JP2854075B2 - 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 the power factor of AC power by extending the 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 for DC current of this type of switching regulator, 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 noise 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 disposed 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 the power factor can be increased, the current rating of the diode bridge 2 and the noise filter NF can be reduced. Large advantages such as miniaturization.

[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 that straddles this inductance becomes extremely large, and the power supply device becomes larger and more expensive. Invite. 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 does not flow 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 noise 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 according to the present invention includes a first rectifier (2) for rectifying an AC input, a small-capacity first capacitor (C1) connected between the rectifier output terminals, and a plus of the first rectifier (2). A first having a first primary winding (Np1) having one end connected to the side rectification output terminal and a reset winding (Nr)
Transformation means (T1), rectification output terminal and first primary winding (Np1)
And a first switching element (4 ') interposed between the first winding and a reset winding (Nr) having one end connected to one end thereof and having a capacity larger than the capacity of the first capacitor (C1) and a first rectifier ( 2) a second capacitor (C2) which is insulated from the input end, and a second capacitor (C2) and a reset winding (Nr) which are forwardly connected to the other end of the reset winding (Nr).
, A first rectifying / smoothing means (5-8) connected to a secondary winding (Ns1) of the first transformer (T1), and a second capacitor (3). A second switching element (4 ") connected to the other end of C2), a first switching element (4 ') and a second switching element (4").
Means (13) for simultaneously turning on / off the second switching element (4 ") and a second capacitor (C
2) a second transformer (T2) having a second primary winding (Np2) connected in series to the second transformer, and a second rectifying and smoothing connected to a secondary winding (Ns2) of the second transformer (T2). Means (9 to 12);
Is provided.

Symbols in parentheses indicate corresponding elements in the embodiment shown in the drawings and described later.

[Action]

When the first switching element (4 ') is on, the first capacitor (C1) has a small capacity, so that the first capacitor (C1) immediately discharges to the first primary winding (Np1) and the first primary winding (Np1) , Mainly the output of the first rectifier (2). When the first switching element (4 ') is turned off, a charging current flows through the first capacitor (C1).
This 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), a flyback generated when the first switching element (4 ') is off is generated. Energy is extracted from the reset winding (Nr) of the first transformer (T1) and charged in the large-capacity second capacitor (C2), which is charged in the second primary winding (N2) of the second transformer (T2). Np2). Thereby, the first
When the second switching element (4 ″) that is turned on / off in synchronization with 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 first switching element (4 ') and the second switching element (4 ") reliably perform switching-on operations in the valley portion. (Near phase zero, near π), the conduction loop of the first rectifier (2) and the first primary winding (Np1) is maintained, and an alternating current flows in a wide range of half-waves of the alternating-current input voltage. Power factor improves.

A second capacitor (C2), a second rectifier (3),
The series circuit composed of the reset winding (Nr) and the series circuit composed of the second capacitor (C2), the second primary winding (Np2), and the second switching element (4 ″) are insulated from the AC input circuit. Therefore, there are advantages such as safety standards and arrangement.

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

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, a first switching element 4 'for driving a first transformer T1 and a second switching element 4 "for driving a second transformer T2 are simultaneously driven at a high frequency (normally 20 to 200 KHz) by a drive transformer T3. The first and second switching elements 4 ', 4 "operate in the same manner as the switching element 4 shown in the conventional example.

The first capacitor C1 is small enough to function as a noise filter for preventing the switching frequency of the first switching element 4 'for driving the first transformer T1 and its harmonic noise from flowing out to the input AC power supply line. Of capacity.

In a switching regulator having an output capacity of 150 to 200 W class, the smoothing capacitor C1 is several μF (10
(μF or less) is sufficient, but a film type or a laminated type having good high frequency characteristics is preferable 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 first transformer T1.
The second primary winding Np2 of T2 and the second switching element 4 ″ for driving the second transformer T2 also form a series circuit. The two series circuits are not directly connected to the AC input circuit,
In other words, the use of an insulating structure has advantages in terms of safety standards and arrangement.

Also, the flyback energy charging capacitor C2
Satisfies the function sufficiently with 10 to 100 μF, so that the combination of the first and second capacitors C1 and C2 is sufficiently superior when compared with the conventional smoothing capacitor C1 in size and cost.

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

With such a configuration, the first switching element 4 'and the second switching element 4 "can operate reliably and continue to extract energy even in the valley portion of the pulsating voltage (FIG. 2b). The time during which the input current (AC current) flows increases, and the 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. It becomes a flow. This pulsating current is applied to the first primary winding Np1 of the first transformer T1 and the first secondary winding Ns1
Are generated by the rectifying and smoothing circuits 5 to 8 and output as a large capacity output Vout1. This large-capacity output Vout1 includes an input frequency ripple. This large capacity output Vout1 with 150W class output capacity
When the voltage is 24V (approximately 5A), input voltage ripples of about 1-3V are included. In the case of power supplies for electronic devices such as copiers,
Normally, 24 V 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
Vout2 is applied to the second primary winding Np2 of the second transformer T2. The terminal voltage waveform of the capacitor C2 is sufficiently smoothed as shown in Fig. 2e, and the small-capacity output Vout2 operates exactly the same as a general switching regulator, has high stability, has no ripple, and It is most suitable as a 5V power supply required for controlling electronic devices.

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. 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 power supply 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. Further, a second capacitor (C2),
A series circuit including a second rectifier (3) and a reset winding (Nr); a second capacitor (C2); and a second primary winding (Np).
2) Since the series circuit composed of the second switching element (4 ") has an insulation configuration with respect to the AC input circuit, there are advantages in terms of safety standards and arrangement.

[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, T4: Transformer 4 ', 4 ": Switching element (switching element) 5, 9: Diode, 6, 10: Choke coil 7, 11: Diodes, 8, 12: smoothing capacitors (5 to 8: first rectifying and smoothing means), (9 to 12: second rectifying and smoothing means) 13: pulse width control circuit (drive means) C1: first capacitor (first Capacitor) C2: Second capacitor (second capacitor) Np1: First primary winding (first primary winding), Np2: Second primary winding (second primary winding) Ns1: First secondary winding ( 1st secondary winding), Ns2: 2nd secondary winding (2nd 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 first transformer having a first primary winding and a reset winding, one end of which is connected to a positive rectification output terminal of the first rectifier; and an interposed between the rectification output terminal and the first primary winding. A first switching element, and a second capacitor having one end connected to one end of the reset winding and having a capacity larger than the capacity of the first capacitor and having an insulation configuration with respect to an input end of the first rectifier. A second rectifier connected in series with the second capacitor and the reset winding so as to be in a forward direction at the other end of the reset winding, and a secondary winding of the first transformer. A first rectifying / smoothing means, a second switching element connected to the other end of the second capacitor, the first switching element and the second switching element.
Drive means for simultaneously turning on / off the switching element; second transformer having a second primary winding connected in series to the second switching element and the second capacitor; and a secondary transformer of the second transformer. The second connected to the winding
And a rectifying / smoothing means.