JPH08331849A - Rectifying circuit - Google Patents

Abstract

PURPOSE: To reduce size, cost and noise and also make small the variation range of an output voltage by outputting a rectified voltage through a voltage- drop chopper circuit, operating a yoke coil thereof in the current non-continuous mode and controlling the output voltage to the predetermined value which is lower than the peak value of the input voltage. CONSTITUTION: After a commercial power source voltage Vin is rectified with a diode bridge DB, it is then inputted to a voltage-drop chopper circuit 12 via a low-pass filter 11. Here, an inductance value of the choke coil L2 is set so that the choke coil L2 can be operated under the current non-continuous mode even under the maximum load condition to operate FETQ1 with a PIIM control circuit 13 with the predetermined on-duty. An output voltage V0 is inputted to an error amplifier 15 via a differential amplifier 15 and the reference voltage VREF is set so that the output voltage V0 becomes lower than the peak value of the commercial power source voltage Vin . Thereby, the output voltage V0 is controlled to have the constant value even when a load power is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rectifier circuit, and more particularly to
The present invention relates to a rectifier circuit for regulating harmonic current of a power input circuit of electronic equipment.

[0002]

2. Description of the Related Art In recent years, in electronic equipment such as computer equipment, copying machines and printers connected to a commercial power source, problems such as malfunction of the electronic equipment due to waveform distortion (power source harmonic distortion) of the commercial power source line have become serious. There is. In order to suppress the occurrence of such harmonic distortion, laws that regulate the harmonic components of the input current of electronic devices are being developed.

Generally, a capacitor input type rectifier circuit in which a capacitor C4 is provided on the output side of a diode bridge DB2 as shown in FIG. 8 is used for a power supply input circuit (switching power supply) of electronic equipment. Therefore, the current output to the circuit in the subsequent stage (for example, a DC / DC converter or the like) has a peak current waveform including many harmonic components.

Conventionally, in order to regulate such a harmonic component, (A) as shown in FIG. 9, one choke coil L3 is added between a commercial power source and a capacitor input type rectifier circuit. Increase the input angle of the input current.

(B) As shown in FIG. 10, a step-up active filter circuit is used in the power supply input circuit to obtain an input current waveform similar to the input voltage waveform. Has been proposed.

[0006]

However, according to the above method (A), the inductance of the choke coil L3 needs to be about 10 mH, and in order to realize this, the choke coil L3 becomes large and the circuit There is a problem that it is difficult to reduce the size and weight.

FIG. 11 shows an output voltage (voltage after rectification) with respect to the input voltage Vin of the power supply input circuit shown in FIGS.
FIG. 12 is a diagram showing the relationship of Vo, and FIG. 12 is a diagram showing the relationship of the output voltage Vo with respect to the load power Po applied to the power supply input circuit. In both figures, shows the characteristic when the capacitor input type rectifier circuit shown in FIG. 8 is used, and shows the characteristic when one choke coil L3 is added to the capacitor input type rectifier circuit shown in FIG. , Is shown in FIG.
The characteristics when the step-up active filter circuit shown in are used are shown.

As is apparent from FIGS. 11 and 12, in the circuit in which the choke coil L3 is added, the load power P
When o increases or when the input current Iin increases due to the decrease of the input voltage Vin, the impedance of the choke coil L3 significantly decreases the output voltage Vo. Therefore, it is necessary to extend the operating range of elements such as a DC / DC converter connected in the subsequent stage to a low input voltage, or to increase the capacity of the capacitor C4 as a countermeasure against momentary power failure, resulting in increased cost and large power input circuit. However, there is a problem in that

Further, according to the above method (B), the choke coil L3 is generated when the transistor Q3 is in the ON state.
The current ΔI flowing through is expressed by ΔI = (Vin / L5) × Ton, where Ton is the period during which the transistor Q3 is in the on-state and L5 is the inductance of the choke coil L5.
In order to reduce the load of No. 3, it is necessary to increase the inductance of the choke coil L5. Therefore, it is necessary to increase the size of the choke coil L5 or increase the current capacity of the transistor Q3. Further, since energy is stored in the choke coil L5 only when the transistor Q3 is in the ON state, it is necessary to increase the peak value of the current flowing through the transistor Q3. Furthermore, as shown in FIG. 10, a complicated control circuit is required to realize the boost type active filter circuit. Therefore, even if the method (B) is used, there is a problem in that efficiency is reduced due to complication of the power supply input circuit, the power supply input circuit is increased in size, noise is increased, and cost is significantly increased.

The present invention has been made in order to solve the above problems, and realizes a relatively small size, low cost, and low noise, and reduces the operating input voltage range of elements connected in the subsequent stage. It is an object of the present invention to provide a rectifier circuit for regulating harmonic current of a power supply input circuit, which can reduce the size of the element and reduce the cost.

[0011]

In order to achieve the above object, a rectifying circuit of the present invention has a rectifying means for rectifying an input voltage input to an electronic device, a choke coil and a switch element. A step-down chopper circuit for stepping down the input voltage rectified by the control means, and a control for controlling the switch element at a frequency sufficiently higher than the commercial frequency and with an on-duty small enough for the choke coil to operate in the current discontinuous mode. Means, and output voltage control means for controlling the output voltage of the step-down chopper circuit to a predetermined value lower than the peak value of the input voltage.

It is preferable that the control means controls the switching element with a duty corresponding to the load power of the electronic device.

The control means preferably controls the switch element with a duty corresponding to the input voltage.

The control means may maintain the switch element in the ON state when the value of the input voltage is lower than the output voltage of the step-down chopper circuit.

The predetermined value is preferably set according to the conduction angle of the input current.

It is preferable that the inductance of the choke coil is set to a value at which the choke coil can operate in the current discontinuous mode even when the load power is maximum.

[0017]

According to the rectifier circuit of claim 1, after the input voltage rectified by the rectifying means is stepped down / smoothed by the step-down chopper circuit, the output voltage control means sets it to a predetermined value lower than the peak value of the input voltage. Controlled. Also, the control means controls the switching element at a frequency sufficiently higher than the commercial frequency and at an on-duty small enough to allow the choke coil to operate in the current discontinuous mode.

According to the rectifier circuit of the second aspect, the switch element is controlled with the duty according to the load power of the electronic device.

According to the rectifier circuit of the third aspect, the switch element is controlled with the duty corresponding to the input voltage.

According to the rectifier circuit of the fourth aspect, when the value of the input voltage is lower than the output voltage of the step-down chopper circuit, the switch element is maintained in the ON state.

According to the rectifier circuit of the fifth aspect, the predetermined value is set according to the conduction angle of the input current.

According to the rectifier circuit of the sixth aspect, the inductance of the choke coil is set to a value at which the choke coil can operate in the discontinuous current mode even when the load power is maximum.

[0023]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is an electric circuit diagram showing the configuration of a rectifier circuit used in the power supply input circuit of the electronic apparatus according to this embodiment.

In the figure, the rectifier circuit according to this embodiment has a diode bridge DB, and the diode bridge DB is connected to a commercial power source Vin. The output terminal of the diode bridge DB is a low-pass filter 11 composed of capacitors C1 and C2 and a coil L1, a FET transistor Q1 (hereinafter referred to as FET Q1) which is a switching element, and a flywheel diode D.
1 (hereinafter referred to as diode D1), choke coil L
It is connected to a circuit such as a DC / DC converter in the subsequent stage via a step-down chopper circuit 12 composed of 2 and a smoothing capacitor C3. Specifically, the output side of the diode bridge DB is connected to the connection point between the coil L1 and the capacitor C1 of the low pass filter 11, and the connection point between the coil L1 and the capacitor C2 is connected to the cathode of the diode D1 of the step-down chopper circuit 12. The low-pass filter 11
The connection point between the capacitors C1 and C2 is connected to the source of the FET Q1. The drain of FET Q1 is a diode D
1 and the connection point between the drain of the FET Q1 and the anode of the diode D1 and the smoothing capacitor C.
A choke coil L2 is connected between the two. In this embodiment, the inductance value of the choke coil L2 is set so that the choke coil L2 can operate in the current discontinuous mode even at the maximum load.

The output terminal of the step-down chopper circuit 12 is connected to the input terminal of the differential amplifier 15, and the differential amplifier 1
The output terminal of 5 is connected to one input terminal of the error amplifier 14. The other input terminal of the error amplifier 14 is connected to the reference voltage Vref, and the output terminal is connected to the PWM control circuit 13. Output voltage Vo of the chopper circuit
Is input to the error amplifier 14 via the differential amplifier 15 and compared with the reference voltage Vref. Then, a signal corresponding to the difference between the output voltage Vo and the reference voltage Vref is input from the error amplifier 14 to the PWM control circuit 13. PWM
The control circuit 13 inputs a signal corresponding to the output signal of the error amplifier 14 into the FET Q1 of the step-down chopper circuit 12. As a result, the output voltage Vo is feedback-controlled so as to take a constant value according to the reference voltage Vref.

In the above structure, the voltage Vs after the commercial power source Vin is rectified by the diode bridge DB (hereinafter referred to as the rectified voltage) Vs is input to the low-pass filter 11.
The output of the low-pass filter 11 is the step-down chopper circuit 12
Is input to Output voltage Vo of the step-down chopper circuit 12
So as to take a predetermined value, the FET Q1 is controlled at a predetermined frequency sufficiently higher than the commercial frequency of the input commercial power source and at a predetermined on-duty. By such operation, as shown in FIG. 2A, the diode bridge D
The rectified voltage Vs due to B gradually increases, and the rectified voltage Vs
A period in which s is larger than the output voltage Vo, that is, time t1 in FIG.
From time t2 to time t2 and from time t3 to time t4, the input current Is shown in FIG. 2B flows. That is, since the conduction angle of the input current corresponds to the period in which Vs> Vo, the harmonic current is set by setting the output voltage Vo to an appropriate value (for example, Vo ≦ 250V for the 230V input voltage system). It becomes possible to suppress. FIG. 3 shows the load power P
The relationship between the input voltage Vin and the output voltage Vo obtained when o is 200 W is shown in FIG.
Load power Po and output voltage Vo obtained when the voltage is 0V
Shows the relationship with (the straight line in the figure). As is clear from both figures, the output voltage Vo is controlled so as to take a constant value even when the load power Po changes, and the input voltage Vin is controlled.
Is controlled to take a constant value even when is larger than a predetermined value (190V in the illustrated example). Also, the input voltage V
When in is equal to or less than the predetermined value, the FET Q1 is always controlled to be in the ON state, and thus exhibits the same characteristics as the conventional capacitor input type rectifier circuit.

The operation of the power supply input circuit shown in FIG. 1 will be described below with reference to FIG. FIG. 5 is a diagram showing changes in the output current Is of the diode bridge DB and the current I flowing in the choke coil L2.

When Vs> Vo at t1, the current I starts to flow in the choke coil L2. For example, when the FET Q1 is turned on for the period Ton from t2 to t3, the current I flowing through the choke coil L2 increases. Further, when the FET Q1 is turned off at t3, the value of the current I flowing through the choke coil L2 gradually decreases,
It becomes 0 at t4 when the period Toff 'has elapsed from 3. Also,
At the time period To after the FET Q1 is turned off at t3
At t5 when ff has passed, the FET Q1 is turned on again, and the same operation as that after t2 is repeated. The current I flowing in the choke coil L2 that changes in this way is obtained as follows. (A) Period of Vs ≦ Vo When the FET Q1 is in the ON state, the choke coil L2
And the current I flowing in the FET Q1 is: I = 0 ... (1) When the FET Q1 is in the off state, the choke coil L2
And the current I flowing through the diode D1 is as follows: I = 0 (2) (b) Vs> Vo period When the FET Q1 is in the ON state, the choke coil L2
And the current I flowing in the FET Q1 is expressed as I = {(Vs-Vo) / L2} × T (3), where T is the elapsed time after the FET Q1 is turned on, and with time, To increase. The peak value is Ip = {(Vs-Vo) / L2} × Ton ... (4).

On the other hand, when the FET Q1 is off,
Current I flowing through choke coil L2 and diode D1
′ Is represented by I ′ = Ip − {(Vo / L2) × T} (5) and decreases with the passage of time. Therefore, the time Toff ′ until the value of the current I ′ becomes 0 is Toff ′ = {(Vs−Vo) / Vo} × Ton ... (6). In the present embodiment, as shown in FIG. 5, the choke coil 2 has a current discontinuity such that Toff ′ <Toff (Toff is the time during which the FET Q1 is turned off) even under the maximum load. The inductance of the choke coil L2 is determined so that it can operate in the mode. As a result, all the energy stored in the choke coil L2 is released in each cycle.

The value of the input current Is is Is = {(1/2) × Ton × Ip} / T = {Ton ² / (2 × T × L2)} × (Vs-Vo) (7) The input current waveform is proportional to the difference (Vs-Vo) between the input voltage (voltage after rectification) Vs and the output voltage Vo. For example, when the rectified voltage Vs is a sine wave, the input current I
s is a waveform obtained by cutting a part of the sine wave, and the conduction angle of the input current is set as Vo by setting an appropriate value,
It can take any value.

The duty with which the FET Q1 is turned on is preferably set to be sufficiently small so that all the energy stored in the choke coil L2 can be released, as described above.
It is preferably set according to the load power applied to the power supply input circuit to which the rectifier circuit is applied, or according to the input current to the rectifier circuit.

As described above, according to this embodiment,
Since the conduction angle of the current can be set only by setting the reference voltage Vref to an appropriate value, the harmonics can be suppressed with a simpler structure than the conventional one.

Further, as shown in FIG. 4, at the time of low input voltage, it shows the same characteristics as the capacitor input type rectifier circuit, so that the choke coil is simply added to the power input circuit as in the conventional example of FIG. It is possible to prevent the output voltage from decreasing due to an increase in load power. Therefore, it is not necessary to widen the input voltage range of the element connected in the subsequent stage to the low voltage side, and it is not necessary to increase the capacity of the smoothing capacitor as a countermeasure against an instantaneous power failure.

Further, since the output voltage Vo is controlled to be lower than the peak value of the input voltage, the upper limit of the output voltage Vo can be set lower than that of the capacitor input type rectifier circuit, and the input of the element connected in the subsequent stage can be set. The voltage range can be narrowed. Therefore, an element having a low withstand voltage can be used as an element connected in the subsequent stage, and it is possible to reduce the size of the element, reduce noise, and reduce the cost.

Further, when the conventional step-up active filter shown in FIG. 10 is used, the voltage applied to the choke coil is Vs, but according to this embodiment, the voltage applied to the choke coil L2 is (Vs-Vo). Can be lowered to. Therefore, since the inductance of the choke coil L2 can be reduced, the circuit can be downsized and the cost can be reduced. Further, the control circuit can be simplified as compared with the conventional boost active filter.

Further, since the FET Q1 is a series element of the rectifier circuit, the rectifier circuit can be used as an inrush current limiting circuit using the FET Q1. Therefore, it is possible to omit power devices such as triacs and cyclistors as a rush current limiting circuit required for a conventional capacitor input type rectifier circuit and a power source input circuit using a boost type active filter.

Furthermore, since the structure of the rectifier circuit is simplified,
Noise can be reduced. (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 6 is an electric circuit diagram showing the structure of the rectifier circuit according to this embodiment. This embodiment is different in the configuration of the chopper circuit 12 shown in FIG. 1 of the first embodiment described above. That is, in this embodiment, the FET Q is used as the switching element.
Instead of 1, the NPN transistor Q2 is adopted.
The collector of the transistor Q2 is connected to the connection point between the coil L1 of the low-pass filter 11 and the capacitor C2, and the emitter is connected to the cathode of the diode D1. The choke coil L2 is provided between the cathode of the diode D1 and the smoothing capacitor C3. The base of the transistor Q2 is connected to the PWM control circuit 13.

In the above configuration, the output voltage Vo of the chopper circuit 12 'is input to one input terminal of the error amplification circuit 14 and the reference voltage Vr connected to the other input terminal.
ef is compared. Then, the output voltage Vo and the reference voltage V
A signal corresponding to the difference from ref is output from the error amplification circuit 14 to P
It is input to the WM control circuit 13. PWM control circuit 13
Controls a current flowing through the transistor Q2 by causing a control current to flow through the base of the transistor Q2 in accordance with the input signal.

In the choke coil L2, the rectified voltage Vs rectified by the diode bridge DB is output voltage Vs.
The current I flows when it becomes larger than o. Similarly to the FET Q1 of the first embodiment, the transistor Q2 is on / off controlled at a frequency sufficiently higher than the frequency (commercial frequency) of the input voltage Vin and at a predetermined duty.
That is, the current I flowing through the choke coil L2 can be expressed by the above-described equations (1) to (7).

As described above, according to the present embodiment, by using the NPN type transistor as the switching element, the differential amplifier circuit 15 used in the first embodiment is omitted and the simple configuration is omitted. The same effect can be obtained. (Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 7 is an electric circuit diagram showing the structure of the rectifier circuit according to this embodiment. In this embodiment, the oscillator 16 is provided between the PWM control circuit 13 and the input terminal to which the commercial power source is input in the rectifier circuit shown in FIG. 1 of the first embodiment. By increasing the frequency of the oscillator 16 when the input power is turned on, the impedance of the choke coil L2 is apparently increased.

With such a configuration, the rectifier circuit can be used as an inrush current limiting circuit for limiting the inrush current. Therefore, a power device such as a thyristor or a triac can be omitted and the size can be reduced as compared with a conventional rectifier circuit. Higher efficiency and lower cost can be achieved, and harmonics can be suppressed.

[0045]

As described above, according to the rectifying circuit of the first aspect, the rectifying means for rectifying the input voltage input to the electronic device, the choke coil and the switch element are provided.
A step-down chopper circuit for stepping down the input voltage rectified by the rectifying means, and a frequency sufficiently higher than the commercial frequency,
Further, the output voltage of the step-down chopper circuit is lower than the peak value of the input voltage, and a control means for controlling on / off of the switch element with an on-duty small enough to allow the choke coil to operate in a discontinuous current mode. Since the output voltage control means for controlling to a predetermined value is provided, a relatively simpler structure, a lower cost and lower noise can be realized with a simpler configuration than a conventional rectifier circuit, and an element connected in a subsequent stage can be provided. There is an effect that the operating input voltage range can be reduced and the device can be downsized and the cost can be reduced.

According to the rectifier circuit of the fourth aspect, the control means maintains the switch element in the ON state when the value of the input voltage is lower than the output voltage of the chopper circuit. Therefore, the output voltage accompanying the increase in load power is increased. Can be prevented. Therefore, it is not necessary to widen the input voltage range of the element connected in the subsequent stage to the low voltage side, and it is not necessary to increase the capacity of the smoothing capacitor as a measure against an instantaneous power failure.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a rectifier circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a conduction angle in the rectifier circuit shown in FIG.

FIG. 3 is a diagram showing a relationship between an input voltage Vin and an output voltage Vo obtained when the load power Po is 200 W.

FIG. 4 is a diagram showing a relationship between a load power Po and an output voltage Vo obtained when an input voltage Vin is 230V.

5 is a diagram showing changes in an output current Is of a diode bridge DB and a current I flowing in a choke coil L2 in the rectifier circuit shown in FIG.

FIG. 6 is an electric circuit diagram showing a configuration of a rectifying circuit according to a second embodiment of the present invention.

FIG. 7 is an electric circuit diagram showing a configuration of a rectifier circuit according to a third embodiment of the present invention.

FIG. 8 is an electric circuit diagram showing a configuration of a conventional capacitor input type rectifier circuit.

FIG. 9 is an electric circuit diagram showing a conventional rectifier circuit in which one choke coil L3 is added between a commercial power source and a capacitor input type rectifier circuit.

FIG. 10 is an electric circuit diagram of a step-up active filter circuit used in a conventional rectifier circuit.

11 is a diagram showing the relationship between the output voltage Vo and the input voltage Vin of the power supply input circuit shown in FIGS.

FIG. 12 is a diagram showing the relationship between the output voltage Vo and the load power Po of the power supply input circuit shown in FIGS. 8 to 10.

[Explanation of symbols]

12 step-down chopper circuit 13 PWM control circuit (output voltage control means, control means) 14 error amplification circuit (output voltage control means) 15 operation amplification circuit (output voltage control means) DB diode bridge (rectification means) L2 choke coil Q1 FET transistor

Claims (6)

[Claims] 1. A step-down chopper circuit for stepping down the input voltage rectified by the rectifying means, a step-down chopper circuit for rectifying an input voltage input to an electronic device, a choke coil and a switch element, and a frequency more than a commercial frequency. A control means for controlling the switch element at a very high frequency and an on-duty that is small enough to allow the choke coil to operate in a current discontinuous mode; and an output voltage of the step-down chopper circuit that is higher than a peak value of the input voltage. A rectifier circuit, comprising: an output voltage control unit that controls the voltage to a low predetermined value. 2. The rectifier circuit according to claim 1, wherein the control unit controls the switch element with a duty according to a load power of the electronic device. 3. The rectifier circuit according to claim 1, wherein the control unit controls the switch element with a duty according to the input voltage. 4. The control means maintains the switch element in an ON state when the value of the input voltage is lower than the output voltage of the step-down chopper circuit. The rectifier circuit according to item. 5. The rectifier circuit according to claim 1, wherein the predetermined value is set according to a conduction angle of an input current. 6. The inductance of the choke coil is set to a value at which the choke coil can operate in a discontinuous current mode even when the load power is maximum. The rectifier circuit according to any one of items.