JP2724258B2 - Switching power supply - Google Patents

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.

[0002]

2. Description of the Related Art Conventionally, this type of apparatus has been configured as shown in FIG. In FIG. 8, V _AC is the AC power supply, D _B
The diode bridge circuit for rectification, C ₁₁ is a smoothing capacitor, T ₁₁ is the inverter transformer, Q ₁₁ is a switching transistor. S ₁₁ is a switch, R ₁₁ is a resistor constitute a circuit for preventing excessive rush current to the capacitor C ₁₁ at starting the resistor R ₁₁ and the switch S _11. The switch S ₁₁ is intended to be opened only at the start. A rectifying / smoothing circuit including diodes D ₁₂ and D ₁₃ , a coil L ₁₁ and a capacitor C ₁₂ is connected to the secondary winding of the inverter transformer T ₁₁ , and the output voltage V ₀ is supplied to the load.

[0003] In the above prior art configured as described above, to obtain a smoothed to a DC voltage V _CC AC voltage supplied from the AC power supply V _AC capacitor C ₁₁ is full-wave rectified by the diode bridge circuit D _B . The DC voltage V _CC, transistor Q ₁₁ is applied to the primary winding of the inverter transformer and switching at high speed (above 20 KHz). As a result, the AC voltage induced in the secondary winding of the inverter transformer is converted to diodes D ₁₂ , D ₁₃ , coil L ₁₁ , capacitor C
Supplying the output voltage V ₀ to the load by the rectifying and smoothing circuit consisting of ₁₂ rectifying and smoothing it.

[0004] In such a conventional example, in order to prevent the flow of excessive rush current to capacitor C ₁₁ during startup, the switch S ₁₁ are opened, the charging resistor R ₁₁
Capacitor C ₁₁ by is charged to a predetermined voltage. The switch S ₁₁ is closed at the stage of the capacitor C ₁₁ reaches a predetermined voltage.

[0005] When supplying power from the AC power supply V _AC of 50Hz to the conventional example operates as described above, the input current I
The waveform of in is shown in FIG.

[0006] As shown in FIG. 9, until the capacitor C ₁₁ is charged, and sustained inrush current gradually decreases, the capacitor C ₁₁ is the switch S ₁₁ becomes a predetermined voltage is closed, BALS-like A charging current having a high frequency component flows.

[0007]

As described above, in the conventional example described above, since the input current Iin during the normal operation contains many harmonic components, the power factor is 0.5 to 0.5.
It was 6.

[0008] In order to improve this power factor had to the circuit for obtaining a voltage V _CC applied to the inverter transformer T ₁₁ active rectifier filter circuit shown in FIG. 10. This active rectifier filter circuit is to accumulate energy in the choke coil L ₂₁ during conduction of the transistor Q _21, charges the capacitor C ₂₁ during non-conduction of the transistor Q ₂₁ by the energy of the choke coil L _21. Then, and to improve its power factor to 0.9 of by the input current Iin to be controlled on and off of the transistor Q ₂₁ becomes a sine wave.

As described above, the conventional switching power supply device has a problem that the input current Iin during normal operation contains many high-frequency components, which causes harmonic distortion and lowers the power factor. . In order to solve such a problem, it is necessary to add the above-mentioned active filter circuit. In this case, the cost of the device becomes high (1.5 to 2 times). Is newly generated.

Furthermore, in the conventional switching power supply, in order to prevent excessive rush current to the capacitor C ₁₁ at the start, it is necessary to provide a switch S ₁₁ a charge resistor R _11, and the switch S ₁₁ the failure is also Given that a large percentage among the failure cause of the entire apparatus, failure of the order switch S ₁₁ there is also a problem that in some cases reduce the reliability of the device.

An object of the present invention is to provide a switching power supply which can significantly reduce the harmonic component of the input current by using the configuration of the conventional device without using an active filter circuit, and further eliminates the need for an inrush current prevention circuit. Is to do.

[0012]

In order to achieve the above object, the present invention has first, second and third terminals on a primary side, wherein the first terminal and the second terminal are connected to each other. An inverter transformer having a first primary winding provided between terminals, a second primary winding provided between the first terminal and the third terminal, and a secondary winding; A rectifier circuit that rectifies an AC voltage supplied from an AC power supply and has a positive output terminal connected to a first terminal of the inverter transformer, a negative output terminal of the rectifier circuit, and a second output terminal of the inverter transformer. A switching means provided between the inverter transformer, a rectifying / smoothing circuit connected to a secondary winding of the inverter transformer for supplying DC power to a load, and one end connected to a first terminal of the inverter transformer. A capacitor and a cathode at the other end of the capacitor A first diode having an anode connected to a negative output terminal of the rectifier circuit, and a second diode having an anode connected to the other end of the capacitor and a cathode connected to a third terminal of the inverter transformer. And an energy storage means provided in the inverter transformer and storing energy when the switching means is turned on.

[0013]

In the present invention configured as described above, when the positive voltage of the rectifier circuit is higher than the voltage between the terminals of the capacitor, the first primary winding of the inverter transformer is turned on when the switching means is turned on. Current flows from the power supply to supply power to the secondary side, and energy is stored in the energy storage means. When the switching means is non-conductive, the current flowing through the second primary winding by the energy stored in the energy storage means is transferred between the capacitor and the second primary winding.
To charge the capacitor.

When the voltage of the positive electrode of the rectifier circuit is lower than the voltage between the terminals of the capacitor, the discharge current of the capacitor during the conduction of the switching means is reduced by the first primary winding of the inverter transformer and the first diode. , Power is supplied from the capacitor to the secondary side.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a first configuration of the present invention, in which components having the same reference numerals as those of the conventional circuit shown in FIG. Further, T ₁ has an inverter transformer having two primary windings N ₁ and N _{3 on} the primary side, a gap is provided in the core to reduce the magnetic permeability, C ₁ is a capacitor, D ₂ , D _{2 3} is a diode.

The schematic operation of the embodiment constructed as described above will be described with reference to FIG. 2 showing waveforms of respective parts.

[0018] First, in the AC power supply V _AC voltage the positive terminal voltage is higher period than the voltage across the terminals of the capacitor C ₁ of the diode bridge circuit D _B full-wave rectification, from the AC power supply V _AC (50 Hz) A current i ₁ flows through the primary winding N ₁ to supply power to the secondary side. Further, in this period, the charging current i ₂ from the primary winding N ₃ to the capacitor C ₁ by the operation to be described later to charge the capacitor C ₁ flows.

Further, in the diode bridge circuit D positive terminal voltage is lower period than the voltage across the terminals of the capacitor C ₁ of _B, and the capacitor C ₁ discharging current i ₃ is the primary winding N ₁ and the diode D ₂ Because it flows, the capacitor C ₁
Is supplied to the secondary side by the energy stored in the secondary battery. The terminal voltage of the capacitor C ₁ at the points a and b in FIG. 2, can be changed by adjusting the gap of the core of inverter transformer T _1.

Next, detailed operation of this embodiment with reference to enlarged views of respective portions of the waveform at the period t ₁ shown in FIG. Here, the switching frequency of the transistor Q ₁₁ is 50KHz
And

[0021] FIG. 3 is a waveform diagram showing a waveform of each part in the period t _1. In FIG. 3, first, the transistor Q
₁₁ is turned on to the primary winding current i ₁ from the AC power supply V _AC N
Flowing through the _primary. Voltage This current i ₁ to the secondary winding N ₂ is induced, the diode D ₁₂ and the choke coil L ₁₁
Charging current i ₄ to the capacitor C ₁₂ through flow. In addition, magnetic energy is accumulated by the current i _{1 in the} inverter transformer T _{1 in} which the core has a gap and its magnetic permeability is reduced.

[0022] Then, the transistor Q ₁₁ is turned off, counter electromotive force is caused by the energy stored in the inverter transformer T ₁ to the primary winding N _3. This back electromotive force causes a current i ₂ passing through the capacitor C ₁ and the diode D _3.
Flows to charge the capacitor. On the other hand, in the secondary side, and supplies power to the load R _L side current i ₅ flows through the magnetic energy accumulated in the choke coil L _11.

[0023] The amount of energy e accumulated by the current i ₁ to the inverter transformer T ₁ is expressed by the following equation.

[0024] _{e = (L T1 × i P} × t ON) - (2 -side transfer energy) L _T1: 1 winding N ₁ of the inductance i _P: peak value of the collector current of the transistor Q ₁₁ t _ON: transistor or on-time of Q ₁₁ is, the voltage of the positive terminal of the diode bridge circuit D _B is the operation of the present embodiment in greater period than the voltage across the terminals of the capacitor C _1.

Next, the bridge voltage between the terminals of the capacitor C ₁ is diode circuit during the period t ₂ shown in FIG. 2 D _B
And the current i ₁ does not flow. In such period, the primary winding N _1, the discharge current i ₃ of the capacitor C ₁ through the transistor Q ₁₁ and diode D ₂ flows according on and off of the transistor Q ₁₁ as shown in FIG. Operation of the secondary side of this period is the same operation in the period t ₁ previously described.

FIG. 5A is a spectrum diagram of the waveform of the input current in the conventional example, and FIG. 5B is a spectrum diagram of the waveform of the input current in the present embodiment. As is clear from FIG. 5, in the input current of the present embodiment, the harmonic components are reduced as compared with the conventional case. Therefore, the power factor can be improved to about 0.9.

Further, in the present embodiment, because it is configured to charge the capacitor C ₁ by the magnetic energy stored in the inverter transformer T _1, without rush current flows at the start, the inrush current prevention There is no need to provide a circuit.

FIG. 6 is a circuit diagram showing the configuration of the second embodiment of the present invention. The inventors of the present embodiment differs from the first embodiment described earlier, the core of inverter transformer T ₂ without gaps, is that the choke coil CH to the primary winding N ₁ are connected in parallel. Further, different from the on operation, in the diode bridge circuit D positive terminal higher than the voltage the voltage across the terminals a capacitor C ₁ of _B, the magnetic energy is accumulated in the choke coil CH during on of the transistor Q ₁₁ It is. In this case, the primary winding a current i ₆ flows through the closed circuit consisting of the choke coil CH and the primary winding N ₁ Tokyo during off of the transistor Q ₁₁ N ₃
The voltage induced in, thereby charging the capacitor C _1. Other operations are the same as in the first embodiment.

FIG. 7 is a circuit diagram showing the configuration of the third embodiment of the present invention. The inventors of the present embodiment differs from the first embodiment, the core of inverter transformer T ₂ without gaps, is that the choke coil CH is connected in parallel to the primary winding N _3. Further, different from the on operation, in the diode bridge circuit D positive terminal higher than the voltage the voltage across the terminals a capacitor C ₁ of _B, the magnetic energy is accumulated in the choke coil CH during on of the transistor Q ₁₁ It is. In this case at the time of ON of the transistor Q _11, the voltage to the primary winding N ₃ by a current flowing from the AC power supply V _AC to the primary winding N ₁ is induced. Thus the magnetic energy is stored in a current i ₇ flows in a closed circuit consisting of the primary winding N ₃ and the choke coil CH to the choke coil CH. When the voltage on the primary winding N ₃ turns off the transistor Q ₁₁ is no longer induced, the charging current flows from the choke coil to the capacitor C _1. Other operations are the same as in the first embodiment.

[0030]

As described above, according to the present invention,
Without using an active filter circuit, by using a configuration of a conventional apparatus it can significantly reduce the harmonic component of the input current, further conventional unnecessary inrush current preventing circuit to eliminate the need for capacitor C ₁₁ (FIG. 8) Becomes Therefore, as compared with the case where an active filter circuit is used to improve the power factor, not only can the device be made inexpensive and small and light, but also the failure caused by the inrush current prevention circuit can be completely eliminated. Thus, a more reliable power supply device can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is a waveform chart showing waveforms at various parts in the first embodiment.

FIG. 3 is a waveform chart showing waveforms at various parts in the first embodiment.

FIG. 4 is a waveform chart showing waveforms at various parts in the first embodiment.

FIG. 5 is a spectrum diagram of a waveform of an input current.

FIG. 6 is a circuit diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a third example of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a conventional device.

FIG. 9 is a waveform diagram showing a waveform of an input current of the conventional device.

FIG. 10 is a circuit diagram showing a configuration of an active rectification filter circuit.

[Explanation of symbols]

V _AC AC power D _B diode bridge circuit _{D 2, D 3, D 12} , D 13 diodes C _1, C ₁₂ capacitor T _1, T ₂ inverter transformer N _1, N _{3 1} winding N ₂ 2 winding Q ₁₁ switching transistors L _11, CH choke coil

Claims (4)

(57) [Claims] A first primary winding provided between the first terminal and the second terminal; a first primary winding provided between the first terminal and the second terminal; An inverter transformer having a second primary winding and a secondary winding provided between the first terminal and the third terminal; an AC voltage supplied from an AC power supply; A rectifier circuit connected to a first terminal of the inverter transformer; a switching means provided between a negative output terminal of the rectifier circuit and a second terminal of the inverter transformer; A rectifying / smoothing circuit connected to the next winding and supplying DC power to a load; a capacitor having one end connected to a first terminal of the inverter transformer; a cathode connected to the other end of the capacitor, and an anode connected to the rectifier. Connect to the negative output terminal of the circuit. A capacitor charging / discharging circuit comprising: a first diode connected to the capacitor; a second diode having an anode connected to the other end of the capacitor and a cathode connected to a third terminal of the inverter transformer; And an energy storage means for storing energy when the switching means is turned on. 2. The switching power supply according to claim 1, wherein the energy storage means is a gap provided in a core of the inverter transformer. 3. The switching power supply according to claim 1, wherein the energy storage means is a choke coil connected between a first terminal and a second terminal of the inverter transformer. 4. The switching power supply according to claim 1, wherein the energy storage means is a choke coil connected between a first terminal and a third terminal of the inverter transformer.