, the tertiary winding 49 of the transformer 52 is connected to the smoothing capacitors 45 and 46 connected in series via the diode 33. On the other hand, in FIG. 2 showing the second embodiment, the tertiary winding 49 of the transformer 52 is the smoothing capacitor 39 of the rectifying / smoothing circuit 35 on the secondary side of the transformer 52.
Is connected between the terminals.

Therefore, in FIG. 2, when the switching element 34 is turned off, the currents of the inductors 42 and 43 flow into the smoothing capacitors 45 and 46 via the control windings 50 and 51 of the transformer 52, and at the same time, the control winding of the transformer 52. As a result of flowing through 50 and 51, the corresponding current is
It flows from the tertiary winding 49 of the transformer 52 through the diode 33 into the smoothing capacitor 39 of the rectifying and smoothing circuit 35.

That is, while the switching element 34 is off due to such a current flow, the inductors 42, 4 are
The energy stored in 3 is the smoothing capacitor 4
5, 46 and the smoothing condenser 39 of the rectifying and smoothing circuit 35. Other operations are the same as those in FIG. 1, and equivalent effects can be obtained.

FIG. 3 shows a third embodiment. In the third embodiment, the tertiary winding 49 and the diode 33 of the transformer 52 found in the first and second embodiments are omitted. The energy of the smoothing capacitors 45 and 46 is stored in the transformer 52 while the switching element 34 is on, and the energy stored in the transformer 52 is stored while the switching element 34 is off.
At the same time as being sent to the load 40 via the inductor 4
The currents 2, 43 are the control windings 50, 51 of the transformer 52.
Through the smoothing capacitors 45, 46 through the control windings 50, 51 of the transformer 52 at the same time,
A current corresponding thereto flows from the secondary winding 48 of the transformer 52 into the smoothing capacitor 39 of the rectifying / smoothing circuit 35. That is, while the switching element 34 is off, the energy stored in the inductors 42 and 43 is sent to the smoothing capacitors 45 and 46 and the capacitor 59 of the rectifying and smoothing circuit 39. Other operations are the same as those in FIG. 1, and equivalent effects can be obtained.

FIG. 4 shows a fourth embodiment. In the fourth embodiment, a capacitor 53 is connected between the terminals of the switching element 34 of the third embodiment shown in FIG. This operation is performed after the exciting current of the transformer 52 is reset to zero ampere while the switching element 34 is off, and then the exciting inductance of the transformer 52 and the capacitor 5
3 resonates and lowers the voltage between the terminals of the switching element 34 to around 0 volt before the switching element 34 turns on, so that the switching loss at the time of turning on the switching element can be reduced.

FIG. 5 shows a fifth embodiment. In the fifth embodiment, capacitors 54 and 55 are connected in series with the control windings 50 and 51 of the transformer 52 of the third embodiment shown in FIG. 3, and the diodes 56 and 57 are connected in parallel to the series circuit. It is connected.

When the switching element 34 is on, the currents in the inductors 42 and 43 pass through the capacitors 54 and 55 to the control windings 50 and 51 of the transformer 52 and the primary winding 47,
Since the capacitors 54 and 55 start to have a voltage and the voltage becomes higher than the voltage of the smoothing capacitors 45 and 46, the current of the inductors 42 and 43 passes through the diodes 56 and 57,
It flows into the smoothing capacitors 45 and 46. That is, the switching element 34 even though on, the boost time of the inductor 42 and 43 is shortened, this boosting time higher input voltage V _in is shortened.

While the switching element 34 is off,
The currents of the inductors 42 and 43 flow into the smoothing capacitors 45 and 46 via the diodes 56 and 57, and at the same time, the exciting current from the control windings 50 and 51 of the transformer 52 causes the capacitors 54 and 55 and the diodes 56 and 57 to pass. Flow through the capacitors 54 and 55 to the switching element 3
4 is charged in the opposite direction to the ON period and the voltage drops. That is, in this fifth embodiment, in order to boost time of the inductor 42 and 43 becomes shorter the higher the input voltage V _in, the switching device 34 is a mode of continuous does not return to zero amperes during the off Also, the currents of the inductors 40 and 43 have a waveform _in which the input current waveform I _in generally corresponds to a sine wave, and the power factor increases.

FIG. 6 shows a sixth embodiment. In the sixth embodiment, instead of the series circuit of the primary winding 47 and the switching element 34 of the third embodiment shown in FIG. 3, the first switching element 63, the primary winding 47 of the transformer 52 and the The series circuit of the second switching element 64 is connected between the terminals of the smoothing capacitors 45 and 46 connected in series, and the first switching element 63 and the primary winding 47 are further connected.
The first diode 62 is connected between the connection point between the second switching element 64 and the primary winding 47, and the positive side electrode of the smoothing capacitor 45. Between the second diode 61 and
Are connected.

In this circuit example, since the first and second switching elements 63 and 64 are always turned on or off at the same time, the smoothing capacitors 45 and 46 are in the ON state while the two switching elements 63 and 64 are on. Voltage of primary winding 47
Energy of the smoothing capacitors 45 and 46 is sent to the load 40 from the primary winding 47 of the transformer 52, the secondary winding 48, and the rectifying and smoothing circuit 34. At the same time, the currents in the inductors 42 and 43 are
Control windings 50, 51 to the first switching element 6
3, the primary winding 47, and the second switching element 64.

On the other hand, the first and second switching elements 6
During a period in which the transformers 3 and 64 are off, the excitation energy of the transformer 52 is supplied to the smoothing capacitors 45 and 46 from both terminals of the primary winding 47 of the transformer 52 via the first diode 62 and the second diode 61, respectively. It is sent to the smoothing capacitors 45 and 46 through a path between the terminals. In addition, the currents of the inductors 42 and 43 are controlled by the control winding 5 of the transformer 52.
0, 51 to the smoothing capacitors 45, 46 and, at the same time, a current flows in the control windings 50, 51 of the transformer 52. As a result, a corresponding current flows from the primary winding 47 of the transformer 52 to the first winding 47. The current flows to the smoothing capacitors 45 and 46 via the diode 62 and the second diode 61.

[0057]

As described above, according to the present invention, the smoothing capacitor is connected between the output terminals of the full-wave rectifier connected to the AC power source, and the primary winding of the transformer and the switching element are connected between the terminals of the smoothing capacitor. A series circuit is connected, a rectifying / smoothing circuit is connected to the secondary winding of the transformer, and power is supplied to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, the output voltage of the rectifying / smoothing circuit is regulated. In a switching power supply device including a control circuit that controls the switching element so that the voltage of each of the inductors and the control winding of the transformer is connected in series between the output terminal of the full-wave rectifier and each terminal of the smoothing capacitor. A circuit is connected, and the smoothing capacitor is formed by connecting a first smoothing capacitor and a second smoothing capacitor in series, and the first smoothing capacitor and the second smoothing capacitor are connected. A switch element is interposed between a connection point with a capacitor and one end of the AC power supply, the switch element is turned on during a period when the output voltage of the AC power supply is low, and a period during which the output voltage of the AC power supply is high. Since it is configured to be turned off, the terminal voltage of the first and second smoothing capacitors is applied to the primary winding of the transformer when the input voltage is low, although the operation is equivalent to that of the conventional circuit. In comparison with a device that has only one smoothing capacitor and does not have a switch element that is in the off state when the output voltage of the AC power supply is high, the voltage is applied twice, and the secondary winding of the transformer and the control are controlled. The number of turns of the winding can be halved, so that the current flowing through the switching element is halved, and the passing current of the switching element can be reduced.
Even in a wide input voltage range, a high power factor and high efficiency switching power supply can be realized.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a second embodiment of the switching power supply device of the present invention.

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

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

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

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

FIG. 7 is a configuration diagram of a switching power supply device for explaining a problem to be solved by the invention.

8 is an operation waveform diagram of each part of the switching power supply device of FIG.

FIG. 9 is an operation waveform diagram of each part of the switching power supply device when the voltage doubler rectifier circuit is used as the input circuit.

10 is an operation waveform chart of each part of FIG.

FIG. 11 is an equivalent circuit diagram of the first embodiment of the present invention.

FIG. 12 is an equivalent circuit diagram of the first embodiment of the present invention.

FIG. 13 is an equivalent circuit diagram of the first embodiment of the present invention.

[Explanation of symbols]

 20 Commercial AC power supply 21 Full-wave rectifier 22, 23, 24, 25 Diode 33 Diode 34 Switching element 35 Rectification smoothing circuit 40 Load 41 Control circuit 42, 43 Inductor 44 Switch element 45, 46, 39 Smoothing capacitor 47 Primary winding 48 Two Next winding 49 Third winding 50,51 Control winding 52 Transformer 53,54,55 Capacitor 56,57,61,62 Diode 63,64 First and second switching element

Front page continuation (72) Inventor Haruo Watanabe 10-13 Minamimachi, Hanno City, Saitama Shindengen Industrial Co., Ltd. (72) Inventor Yoshinori Kobayashi 10-13 Minamimachi, Hanno City, Saitama Shindengen Industrial Co., Ltd. Inside the ceremony company factory (72) Inventor Yutaka Sekine 10-13 Minamimachi, Hanno City, Saitama Shindengen Industrial Co., Ltd. Inside the company company (72) Takuya Ishii 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. A smoothing capacitor is connected between the output terminals of a full-wave rectifier connected to an AC power source, and a primary winding of a transformer and a series circuit of a switching element are connected between the terminals of the smoothing capacitor. A rectifying / smoothing circuit is connected to the secondary winding, power is supplied to a load connected between the output terminals of the rectifying / smoothing circuit, and at the same time, the switching is performed so that the output voltage of the rectifying / smoothing circuit becomes a specified voltage. In a switching power supply device including a control circuit for controlling elements, a series circuit of an inductor and a control winding of the transformer is connected between an output terminal of the full-wave rectifier and each terminal of the smoothing capacitor, and the smoothing capacitor is connected. Is composed of a series connection of a first smoothing capacitor and a second smoothing capacitor, and a connection point between the first smoothing capacitor and the second smoothing capacitor and the alternating current A switch element is interposed between the one end of the power source and the switch element, and the switch element is turned on when the output voltage of the AC power supply is low and turned off when the output voltage of the AC power supply is high. Switching power supply. 2. A capacitor is inserted in series with the control winding,
The switching power supply device according to claim 1, wherein a diode is connected in parallel to the series circuit of the control winding and the capacitor.