JP3096211B2 - Switching regulator - 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 regulator for reducing a harmonic component of an AC input current.

[0002]

In general, in order to reduce the harmonic components flowing from the switching regulator to the commercial power supply side must improve the power factor of the switching regulator, the AC input to the AC input current waveform I _AC To this voltage waveform must be close to the (sine wave) V _AC.

A conventional example is disclosed, for example, in Japanese Patent Application Laid-Open No. H4-2135.
FIG. 9 and FIG. 10 show the configuration and main signals, respectively. In FIG. 9 , the commercial AC power supply 2
Voltage (voltage V _AC , current I _AC ) supplied from the rectifier 4 is full-wave rectified by the rectifier 4, and the rectified voltage V _IN = | V _AC | And a DC voltage V ₀ is obtained.

The first power converter 8 includes a choke coil C
And H, the switching transistor Q _S and PWM (pulse width modulation) control circuit 16 is constituted by a flywheel diode D1 and a smoothing capacitor C1. Second
Power conversion unit 10 of is constituted by a switching transistor Q _S and PWM control circuit 16 and the high-frequency transformer T, therefore, first, the second power conversion unit 8, 10 share a switching transistor Q _S.

[0005] In such a configuration, the rectification of the period T the voltage V _IN is fast, as shown in FIG. 10 (period t = t _ON + t
_OFF ), the current is turned on and off (switched), and a triangular wave current I _I having a period t flows through the choke coil CH. Here, in order to improve the power factor, the AC input current waveform I _AC must be close to the AC input voltage waveform (sine wave) V _AC . For this reason, a choke coil CH having a small inductance is used. The triangular wave flowing through the coil CH is configured to make the peak current proportional to the input voltage V _IN .

[0006]

[SUMMARY OF THE INVENTION However, in such a conventional switching regulator, so to reduce the inductance of the choke coil CH to approximate the AC input current waveform to the AC input voltage waveform, the switching transistor Q _S and diode D1 A large current rating must be used, and the effective current flowing through the choke coil CH also increases, resulting in a problem that the amount of heat generated also increases.In addition, the pulse noise transmitted to the AC input line also increases. There is a problem that becomes.

Therefore, in the conventional switching regulator, in order to solve these problems, there is a problem that a radiator and a noise filter are increased, and the size and cost are increased. An object of the present invention is to provide a switching regulator capable of improving a power factor by bringing an AC input current waveform closer to an AC input voltage waveform with a small and inexpensive configuration in view of such a conventional problem. .

[0008]

In order to achieve this object, the present invention switches the voltage rectified by the rectifier circuit by switching means, supplies the voltage to the primary winding of the inverter transformer, and outputs the voltage from the secondary winding. It is intended for switching regulators that obtain voltage.

In such a switching regulator, a choke coil stores energy by a voltage rectified by a rectifier circuit when the switching means is on, and is charged by energy stored by the choke coil when the switching means is off. A smoothing capacitor connected so as to be discharged through the primary winding of the inverter transformer when the switching means is on, and a diode for preventing charging of the smoothing capacitor by the rectified voltage when the switching means is off. The current flowing through the choke coil is smaller than the smoothing capacitor, and the current flowing through the choke coil is charged as the charging current when the switching means is turned on, so that the charging current decrease due to the progress of the charging flows to the primary winding of the inverter transformer. With a connected capacitor The features.

[0010]

According to the switching regulator of the present invention, the current flowing through the choke coil is charged by the capacitor having a smaller capacity than the smoothing capacitor when the switching means is turned on, and the charging voltage increases to charge the smoothing capacitor. When the voltage reaches the voltage, the current flowing through the choke coil is shunted by discharging, so that the current flowing through the choke coil when the switching means is turned on becomes a substantially rectangular wave instead of a triangular wave, and the peak value can be reduced. Therefore, since it is not necessary to reduce the inductance of the choke coil, it is not necessary to use a large radiator or a noise filter, so that the size and cost can be reduced.

Further, since the envelope of the current flowing through the choke coil is proportional to the instantaneous peak value of the rectified voltage, the AC input current approaches a sine wave, and therefore, the pulse noise transmitted to the AC input line by improving the power factor is improved. Can be reduced.

[0012]

EXAMPLES In FIG. 1, the AC voltage (voltage V _AC, current I _AC) of the period T supplied from the AC power source 2 is full-wave rectified by a rectifier 4. The output side of the rectifier 4 choke coil CH, the switching transistor Q _S, via a capacitor C _P having a small capacity is connected to the input side of the rectifier 4, a switching transistor Q _S pulse width variable control signal by a PWM control circuit 16 Speed (period t = t _ON + t
_OFF ) to turn on and off (switch). Here, the AC voltage V _AC is frequency 50 or 60 Hz, the switching transistor Q ON / OFF frequency of _S is several tens to several hundreds kH
z.

A series circuit of a diode D1 and a large-capacity smoothing capacitor C1 is connected to both ends of the choke coil CH. A connection point of the diode D1 and the smoothing capacitor C1 is connected to the primary winding L1 of the transformer T via a diode D2. Connected to one end. One end of the primary winding L1 of the transformer T is also connected to the input side of the connection point of the capacitors C _P and the rectifier 4 through a diode D4, a capacitor C _P
And the connection point of the switching transistor Q _S is connected to the other end of the primary winding L1.

[0014] At both ends of the secondary winding L2 of the transformer T are connected in series circuit of a rectifying diode D 3 and the smoothing capacitor C2, both ends of the smoothing capacitor C2 load R _L is connected. PWM control circuit 16 controls the pulse width of the switching transistor Q _S to a predetermined voltage by detecting the voltage across the smoothing capacitor C2 is turned on (duty ratio).

[0015] In the first period t _ON1 when the capacitor C _P is the switching transistor Q _S is on, the output side of the rectifier 4 → choke coil CH → switching transistor Q _S → capacitor C _P → in the direction of the input side of the rectifier 4 It is charged by the flowing current, and when the charging voltage rises and reaches the charging voltage C1 of the smoothing capacitor, it is discharged at the next t _ON2 , thereby shunting the current flowing through the choke coil CH into a substantially rectangular wave.

Next, the operation of the embodiment of FIG. 1 will be described with reference to FIGS. 2 (a) shows a first section t ₂ ON period t _ON of the switching transistor Q _S, 2
(B) shows the relationship between the _AC input voltage VAC and the AC input current _IAC . In FIG. 2 (a) and FIG. 6, when the switching transistor Q _S is turned on, a current I ₁ flows in the direction of the choke coil CH → switching transistor Q _S → capacitor C _P, and gradually charge the capacitor C _P of small capacity At the same time the energy is accumulated in the primary winding L1 and a current I ₂ flows through the charging voltage of the large-capacity smoothing capacitor C1. Since the peak value of the current I ₁ at this time is substantially proportional to the instantaneous peak value of the rectified voltage V _IN, is substantially proportional to the AC input current waveform I _AC AC input voltage V _AC as shown in FIG. 2 (b).

[0017] FIG. 3 (a) charging current I ₁ 'and the smoothing capacitor C1 of the capacitor C _P when the charging voltage V _CP is close to the charging voltage V _C of the smoothing capacitor C1 is charged capacitor C _P is gradually shows the discharge current I _2, FIG. 3 (b) shows an AC input current I _AC relationship between the AC input voltage V _AC. In FIG. 3A and FIG.
In _ON2, the charge voltage V _CP of the capacitor C _P approaches the charging voltage V _C of the smoothing capacitor C1, current I ₁ 'is flowed primary winding L1 half of the transformer T, transformer T than the charging current of the capacitor C _P The current shunted to the primary winding L1 increases, and at the end of the section t _ON2 , all the current I ₁ ′ flows to the primary winding L1.

[0018] In this case, 1 since the winding L1 charging voltage V _C of the smoothing capacitor C1 is applied, the charging current I ₁ of the capacitor C _P when the rectified voltage V _IN is lower than the charging voltage V _C flows Disappears. Therefore, as shown in FIG. 3B, when the current | I _AC | flowing through the choke coil CH is superimposed in the _{ON period} t _ON (t _ON1 + t _ON2 ), the AC input current I _AC approaches a sine wave.

FIG. 4 shows the current in the first interval t _OFF1 when the switching transistor Q _S is turned off.
When the switching transistor Q _S is turned off, first of all,
The current I due to the energy stored in the choke coil CH
_As soon as ₃ flows and the smoothing capacitor C1 is charged,
Capacitor C _P is discharged by the current I ₄ generated from the primary winding L1 of the transformer T.

[0020] Figure 5 shows the current in an off period t _OFF2 after the capacitor C _P has completed the discharge capacitor C _P
At the same time but the smoothing capacitor C1 the current I ₃ flows is charged by energy accumulated when completing the choke coil CH discharge, the load current I ₅ flows through the secondary winding L2 of the transformer T.

Therefore, according to the embodiment of FIG. 1, the current | I _AC |
_{Since the current} is divided into the primary winding L1 of the transformer T by _P, the applied voltage of the choke coil CH becomes smaller than that of the conventional example even if the inductance of the choke coil CH is the same, as shown in FIG. The waveform of the current I | I _AC | flowing through the choke coil CH in the _ON section t _ON becomes close to a substantially rectangular wave, and the peak value can be reduced.

The current flowing through the choke coil CH |
Since the envelope of I _AC | is proportional to the instantaneous peak value of the rectified voltage V _IN = | V _AC |), the AC input current I _AC approaches a sine wave,
Therefore, it is possible to improve the power factor and reduce the pulse noise transmitted to the AC input line.

[0023] Figure 7 shows another embodiment of the present invention, in this embodiment, the choke coil CH, the diode D4, the step-down dither circuit comprising the smoothing capacitor C1 and the inverter circuit capacitor C _P is provided .

[0024] In this embodiment, the switching transistor Q when _S is turned on, current from the rectifier 4, on the section t _ON1 is the choke coil CH → small capacitor C
_P → capacitor C flows through the switching transistor Q _s
P is charged, and in the _ON period t _ON2 , the capacitor C is charged by the energy stored in the primary winding L1 of the transformer T.
The charging voltage of _P becomes 1 of the transformer T via the diode D1.
It flows to the next winding L1.

In another embodiment shown in FIG. 8 , when the switching transistor Q _S is turned on, the current from the rectifier 4 flows through the choke coil CH → the small-capacity capacitor C _P → the switching transistor Q _S during the ON _period t _ON1. Thus, the capacitor _CP is charged. Then, the ON section t _ON2
Discharge of the capacitor C _P in is carried out in the flyback energy using a coil L _P and diodes D9, D10.

[0026]

As described above, according to the present invention, the current flowing through the choke coil is charged by the capacitor having a smaller capacity than the smoothing capacitor when the switching means is turned on.
When the charging voltage rises and reaches the charging voltage of the smoothing capacitor, the current flowing through the choke coil is shunted by discharging, so that the current flowing through the choke coil does not become a triangular wave but becomes a substantially rectangular wave when the switching means is on. That is, the peak value can be reduced.

Accordingly, since it is not necessary to reduce the inductance of the choke coil, it is not necessary to use a large radiator or a noise filter, and the size and cost can be reduced. Also, since the envelope of the current flowing through the choke coil is proportional to the instantaneous peak value of the rectified voltage, the AC input current approaches a sine wave, thus improving the power factor and reducing the pulse noise transmitted to the AC input line. Can be.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a switching regulator according to the present invention.

FIG. 2 is an explanatory diagram showing a state of charging a capacitor in FIG. 1;

FIG. 3 is an explanatory diagram showing a state of discharging a capacitor in FIG. 1;

FIG. 4 is an explanatory diagram showing a state in which switching is off in FIG. 1;

FIG. 5 is an explanatory diagram showing a state in which switching is off in FIG. 1;

FIG. 6 is a waveform diagram showing main signals during switching in FIG.

FIG. 7 is a circuit diagram showing a switching regulator according to another embodiment.

FIG. 8 is a circuit diagram showing a switching regulator according to another embodiment.

FIG. 9 is a circuit diagram showing a conventional switching regulator.

FIG. 10 is a waveform chart showing main signals in FIG. 9 ;

[Explanation of symbols]

2: AC power supply 4: Rectifier 16: PWM control circuit CH, CH1, CH2: choke coils C1, C2: smoothing capacitor Q _S: Switching transistor T: Transformer D1 to D10: Diode C _P: capacitor R _L: Load

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M ^7/ 00-7/40 H02M 3/28 H02M 7/48

Claims (1)

(57) [Claims] 1. A switch for rectifying a voltage rectified by a rectifier circuit.
A switching regulator that switches by a switching means and supplies the primary winding of an inverter transformer to obtain an output voltage from a secondary winding. When the switching means is on, energy is supplied by a voltage rectified by the rectifier circuit. A choke coil to be stored, which is connected so as to be charged by energy stored by the choke coil when the switching means is off and discharged via a primary winding of the inverter transformer when the switching means is on; A smoothing capacitor, a diode for preventing charging of the smoothing capacitor by the rectified voltage when the switching means is off, and a smaller capacity than the smoothing capacitor, and the choke coil having a smaller capacity than the smoothing capacitor when the switching means is on. The flowing current becomes the charging current and And a capacitor connected to the primary winding of the inverter transformer so as to allow a decrease in charging current due to the progress of the charging to flow through the primary winding of the inverter transformer.