JP3066730B2 - Harmonic current suppression circuit - 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 power supply of the capacitor input type, and more particularly to a harmonic current suppressing circuit for suppressing a harmonic of an input current and improving a power factor.

[0002] A capacitor input type switching power supply circuit obtains a desired DC output from an AC power supply by combining a capacitor input type rectifier circuit and a switching power supply.

In such a capacitor input type switching power supply, it is necessary to suppress harmonics of the input current due to a narrow conduction angle of the input current and to improve the power factor of the power supply.

[0004]

2. Description of the Related Art FIG. 4 shows a conventional switching power supply circuit, and exemplifies a case of a forward converter type switching power supply circuit. In the figure,
R is a power rectifier, which is composed of diodes D _{1 to} D ₄ . C ₁ is an input capacitor, and T is a main transformer. N _{1 and} N ₂ are windings of the main transformer T, respectively.
N ₁ is the primary winding, N ₂ is the secondary winding. Q is the main switch, D _5, D ₆ is output rectifier, L ₂ is output smoothing choke,
C ₂ is an output smoothing capacitor, and L is a load. Also v _in
Is an AC input voltage, i _in is an input current, and v _c1 is a voltage of the input capacitor C ₁ .

FIG. 5 is a diagram showing a relationship between an input voltage and an input current in a conventional circuit. The operation of the conventional capacitor input type switching power supply circuit will be described below with reference to FIGS.

[0006] The AC input voltage v _in the rectified output by the power rectifier D ₁ to D ₄ consisting of the bridge circuit obtained by full-wave rectification,
By smoothing in addition to the input capacitors C _1, to obtain a voltage v _c1 to the input capacitor C _1. This voltage _vc1 is
Via the main switch Q in addition to the primary winding N ₁ of the main transformer T, switching in response to the excitation pulse from not shown main switch Q excitation circuit.

Thus, when the main switch Q is turned on,
With store energy in the exciting inductance of the primary winding N ₁ of the main transformer T, two by transmitting a direct current energy to the primary side, the secondary winding N output rectifier a voltage generated in ₂ D
_5, rectified by D _6, by smoothing by the output smoothing choke L ₂ and the output smoothing capacitor C _2, to obtain a DC output voltage to a load L.

[0008]

[SUMMARY OF THE INVENTION In the rectifier circuit of a capacitor input type, AC input voltage v _in is the input capacitor C ₁ in the voltage v only during periods of high than _c1 input current i _in
Flows, and no input current flows during other periods.

In this case, since the conduction angle of the input current i _in is narrow, the input current i _in becomes pulse-like, and the input current contains considerable harmonics. Such harmonics become high-frequency noise and cause various obstacles to communication devices and other electronic devices.

[0010] There is a tendency that such harmonic disturbances are legally regulated. Therefore, it is necessary to suppress the harmonic current in a capacitor input type switching power supply circuit. There has been a problem that a switching power supply circuit taking such a harmonic suppression measure has not been proposed.

Also, in the conventional capacitor input type switching power supply circuit, since the conduction angle of the input current is narrow, the apparent power is large and the power factor is low. Therefore, there is a problem that the power supply equipment becomes large and the equipment cost increases.

An object of the present invention is to solve such a problem of the prior art. In a capacitor input type switching power supply circuit, a conduction angle of an input current is widened to effectively suppress a harmonic current. To improve the power factor of the power supply circuit,
An object is to provide a harmonic current suppression circuit.

[0013]

Means for solving the problems of the present invention will be described below.

(1) a power supply rectifier R for rectifying an AC power supply;
Input capacitor C for smoothing this rectified output₁ Consisting of
For a capacitor input type power supply circuit,
Sensor C₁ The primary winding N of the main transformer T₁ And Lord Sui
Switch Q, and turn the main switch Q on and off.
Rectifies the power transmitted to the secondary side of the main transformer T when
Power supply in a switching power supply circuit
Output terminal of rectifier R and input capacitor C₁ For boost between
Capacitor C_Three Into the main transformer T
Lamp winding N_Three And the clamp winding N_Three One end of
To diode D ₇ And connected to the output terminal of the power rectifier R
And the other end is the input capacitor C₁ To the booster
Densa C_Three Charging voltage v_c2Corresponds to the output of the power rectifier R.
And the input capacitor C₁ Voltage v_c1Will have the opposite polarity
And boost capacitor C _Three Power supply at both ends
Diode D for transmitting the output current of current sink R₈ Connect
You.

(2) a power rectifier R for rectifying an AC power;
Input capacitor C for smoothing this rectified output₁ Consisting of
For a capacitor input type power supply circuit,
Sensor C₁ The primary winding N of the main transformer T₁ And Lord Sui
Switch Q, and turn the main switch Q on and off.
Rectifies the power transmitted to the secondary side of the main transformer T when
Power supply in a switching power supply circuit
Output terminal of rectifier R and input capacitor C₁ For boost between
Capacitor C_Three Into the main transformer T
Lamp winding N_Three And the clamp winding N_Three One end of
To diode D ₇ And connected to the output terminal of the power rectifier R
And the other end is inductor L_Three Input capacitor C₁ To
Connect to boost capacitor C_Three Charging voltage v_c2But
For the output of the source rectifier R, the input capacitor C₁ Voltage
v_c1And the polarity of the power rectifier R
Force end and clamp winding N_Three And inductor L_Three Between connection points with
And a diode D transmitting the output current of the power rectifier R.₈ 
Connect.

[0016]

FIG. 1 shows an embodiment (1) of the present invention and illustrates a case of a switching power supply of a forward converter type. The same meaning as in FIG. 4 in the same numbers in _{FIG., N 1, N 2, N} 3 are each a winding of the main transformer T, N ₁ is the primary winding, N ₂ the secondary winding , N ₃ is the clamping winding. Also, C ₃ is the step-up capacitor, D _7, D ₈ is diode, L ₁ is an inductor.

The power supply rectifier R, the input capacitor C ₁ , the windings N _{1 and} N _{2 of the} main transformer T, the main switch Q, the output rectifiers D _{5 and} D ₆ , the output smoothing choke L ₂ , and the output smoothing capacitor in the circuit of FIG. The operation related to C ₂ as a capacitor input type switching power supply circuit is the same as that of the conventional circuit shown in FIG. 4, and therefore detailed description is omitted.

[0018] In the switching power supply circuit shown in FIG. 1, during on of the main switch Q, together with storing energy in the exciting inductance of the primary winding N ₁ of the main transformer T, and transmits the DC energy to the secondary side. And when off of the main switch Q, by the voltage generated in the clamp winding N ₃ based on the excitation energy of the main transformer T, by charging the step-up capacitor C ₂ through the diode D _7, the charging voltage in the capacitor C ₂ generate _vc2 .

The polarity of the charging voltage v _c2 boost capacitor C _2, to the power rectifier R side, a reverse voltage v _c1 of the input capacitor C _1. Therefore, the input capacitor C ₁
Since the current flows from the power rectifier R even during a period in which the rectified output voltage of the power rectifier R is lower than the voltage _vc1 , the conduction angle can be widened.

In FIG. 1, a diode D ₈ is provided to prevent the current for charging the capacitor C ₁ from the power rectifier R from being cut off by the capacitor C ₃ when the power is turned on. Thus, when power is turned on, it is possible to quickly charge the input capacitor C _1.

[0021] In the power supply rectifier R, the low-pass filter consisting of an inductor L ₁ and capacitor C ₄ is inserted between the AC input power v _in (LPF) is generated with the switching of the main switch Q, the switching frequency It is provided to prevent a nearby high-frequency current from flowing out to the AC input power supply side.

The switching power supply circuit shown in FIG.
There is a problem that the secondary-side output voltage of the main transformer T may decrease based on the voltage generated by the clamp winding.

FIG. 2 shows an embodiment (2) of the present invention, and illustrates the case of a flyback type switching power supply circuit. The same meaning as in FIG. 1 with the same symbols, in the drawing, L ₃ is an inductor.

In the embodiment (2) shown in FIG.
When the main switch Q is on, the input capacitor C₁From primary volume
Line N₁Current flows through the diode D₈ and
Inductor L_Three Through the primary winding N₁ Current flows through the primary
Winding N₁ Excitation inductance and inductor L_Three Energy
Lugie is stored. Primary winding when main switch Q is off
N₁ Energy stored in the excitation inductance of
The secondary winding N_Two The voltage generated at the diode D_Five To
Rectified through the capacitor C_Two And load L
To obtain a DC output voltage,_Three Departs at
Generated voltage and inductor L_Three The reverse voltage and
Iod D₇ Through the capacitor C _Three Is the voltage v_c2To
Charged.

The polarity of the charging voltage v _c2 boost capacitor C _3, to the power rectifier R side, a reverse voltage v _c1 of the input capacitor C _1. Therefore, the input capacitor C ₁
Since the current flows from the power rectifier R even during a period in which the rectified output voltage of the power rectifier R is lower than the voltage _vc1 , the conduction angle can be widened.

In FIG. 2, when the main switch Q is turned off, the voltage generated in the secondary winding N ₂ is proportional to the voltage of the clamp winding N ₃ according to the turns ratio. Therefore, higher input voltage lowers the voltage of the capacitor C _3, the generation voltage of the clamp winding N ₃ is lowered, also decreases voltage generated in the winding N ₂ of the secondary side.

[0027] Therefore, even when the voltage of the boost capacitor C ₃ is lowered, a voltage is generated in the clamping winding N _3, to the output voltage of the secondary side is not adversely, insert the inductor L ₃ ing.

FIG. 3 shows the relationship between the input voltage and the input current in the circuit of the present invention, which is obtained by simulation of the circuit of FIG. It is clear that the conduction angle of the input current is wider than in the conventional case shown in FIG.

In the circuit shown in FIG. 1 or FIG. 2, a low-pass filter is provided between the AC power supply and the power supply rectifier R in order to prevent a high-frequency current based on switching from leaking to the AC power supply side. It is necessary to insert.

As a method of improving the power factor of a switching power supply circuit, a method of using a choke input type rectifier circuit is conventionally known. However, there is a limit to the power factor improvement in the case of a choke input type rectifier circuit,
It is not preferable because the part shape becomes large.

As another method of improving the power factor of the switching power supply circuit, there is a method in which the switching power supply has two stages by using a boost converter. In this case, the power factor is sufficiently improved, but the efficiency is reduced. Further, the circuit scale is increased and the cost is increased, which is not preferable.

On the other hand, in the switching power supply circuit to which the harmonic current suppressing circuit of the present invention is applied, the power factor is improved by increasing the conduction angle of the input current. Therefore, a decrease in efficiency can be suppressed, and an increase in the number of parts is small, so that an increase in cost can be prevented.

[0033]

As described above, according to the present invention, in the switching power supply circuit of the capacitor input rectification type, the conduction angle of the input current is widened, so that the harmonic component of the input current can be reduced. It becomes possible to improve the power factor of the AC input power supply.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment (1) of the present invention.

FIG. 2 is a diagram showing an embodiment (2) of the present invention.

FIG. 3 is a diagram showing a relationship between an input voltage and an input current in the circuit of the present invention.

FIG. 4 is a diagram showing a conventional switching power supply circuit.

FIG. 5 is a diagram showing a relationship between an input voltage and an input current in a conventional circuit.

[Explanation of symbols]

R mains rectifier C ₁ input capacitor C ₃ boosting capacitor T main transformer N ₁ primary winding N ₃ clamp windings Q main switching D ₇ diode D ₈ diode L ₃ Inductors

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 1/12 H02M 7/217

Claims (2)

(57) [Claims] 1. A capacitor input type power supply circuit comprising a power supply rectifier for rectifying an AC power supply and an input capacitor for smoothing the rectified output, a primary winding of a main transformer and a main switch being provided at both ends of the input capacitor. A switching power supply circuit for rectifying power transmitted to the secondary side of the main transformer to obtain a DC output when the main switch is turned on and off, wherein an output terminal of the power rectifier, an input capacitor and A step-up capacitor is inserted between the input terminals and a clamp winding is provided on the main transformer. One end of the clamp winding is connected to the output terminal of the power rectifier via a first diode, and the other end is connected to the input terminal. Connected to a capacitor so that the charging voltage of the boosting capacitor has a polarity opposite to the voltage of the input capacitor with respect to the output of the power rectifier. , Harmonic current suppression circuit further characterized by connecting a second diode for transmitting the output current of the power source rectifier to both ends of the step-up capacitor. 2. A capacitor input type power supply circuit comprising: a power supply rectifier for rectifying an AC power supply; and an input capacitor for smoothing the rectified output. A switching power supply circuit for rectifying power transmitted to the secondary side of the main transformer when the main switch is turned on and off to obtain a DC output, wherein an output terminal of the power rectifier, an input capacitor, A step-up capacitor is inserted in between, a clamp winding is provided in the main transformer, one end of the clamp winding is connected to the output terminal of the power rectifier through a first diode, and the other end is connected to an inductor. Connected to the input capacitor, the charging voltage of the boosting capacitor is opposite to the voltage of the input capacitor with respect to the output of the power rectifier. Wherein a second diode for transmitting the output current of the power rectifier is connected between the output terminal of the power rectifier and a connection point between the clamp winding and the inductor. .