JPH05300734A - Switching regulator - Google Patents

Abstract

PURPOSE:To improve a power factor and to downsize an apparatus and decrease the cost of the apparatus by linearizing the waveform of AC input current. CONSTITUTION:After AC inputted from an AC power supply 1 to the primary side of an apparatus is full wave-rectified by a rectifier circuit 2, AC in the state of unsmoothed full sine waveform is switched by a switching element 5. In this case, a pulse-width modulation control circuit 14 changes a switching pulse-width into an inverse sine waveform so that the pulse width is long when voltage is low and short when voltage is high. A high-frequency pulse, which is pulse-width modulated into the inverse sine waveform by such switching, is outputted to the secondary side; formed into a smooth DC output voltage Vo through a rectifier and smoothing circuits 7, 8, 9, 10; and supplied to a load. When the DC output voltage Vo is going to change by the variation of AC input voltage or load, the pulse-width modulation control circuit 14 controls the whole pulse width according to the change so that the output voltage Vo is maintained at a constant value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator, that is, a high frequency switching type DC stabilized power supply.

[0002]

2. Description of the Related Art FIG. 9 shows a schematic circuit diagram of a conventional switching regulator. On the primary side, an AC power supply 1, a full-wave rectifier 2, an input smoothing capacitor 3a, a primary winding of a high frequency transformer 4, and a high frequency semiconductor switching element such as an FET 5 (field effect transistor) are provided. The main circuit is configured. The gate terminal of the FET 5 is connected to the gate output terminal of the pulse width modulation (PWM) control circuit 6. On the other hand, on the secondary side, a secondary winding of the high frequency transformer 4, a rectifying diode 7, a commutation flywheel diode 8, a smoothing choke coil 9, and an output smoothing capacitor 10 constitute a main circuit. ing. The output voltage detection resistor 11 and the voltage dividing resistor 12 are connected to the output terminal of the secondary side main circuit, and the load circuit of the load 13 is connected to the output terminal. The divided voltage between the output voltage detecting resistor 11 and the voltage dividing resistor 12 is connected to the output voltage input terminal of the pulse width modulation control circuit 6.

In this switching regulator, the alternating current supplied from the alternating-current power supply 1 is full-wave rectified by the full-wave rectifier 2 and smoothed by the input smoothing capacitor 3a to generate a DC voltage containing a ripple component as shown in FIG. Occur. This DC voltage is switched by the FET 5 to become a high frequency pulse voltage, which is transformed into a required voltage by the high frequency transformer 4. The transformed high frequency pulse voltage is smoothed by the rectifying diode 7, the commutation flywheel diode 8, the smoothing choke coil 9 and the output smoothing capacitor 10, and becomes a direct current as shown in FIG.

If the AC input voltage and the load are constant, the pulse width of the high frequency pulse voltage is constant, and the load is always supplied with a constant DC voltage V ₀ . However, since the output voltage V ₀ tends to change with the change of the AC input voltage or the load, the pulse width modulation control circuit 6 is detected by the divided voltage between the output voltage detecting resistor 11 and the voltage dividing resistor 12. By changing the gate output to the FET 5 according to the voltage change ΔV, the pulse width of the primary side high frequency pulse voltage is controlled to make the output voltage V ₀ constant.

[0005]

However, in the conventional switching regulator, a DC voltage containing a ripple component as shown in FIG. 10 is applied to both ends of the input smoothing capacitor 3a to charge the ripple portion. As a result of the current concentration, the AC input current has a non-linear waveform including many third, fifth, etc. odd harmonics as shown in FIG. For this reason, as this type of switching regulator has become widespread, harmonic interference such as heat generation in a transformer in a substation on an input distribution line or generation of abnormal noise has become a problem in recent years. Further, there is a problem that a large amount of reactive current flows due to the advance power factor and the wiring capacitance increases. Furthermore, since the input-side smoothing capacitor 3a on the primary side smoothes the low-frequency AC input, it has a large capacity, and the device becomes large in size.
The cost was increased. The present invention has been made in view of the above problems, and an object of the present invention is to provide a switching regulator that is small in size, inexpensive, while linearizing the waveform of an AC input current to improve the power factor.

[0006]

In order to achieve the above object, the conventional smoothing capacitor for input is omitted from the primary side.
It is integrated with the output smoothing capacitor on the secondary side to allow the pulse width control circuit to perform pulse width control of sine wave inverse modulation type. That is, according to the present invention, a rectifying circuit not including a smoothing circuit and a switching element are provided on the primary side of a high frequency transformer, a high frequency filter is provided on the AC input side of the rectifying circuit, and a rectifying and smoothing circuit is provided on the secondary side. With the provision
The pulse width of the voltage switched by the switching element is controlled in an inverse sine wave shape so that the pulse width is long when the voltage is low and short when the voltage is high, and the entire pulse width is also adjusted based on the change in the DC output voltage. A pulse width modulation control circuit for controlling is provided.

[0007]

According to the above construction, the alternating current input to the primary side from the alternating current power source is full-wave rectified by the rectifier circuit, and then switched by the switching element in the state of the unsmoothed sine full-wave waveform. The pulse width switched here changes in an inverse sine wave shape by the pulse width modulation control circuit so that it is long when the voltage is low and short when the voltage is high. The high-frequency pulse whose pulse width is modulated in the inverse sine wave shape by this switching is output to the secondary side, rectified,
After passing through the smoothing circuit, a smooth DC output voltage is supplied to the load. When the DC output voltage changes due to a change in the AC input voltage or the load, the pulse width modulation control circuit controls the entire pulse width according to the change, so that the output voltage is maintained constant.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a schematic circuit of a switching regulator according to the present invention. This circuit omits the input smoothing capacitor 3a of the conventional switching regulator circuit shown in FIG. 9 and includes it in the output smoothing capacitor 10, and
While the LC high frequency filter 3 is provided on the input side of the rectifier circuit 2, a sine wave inverse modulation type pulse width modulation control circuit 14 is provided in place of the pulse width modulation control circuit 6, and other than that is the same as a conventional circuit. Since they have the same configuration, corresponding parts are designated by the same reference numerals.

FIG. 2 shows the sine wave inverse modulation type pulse width modulation control circuit 14, which is composed of a primary side circuit and a secondary side circuit insulated by a photocoupler 15. The primary side circuit is mainly a control auxiliary constant voltage circuit 16,
Clock pulse generation circuit 17 and sawtooth wave generation circuit 18
, Pulse width control comparator 19, and photocoupler 1
5, the phototransistor 20 and the secondary side circuit are composed of the light emitting diode 21 of the photocoupler 15 and the shunt regulator 22.

The control auxiliary constant voltage circuit 16 is taken out from the output side of the full-wave rectifier 2 as a divided voltage between the resistor 23 and the resistors 24 and 25, and the diode 26 and the smoothing capacitor 27.
It is a circuit that makes the voltage rectified by the constant voltage. Then, the photocoupler 15 is connected to the control auxiliary constant voltage circuit 16.
The phototransistor 20 and the resistor 28 are connected in series. The clock pulse generation circuit 17 has a duty ratio of 50 from the constant voltage obtained by the auxiliary constant voltage circuit 16.
The frequency in% is preferably above the audible frequency (eg 20K
(Hz) clock pulse.

One input terminal of the sawtooth wave generating circuit 18 is connected to the output terminal of the clock pulse generating circuit 17, and the other input terminal is connected to the midpoint between the resistors 23 and 24 and the resistor 25. The output terminal is connected to the positive side input terminal of the pulse width control comparator 19. The negative side input terminal of the pulse width control comparator 19 is connected to the middle point between the emitter of the phototransistor 20 and the resistor 28. The positive side terminal of the light emitting diode 21 of the photocoupler 15 is connected to the positive side output terminal of the secondary side main circuit via the resistor 29, and the negative side terminal is connected to the cathode side terminal of the shunt regulator 22. The comparison input terminal of the shunt regulator 22 is connected to the midpoint between the output voltage detecting resistor 11 and the voltage dividing resistor 12 of the secondary side main circuit, and the anode side terminal is connected to the minus side output terminal of the secondary side main circuit. Has been done.

The operation of the switching regulator having the above configuration will be described below. The sinusoidal alternating current supplied from the alternating-current power supply 1 is rectified by the full-wave rectifier 2 into the sinusoidal full-wave pulsating flow waveform shown in FIG. 3, and is supplied to the primary side of the high-frequency transformer 4. On the other hand, the sine wave inverse modulation type pulse width modulation control circuit 14 performs width modulation as shown by E in FIG.
Since a drive pulse signal of Hz is applied to the gate terminal of the FET 5, the FET 5 switches (chops) the sinusoidal full-wave voltage on the primary side to become a high frequency carrier to the secondary side. The operation of the sine wave inverse modulation type pulse width modulation control circuit 14 will be described later in detail.

1 switched by the FET 5
The high-frequency pulse voltage on the secondary side is transformed by the high-frequency transformer 4, and as shown in FIG. 5, when the voltage (Vs) is low, T
The waveform of the inverse sine wave is such that on is long and Ton becomes shorter as it approaches the peak voltage (VsP) of the phase π / 2, and is output to the secondary side. The high-frequency pulse voltage on the secondary side is converted into a direct current again by the rectifying diode 7, and further smoothed by the commutation flywheel diode 8, the smoothing choke coil 9 and the output smoothing capacitor 10 and output.

The output voltage V _{0 at} this time is expressed by the following equation. V ₀ = Ton / T × Vs Instantaneous value (1) Here, Ton has an inverse sine wave shape as described above, and Vs
Is a sine wave, the output voltage V ₀ has a flat DC waveform as shown by the alternate long and short dash line in FIG. High frequency transformer 4
The currents on the primary side and the secondary side have a waveform similar to the high frequency pulse voltage shown in FIG. Further, the AC input current with respect to the secondary-side high-frequency pulse voltage becomes a linear waveform approximate to a sine wave by passing through the high-frequency filter 3 provided on the input side of the rectifier 2, and near the maximum value as in the conventional case shown in FIG. The electric current will not be concentrated on. The input current is further linearized as the maximum instantaneous value (VsP) of the secondary side high frequency pulse voltage is made sufficiently large (for example, four times or more) with respect to the DC output voltage V ₀ .

By the way, if the AC input voltage and the load are constant, the drive pulse signal shown in FIG. 4E is output from the sine wave inverse modulation type pulse width modulation control circuit 14 to the FET 5 for switching, so that the load is present. DC output voltage V ₀
Is obtained. Now, when the AC input voltage or the load fluctuates and the output voltage V ₀ is about to change, the sine wave inverse modulation type pulse width modulation control circuit 14 causes the drive pulse whose width is entirely modulated according to the change of the output voltage V _0. Is output to the FET 5, the output voltage V ₀ is maintained constant. That is, the sine wave inverse modulation type pulse width modulation control circuit 14 outputs to the FET 5 a drive pulse for simultaneously performing pulse width modulation for making the input current sinusoidal and pulse width modulation for making the voltage constant, It is possible to make the input current sinusoidal and the output voltage constant. The operation of the sine wave inverse modulation control circuit 14 will be described in detail below.

Sine wave inverse modulation type pulse width modulation control circuit 14
The sawtooth wave generation circuit 18 of the clock pulse generation circuit 1
The high-frequency clock pulse output from A in FIG. 4 and having a duty of 50% is pulse-width-modulated by the input AC sine wave synchronization signal indicated by B in the same figure as shown in C in the figure. It outputs to the plus side input terminal of the control comparator 19. On the other hand, the shunt regulator 22 compares the output voltage detected as the divided voltage between the output voltage detecting resistor 11 and the voltage dividing resistor 12 with the reference voltage and amplifies the variation. As a result, the light emitting diode 2 of the photocoupler 15
A current proportional to the variation of the output voltage flows through the resistor 1 to emit light, and an output current according to the amount of light received from the light emitting diode 21 flows through the phototransistor 20. The current flowing through the resistor 28 in the phototransistor 20 is proportional to the variation of the output voltage, and the detection voltage detected between the emitter of the phototransistor 20 and the resistor 28 is also proportional to the variation of the output voltage.

The pulse width control comparator 19 detects a sawtooth wave output from the sawtooth wave generating circuit 18 as shown by C in FIG. 4 and D in FIG. 4 detected between the phototransistor 20 and the resistor 28. A pulse voltage whose pulse width is modulated is output to the gate terminal of the FET 5 as indicated by E in FIG. Therefore, if the output voltage V ₀ drops by ΔV, the detection voltage applied to the negative side terminal of the pulse width control comparator 19 drops accordingly, and the driving output from the pulse width control comparator 19 to the gate terminal of the FET 5 is performed. The pulse width of the pulse signal is expanded. As a result, Ton of the secondary side pulse voltage of the high frequency transformer 4 increases, and as is apparent from the above formula (1), the output voltage V ₀ increases by ΔV and is controlled to be constant.

In this embodiment, when the load is large, as shown in FIG. 7, a ripple voltage appears in synchronization with the time when the AC input voltage becomes 0 V. This is due to the capacitance of the output smoothing capacitor 10. Can be reduced by increasing. FIG. 8 shows a circuit of a full-bridge type switching regulator which is most suitable when the output is large. In this circuit, a semiconductor switching element 4
The FETs 5a, 5b, 5c, 5d are connected in a bridge shape, the secondary voltage transformed through the high frequency transformer 4 is full-wave rectified by the high frequency diodes 7a and 7b, and a constant voltage is supplied to the load as described above. It was done like this.

[0019]

As is apparent from the above description, the present invention has the following effects. The primary side of the high-frequency transformer directly switches the sine-wave full-wave rectified waveform and outputs the high-frequency pulse whose pulse width changes to an inverse sine wave to the secondary side. The flowing current becomes a high frequency pulse current, and the alternating current input current consisting of this high frequency pulse is linearized in a sinusoidal shape by passing through a high frequency filter provided on the input side of the rectifier. Therefore, a non-linear component including odd harmonics does not appear in the input current as in the conventional case, and abnormal heat generation and noise of the transformer in the substation in the input wiring path are reduced. The frequency of the switching operation by the switching element is extremely high, and the high frequency pulse obtained by this switching is applied to the output smoothing capacitor via the secondary side choke coil, so the power factor is improved and the reactive current is reduced, and
The choke coil is miniaturized. There is no large-capacity input smoothing capacitor for smoothing low-frequency AC input on the primary side,
The output smoothing capacitor on the secondary side smoothes high frequency pulses and has a very small ripple current, and its capacity is smaller than that of the conventional input smoothing capacitor plus the output smoothing capacitor. So
The device becomes smaller and cheaper.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a sine wave inverse modulation type pulse width modulation control circuit.

FIG. 3 is a waveform diagram of the output voltage of the primary side rectifier.

FIG. 4 is a diagram showing a pulse forming process by a sine wave inverse modulation type pulse width modulation control circuit.

FIG. 5 is a waveform diagram of a secondary side high frequency pulse voltage.

FIG. 6 is a waveform diagram of an input current according to the present invention.

FIG. 7 is a waveform diagram of an output voltage when there are many ripples according to the present invention.

FIG. 8 is a circuit diagram of another embodiment of the switching regulator.

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

10 is an output waveform diagram of the primary side smoothing capacitor of the conventional switching regulator shown in FIG.

11 is a waveform diagram of an input current of the conventional switching regulator shown in FIG.

12 is a waveform diagram of the output voltage of the conventional switching regulator shown in FIG.

[Explanation of symbols]

1 ... AC power supply, 2 ... Full wave rectifier (rectifier circuit), 3 ... High frequency filter,
4 ... High frequency transformer, 5 ... FET (switching element), 7 ... Rectifier diode, 8 ... Commutation flywheel diode, 9 ... Smoothing choke coil, 1
0 ... Output smoothing capacitor, 14 ... Pulse width modulation control circuit.

Claims (1)

[Claims] 1. A rectifier circuit not including a smoothing circuit and a switching element are provided on the primary side of the high frequency transformer, a high frequency filter is provided on the AC input side of the rectifier circuit, and rectification and smoothing are provided on the secondary side of the high frequency transformer. In addition to providing a circuit, the pulse width of the voltage switched by the switching element is controlled in an inverse sine wave shape so that it is long when the voltage is low and short when the voltage is high. A switching regulator having a pulse width modulation control circuit for controlling the pulse width of the switching regulator.