JPH0315264A - Input current waveform shaping circuit - Google Patents

Abstract

PURPOSE:To improve power factor by comparing input voltage with a voltage proportional to the input current to a transforming/smoothing means and controlling ON time of a switching element. CONSTITUTION:An input current waveform shaping circuit comprises a booster chopper as a transforming/smoothing means, a control circuit 11, and a feedback circuit III as an amplification factor varying means. The control circuit compares the input voltage with a voltage proportional to the input current to the chopper I and control is made such that on time of a switching transistor 9 is lengthened while off time thereof is shortened when the proportional voltage is low.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application)] The present invention relates to an input current waveform shaping circuit used as a power source for office automation (0^) equipment and the like.

(Conventional technology) Conventionally, commercial electricity i1iK (IOOV /501-1
When rectifying and smoothing a current or voltage supplied from a source (such as 2) to convert it into a direct current, a circuit as shown in FIG. 3 is used.

That is, the current or voltage supplied from the AC power supply 1 is rectified by the diode bridge 2 and smoothed by the capacitor 3.

The voltage waveforms and current waveforms of each part in FIG. 3 are as shown in FIG. 4. That is, when an input voltage as shown in FIG. 2(a) is supplied from the AC power source 1, the voltage across the terminals of the capacitor 3 becomes as shown by the solid line in FIG. 2(b). Here, the dotted line in FIG. 3B shows the voltage waveform applied to the load when the capacitor 3 is not present.

The input current is as shown in (c) of the same figure.
), it flows only while the dotted line and solid line overlap.

However, in such a circuit, the input current is as shown in Figure 4 (C).
As shown in FIG. 3B, since the current flows only near the peak of the voltage in FIG. 3B, the peak value of the current becomes large, which distorts the voltage waveform.

In addition, the efficiency of the AC power supply 1 also decreases accordingly.

(Problems to be Solved by the Invention) As described above, in the conventional circuit described above, the efficiency of the AC power supply 1 decreases.

The present invention has been made under these circumstances, and an object of the present invention is to provide an input current waveform shaping circuit that can improve the power factor of power supplied from a power supply.

[Structure of the Invention] (Means for Solving the Problems) The input current waveform shaping circuit of the present invention has a switching element and transforms and smoothes the input voltage based on the switching operation of the switching element. The input voltage is compared and amplified with a proportional voltage proportional to the input current flowing through the transformer smoothing means, and if the proportional voltage is lower than the input voltage, the on time of the switching element is lengthened and the off time is shortened. It is equipped with a control means for controlling the switching element to shorten the on time and lengthen the off time when the voltage is high, and an amplification factor varying means for varying the amplification factor of the control means according to the load of the transformer smoothing means. It is.

(Function) In the input current waveform shaping circuit of the present invention, the transformation and smoothing means transforms and smoothes the input voltage based on the switching operation of the switching element. At this time, the control means compares and amplifies the input voltage with a proportional voltage proportional to the input current flowing through the transformer smoothing means, and if the proportional voltage is lower than the input voltage, the on time of the switching element is lengthened and the off time is shortened,
When the proportional voltage is higher than the input voltage, the on-time of the switching element is controlled to be shortened.

As a result, the input current waveform can be made similar to the input voltage waveform.

Further, since the control value varying means varies the amplification factor of the control means according to the load of the transformer smoothing means, the input current can also be set to a value according to the load.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 shows an input current waveform shaping circuit showing one embodiment of the present invention.

As shown in the figure, the input current waveform shaping circuit is equipped with a boost chopper I as a transformer smoothing means, a control circuit (2) as a control means, and a feedback circuit (2) as an amplification factor varying means.

The boost chopper I is equipped with a choke coil 7 that blocks the flow of an AC component from a diode bridge 6 that rectifies the current or voltage from the AC power supply 5. The choke coil 7 includes a secondary coil 8b of a current transformer 8 having a primary coil 8a and a secondary coil 8b.
via switching transistor 9 and diode 1
0 is connected. A capacitor 11 is connected to the diode 10 for smoothing the pulse voltage supplied via the diode 10 and supplying a DC voltage to the load.

The control circuit (2) is equipped with a diode 12 and a capacitor 13 that rectify and smooth the output of the current transformer 8 to obtain a voltage proportional to the peak value of the pulse current flowing through the transistor 9. Resistors 14 and 15 are connected to the capacitor 13 to divide the voltage of the capacitor 13. A non-inverting input terminal of an amplifier 17 for amplifying the voltage divided by these resistors 14 and 15 is connected via a resistor 16 between the resistors 14 and 15. A resistor 18 is connected to the inverting input terminal of the amplifier 17.

The characteristics of the arithmetic amplifier 17 are adjusted by these resistors 16 and 18.

Further, a resistor 19 for setting the gain range of the operational amplifier 17 is connected between the inverting input terminal and the output side of the operational amplifier 17.
．． 20 are connected in parallel.

The gain of the operational amplifier 17 is determined by the ratio of the resistor 18 to the combined resistance of the resistors 19 and 20 and the impedance of a phototransistor 39, which will be described later.

A non-inverting input terminal of an operational amplifier 22 is connected to the output side of the operational amplifier 17 via a resistor 21 . A resistor 23 is connected to the inverting input terminal of the operational amplifier 22. Connected to the resistor 23 are resistors 24 and 25 that divide the output voltage from the diode bridge 6 described above. A resistor 2 is connected between the output side and the inverting input terminal side of the operational amplifier 22.
6 is connected.

The characteristics of the submerging amplifier 22 are adjusted by these resistors 21, 23, and 26.

An inverting input terminal of a comparator 27 is connected to the output side of the operational amplifier 22. An oscillator (OSC) that generates a sawtooth wave with a constant period is connected to the non-inverting input terminal of the comparator 27.
28 are connected. Two drive circuits are connected to the output side of the comparator 27 to turn on/off the transistor 9 according to the output pulse of the comparator 27.

The feedback circuit (2) is equipped with resistors 30 and 31 that divide the DC voltage from the capacitor 11.

There is. A resistor 32 and a Zener diode 33 for obtaining a constant voltage are connected in parallel to the resistors 30 and 31. In addition, the operational amplifier 3 is connected between the resistors 30 and 31 via the resistor 34.
The inverting input terminal of No. 5 is connected. A non-inverting input terminal of an operational amplifier 35 is connected between the resistor 32 and the Zener diode 33 via a resistor 36. A resistor 37 is connected to the output side and the inverting input terminal side of the operational amplifier 35.

The characteristics of the operational amplifier 35 are adjusted by these resistors 34, 36, and 37.

On the output side of the operational amplifier 35, a photocoupler 40 consisting of a photodiode 38 and three phototransistors is installed.
is connected. A limiting resistor 41 that limits the amount of current flowing through the photodiode 38 is connected to the photodiode 38 .

Note that 42 in the figure indicates a load.

Next, the operation of the input current waveform shaping circuit having such a configuration will be explained using FIG. 2.

Note that when the AC power supply 5 starts applying voltage, the voltage of the capacitor 11 is 0, so the input current waveform or the initial operation of the shaping circuit is slightly different from the normal operation, but here we will explain the normal operation. I will only explain.

First, when a voltage having the waveform shown in FIG. 12A is applied from the AC power source 5, this applied voltage is rectified by the diode bridge 6 into the waveform shown in FIG.

Here, the voltage of the capacitor 11 constituting the boost chopper I is set to be higher than the peak of the waveform shown in FIG.

That is, when the transistor 9 is turned on, the current flowing through the choke coil 7 is stored as energy. Next, when the transistor 9 is turned off, the output voltage of the choke coil 7 becomes higher than the input voltage due to the energy stored in the choke coil 7, and as a result, charge is stored in the capacitor l1 through the diode 10.

Next, the operation of the transistor 9, which is turned on/off by the control circuit (2), will be explained.

First, the oscillator 28 supplies a sawtooth high frequency wave as shown in FIG. 2(c). However, the high frequency at this time is, for example, 2
Since it is a high frequency wave of about 0 KHz, the waveform is actually very thin, but for convenience of explanation, it is made rough, and the corresponding waveforms in (d) to (g) of the same figure are also made rough.

When the transistor 9 is turned on, the current flowing through the choke coil 7, that is, the entire input current supplied from the AC power supply 5 (however, the current flowing through the resistor 24 is ignored because it is a minute current) flows through the transistor 9. .

At this time, the current flowing through the transistor 9 is A in FIG.
- A slope proportional to the potential difference between points C, that is, the height of the voltage at one point in the figure (b) (the ON time of transistor 9 is very short, so it can be considered as an almost constant voltage during that time) It increases.

On the other hand, when the transistor 9 is turned off, the current flowing through the choke coil 7, that is, the entire input current flows through the diode 10 as described above.
The current flowing through 0 is the potential difference between points A and B (VA<VB)
decreases with a slope proportional to .

Therefore, the peak value of the current flowing through the choke coil 7 during this period is the peak current when the transistor 9 is on.
A voltage proportional to this is stored as an electric charge in the capacitor 13 via the primary coil 8a of the current transformer 8 and the diode 12.

Next, the voltage of the capacitor 13 is divided by resistors 14 and 15 and then applied to the operational amplifier 17 . The voltage amplified by the operational amplifier 17 is applied to the non-inverting input terminal of the operational amplifier 22. At this time, a voltage obtained by dividing the voltage between points A and C by a resistor 24.25 is applied to the inverting input terminal of the operational amplifier 22, and the operational amplifier 2
2 compares this divided voltage with the amplified voltage from the operational amplifier 17 and amplifies the difference. That is, when the voltage amplified by the operational amplifier 17, which is proportional to the input current, is lower than the voltage divided by the resistor 24.25, the output voltage is increased, and in the opposite case, the output voltage is amplified to become lower.

The output from operational amplifier 22 is compared to the sawtooth wave from oscillator 28 by comparator 27. At this time, the comparator 27 outputs the pulse shown in (d) or (f) to the two drive circuits (however, the pulse shown in (d) or (f)
) will be described later).

Transistor 9 is then turned on by drive circuit 29 when the output from operational amplifier 22 is lower than the sawtooth waveform from oscillator 28 . On the other hand, transistor 9
is turned off by the two drive circuits when the output from operational amplifier 22 is higher than the sawtooth waveform from oscillator 28.

As a result, when the voltage amplified by the operational amplifier 17, which is proportional to the input current, is lower than the voltage divided by the resistors 24 and 25, the on time of the transistor 9 becomes longer and the off time becomes shorter. - The current flowing through the coil 7 tends to increase on average. Conversely, if the voltage amplified by the operational amplifier 17, which is proportional to the input current, is higher than the voltage divided by the resistors 24 and 25, the on-time of the transistor 9 will be short and the off-time will be long. The current flowing through the choke coil 7 tends to decrease on average.

As a result, the current flowing through the choke coil 7, that is, the input current waveform supplied from the AC power supply 5, becomes similar to the input voltage waveform on average.

Next, the operation of the transistor 9 based on the feedback circuit (2) will be explained.

First, the operational amplifier 35 amplifies the difference between the voltage from the capacitor 11 divided by the resistors 30 and 31 and the reference voltage from the Zener diode 15.

At this time, when the voltage of the capacitor 11 is low, that is, when the load is heavy, the output of the operational amplifier 35 becomes high, which causes the phototransistor 3 of the photocoupler 40 to
impedance becomes low.

As a result, the impedance of the three phototransistors becomes low, and the amplification factor of the operational amplifier 17 becomes low.

Conversely, when the voltage of the capacitor 11 is high, that is, when the load is light, the output of the operational amplifier 35 becomes low, thereby increasing the impedance of the three phototransistors of the photocoupler 4o.

As a result, the impedance of the phototransistor 39 increases, so that the amplification factor of the operational amplifier 17 increases.

When the voltage of the capacitor 11, that is, the output voltage is low, the amplification factor of the operational amplifier 17 becomes low, and as a result, the current flowing through the choke coil 7 increases overall as shown in FIG.

On the other hand, when the output voltage is high, the amplification factor of the operational amplifier 17 becomes high, and as a result, the current flowing through the choke coil 7 becomes smaller overall as shown in FIG. 2(g).

As described above, in this embodiment, the operational amplifier 22 compares the voltage obtained by dividing the voltage between points A and C with the resistor 24.25 and the amplified voltage from the operational amplifier 17, and amplifies the difference. . Next, the comparator 27 compares the output from the operational amplifier 22 and the sawtooth wave from the oscillator 28 and outputs the comparison result to the drive circuit 29. The transistor 9 is then turned on by the two drive circuits when the output from the operational amplifier 22 is lower than the sawtooth wave from the oscillator 28, and vice versa. At this time, the drive circuit 29 turns it off.

As a result, when the voltage amplified by the submersible amplifier 17, which is proportional to the input current, is lower than the voltage divided by the resistors 24 and 25, the on time of the transistor 9 becomes longer and the off time becomes shorter. The current flowing through the choke coil 7 tends to increase on average. Conversely, when the voltage amplified by the operational amplifier 17, which is proportional to the input current, is higher than the voltage divided by the resistors 24 and 25, the on time of the transistor 9 is short and the off time is long, so 7 tends to decrease on average.

As a result, the input current waveform can be made similar to the input voltage waveform.

Furthermore, when the output of the operational amplifier 35 is high, the amplification factor of the operational amplifier 17 becomes small because the impedance of the phototransistor 39 of the photocoupler 40 becomes low. On the other hand, when the output of the operational amplifier 35 is low, the impedance of the phototransistor 39 becomes high.
growing.

As a result, the input from the AC power supply 5 can be set to a value corresponding to the load 42.

[Effects of the Invention] As explained above, according to the input current waveform or shaping circuit of the present invention, the input current waveform can be made similar to the input voltage waveform, so the power factor of the power supplied from the ill can be improved. can be achieved. Furthermore, since the control value variation means varies the amplification factor of the control means according to the load of the transformer smoothing means,
The input current can also be set to a value depending on the load.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an input current waveform shaping circuit showing an embodiment of the present invention, and FIGS. 2(a) to (g) are waveform diagrams for explaining the operation of the input current waveform shaping circuit of FIG. , Figure 3 is a circuit diagram showing a circuit used to rectify and smooth current from a conventional commercial power source to convert it to direct current, and Figure 4 is a waveform diagram showing voltages and currents at various parts of the circuit in Figure 3. be. 5... AC power supply, 6... diode bridge, 7.
・・Choke coil, 8・・Current transformer, 9・
... Switching transistor, 10... Diode, 11... Capacitor, 17, 22.35... Operational amplifier, 27... Comparator, 28... Oscillator, 29.
... Drive circuit, 33... Zener diode, 40.
...Photocoupler, 38...Photodiode, 3...Phototransistor, 42...Load.

Claims (1)

[Claims] (1) Comparison of a transformer smoothing means that has a switching element and transforms and smoothes an input voltage based on the switching operation of the switching element, and a proportional voltage that is proportional to the input voltage and the input current flowing through the transformer smoother. When the proportional voltage is lower than the input voltage, the on time of the switching element is lengthened and the off time is shortened, and when the proportional voltage is higher than the input voltage, the on time of the switching element is shortened and the off time is lengthened. 1. An input current waveform shaping circuit comprising: a control means for controlling the amplification factor of the control means in accordance with a load of the transformer smoothing means;