JP2790326B2 - Switching regulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, and more particularly, to a switching regulator that improves a power factor of an AC input by extending a time during which an AC input current of a full-wave rectifier circuit flows.

[Conventional technology]

Conventionally, in a full-wave rectifier circuit using a diode bridge, which is used as a DC power supply of a switching regulator of this type, there is a smoothing capacitor input type as a general circuit, but the ripple value of the rectified DC voltage is reduced. Therefore, it is necessary to considerably increase the capacity of the smoothing capacitor. For this reason, the peak value of the rectified current increases, the power factor decreases, and the charging current generates heat due to the internal loss of the smoothing capacitor, resulting in a shortened life.
In addition, since the input power is large and adverse effects such as generation of harmonics cannot be ignored, the stability of the system is reduced, and a high-capacity noise filter circuit and a fuse or breaker for input protection are required.

A rectifying / smoothing circuit that solves this kind of difficulty is disclosed in
No. 107457 proposes this. In this rectifying / smoothing circuit, the smoothing capacitor is connected via an impedance element to the output terminal of the diode bridge for full-wave rectifying the AC input, and a diode is connected in parallel with the impedance element. At the time, the charging current flows to the smoothing capacitor through the impedance element, so that the peak value is suppressed. At the time of discharging, the impedance element is bypassed by the diode connected in parallel with the impedance, so that the power loss due to the impedance element is prevented.

FIG. 3 shows another conventional example. This is a general electric circuit of a one-stone forward type two-output switching regulator. The AC power from the AC power supply 1 passes through the nozzle filter NF, is full-wave rectified by the diode bridge 2, and is smoothed by the large-capacity smoothing capacitor C1. The DC power charged in the smoothing capacitor C1 is the primary winding of the transformer T4.
The switching element 4 supplied to a series circuit of Np and the switching element 4 and driven at a high frequency (normally 20 to 200 KHz)
Is turned on / off. As a result, an AC voltage is generated in the secondary windings Ns1 and Ns2 of the transformer T4, and these are diodes.
Only when the switching element 4 is turned on when it is rectified by the switching elements 5 and 9, it is applied to the choke input type smoothing circuit composed of the chokes 6 and 10 and the large-capacity capacitors 8 and 12. As a result, the DC voltages Vout1 and Vout2 appear on the capacitors 8 and 12.

The diodes 7 and 11 are commutation diodes for continuously outputting the energy stored in the chokes 6 and 10 when the switching element 4 is on when the switching element 4 is off.

The pulse width control circuit 13 for controlling the on / off of the switching element 4 compares the DC output voltage Vout2 with a reference voltage,
The difference signal is pulse-width-modulated at a predetermined frequency, and a drive signal is applied between the base and the emitter of the switching element 4 via the drive transformer T3 to drive the switching element 4. In response to the signal, the output voltage Vout2 is narrower if higher than the reference voltage, and wide if lower. This operation stabilizes the DC output voltage so that it is always constant.

The reset winding Nr arranged on the primary side of the transformer T4 supplies flyback energy generated in the primary winding Np of the transformer T4 when the switching element 4 is turned off to the diode 3, the reset winding Nr and the smoothing energy. This is a series circuit composed of the capacitor C1 and is intended to return to the smoothing capacitor C1.

In order to stabilize the operation, the smoothing capacitor C1 has a large capacity (about 1000 μF at 100V input and 150W output), and the DC output of the diode bridge 2 is sufficiently smoothed as shown in FIG. 4b. . However, the AC input current does not flow when the peak value of the AC input voltage waveform shown in FIG. 4a is lower than the voltage across the smoothing capacitor C1. Therefore, the current at the DC output terminal of the diode bridge 2 has a waveform shown in FIG. 4c, and the AC input current has a waveform as shown in FIG. 4d.

100V input, 150W output, smoothing capacitor C1 = 1000μ
F, conversion efficiency 77%, input current peak value 12A,
The effective value is 3.6A and the power factor is 0.56. The power factor of the switching regulator in the conventional example is generally said to be 0.5 to 0.6. If this power factor can be increased, the current rating of the diode bridge 2 and the noise filter N can be reduced. Greater merits such as conversion.

[Problems to be solved by the invention]

However, according to the rectifying / smoothing circuit disclosed in JP-A-63-107457, when a resistor is used as an impedance element, a peak value of an AC input voltage is high, and therefore, a resistance of several Ω to several tens Ω is required to suppress a charging current. And the charging loss of the smoothing capacitor C1 due to this is extremely large. When a coil is used as the impedance element, an inductance of several mH to several H is required to suppress the charging current. Therefore, the coil providing this inductance becomes extremely large, resulting in an increase in the size and cost of the power supply device. . Also, the bypass diode must have a high withstand voltage and a high rated current, and this loss and cost cannot be ignored. Furthermore, since the AC input current flows only when the peak value of the AC input voltage waveform is higher than the voltage across the smoothing capacitor, there is a slight difficulty in improving the power factor.

The conventional example shown in FIG. 3 has the problem described above.
In other words, the peak value of the rectified current increases, the power factor decreases, and the charging current generates heat due to the internal loss of the smoothing capacitor, resulting in a shortened life. In addition, since the input power is large and adverse effects such as generation of harmonics cannot be ignored, the stability of the system is reduced, and a high-capacity nozzle filter circuit,
A fuse or breaker for input protection is required.

An object of the present invention is to reduce power loss and improve power factor without increasing the size and cost of an electric circuit.

[Means for solving the problem]

The switching regulator of the present invention comprises a first rectifier (2) for rectifying an AC input, a first capacitor (C1) having a small capacity connected between the rectified output terminals thereof, and a first capacitor (C1) having a capacity larger than this capacity. A second capacitor (C2) having one end connected to the negative output terminal of the first rectifier (2); and a first primary winding (one end connected to the positive rectifier output terminal of the first rectifier (2)). Np1) and a first capacitor having a reset winding (Nr) having one end connected to the other end of the second capacitor (C2).
Transformer means (T1), the rectified output terminal and a first primary winding (Np
A switching element (4) inserted between
The negative rectification output terminal of the first rectification means (2) and the reset winding (Nr) are connected in such a manner as to be forward from the negative rectification output terminal of the rectification means (2) to the other end of the reset winding (Nr). A second rectifying means (3) interposed between the other ends, a first rectifying and smoothing means (5 to 8) connected to the secondary winding (Ns1) of the first transformer (T1), Drive means (13) for turning on / off the switching element (4); and second transformer means having a second primary winding (Np2) connected in series to the switching element (4) and a second capacitor (C2). (T2)
And second rectifying and smoothing means (9 to 12) connected to the secondary winding (Ns2) of the second transformer (T2). Symbols in parentheses indicate corresponding elements in the embodiment shown in the drawings and described later.

[Action]

When the switching element (4) is on, the first capacitor (C1) has a small capacity, so the first primary winding (Np
1), and the output of the first rectifier (2) is mainly supplied to the first primary winding (Np1). When the switching element (4) is turned off, a charging current flows through the first capacitor (C1). However, since the capacitance is small, the peak current value is low.

Since the second rectifier (3) is connected in series to the large-capacity second capacitor (C2) and the reset winding (Nr), the flyback energy generated when the switching means (4) is off is: It is taken out from the reset winding (Nr) of the first transformer (T1) and charged into the large-capacity second capacitor (C2), which is charged to the second primary winding (Np2) of the second transformer (T2). Applied. Thereby, when the switching element (4) is on, the second capacitor (C2)
Supplies power to the second primary winding (Np2) of the second transformer (T2).

The second capacitor (C2) is connected to the second primary winding of the second transformer (T2) even at the valley portion of the pulsating voltage (near zero level of the AC input voltage) at the DC output terminal of the first rectifier (2). Since power is supplied to the line (Np2), the switching means (4) reliably performs a switching-on operation at the valley portion. As a result, even in the low AC input region (near phase zero, near π), the energization loop of the first rectifying means (2) and the first primary winding (Np1) is maintained, and the AC input voltage is within a wide range of half-waves. The alternating current flows, and the power factor of the AC input is improved.

In the present invention, the intended operation is performed without the first capacitor (C1). However, the switching frequency and its harmonic nozzle may flow out to the input AC power supply line. ) Is used as a noise filter to prevent this.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

FIG. 1 shows an embodiment of the present invention. In FIG. 1, the same or corresponding parts as those in the conventional example shown in FIG. A description of these will be omitted.

In FIG. 1, the first capacitor C1 has a small capacitance sufficient to function as a noise filter for preventing the switching frequency of the switching element 5 and its harmonic noise from flowing out to the input AC power supply line. In the case of a switching regulator having an output capacity of 150 to 200 W class, a capacitor of several μF (10 μF or less) is sufficient as the smoothing capacitor C1. This smoothing capacitor C1
Is preferably a film type or a laminated type having good high frequency characteristics for use in a high frequency range.

The second capacitor C2 is a flyback energy charging capacitor, and forms a series circuit with the diode 3 and the reset winding Nr of the transformer T1. Since the flyback energy charging capacitor C2 sufficiently satisfies the function at 10 to 100 μF, the sum of the first and second capacitors C1 and C2 is the same as the conventional smoothing capacitor C1 in size and size.
When comparing costs, they have a significant advantage.

The turns ratio of the primary winding Np1 and the reset winding Nr of the first transformer T1 is substantially one to one.

With this configuration, the switching element 4 can operate reliably even in the valley portion of the pulsating voltage (FIG. 2b) and can continue to extract energy. The spreading power factor is improved.

In the embodiment shown in FIG. 1, the voltage waveform of the DC output portion of the diode bridge 2 with respect to the AC input voltage waveform of FIG. 2a is inferior in the smoothing ability with respect to the commercial frequency as compared with the conventional example, as shown in FIG. 2b. It becomes a pulsating flow. This pulsation is the first
The first secondary winding N is applied to the first primary winding Np1 of the transformer T1.
The AC electromotive voltage generated at s1 is rectified and smoothed by rectification and smoothing circuits 5 to 8, and is output as a large capacity output Votu1. This large-capacity output Vout1 includes an input frequency ripple. This large capacity output Vout with 150W class output capacity
When the voltage of 1 is 24V (about 5A), it includes the input frequency ripple of 1-3V. Normally 24V for power supply for copying machines, etc.
Is generally used for driving a motor, a solenoid or the like, and there is no problem even if such a ripple is included.

The energy charged in the capacitor C2 is a small capacity output
It is applied to the second primary winding Np2 of the second transformer T2 of Votu2. The terminal voltage waveform of the capacitor C2 is sufficiently smoothed as shown in FIG. 2e, and the small-capacity output Votu2 has high stability and no ripple, and is optimal as a 5V power supply necessary for controlling a copying machine or the like.

Since the capacitance of the first capacitor C1 in the input section is small, the current waveform at the output end of the diode bridge 2 is lower than that of the conventional one as shown in FIG. 2c, and the current waveform in the AC input section is as shown in FIG. 2d. And a smooth waveform without any extreme peaks.

When a switching regulator is configured with 100V input, 150W output, first capacitor C1 = 0.22μF, and flyback energy charging capacitor C2 = 100μF, conversion efficiency =
75%, the peak value of the input current is 4.0A, and the effective value is 2.3A. The power factor at this time is greatly improved to 0.87.

〔The invention's effect〕

As described above, according to the switching regulator of the present invention, a stable switching operation can be obtained over a wide range of the output pulsating flow of the first rectifier (2), and the power factor is improved. Therefore, the first rectifier (2), the input circuit fuse,
The input circuit breaker, the input noise filter circuit, and the like are reduced in capacity, size, and cost. Further, since an inrush current prevention circuit is not required, a relatively small and inexpensive power supply device can be used.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing one embodiment of the present invention. FIG. 2a is a time chart showing the AC voltage applied to the diode bridge 2 shown in FIG. FIG. 2b is a time chart showing the DC output voltage of the diode bridge 2 shown in FIG. FIG. 2c is a time chart showing the DC output current of the diode bridge 2 shown in FIG. FIG. 2d is a time chart showing the input current of the diode bridge 2 shown in FIG. FIG. 2e is a time chart showing the voltage of the capacitor C2 shown in FIG. FIG. 3 is an electric circuit diagram showing a conventional switching regulator. FIG. 4a is a time chart showing the AC voltage applied to the diode bridge 2 shown in FIG. FIG. 4b is a time chart showing the DC output voltage of the diode bridge 2 shown in FIG. FIG. 4c is a time chart showing the DC output current of the diode bridge 2 shown in FIG. FIG. 4d is a time chart showing the input current of the diode bridge 2 shown in FIG. 1: AC power supply, NF: Noise filter 2: Diode bridge (first rectifier) 3: Diode (second rectifier), T1: First transformer (first
Transformer) T2: Second transformer (second transformer), T3: Transformer T4: Transformer, 4: Switching element (switching element) 5, 9: Diode, 6, 10: Choke coil 7, 11: Diode , 8,12: smoothing capacitor (5-8: first rectifying and smoothing means), (9-12: first rectifying and smoothing means) 13: pulse width control circuit, C1: first capacitor (first capacitor) C2: Second capacitor (second capacitor) Np1: first primary winding (first primary winding), Ns1: second secondary winding (second secondary winding) Nr: reset winding (reset winding)

Claims (1)

(57) [Claims] 1. A first rectifying means for rectifying an AC input, a small-capacity first capacitor connected between the rectifying output terminals,
A second capacitor having a capacity larger than this capacity, one end of which is connected to a negative output terminal of the first rectifier, a first primary winding having one end connected to a positive rectifier output end of the first rectifier, and A first transformer having a reset winding having one end connected to the other end of the second capacitor; a switching element interposed between the rectified output terminal and the first primary winding;
The first rectifier is inserted between the negative rectifier output terminal of the first rectifier and the other end of the reset winding so as to be forward from the negative rectifier output terminal of the first rectifier to the other end of the reset winding. (2) rectifying means, first rectifying / smoothing means connected to the secondary winding of the first transformer, driving means for turning on / off the switching element, and serially connected to the switching element and the second capacitor. A switching regulator, comprising: a second transformer having a second primary winding; and a second rectifying and smoothing unit connected to a secondary winding of the second transformer.