JP2854081B2 - Switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present embodiment 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 for a 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 use 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 difficulties is disclosed in
It is proposed in JP 07457. 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.
It is rectified by the switching elements 5 and 9 and is applied to the choke input type smoothing circuit composed of the chokes 6 and 10 and the large-capacity capacitors 8 and 12 only when the switching element 4 is on. 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
In the case of switching regulator F, conversion efficiency 77
%, The peak value of the input current is 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 NF can be reduced. Greater merits such as conversion.

[Problems to be solved by the invention]

However, according to the rectifying and smoothing circuit disclosed in Japanese Patent Application Laid-Open No. 63-107457, when a resistor is used as an impedance element, a peak value of an AC input voltage is high, and 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 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 comprises: a first rectifier (2) for rectifying an AC input; a first capacitor (C1) having a small capacity connected between its rectification output terminals; a first rectifier having a capacity larger than this capacity. A second capacitor (C2) having one end connected to a negative output terminal of the means (2); a first primary winding (Np1) having one end connected to both positive output terminals of the first rectifier (2); And first resetting means (T1) having a reset winding (Nr); first rectifying and smoothing means (5 to 5) connected to the first secondary winding (Ns1) of the first converting means (T1).
8); a first switching element (4 ') inserted between the negative output terminal of the first rectifying means (2) and the other end of the first primary winding (Np1); a first switching element (4') ), A first drive means (13 ') for turning on / off; a reset winding (Nr) from a minus side rectification output terminal of the first rectification means (2).
Second rectifying means (3) inserted between the minus side rectified output terminal of the first rectifying means (2) and the other end of the reset winding (Nr) so as to be in the forward direction at the other end of the first rectifying means (2); The other end of the first rectifier (2) and the other end of the second capacitor (C2) are connected in a forward direction from the positive rectifier output terminal of the rectifier (2) to the other end of the second capacitor (C2). Third rectifying means (14) interposed between the terminals; a second switching element (4 ") having one end connected to one end of a second capacitor (C2);
A second drive means (13 ") for turning on / off the switching element (4"); and a second primary winding (Np2) connected in series to the second switching element (4 ") and the second capacitor (C2). And a second rectifying / smoothing means (9, 12) connected to the second secondary winding (Ns2) of the second transforming means (T2).

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.

The large-capacity second capacitor (C2) and reset winding (Nr) have second rectification means (3) and third rectification means (1
Since 4) is connected in series, flyback energy generated when the first switching element (4 ') is turned off is taken out from the first transformer (T1) reset winding (Nr) and has a large capacity. , And is applied to the second primary winding (Np2) of the second transformer (T2). Thus, when the second 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.

The first capacitor (C1) is used as a noise filter for preventing the switching frequency and its harmonic noise from flowing out to the input AC power supply line.

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 pulse width control circuit 1 for controlling ON / OFF of a first switching element 4 'for driving a first transformer T1.
3 'compares the DC output voltage Vout1 with the reference voltage, modulates the difference signal by pulse width at a predetermined frequency, and applies a drive signal between the base and the emitter of the switching element 4' via the drive transformer T3 '. The switching element 4 'is driven in response to the difference signal, and the pulse width at this time is made narrower when the output voltage Vout1 is higher than the reference voltage and wider when the output voltage Vout1 is lower than the reference voltage. The DC output voltage stabilized so as to be always constant by this operation is used as a drive power supply for a motor, a solenoid and the like in the case of a power supply for electronic equipment such as OA equipment.

Similarly, a pulse width control circuit 13 "for controlling ON / OFF of the second switching element 4" for driving the second transformer T2 compares the DC output voltage Vout2 with the reference voltage, and compares the difference signal at a predetermined frequency. Pulse width modulation is performed, and a drive signal is applied between the base and the emitter of the switching element 4 "through the drive transformer T3" to drive the switching element 4 "so that the DC output voltage is always constant. Is used as a control power supply for electronic equipment such as OA equipment.

The first capacitor C1 is a conventional large-capacity capacitor corresponding to a commercial frequency, and a relatively small-capacity input smoothing capacitor corresponding to a switching frequency.
The input power for driving the transformer T1 is output as a power supply Vout1 for driving a motor, a solenoid, and the like.

Further, the smoothing capacitor C1 has a function as a noise filter for preventing the switching frequency and its harmonic noise from flowing out to the input AC power supply line.

This switching capacitor C1 is a few μF (10 μF
The following capacitor 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 medium-capacity smoothing capacitor corresponding to the commercial frequency, and forms a series circuit with the diode 14 at the DC output terminal of the diode bridge 2 so as to be in parallel with the smoothing capacitor C1. The second primary winding Np2 of the second transformer T2 and the second switching element 4 ″ also form a series circuit, and the power of the second smoothing capacitor C2 is used as an input power supply for driving the second transformer T2, and a control power supply Vout2 is used. Is output.

When the first switching element 4 'is off, flyback energy generated in the first transformer T1 is extracted from the reset winding Nr of the first transformer T1, and the reset winding Nr
→ Diode 14 → Smoothing capacitor C2 → Diode 3 →
In the circuit consisting of the reset winding Nr, the smoothing capacitor C2
Is charged.

Further, the smoothing capacitor C2 satisfies the function sufficiently at about several μF to about 100 μF, so that the first and second capacitors C2 are used.
The combination of 1 and C2 is sufficiently superior when compared in size and cost with the conventional smoothing capacitor C1.

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 this configuration, the switching element operates reliably even in the valleys of the pulsating voltage (FIG. 2b) and energy can be continuously extracted, thereby extending the time for the input current (AC current) to flow. Power factor improves.

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 voltage is applied to the first primary winding Np1 of the transformer T1, and is switched by the first switching element 4 '. 1st secondary winding Ns1
Is generated by the rectifying and smoothing circuits 5 to 8 and output as a large-capacity driving power supply output Vout1. The driving power supply output Vout1 includes a part of the input frequency ripple. When the output voltage of this driving power supply Vout1 is 24V (about 5A) with 150W class output capacity,
Includes 2V input frequency ripple. In the case of power supplies for electronic equipment such as OA equipment, 24 V is generally used for driving motors, solenoids, and the like, and there is no problem even if such a ripple is included.

The second capacitor C2 is charged from the DC output section of the diode bridge 2 via the diode 14,
This prevents backflow to the first transformer T1. Moreover, the second
As described above, the flyback energy generated in the first transformer T1 is also charged in the capacitor C2.

The energy charged in the second capacitor C2 is applied to the second primary winding Np2 of the second transformer T2 of the small-capacity control power supply output Vout2. The terminal voltage waveform of the second capacitor C2 is sufficiently smoothed as shown in FIG. 2e, and the control power supply output Vout2 operates exactly the same as a general switching regulator, and has high stability and no ripple. , OA
It is most suitable as a 5V power supply required for controlling electronic devices such as devices.

As described above, the small-capacity input smoothing capacitor C1 outputs large power, and the medium-capacity input smoothing capacitor C2 outputs small power in two circuits (converter circuits). As shown in FIG. 2c, the current waveform at the output terminal, and the current waveform at the AC input section, as shown in FIG. 2d, both have a longer current flowing time and a reduced peak current as compared with the conventional example.

When a switching regulator is configured with 100V input, 150W output, first capacitor C1 = 0.15μF, and second capacitor C2 = 47μF, conversion efficiency 74.2%, peak value of input current 6.
4A, effective value 2.38A, which is smaller than the conventional value. The power factor at this time is greatly improved to 0.85.

In the present embodiment, the first converter circuit composed of the first transformer T1 is a single-forward system,
Although the second converter circuit composed of the transformer T2 is a flyback system, a similar result can be obtained in any system.

〔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, and the safety of the device is improved.

[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 second 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 direct 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, T3 ', T3 ", T4: transformer 4: switching element 4': first switching element (first switching element) 4": second Switching element (second switching element) 5, 9: diode, 6, 10: choke coil 7, 11: diode, 8, 12: smoothing capacitor (5 to 8: first rectifying and smoothing means), (9, 12: 13: pulse width control circuit (first drive means) 13 ″: pulse width control circuit (second drive means) C1: first capacitor (first capacitor) C2: Np1: First primary winding (first primary winding), Np2: Second primary winding (second primary winding) Ns1: First secondary winding (first secondary winding) Winding), Ns2: 2nd secondary winding (2nd secondary winding) Nr: reset winding (reset winding)

Claims (1)

(57) [Claims] 1. A first rectifier for rectifying an AC input; a first capacitor having a small capacity connected between the rectifier output terminals thereof; one end connected to a minus output terminal of the first rectifier having a capacity larger than the first capacitor; A first capacitor having a first primary winding and a reset winding both having one end connected to a positive-side rectification output terminal of the first rectifier; first and second capacitors of the first transformer; A first rectifying / smoothing means connected to the secondary winding; a first switching element interposed between a negative output terminal of the first rectifying means and the other end of the first primary winding; A first drive means for turning on / off; a negative rectification output terminal of the first rectification means and the other end of the reset winding so as to be forward from the negative rectification output terminal of the first rectification means to the other end of the reset winding. Second rectifying means interposed between the ends; A third interposed between the positive-side rectified output terminal of the first rectifier and the other end of the second capacitor so as to be in a forward direction from the positive-side rectified output terminal of the first rectifier to the other end of the second capacitor. Rectifying means; a second switching element having one end connected to one end of the second capacitor;
Second drive means for turning on / off the second switching element; second transformer means having a second primary winding connected in series to the second switching element and the second capacitor; and A second rectifying / smoothing means connected to the second secondary winding.