JP3045204B2 - Switching power supply - 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 used by connecting to an AC power supply.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional typical switching power supply unit connected to a commercial AC power supply has input terminals 1 and 2 connected to a commercial AC power supply of, for example, 100 V and 50 Hz. A line filter 6 comprising a capacitor 3 and inductance coils 4 and 5 connected thereto;
A bridge type full-wave rectifier circuit 7 connected to the input terminals 1 and 2 via the line filter 6, and a relatively large electrolytic capacitor connected between a pair of output terminals of the full-wave rectifier circuit 7 A smoothing capacitor 8 composed of
A transformer including a secondary winding 9 and a secondary winding 10, and a field effect transistor or FET 12 as a conversion switching element connected between both terminals of the smoothing capacitor 8 via the primary winding 9, The rectifying / smoothing circuit 15 includes a diode 13 and a smoothing capacitor 14 connected to the secondary winding 10, and a feedback control circuit 18 that detects the voltage between the output terminals 16 and 17 and performs PWM control on the FET 12.

In this circuit, a smoothing capacitor 8 functions as a DC power source with little ripple, and a DC voltage
2, and the voltage of the secondary winding 10 is rectified and smoothed. As a result, a stabilized DC voltage is obtained at the output terminals 16 and 17.

[0004]

In the conventional circuit shown in FIG. 1, the smoothing capacitor 8 is charged to a value near the peak of the AC power supply voltage. Current flows, the input current waveform does not become a sine wave, and the power factor is poor.

It is an object of the present invention to provide a switching power supply capable of improving the power factor and reducing harmonic components with a simple configuration.

[0006]

According to the present invention, there is provided an input terminal to which an AC voltage is supplied, a rectifier circuit connected to the input terminal, and a rectifier circuit.
The converter comprises a converter connected without passing through a smoothing circuit, and a feedback control circuit for controlling the converter so that the output voltage of the converter is constant. The converter includes a primary winding and a secondary winding. And a switching element connected between the pair of output terminals of the rectifier circuit via the primary winding, and a rectification smoothing circuit connected to the secondary winding. An output voltage detecting means of the rectifying and smoothing circuit, a reference voltage source, an error amplifying means for generating an error output between a detection voltage detected by the output voltage detecting means and a reference voltage of the reference voltage source, A control signal forming circuit for forming a control signal for controlling on / off of the switching element based on an output of the amplifying means; and a ripple component of an output voltage of the rectifier circuit and an output voltage of the rectifier smoothing circuit. Phase correction for the child to correct the phase difference of
Capacitor and the same frequency components as the frequency of the output voltage of the rectifier circuit included in the output voltage of the rectifying and smoothing circuit
Gain correction means for lowering the gain with respect to
The control signal forming circuit includes: a sawtooth wave generator;
The output of the sawtooth wave generator is compared with the output of the error amplifier.
Forming a control pulse for the switching element.
And a gain correction means,
Connected between the error amplification means and the comparator
Amplifying circuit and rectified output adding means,
The gain at twice the frequency of the AC voltage is 2
Than the gain in the frequency range lower than twice the frequency
The error amplification means is set low and the error amplification transformer is
A transistor whose base is
Output means, the emitter of which is connected to the
Connected to a reference voltage source, and the phase correction capacitor,
Connected between the base and collector of the transistor
And the rectification output adding means is provided before the input of the amplification circuit.
The present invention relates to a switching power supply device characterized in that the output voltage of the rectifier circuit is attenuated and added . A low-pass filter is provided as claimed in claim 2.
Is desirable.

[0007]

[Operation and Effect] The invention of each claim has the following operation and effect.
You. (A) In the present invention, since no smoothing circuit is provided at the output stage of the rectifier circuit, a non-smoothed voltage is applied to the series circuit of the primary winding and the switching element, which is turned on / off by the switching element. As a result, the output voltage of the rectifying / smoothing circuit connected to the secondary winding of the transformer includes a ripple component corresponding to the rectified waveform of the AC power supply voltage. The feedback control circuit changes the ON time width of the switching element in inverse proportion to the detected voltage value. If the phase correction component according to the invention is
Assuming that no capacitor is provided, normal operation becomes impossible because the phases of the primary-side voltage and the ripple component of the output voltage of the secondary-side rectifying / smoothing circuit do not match. on the other hand,
When the capacitor for phase correction according to the present invention is provided, the phase of the voltage on the primary side and the phase of the ripple component on the secondary side are apparently coincident with each other, and a stable operation becomes possible. (B) By providing the gain correction means and the rectification output addition means , it is possible to perform pulse width control with less influence of output voltage ripple, and the phases of the input voltage and the input current are almost coincident, and the power factor is improved. You. (C) connecting a phase correction capacitor between the base and the collector of the transistor for error amplification to correct the phase;
Therefore, the stabilization of the operation by the phase correction can be easily achieved. (D) When the output of the rectifier circuit is attenuated and added to the input of the gain correction amplifier circuit, the waveform of the AC input current can be made closer to the AC input voltage. That is, by attenuating and adding the output of the rectifier circuit, the responsiveness to the load fluctuation (the responsiveness in the high frequency region) is reduced to some extent without significantly reducing the gain of the amplifying circuit with respect to the frequency twice the AC voltage. The distortion of the waveform of the input current can be reduced while securing the same. More specifically, if the gain in the high frequency region of the amplifier circuit for the error signal line is extremely low , the response of the voltage control to a load change becomes poor.
When the load response is regarded as important, it is better not to lower the gain of the amplifier circuit in the high frequency region. However, high frequency
If the gain of the band is high, the distortion of the waveform of the input current increases. Therefore, the feedback control is adjusted so that the output of the rectifier circuit is attenuated and added to the input of the amplifier circuit to correct the waveform distortion.

[0008]

Next, a switching power supply according to an embodiment of the present invention will be described with reference to FIGS. However, FIG.
In the figure, the same reference numerals are given to the parts common to FIG. 1 and the description thereof is omitted.

The circuit of FIG. 2 eliminates the smoothing capacitor 8 from the circuit of FIG. 1, and instead includes a low-pass filter 19 that allows the output waveform of the rectifier circuit 7 to pass therethrough.
Further, a modified feedback control circuit 18a is provided in place of the control circuit 18 of FIG.
And a series regulator 15 is added in between. The other circuit configuration in FIG. 2 is the same as that in FIG.

The low-pass filter 19 is connected between a pair of power supply lines 7a and 7b between the full-wave rectifier circuit 7 and the primary winding 9, and has two capacitors C1 and C2 and two inductance elements L1 and L2. Consisting of The two capacitors C1 and C2 are connected in parallel to the pair of lines 7a and 7b and have a very small capacitance of, for example, 0.33 μF and 2 μF. Two inductance elements L1, L2
Are connected in series to the lines 7a and 7b, for example, 2
Each has 80 μH. This low-pass filter 19 is for preventing the input current from being interrupted due to the on / off operation of the FET 12 as a switching element.
Is essentially different from the smoothing capacitor 8 of FIG.
Is passed substantially as it is.
Therefore, this low-pass filter 19 can be called a high-frequency component removal filter.

The feedback control circuit 18a includes a voltage detecting means 22
, An error amplifying means 23, a gain correcting amplifying circuit 24 as a frequency characteristic setting means, a comparator 25, a sawtooth wave generator 26, a capacitor 27 as a phase correcting means, and a waveform correcting resistor 28. . Control circuit 1
8a, the amplifier circuit 24 and the phase correction capacitor 27
The other parts except for the waveform correction resistor 28 are the same as those of the known constant voltage control circuit.

The output voltage detecting means 22 is composed of voltage dividing resistors 29 and 30 connected between a pair of output terminals 16 and 17, and is configured to obtain a detected voltage from a voltage dividing point 31. ing. The error amplifier 23 includes a Zener diode 32 and a resistor 33 as a reference voltage source.
A transistor 34 as an error amplifier, a light emitting diode 35 for insulation separation, a current limiting resistor 36,
It comprises a phototransistor 37 and a resistor 38. The base of the transistor 34 is connected to the voltage detection voltage dividing point 31, the emitter is connected to the Zener diode 32, and the collector is connected to the light emitting diode 35. The cathode of the Zener diode 32 is connected to the output terminal 16 via the resistor 33 and the anode is connected to the lower output terminal 17, that is, the ground, so that a reference voltage can be applied to the emitter of the transistor 34. The transistor 34 generates an error output between the sum of the reference voltage of the Zener diode 32 and the base-emitter voltage V _BE of the transistor 34 and the detection voltage at the voltage dividing point 31. The light emitting diode 35 is connected to the collector of the transistor 34 and the output terminal 16.
Are connected through the resistor 36, and the light emitting state corresponding to the error output is obtained. The phototransistor 37 optically coupled to the light emitting diode 35
5 and a conductive state corresponding to the light output of FIG. 5 is generated, and an output voltage that changes in inverse proportion to the detected voltage is generated. In order to convert the resistance change of the phototransistor 37 into a voltage change, the phototransistor 37 is connected to the DC power supply terminal 3 via a resistor 38.
9 is connected. The voltage between the output terminals 16 and 17 is 120 V, the resistor 29 is about 56 KΩ, and the resistor 30 is about 6 KΩ.
KΩ, the resistor 36 is about 22 KΩ, and the capacitor 27 is about 0.2 KΩ.
33 μF and the resistance 38 are 1.5 KΩ.

The output of the phototransistor 37 is not directly input to the comparator 25 but is input via the amplifier circuit 24. The amplifier circuit 24 includes two transistors 40, 4
1, a resistor 42, a gain correcting resistor 43 and a capacitor 44 . In the frequency-gain characteristic line of the amplifier circuit 24, the capacitor 44 and the resistor 43 for lowering the gain in the region of 100 Hz are connected in parallel to the resistor 38 for obtaining an error output. The base of transistor 40 is connected to the collector of phototransistor 37, and the emitter is connected to power supply terminal 39 via resistor 42.
The base of the succeeding transistor 41 is connected to the emitter of the preceding transistor 40, the emitter is connected to the power supply terminal 39, and the collector is connected to the collector of the preceding transistor 40. A resistor 42 in the amplifier circuit 24,
The value of 43 is 560Ω and 100Ω, and the value of capacitor 44 is 4.7 μF.

One input terminal of the comparator 25 is connected to the collector of the transistor 41, the other input terminal is connected to the sawtooth generator 26, and the output terminal is connected to the control terminal (gate) of the switching FET 12. .

The current waveform correcting resistor 28 has a value of 1.5 MΩ and is connected between the output line 7 a of the rectifier circuit 7 and the phototransistor 37.

A series regulator 21 connected between the output terminals 16 and 17 and the load 20 connects a transistor in series with a power supply line and controls the transistor to stabilize the output voltage. In the example, it is provided to reduce the ripple component of the output of the rectifying / smoothing circuit 15.

[0017]

[Operation] In the circuit of FIG. 2, for example, a sine-wave AC voltage of 100 V, 50 Hz is full-wave rectified by a bridge type full-wave rectification circuit, becomes an input voltage Vin shown in FIG. 3, and is sent to a converter portion. The repetition frequency of the input voltage Vin for this full-wave rectification is 100 Hz, which is twice the frequency of the AC power supply, 50 Hz. Since the low-pass filter 19 is for removing high-frequency components, the input voltage Vin of 100 Hz is passed substantially as it is. As a result, the primary winding 9 and the switching FE
The non-smoothed input voltage Vin is applied as it is to the series circuit composed of T12. Therefore, the FET 12 turns on and off the non-smooth input voltage Vin at a repetition frequency sufficiently higher than this. If F has a constant period and a uniform pulse width,
Assuming that the ET 12 is turned on and off, the amplitude value of the current flowing during the on period changes in accordance with the change in the amplitude value of the input voltage Vin. Then, the input current Iin in a state where the envelope detection is performed is obtained by the operation of the low-pass filter 19. As a result, the input voltage Vin of the sine wave full-wave rectified waveform
An input current Iin having the same waveform as the above is obtained, and a current having substantially the same phase as the voltage is obtained at the input terminals 1 and 2.

By connecting the conventional feedback control circuit 18 shown in FIG. 1 to the feedback control circuit 18a shown in FIG.
Oscillation occurs due to the phase difference of approximately 90 degrees between the primary side voltage of 1 and the ripple component of the secondary side output voltage, and normal operation becomes impossible. On the other hand, in the circuit of FIG. 2 according to the present invention, the capacitor 27 between the base and the collector of the error amplification transistor 34 is connected to the output line 7a of the
The phase difference between the voltage 7b, that is, the input voltage Vin to the switching unit and the ripple waveform of the output voltage of the rectifying / smoothing circuit 15 on the secondary side is corrected, so that both seem to be substantially in phase. That is, the capacitor 27 acts to advance the phase of the output voltage. As a result, feedback control without a phase difference becomes possible, and normal feedback operation becomes possible. However, simply correcting the phase with the capacitor 27 does not achieve the power factor improvement.

That is, when the input voltage Vin of FIG. 3 is turned on / off by a series circuit of the primary winding 9 and the FET 12 in a state where the phase correction capacitor 27 is provided but the gain correction capacitor 44 is not provided, the output terminal is output. The 100 Hz ripple component between 16 and 17 is phase corrected and enters the error output, and the ripple component of this error output is output from the comparator 25.
And the pulse width becomes narrow when the amplitude of the input voltage Vin is high, and conversely, the pulse width becomes wide when the amplitude of the input voltage Vin is low, resulting in a phase mismatch between the voltage and the current. Rate improvement becomes impossible.

On the other hand, when the frequency gain characteristic adjusting capacitor 44 is added, each part changes as shown in FIG. 3 and the power factor can be improved. Next, this operation will be described. In the conventional method without the capacitor 44, the gain of the amplifier circuit 24 or the gain of the feedback control circuit 18 is flat up to 100 Hz or more as shown by the frequency-gain characteristic line A in FIG. respond. On the other hand, the gain of the amplifier circuit 24 provided with the capacitor 44 according to the present invention, that is, the gain of the error signal transmission path is shown in FIG.
As shown by the characteristic line B, the frequency decreases at a frequency lower than 100 Hz, and at 100 Hz, it is significantly lower than the characteristic line A. 1
A low gain at 00 Hz means that PWM control with poor response corresponding to a ripple component at 100 Hz is being performed. As a result, it is possible to perform control with a small change in the duty ratio of the PWM pulse due to the ripple component. As a result, as shown in FIG. 3, a control with a small change in the width of the PWM pulse is achieved irrespective of the change in the input voltage Vin, and the amplitude of the input current Iin changes corresponding to the input voltage Vin and becomes substantially in phase. , Power factor improvement is achieved.

Next, the operation of the capacitor 44 of FIG. 2 will be described in more detail. Even if the resistance of the phototransistor 37 changes due to the ripple corresponding to the input voltage Vin, the capacitor 44 absorbs this change, and the transistor 40 hardly responds to the ripple component. As a result, it is possible to apply a voltage from which fluctuation due to ripple has been removed to the non-inverting input terminal of the comparator 25.

In order to form a PWM pulse which does not completely respond to the ripple component, the pulse width is set to 100H from the characteristic line B in FIG.
It is necessary to further reduce the gain at z. However, if the gain in the high frequency region is excessively reduced, the responsiveness of the feedback control circuit 18a to a change in the load 20 or a change in the input AC voltage in a cycle shorter than the cycle of the ripple component included in the output voltage Vin of the rectifier circuit 7 will be described. Gets worse. Therefore,
In this embodiment, the gain at 100 Hz is not zero. Therefore, the feedback control circuit 18a slightly responds to the ripple component, causing a waveform distortion in the input current Iin, resulting in a waveform shown by a dotted line in FIG. In order to correct this as shown by the solid line, in this embodiment, the resistor 28 is connected to the input terminal of the amplifier circuit 24. As a result, the input voltage Vin is attenuated by the resistor 28, input to the amplifier circuit 24, and added to the output of the error amplifier 23. Adding the correction voltage means that the input of the comparator 25 does not change even though the voltages of the output terminals 16 and 17 are rising. Since the correction voltage applied through the resistor 28 is obtained by dividing the input voltage Vin, the input voltage of the comparator 25 is changed with the same amplitude change as the input voltage Vin, and the amplitude of the input voltage Vin is changed. Is corrected so that the pulse width (duty ratio) of the PWM pulse becomes larger as the value of. As a result, the peak region of the waveform of the input current Iin is increased from the dotted line to the solid line, and the waveform has a good approximation to a sine wave.

As described above, according to this embodiment, the power factor can be greatly improved. Further, the waveform of the AC input current can be improved, and the harmonic current can be greatly reduced. Further, since no smoothing capacitor is connected to the output stage of the rectifier circuit 7, no inrush current flows, and this countermeasure becomes unnecessary. When the series regulator 21 is provided, the overall efficiency is reduced by about 2% as compared with the conventional step-down converter.
Since the series regulator 21 is for removing ripples,
The loss here is relatively small.

[0024]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) Instead of the transistor 34 in FIG. 2, an error amplifier 34a composed of, for example, an operational amplifier may be used as shown in FIG. In this case, the phase correcting capacitor 27 is connected between the inverting input terminal and the output terminal of the amplifier 34a. (2) As shown in FIG. 6, for example, an operational amplifier 41a can be used instead of the transistors 38 and 39 as amplifiers in the amplifier circuit 24 of FIG. In this case, the frequency gain characteristic correcting capacitor 44 and the resistor 43 are connected between the inverting input terminal and the output terminal of the operational amplifier 41a. (3) The FET 12 as a switching element can be a bipolar transistor or the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a conventional switching power supply device.

FIG. 2 is a circuit diagram showing a switching power supply according to an embodiment of the present invention.

FIG. 3 is a waveform diagram showing Vin, a PWM pulse, and Iin of the circuit of FIG. 2;

4 is a frequency-gain characteristic diagram in a transmission path between the error amplifying unit and the comparator in FIG.

FIG. 5 is a diagram illustrating an error amplifier circuit according to a modification.

FIG. 6 is a diagram illustrating a frequency-gain characteristic correction circuit according to a modified example.

[Explanation of symbols]

 7 Rectifier circuit 12 Switching FET 27 Capacitor for frequency-gain characteristic correction 29 Capacitor for phase correction

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-230755 (JP, A) JP-A-63-190557 (JP, A) JP-A-3-230760 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/335

Claims (2)

(57) [Claims] 1. An input terminal to which an AC voltage is supplied, a rectifier circuit connected to the input terminal, a converter connected to the rectifier circuit without a smoothing circuit, and an output voltage of the converter. A feedback control circuit for controlling the converter so as to have a constant value. The converter includes a transformer having a primary winding and a secondary winding, and the primary control circuit disposed between a pair of output terminals of the rectifier circuit. A switching element connected via a winding, and a rectifying / smoothing circuit connected to the secondary winding, wherein the feedback control circuit includes an output voltage detecting unit of the rectifying / smoothing circuit, a reference voltage source, Error amplifying means for generating an error output between the detected voltage detected by the output voltage detecting means and a reference voltage of the reference voltage source; and controlling the on / off of the switching element based on an output of the error amplifying means. A control signal forming circuit for forming a that control signal, the phase correction capacitor for correcting the phase difference between the ripple component of the output voltage of the output voltage and the rectifying smoothing circuit of the rectifier circuit, the output voltage of the rectifying and smoothing circuit and a gain correcting means for reducing the gain for the same frequency component as the frequency of the output voltage of the rectifier circuit included, the control signal forming circuit
Is the sawtooth wave generator and the output of the sawtooth wave generator
And the output of the error amplifying means.
Comparator for forming control pulses for switching elements
Et made, said gain correcting means, wherein said error amplifying means compactors
Amplifying circuit and rectified output adding means connected between the rectifier and the rectifier
And a frequency twice as high as the AC voltage of the amplifier circuit.
In the frequency region where the gain is lower than the double frequency.
Is set lower than the gain in the range, the error amplification means includes an error amplification transistor,
The base of this transistor is connected to the voltage detecting means.
And the emitter of this transistor is connected to the reference voltage source.
The phase correction capacitor is connected to the transistor.
Rectifier output adding means connected between the base and the collector of the
A switching power supply device for attenuating and adding an output voltage of a flow circuit . 2. The method according to claim 1, further comprising :
Between the rectifier circuit and the output of the rectifier circuit.
Low-pass filter for removing high-frequency components
The switching power supply device according to claim 1, wherein the switching power supply device is provided.