JPH04331462A - Switching power supply - Google Patents

Abstract

PURPOSE:To suppress higher harmonic distortion of commercial power supply by constituting an active smoothing filter of a rectifying/smoothing circuit comprising a low capacity capacitor and a switching frequency control resonant converter circuit. CONSTITUTION:Since a smoothing capacitor 3 connected with a full-wave rectifying circuit 2 has low capacity, DC output contains ripple of double frequency that of commercial power supply. The DC output is then inverted through a switching power supply system comprising a switching frequency control current resonant converter 4 to produce an AC output which is fed through an insulating converter transformer 7 to a rectifying/smoothing circuit 8. A control circuit 9 controls the control current of the control winding of a DC/AC power supply regulation transformer 5 so that the average value of the DC output from the rectifying/smoothing circuit 8 containing the double frequency component will be constant.

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 capable of suppressing harmonic distortion of an AC power supply.

0002

[Prior Art] Conventionally, as a measure to reduce harmonic distortion of a commercial AC input power source, as explained in "Electric Kyodo Research" Vol. 46, No. 2, AC reactor insertion method, active smoothing filter method, etc. , a transformer system is being considered.

The above-mentioned AC reactor insertion method is a method in which an AC reactor is inserted on the AC input side of a full-wave rectifier/capacitor smoothing circuit, which is a basic representative example of general-purpose home appliances.
The charging current to the capacitor is limited by the impedance of the AC reactor, widening the conduction angle and reducing harmonic components.

[0004] The active smoothing filter method is a step-up chopper, which is a non-isolated switching regulator with an output voltage higher than the input voltage, instead of the full-wave rectifier/capacitor smoothing circuit. It has a converter added. The operation is as follows. The pulse waveform, which has been double-wave rectified by the bridge rectifier, is switched over the entire cycle at a frequency of several tens of kHz or more. Therefore, the input current waveform will be the average value for each period of the switching current, and even if there is a large capacitor in the load, it will be equivalent to a pure resistive load, and the input switching current will flow in a sine wave shape from a macroscopic perspective, causing harmonics. It is possible to reduce the

The above transformer system is capable of reducing harmonics by expanding the current conduction angle due to the choke effect of the transformer and lowering the voltage on the secondary side.

[0006]

[Problems to be Solved by the Invention] By the way, the above-mentioned AC reactor insertion method, the above-mentioned active smoothing filter method,
Each of the above transformer systems has the following drawbacks.

[0007] In the above AC reactor insertion method, the weight and size of the device are large and the cost is high. In particular, AC reactors are expensive compared to other parts. Furthermore, since the AC smoothed DC voltage decreases, it is necessary to redesign the switch regulator at the subsequent stage, resulting in a decrease in efficiency. Furthermore, there is also an effect on electronic equipment due to magnetic flux leakage from the device.

In the active smoothing filter method described above, the noise level increases due to electromagnetic interference (EMI) generated from the switching semiconductor. Furthermore, in addition to the function of a switching power supply, a switching control means for making input voltage and input current proportional, a starting circuit, software functions, etc. make the circuit complex, increasing the number of component parts, and increasing cost. Furthermore, since it is a non-isolated system, it must be isolated with a switching regulator in the subsequent stage.

[0009] The transformer method described above is limited to small capacity (30W or less) electronic equipment, but the equipment becomes large in size for commercialization.

Considering the disadvantages of the above three systems, the AC reactor insertion system and the transformer system are not sufficiently marketable with the current technology due to the problem of increasing the size of the equipment. The active smoothing filter method described above can be put to practical use if integration including the active smoothing filter section and the switching transistor is solved.

The circuit system of the active filter circuit using the active smoothing filter system is "electronic technology" 1.
As explained in the March 1990 Special Issue, the non-isolated boost chopper circuit uses either the PWM (Pulse Width Modulation) method with a fixed switching frequency or the RCC (Ringing Choke Converter) method with a variable switching frequency. The problem is that the level of electromagnetic interference generated by the semiconductor is high because the switching semiconductor repeats ON-OFF switching operations using trapezoidal or triangular waves. In addition, in the case of an isolated type, it becomes a flyback converter, which increases power loss and further increases the noise level. Furthermore, in addition to the functions of a switching power supply, there is also a means to detect the input voltage and input current so that the input current is proportional to the input voltage, as well as a startup circuit and software functions, making the circuit complex, increasing the number of components, and increasing the cost. It becomes a cost.

In addition, in the conventional switching power supply system that suppresses the AC ripple voltage to 50 mV or less and maintains the DC output voltage constant against changes in the AC input voltage and load fluctuations, the AC input rectifying and smoothing capacitor is used as an AC input rectifying and smoothing capacitor. An electrolytic capacitor with a large capacitance is used, for example, when the load power is 15
When the AC input rectifying capacitor is set to 820μF at 0W, as shown in Figure 2, an AC line current containing many harmonic components flows to charge the capacitor, causing waveform distortion of the sine wave commercial AC voltage, causing power The ratio is between 0.5 and 0.7.

[0013] The present invention was proposed in view of the above-mentioned circumstances, and it is an object of the present invention to improve the power factor by configuring an active filter circuit using a switching power supply system using a switching frequency control type resonant converter circuit. This is the purpose.

[0014]

[Means for Solving the Problems] In order to solve the above-mentioned problems, a switching power supply device according to the present invention includes a rectifying and smoothing circuit using a small capacitor as a circuit for rectifying and smoothing a commercial AC input power supply, and the above-mentioned rectifying and smoothing circuit. a switching frequency control type resonant converter circuit in which the switching frequency is controlled to switch and control the output from the rectifying and smoothing circuit;
A primary winding to which the output from the switching frequency control resonant converter circuit is supplied, and a secondary winding insulated from the primary winding, the winding directions of each winding being orthogonal to each other. a transformer circuit section having a controlled winding and a control winding; a control circuit that controls the switching frequency in a direction that keeps the average value of the DC output voltage from the transformer circuit section constant; It is configured with a rectifying and smoothing circuit including a rectifying and smoothing capacitor that determines the ripple voltage of the DC output voltage together with the load power.

[0015]

[Operation] An active smoothing filter composed of a rectifying and smoothing circuit using a small capacitance capacitor and a switching frequency control type resonant converter circuit can improve the power factor by reducing the harmonic current of the commercial power supply.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a switching power supply device according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram showing a switching power supply device for power factor correction according to an embodiment of the present invention.

The configuration of the embodiment of the switching power supply device for power factor improvement shown in FIG. 1 is as follows. The DC input power source is obtained, for example, by rectifying and smoothing a commercial AC input power source 1 using a diode bridge type full-wave rectifier 2 and a small capacitance capacitor 3.

This DC input power is supplied via the primary winding Na of the power regulation transformer 5 to a series resonant circuit consisting of the capacitor 6 and the leakage inductance of the primary winding N1 of the isolation transformer 7. The power regulation transformer 5 has a primary winding Na and two secondary windings NB1 and NB2, and as shown in FIGS. 5 and 6,
The control winding NC is wound in a direction perpendicular to the winding directions of the windings NB1 and NB2.

In connection with the secondary windings NB1 and NB2 of the power regulation transformer 5, a resonant converter circuit 4 is provided for controlling on/off switching of the current of the DC input power supply. This resonant converter circuit 4
, a switching transistor Q1 with a diode DB1 connected between the emitter and the base, and a switching transistor Q2 with a diode DB2 connected between the base and ground are connected in series, and the transistor Q1
is the above DC input power supply and power regulation transformer 5
The transistor Q2 is inserted and connected between the primary winding Na of the power regulation transformer 5.
It is inserted between a and ground. Transistor Q1
The secondary winding NB1 of the power regulation transformer 5 is connected between the emitter and base of the power supply regulation transformer 5 in parallel with the diode DB1.
A series resonant circuit consisting of a resistor RB1, a capacitor CB1, and a secondary winding NB2 of a power regulation transformer 5, a resistor RB1, and a capacitor C are connected between the emitter and base of the transistor Q2 in parallel with the diode DB2.
A series resonant circuit with B1 is connected. Furthermore, a starting resistor RS1 is inserted and connected between the DC input power source and the base of the switching transistor Q1, and a starting resistor RS2 is inserted and connected between the collector and base of the switching transistor Q2.

Next, the isolation transformer 7 has an insulated primary winding N1 and a secondary winding N2.
A rectifying and smoothing circuit 8 having diodes D1, D2, D3 and smoothing capacitors C0, C0' is connected to the next winding N2. and is sent to the control winding NC of the power regulation transformer 5.

The control circuit 9 includes a transistor Q3 whose base is supplied with the DC output voltage via voltage dividing resistors R1 and R2, and a reference voltage Zener diode connected to the emitter of the transistor Q3 together with a resistor R4. DK and a feedback capacitor Cf inserted between the collector and base of this transistor Q3,
The transistor Q3 has a collector connected to a resistor R3 and a transistor Q4 whose base is connected.

Next, the general operation of the switching power supply device having the above configuration will be explained. For example 100
AC output from a commercial AC power supply 1 of V is rectified and smoothed by a diode bridge type full-wave rectifier 2 and a small capacitor 3. Here, set the value of the small capacitor 3 above to 0.
．． If it is 1 to 0.22 μF, the DC input voltage Ei is as shown in Figure 3.
A sine wave pulsating current voltage is obtained as shown in FIG. 2 and is supplied to the isolation transformer 7 via the resonant converter circuit 4 and the power regulation transformer 5 shown in FIGS. 5 and 6. The control circuit 9 detects the average value of the DC output voltage obtained at the secondary winding N2 of the isolation transformer 7, and controls the DC output voltage flowing through the control winding Nc of the power regulation transformer 5 so that the average value is constant. Control current Ic is controlled.

The ripple voltage of the DC output voltage is determined by the load power and the capacitance of the rectifying and smoothing capacitor C0 of the rectifying and smoothing circuit 8, and is controlled so that the AC input current has a waveform that is almost similar to the input voltage. , as shown in Figure 3, the DC output voltage E0 has a sinusoidal waveform that is twice the AC input power supply frequency.
becomes.

Switching transistors Q1, Q2
In the resonant converter circuit 4, the switching frequency is determined by the secondary winding NB1, the resistor RB1, the capacitor CB1, and the secondary winding of the power regulation transformer 5, which constitute the self-excited oscillation circuit.
It is determined by the next winding NB2, resistor RB2 and capacitor CB2. Therefore, the inductance of the secondary windings NB1 and NB2 of the power regulation transformer 5 is changed to the control winding NC of the power regulation transformer 5.
The switching frequency is controlled by controlling the control current IC flowing through the circuit. Therefore, the high-frequency sinusoidal current I1 that can be obtained in a series resonant circuit with a fixed resonance frequency formed by the series resonant capacitor 6 and the leakage inductance of the primary winding N1 of the isolation transformer 7 is applied to the switching transistors Q1 and Q2, respectively. 4
The currents ICP1 and ICP2 flow as shown in FIG.

When the input voltage Ei is 10V or less, the high frequency sinusoidal current I1 does not flow, and a dead time td of the AC input current IAC as shown in FIG. 3 occurs, and the AC input current I
Although AC is not continuous, a decrease in power factor has little effect because the load power does not have much effect on the input power near the zero cross.

According to experiments, in this embodiment shown in FIG. 1, the load power was 150 W and the switching frequency range was 50
In a switching power supply of kHz to 100kHz, the small capacity capacitor Ci is 0.22μF/200V, and the rectification and smoothing electrolytic capacitor C0 of the rectification and smoothing circuit 8 is 10
Similarly, the rectifying and smoothing electrolytic capacitor C0' of the rectifying and smoothing circuit 8 is 1000 μF/25V.
, and the feedback capacitor Cf of the control circuit 9 to 47μF/
The operating waveform when set to 6.3V is shown in Figure 3,
The power factor was 0.96. The harmonic distortion of the AC input current IAC is reduced, and the AC input voltage VAC is improved to have a sinusoidal waveform.

The larger the capacitance of the feedback capacitor Cf for controlling the average value of the DC output voltage to be constant, the more trapezoidal the envelope of the current I1 of the DC input power supply becomes. Since the transient response characteristics due to sudden changes in load are determined by the time constant, if the feedback capacitor Cf is selected to be too large, the high-speed tracking time will become longer.

FIG. 7 shows the control characteristics of the control current IC of the power regulation transformer 5 with respect to changes in the main load current IL and AC input voltage. The horizontal axis shows the main load current IL, and the vertical axis shows the power regulation transformer 5.
Take the control current IC. When the main load current IL is kept constant and the control current IC of the power regulation transformer 5 is compared with respect to changes in the AC input voltage, the control current IC increases as the AC input voltage increases.

Another embodiment of the invention is shown in FIGS. 8 and 9. Figure 8 shows a switching frequency fixed inductance control current resonant converter that improves the power factor by adding a power choke coil and controlling the inductance of the primary winding N1 and secondary winding N2 of the power regulation transformer. This is a switching power supply circuit for power factor improvement. FIG. 9 shows a switching power supply circuit for power factor correction using a switching frequency fixed inductance control type voltage resonant converter when a small capacity load is applied.

That is, the present invention including other embodiments replaces the large capacity electrolytic capacitor of the conventional electrolytic capacitor input rectifying and smoothing circuit with a small capacity capacitor, obtains a sine wave ripple DC voltage of twice the commercial frequency, and performs switching. In a switching power supply system using a frequency-controlled current resonant converter circuit, high-frequency sinusoidal waveform operation is performed via the isolated primary and secondary windings of the isolated converter transformer, and by the rectifying and smoothing circuit using the secondary electrolytic capacitor.
The control current of the control winding of the DC power regulation transformer is controlled so that the average value of the DC output voltage including twice the commercial frequency remains constant, and the switching frequency of the resonant converter circuit is controlled, thereby reducing the power factor. This is a measure of improvement.

[0031]

Effects of the Invention In the switching power supply device according to the present invention, the power factor is improved by the active smoothing filter configured by the rectifier smoothing circuit using a small capacity capacitor and the switching frequency control type resonant converter circuit, and the harmonics of the commercial power supply are reduced. Distortion can be reduced. Furthermore, the level of electromagnetic interference generated by switching semiconductors is small compared to conventional RCC (ringing choke converter) or PWM (pulse width modulation) converter circuits, and the electromagnetic interference generated by switching semiconductors is small compared to conventional RCC (ringing choke converter) or PWM (pulse width modulation) converter circuits. Since the control current is configured with a simple self-oscillation type control circuit, the cost is low. Furthermore, the primary winding and the secondary winding can be insulated by the isolation transformer, and the regulator at the subsequent stage can be non-insulated, allowing for miniaturization and high efficiency. The DC output voltage on the secondary side of the isolation transformer is higher than the average value of the DC input voltage due to the turns ratio of the isolation transformer.
It can be selected arbitrarily and has a degree of freedom in design.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a switching power supply device for power factor correction as an embodiment of the present invention.

FIG. 2 is a waveform diagram showing the waveforms of an AC line current and a commercial AC voltage when a large capacitance electrolytic capacitor is used as an AC input rectifying and smoothing capacitor in a conventional switching power supply device.

FIG. 3 is a waveform diagram showing currents and voltages at various parts in the device of FIG. 1;

4 is an enlarged view of the high frequency sine wave current I1 shown in FIG. 3 and a waveform diagram showing the current flowing through the switching transistor.

FIG. 5 is a perspective view showing the structure of a power regulation transformer used in the embodiment and other embodiments of the present invention.

FIG. 6 is a perspective view showing the structure of a power regulation transformer used in the embodiment and other embodiments of the present invention.

FIG. 7 is a characteristic diagram showing control characteristics of the control current of the power regulation transformer with respect to changes in main load current and AC input voltage.

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

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

[Explanation of symbols]

2...Full wave rectifier 3...Smoothing small capacity capacitor 4...Resonant converter circuit 5...Power regulation transformer 7...
・Isolation transformer 8... Rectifier smoothing circuit 9... Control circuit

Claims (1)

[Claims] 1. A rectifying and smoothing circuit using a small capacity capacitor as a circuit for rectifying and smoothing a commercial AC input power supply, and a switching frequency control type resonant converter circuit in which the switching frequency is controlled for switching the output from the rectifying and smoothing circuit. , a primary winding to which the output from the switching frequency control type resonant converter circuit is supplied, a secondary winding insulated from this primary winding, and the winding directions of the respective windings are mutually aligned. a transformer circuit section having a controlled winding and a control winding that are orthogonal to each other; a control circuit that controls the switching frequency in a direction that keeps the average value of the DC output voltage from the transformer circuit section constant; and the transformer circuit section. A switching power supply device having a rectifying and smoothing circuit including a rectifying and smoothing capacitor that determines the ripple voltage of the DC output voltage from the DC output voltage along with the load power.