JPH09117146A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC input switching power supply in which high power factor is ensured while reducing the size and cost without requiring a component having high withstand voltage. SOLUTION: Under light load, voltage vC1 of an electrolytic capacitor C1 increases and the voltage vL3 of tertiary winding TL3 of a transformer T increases in proportion to the voltage vL3 thus lowering the voltage vL1 of a choke coil L1 during the conduction interval of an FET Q1. Consequently, the current flowing through the passage between the coil L1 and FET Q1 decreases to reduce the energy being stored in the coil L1 during the conduction interval of FET Q1 thus decreasing the charging current for the capacitor C1 being fed from the primary winding TL1 proportionally. Furthermore, the charging current for the capacitor C1 being fed from the coil L1 during off interval of FET Q1 also decreases and fed back to lower the voltage vC1. When the voltage VC1 increases, the voltage VL3 of winding TL3 increases to shorten the interval where the input voltage vi > the voltage vL3 thus shortening the conduction interval of input current. Consequently, the feedback for causing the step-up chopper operation is reduced thus suppressing increase of the voltage VC1 furthermore.

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 that improves a power factor and reduces harmonic components of an input current.

[0002]

2. Description of the Related Art Recently, a switching power supply device for electronic equipment is intended to improve a power factor for an alternating current (AC) power supply and reduce a high frequency component so as to eliminate interference with peripheral circuits and peripheral equipment. Is required. As an example,
The description example shown in “1992 Switching Power Supply System Symposium Material: S7-3-5, 1- (a) of FIG. 6” is known.

FIG. 19 is a circuit diagram showing the configuration of this switching power supply device, and FIG. 20 is a diagram for explaining voltage and current waveforms in this operation. 19 and 20, in this example, the basic configuration is a separately-excited switching regulator, AC from a commercial power source (AC) or the like is rectified through a low-pass filter (LPF) 1a and a bridge rectifier 1b, and this voltage is choked. L
1, the voltage is applied to the winding start end of the transformer T through the diode D1.

The winding end of the primary winding of the transformer T is
The switching element for switching operation, for example, is connected to the drain of a field effect transistor (FET) Q1, the source of the FET Q1 is grounded, and the gate is supplied with a switching drive signal from the pulse width (PWM) control circuit 2. Thus, the FET Q1 performs a switching operation of conducting / non-conducting.

By this switching operation, an alternating current is led to the secondary winding of the transformer T, and this alternating current is rectified by the diode D3 connected to the winding start end of the secondary winding and the diode D4. This pulsating flow is converted into a direct current by the smoothing circuit of the choke coil L2 and the electrolytic capacitor C2 and applied to the load RL. The supply voltage of this load RL is used as the output voltage detection circuit 3
Then, the voltage fluctuation is detected and output to the pulse width control circuit 2, and a switching drive signal corresponding to the voltage fluctuation is supplied to the FET Q1 to control the output voltage to be constant.

Further, in this example, the choke coil L1
A diode D2 is connected between the connection point between the winding and the diode D1 and the winding end of the primary winding of the transformer T and the drain of the FET Q1. Further, an electrolytic capacitor C1 is connected between the winding start of the primary winding and ground. Are connected. This circuit converts electric power by the switching operation of the FET Q1 and operates as a so-called step-up chopper.

When the FET Q1 is turned on, a current corresponding to the input voltage flows through the choke coil L1 as shown in FIG. 20, and when it is turned off, the counter electromotive voltage of the choke coil L1 charges the electrolytic capacitor C1. FE like this
The choke coil L1 is generated by the switching operation of TQ1.
Choke coil L1 so that the current flowing through it becomes discontinuous
When the inductance value of is set, the average value of the current flowing through the choke coil L1 which is an AC input current is a current proportional to the AC voltage, and the input power factor is improved.

[0008]

However, in the switching power supply device of the conventional example described above, the ON time ratio of the switching element stabilizes the output voltage even when the load RL shown in FIG. 19 has a small current consumption Io. The voltage Vc1 of the electrolytic capacitor C1 at this time is obtained by solving the following equation with this voltage Vc1 since the voltage Vc1 does not operate at a constant voltage.

[0009]

(Equation 1)

FIG. 21 shows the voltage Vc1 of the electrolytic capacitor C1.
FIG. 6 is a characteristic diagram derived from equation (1) showing an example of the relationship between the load current and the load current. In FIG. 21, the voltage Vc1 of the electrolytic capacitor C1 at a light load has a very large value as shown by the curve plotted with circles (◯). In this conventional example, the number of turns N1 of the primary winding TL1 of the transformer T is 34 turns (T),
The number of turns N2 of the secondary winding TL2 is 4T, the inductance of the choke coil L1 is 50 μH, the input voltage Vi is direct current (DC) 100V, and the output voltage Vo is 5V.
Is the case.

Thus, the voltage Vc of the electrolytic capacitor C1 is
Since 1 becomes extremely high, the electrolytic capacitor C1, the diode D1, the diode D2, and the switching element F
It is necessary to use a high withstand voltage component for the ETQ1 and the like, and the external shape of the component becomes large, which hinders miniaturization, and has the drawbacks of high cost. The present invention is to solve the above problems in the conventional technique, eliminates the need to use high voltage components, downsizing,
Provided is a switching power supply device that enables cost reduction.

[0012]

In order to achieve this object, the switching power supply device of the present invention rectifies a commercial AC power supply with a diode connected in a bridge and smoothes its DC output with a capacitor. The DC voltage is chopped by a switching element through the primary winding of the transformer, the AC voltage generated in the secondary winding of the transformer is rectified and smoothed, and the DC voltage is output. The first choke coil, the tertiary winding of the transformer, and the first diode are connected in series between the DC output terminal of the diode connected in the bridge connection, the primary winding of the transformer, and the connection point of the switching element. And connecting the anode of the second diode to the connection point of the first coil and the tertiary winding of the transformer,
The cathode of the diode is connected to the connection point between the capacitor and the primary winding of the transformer.

A choke coil and a first diode are connected in series between the DC output terminal of the diode connected in the bridge and the intermediate tap of the primary winding of the transformer, and the first coil and the first diode are connected in series. Second at the connection point of the diode
The anode of the diode is connected, and the cathode of the second diode is connected to the connection point between the capacitor and the primary winding of the transformer.

Further, between the DC output terminal of the diode connected in bridge and the center tap of the primary winding of the transformer,
The first coil and the first diode are connected in series, the anode of the second diode is connected to the center tap of the first coil, and the cathode of the second diode is connected to the capacitor and the primary winding of the transformer. It is connected to the connection point.
Further, in these switching power supply devices, the voltage detection control unit detects the voltage value of the commercial AC power supply and outputs a control signal, and the switching unit has one end of the first coil or its intermediate tap and the primary of the transformer. A plurality of diodes connected to the plurality of intermediate taps of the winding are selectively connected or disconnected by a control signal from the voltage detection control unit.

Further, a voltage detection control section for detecting a voltage value of the commercial AC power source and outputting a frequency variable control signal,
The variable impedance element is provided between one end of the first choke coil and the anode of the second diode, or between the DC output end of the diode bridge-connected and the first choke coil. Furthermore, a voltage detection control unit that detects the voltage value of the commercial AC power source and outputs a frequency variable control signal is provided, and a core that partially has a gap with respect to the cross-sectional area is used for the first choke coil. ing.

In such a switching power supply device of the present invention, when the AC voltage of the secondary winding of the transformer is converted to DC and supplied to the load, the voltage of the capacitor is reduced when the load is light and the current is reduced. However, since the voltage of the tertiary winding of the transformer also increases at the same time, the period during which the commercial AC power supply voltage is higher than the voltage of the tertiary winding of the transformer decreases. This reduces the period of the boosting operation. In addition, the voltage applied to the first coil is reduced, the energy stored in the first coil is reduced, and the amount of charge to the capacitor is reduced, so that the voltage of the capacitor is prevented from rising. Therefore, it is not necessary to use a high withstand voltage component for the peripheral circuit including the capacitor, and the size and cost can be reduced.

Further, by selectively connecting a diode provided between the first coil and a plurality of intermediate taps of the primary winding of the transformer with a control signal, an optimal boost ratio and an optimal input can be obtained. Set to the conduction angle of the current. Therefore, the voltage boosting ratio of the capacitor can be made to correspond to the input voltage, for example, the input AC voltage 100V, 200V. In other words, this switching power supply device can be used in various electronic devices,
Versatility is improved.

Further, the voltage value of the commercial AC power supply is detected, a frequency variable control signal is output, and between the one end of the first choke coil and the anode of the second diode,
Or the DC output end of the diode connected in bridge and the first
The variable impedance element is connected between the choke coils. Further, the first choke coil is used in the core partially having a gap with respect to the cross-sectional area. When the switching frequency is increased, the inductance of the first choke coil is equivalently increased, and the switching frequency is increased. Compared to the case only, the voltage boosting ratio of the electrolytic capacitor can be greatly changed. As a result, when the input voltage is high, the voltage boosting ratio of the electrolytic capacitor is reduced by a small change in the switching frequency without adding any special parts, and the withstand voltage is low for the primary side parts such as the electrolytic capacitor and switching element. The parts can be used.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a switching power supply device of the present invention will be described in detail with reference to the drawings. In the following text and drawings, the same components as those in the previous FIG. 19 are designated by the same reference numerals. FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a switching power supply device of the present invention, and FIG. 2 is a waveform diagram of voltage and current of each part. In addition,
The control circuit (switching control circuit 2 and output voltage detection circuit 3) in FIG. 1 is omitted in the drawings after FIG. In FIGS. 1 and 2, the basic configuration of the first embodiment is a separately excited switching regulator. A bridge rectifier 1b that outputs an input voltage vi rectified by removing noise in its high frequency band from an alternating current from a commercial power source (AC) or the like, and the input voltage vi are input to the bridge rectifier 1b, as shown in FIG. Generating the voltage vL1 and
A choke coil L1 through which the current iL1 shown in (b) flows is provided.

Further, the current iTL1 shown in FIG. 2 (h) is applied to the winding start end of the primary winding TL1 through the diode D1 which outputs the current iD1 shown in FIG. 2 (d).
Where the transformer flows and the primary winding TL of this transformer T
The end of winding of No. 1 is connected to the drain, and the source is grounded to perform a switching operation to generate the voltage vQ1 shown in FIG. 2 (f) and the current iQ shown in FIG. 2 (g).
1, a field effect transistor (FET) Q1 as a switching element is provided.

An alternating voltage is induced in the secondary winding TL2 of the transformer T by the switching operation of the FET Q1, and the diode D for applying the alternating voltage to rectify the voltage.
3 and D4 and the currents iD3 and iD shown in FIGS.
4 has a coil L2 for smoothing and an electrolytic capacitor C2. Further, the direct current from the smoothing circuit is supplied, the current consumption thereof changes, the load RL that becomes a light load or a heavy load, and the fluctuation of the supply voltage of this load RL are detected, and this fluctuation voltage is detected by the pulse width control circuit. 2 and supplies a switching drive signal corresponding to the voltage fluctuation to the FET Q1 to control the output voltage to be constant.

Further, in this example, as will be described later in detail, a step-up chopper section for performing a power conversion operation is provided. This step-up chopper part includes the FET Q1, the choke coil L1, and the diode D1 as well as the choke coil L1.
The other end is connected to one end thereof to generate the voltage vL3. An anode is connected to the tertiary winding TL3 of the transformer T and the other end of the tertiary winding TL3, and a cathode is connected to a connection point of the winding end end of the primary winding TL1 of the transformer T and the drain of the FET Q1. Diode D
2 and an electrolytic capacitor C1 connected between the winding start end of the primary winding TL1 and the ground.

Next, the operation of the first embodiment will be described. FIG. 3 is a diagram for explaining a switching operation under a light load or a heavy load, and FIG. 4 is a diagram for explaining a conduction angle and the like under a light load or a heavy load. FIG.
FIG. 4 is a circuit diagram for explaining a current path during operation.
1 to 5, the current iL1 flowing in the choke coil L1 due to the switching operation of the FET Q1 is shown in FIG.
The inductance value is set so as to be discontinuous as shown in. In addition, the supply voltage of the load RL is divided by the output voltage detection circuit 3, for example, a resistor to detect fluctuation, and the fluctuation is output to the pulse width control circuit 2. A switching drive signal corresponding to this fluctuating voltage is supplied to the FET Q1 to control the output voltage to be constant. The voltage vL3 generated in the tertiary winding TL3 during the conduction period in the switching operation of the FET Q1 is calculated by the following equation (2) from the voltage vC1 of the electrolytic capacitor C1, the winding number N3 of the tertiary winding TL3 and the winding number N1 of the primary winding TL1. ).

Voltage vL3 = vC1 × N3 / N1 (2) Here, the input current flows during the conduction period of voltage vL3 <input voltage vi. At this time, in the conduction period of the FET Q1, the current i shown in FIG. 5 in which energy is stored in the choke coil L1.
1 (iL1, iL3, iD2a, iQ1), a current i3 shown in FIG. 5 proportional to the current i1, and a load current i4.
Then, a current i2 proportional to the load current i4 flows. F
During the non-conduction period of ETQ1, a current i5 that supplies the energy stored in the choke coil L1 to the electrolytic capacitor C1 during the conduction period and a current i6 that supplies the energy stored in the coil L2 during the conduction period to the load RL flow.

During the period of voltage vL3> input voltage vi, the input current stops flowing. During the conduction period of the FET Q1, the current i4 supplied to the load RL flows, and further, the current i2 proportional to the current i4 flows. During the non-conduction period of the FET Q1, the current i6 that supplies the energy stored in the coil L2 to the load RL during the conduction period flows. Here, the electrolytic capacitor C1 is charged by the current i3 during the conduction period of the FET Q1,
The discharge is performed by the current i5 during the non-conduction period of the FET Q1, and the discharging is performed by the current i2 during the conduction period of the FET Q1.

When the current flowing through the load RL is reduced, the current i2 discharged from the electrolytic capacitor C1 decreases and the voltage vC1 shown in FIG. 1 increases. When this voltage vC1 becomes higher, the voltage vL3 becomes higher in proportion to the voltage vC1, and the voltage vL1 (= vi-vL) of the choke coil L1 during the conduction period of the FET Q1 when the input current flows.
Since 3) becomes low, the current i1 in FIG. 5 decreases. The decrease in the current i1 reduces the energy stored in the choke coil L1 during the conduction period of the FET Q1.

Therefore, the current i5 also decreases, and the current i3 proportional to this current i5 also decreases. That is,
Feedback is applied so that the current i3 and the current i5 charged in the electrolytic capacitor C1 are reduced and the voltage vC1 is lowered. Further, when the voltage vC1 becomes high, the voltage v of the tertiary winding TL3 becomes
L3 increases, the period of input voltage vi> voltage vL3 decreases, and the conduction period of the input current decreases, which shortens the period during which the boost chopper operates, which also suppresses the increase in voltage vC1 of electrolytic capacitor C1. It takes a return to do.

Next, the operation of an actual circuit example will be described. In the configuration shown in FIG. 1, the voltage vC1 of the electrolytic capacitor C1 is a solution obtained by solving the following equation (3) for the voltage vC1, and the voltage vC1 of the electrolytic capacitor C1 is lower than that of the conventional example even when the load RL has a small current. It becomes a value.

[0029]

(Equation 2)

FIG. 6 is a characteristic diagram showing an example of the relationship between the voltage Vc1 of the electrolytic capacitor C1 and the load current in the first embodiment. In FIG. 6, an electrolytic capacitor C1
The relationship between the voltage Vc1 and the load current is as a curve plotted with squares (□). In this example, as in the conventional example, the number of turns N1 of the primary winding TL1 of the transformer T is 34 turns (T), the number of turns N2 of the secondary winding TL2 is 4T, and
This is the case where the input voltage Vi is direct current (DC) 100V and the output voltage Vo is 5V. Furthermore, the tertiary winding TL of the transformer T
When the number of turns N3 of 3 is 14T, the inductance of the choke coil L1 is 10 μH, and the load current Io is 20 amperes (A), the voltage vC1 of the electrolytic capacitor C1 becomes equal to that of the conventional example shown in FIG. Yes,
As shown in FIG. 6, the voltage vC1 of the electrolytic capacitor C1 is as shown in FIG. 21 when the current Io of the load RL becomes small.
The voltage is lower than that of the conventional example shown in.

In this way, it is possible to suppress an increase in the voltage vC1 of the electrolytic capacitor C1 even when the load RL is light. As a result, it is not necessary to use high withstand voltage components for the electrolytic capacitor C1 and its peripheral circuits, which leads to downsizing,
Cost reduction is possible. FIG. 7 is a circuit diagram showing the configuration of the second embodiment. In FIG. 7, the second embodiment is a circuit basically similar in configuration and equivalently equivalent to the first embodiment shown in FIG. In the second embodiment, the transformer T having an intermediate tap is provided with the conventional circuit configuration.
It is sufficient to use only two primary windings TL1a. That is, there is an advantage that the tertiary winding TL3 becomes unnecessary, the configuration on the circuit board is simplified, and the size can be reduced.

FIG. 8 is a circuit diagram showing the configuration of the third embodiment. In FIG. 8, this example uses a choke coil L1a provided with an intermediate tap, and the anode of a diode D1 is connected to this intermediate tap. In the third embodiment, the inductance of the primary winding TL1a increases during the conduction period of the FET Q1, and the inductance of the primary winding TL1a decreases during the non-conduction period of the FET Q1. As a result, the upper limit of the inductance for making the current iL1 of the choke coil L1 discontinuous increases,
According to the equation (2), the voltage boosting ratio of the electrolytic capacitor C1 with respect to the input voltage vi can be reduced.
The other operations are the same as those in the first embodiment.

FIG. 9 is a circuit diagram showing the structure of the fourth embodiment. In FIG. 9, in this example, when the supply voltage from an alternating current (AC) power supply is continuously variable from 100 V to 200 V, the operation is automatically switched between 100 V and 200 V. Here, the diode D2 is connected between one intermediate tap of the primary winding TL1b of the transformer T3 having two intermediate taps and the connection point of the choke coil L1 and the diode D1. A switch SW2 and a diode D5 are connected in series between the connection point between the choke coil L1 and the diode D1 and the other intermediate tap.

In the fourth embodiment, the bridge rectifier 1
The output voltage of b is detected by the voltage detection control circuit 5, and it is determined whether the voltage supplied from the AC power supply is, for example, 100 V or 200 V. When it is 100 V, the movable contact of the switch SW2 is set to drive continuity. To do. When the voltage is 200 V, the movable contact of the switch SW2 is not driven and set to be non-conductive. That is, the choke coil L during the switch-on period
1 is changed so that the voltage boosting ratio of the electrolytic capacitor C1 corresponds to the input voltage vi.

FIG. 10 is a circuit diagram showing the configuration of the fifth embodiment. In FIG. 10, this example uses a choke coil L1a having an intermediate tap and a transformer T2 having an intermediate tap. A diode D6 is connected between the center tap of the choke coil L1a and the winding start end of the primary winding TL1a. Further, the switch SW2 and the diode D2a are connected in series between the switch SW3 and the intermediate tap of the diode D line TL1a between the other end of the choke coil L1a and the winding start end of the primary winding TL1a. Further, the other end of the choke coil L1a and the primary winding T
A diode D2b is connected to another intermediate tap of L1a.

In the fifth embodiment, the bridge rectifier 1
The output voltage of b (input voltage vi) is detected by the voltage detection control circuit 5, the switches SW2 and SW3 are switched, and the voltage boosting ratio of the electrolytic capacitor C1 is made to correspond to the voltage (input voltage vi) from the AC power supply. . FIG. 11 is a circuit diagram showing the configuration of the sixth embodiment. In FIG. 11, this example is
A choke coil L1a provided with an intermediate tap and a transformer T3 provided with two intermediate taps are used. A diode D6 is connected between the center tap of the choke coil L1a and the winding start end of the primary winding TL1b. Also,
A diode D1 is connected between the other end of the choke coil L1b and one intermediate tap of the primary winding TL1b. Middle tap of choke coil L1a and primary winding TL
The switch SW2 and the diode D5 are connected in series with the other middle tap of 1b.

In the sixth embodiment, the bridge rectifier 1
The output voltage of b is detected by the voltage detection control circuit 5, the switch SW2 is switched, and the voltage boosting ratio of the electrolytic capacitor C1 is made to correspond to the supply voltage (input voltage vi) from the AC power supply. FIG. 12 is a circuit diagram showing the configuration of the seventh embodiment. In FIG. 12, this example is an example using a flyback converter.
4 primary coil TL1c stores energy and FET
Energy is led to the secondary coil TL2a when Q1 is not connected. The operation of the boost chopper section is similar to that of the first embodiment and so on, and the advantages thereof are also the same.

FIG. 13 is a circuit diagram showing the structure of the eighth embodiment. In FIG. 13, in this example, the variable inductance element Z1 is connected between the first choke coil L1 and the anode of the second diode D2a, and the input voltage is detected, and the detected value is detected. A voltage detection control unit 10 that outputs a frequency control signal to the PWM control circuit 2 is provided. The voltage detection control unit 10 includes an input voltage detection circuit 10a and a PFM control circuit 10b. The variable inductance element Z1 uses, for example, a saturable inductor. In the eighth embodiment, when the switching frequency is high as shown in FIG.
As shown in (b), when it changes to a low case, a current flows in the first choke coil L1 from the point where the saturable inductance element Z1 is saturated. That is, when the switching frequency is increased, the inductance of the first choke coil L1 is equivalently increased, and the voltage boosting ratio of the electrolytic capacitor C1 can be greatly changed as compared with the case where the switching frequency is increased. Become.

FIG. 15 is a circuit diagram showing the structure of the ninth embodiment. In FIG. 15, in this example, the variable inductance element Z2 is connected between the DC end of the diode 1b bridge-connected and the first choke coil L1.
Further, it has a voltage detection control unit 10 which detects an input voltage and outputs a frequency control signal corresponding to the detected value to the PWM control circuit 2. The voltage detection control unit 10 includes an input voltage detection circuit 10a and a PFM control circuit 10b, and the variable inductance element Z2 uses, for example, a saturable inductor. The operation here is basically the same as that of the eighth embodiment shown in FIG.

FIG. 16 is a circuit diagram showing the structure of the tenth embodiment. In FIG. 16, this example is provided with a voltage detection control unit 10 that detects an input voltage and outputs a frequency control signal corresponding to the detected value to the PWM control circuit 2.
Moreover, as shown in FIG. 17, the first choke coil L1 uses a core in which a gap G is partially provided with respect to the cross-sectional area. The voltage detection control unit 10 includes an input voltage detection circuit 10
a and the PFM control circuit 10b.

Here, the switching frequency is shown in FIG.
When changing as shown in FIG. 18 and changing as shown in FIG. 18B, the first choke coil L1 is
It becomes a transient waveform in which a large current flows from the partial saturation point of the core. The operation here is basically the same as that of the eighth embodiment shown in FIG.

[0042]

As is apparent from the above description, according to the switching power supply device of the present invention, when the voltage of the capacitor becomes high at a light load, the conduction angle of the input current becomes small and the boosting voltage increases. The period during which the chopper operates is shortened, the voltage applied to the first coil is reduced, and the stored energy is reduced.

As a result, the charge amount of the capacitor is reduced, and feedback is applied to suppress the voltage increase, so that the voltage increase amount of the capacitor can be suppressed small. As a result, it is not necessary to use a high withstand voltage component for the peripheral circuit including the capacitor, and it is possible to reduce the size and cost. In addition, the connection between the plurality of diodes provided between the first coil and the plurality of intermediate taps of the primary winding of the transformer is selectively connected or disconnected by a control signal to optimize the conduction angle of the input current. Also, since the voltage applied to the first choke coil is set to the optimum value, it is possible to handle a wide range of input AC voltage. As a result, the switching power supply device can be used in various electronic devices, and versatility is improved.

Further, the first choke coil is used in the core which performs variable frequency control, has a variable impedance element, and has a partial gap with respect to the cross-sectional area, and is equivalent to increasing the switching frequency. The inductance of the first choke coil increases,
Compared to only when the switching frequency is increased, the voltage boost ratio of the electrolytic capacitor can be changed significantly, and when the input voltage is high without adding any special parts,
With a small change in switching frequency, the voltage boosting ratio of the electrolytic capacitor can be reduced, and components with low breakdown voltage can be used as the primary side components such as the electrolytic capacitor and the switching element.

[Brief description of the drawings]

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

FIG. 2 is a waveform diagram of voltage and current of each part in the first embodiment of FIG.

FIG. 3 is a diagram for explaining a conduction angle or the like under a light load or a heavy load in the first embodiment of FIG.

FIG. 4 is a diagram for explaining a switching operation at the time of a light load or a heavy load in the first embodiment of FIG.

5 is a circuit diagram for explaining a current path during operation in the first embodiment of FIG.

6 is a characteristic diagram showing the relationship between the voltage of the electrolytic capacitor and the current of the load in the first embodiment of FIG.

FIG. 7 is a circuit diagram showing a configuration of a second embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a third embodiment of the present invention.

FIG. 9 is a circuit diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 10 is a circuit diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 11 is a circuit diagram showing a configuration of a sixth embodiment of the present invention.

FIG. 12 is a circuit diagram showing a configuration of a seventh embodiment of the present invention.

FIG. 13 is a circuit diagram showing a configuration of an eighth embodiment of the present invention.

FIG. 14 is a waveform diagram of a current flowing through the first choke coil in the eighth embodiment.

FIG. 15 is a circuit diagram showing a configuration of a ninth embodiment of the present invention.

FIG. 16 is a circuit diagram showing a configuration of a tenth embodiment of the invention.

FIG. 17 is a perspective view showing the shape of the core of the first choke coil in the tenth embodiment.

FIG. 18 is a waveform diagram of a current flowing through the first choke coil in the tenth embodiment.

FIG. 19 is a circuit diagram showing a configuration of a conventional switching power supply device.

FIG. 20 is a diagram for explaining voltage and current waveforms in the operation of the conventional example.

FIG. 21 is a characteristic diagram showing an example of the relationship between the voltage of the electrolytic capacitor and the load current in the conventional example.

[Explanation of symbols]

 1a: Low-pass filter 1b: Bridge rectifier 2: Switching control circuit 5: Voltage detection control circuit 10: Voltage detection control unit 10a: Input voltage detection circuit 10b: PFM control circuit C1: Electrolytic capacitors D1, D2a, D3, D4, D5: Diodes L1, L1a, L2: Choke coil TL3: Tertiary winding Q1: FET RL: Load SW2, SW3: Switches T, T2, T3, T4: Transformers TL1, TL1a, TL1b: Primary winding TL2: Secondary winding

Claims (6)

[Claims] 1. A commercial AC power supply is rectified by a diode connected in a bridge, its DC output is smoothed by a capacitor, and this smoothed DC voltage is chopped by a switching element via a primary winding of the transformer. In a switching power supply that rectifies and smoothes an AC voltage generated in a secondary winding and outputs a DC voltage, a DC output terminal of the diode connected in a bridge, a connection point between the primary winding of the transformer and a switching element Between the first choke coil and the tertiary winding of the transformer and the first
Is connected in series, the anode of the second diode is connected to the connection point between the first coil and the tertiary winding of the transformer, and the cathode of the second diode is connected to the capacitor and the primary winding of the transformer. A switching power supply device characterized in that the switching power supply device is connected to the connection point. 2. A commercial AC power supply is rectified by a diode connected in a bridge, its DC output is smoothed by a capacitor, and this smoothed DC voltage is chopped by a switching element via a primary winding of the transformer. In a switching power supply that outputs a DC voltage by rectifying and smoothing an AC voltage generated in a secondary winding, between the DC output terminal of the bridge-connected diode and the intermediate tap of the primary winding of the transformer, The choke coil and the first diode are connected in series and provided.
An anode of a second diode is connected to a connection point between the first coil and the first diode, and a cathode of the second diode is connected to a connection point between the capacitor and the primary winding of the transformer. Switching power supply. 3. A commercial AC power source is rectified by a diode connected in a bridge, its DC output is smoothed by a capacitor, and this smoothed DC voltage is chopped by a switching element via a primary winding of the transformer, In a switching power supply that rectifies and smoothes the AC voltage generated in the secondary winding and outputs a DC voltage, between the DC output end of the diode connected in the bridge and the intermediate tap of the primary winding of the transformer, A first coil and a first diode are connected in series, the anode of the second diode is connected to the intermediate tap of the first coil, and the cathode of the second diode is connected to the primary winding of the capacitor and the transformer. A switching power supply device characterized in that the switching power supply device is connected to the connection point. 4. The switching power supply device according to claim 2 or 3, wherein a voltage detection control unit that detects a voltage value of the commercial AC power supply and outputs a control signal, and one end of the first coil or an intermediate thereof. A switching unit that selectively connects or disconnects a plurality of diodes connected between the tap and a plurality of intermediate taps of the primary winding of the transformer with a control signal from the voltage detection control unit. A characteristic switching power supply. 5. The switching power supply device according to claim 2, wherein a voltage detection control unit that detects a voltage value of the commercial AC power supply and outputs a frequency variable control signal, and one end of the first choke coil. And a variable impedance element connected between the anode of the second diode or between the DC output terminal of the diode connected in bridge and the first choke coil. 6. The switching power supply device according to claim 2 or 3, wherein a voltage detection control section for detecting a voltage value of a commercial AC power supply and outputting a frequency variable control signal, and a partial cross section And a first choke coil using a core provided with a gap in the switching power supply device.