JP2646824B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] A power supply unit that receives commercial power directly and supplies a stabilized DC output for electronic devices such as electronic computers. It is possible to reduce the size and weight while improving the power factor. And also DC
−The purpose of the present invention is to provide a power supply device that can obtain a voltage lower than the input voltage without adding a DC converter and that can obtain a safe output isolated from the primary circuit. A rectifier for rectifying the alternating current, switch means for switching the output of the rectifier at a predetermined frequency, and inputting the output of the rectifier switched by the switch means to the primary side, performing predetermined conversion, and performing secondary conversion on the secondary side. A transformer for outputting, a smoothing means for smoothing the secondary output of the transformer, a detecting means for detecting a current flowing through the smoothing means, and a current detected by the detecting means and a frequency of the AC power supply, Control means for generating a signal for switching the switch means at a predetermined frequency.

[Industrial applications]

The present invention directly receives commercial power (usually 100 VAC),
The present invention relates to a power supply device for supplying a stabilized DC output for an electronic device such as an electronic computer, and more particularly to improvement of a power factor of a switching power supply device which has recently become mainstream.

2. Description of the Related Art In recent years, switching power supplies that are efficient and can be reduced in size and weight have become mainstream as power supplies used for electronic devices such as electronic computers.

As such a switching power supply, a line-operated type that directly rectifies 100 VAC to a DC of about 140 VDC and performs power conversion at a high frequency of several hundred KHz or more is often used.

On the other hand, in recent years, where high performance, power saving, miniaturization, and weight reduction of electronic devices are desired, power supply devices are no exception.

[Conventional technology]

Conventionally, most of the line-operated switching power supply devices employ a capacitor input type rectification method using a bridge rectifier, and FIG. 5 shows a typical configuration example.

Since bridge rectification is a full-wave rectification method,
The voltage waveform obtained by rectifying the power supplied from the rectifier by the bridge rectifier 11 composed of the diodes D1, D2, D3, and D4 has a power source frequency (50 Hz or 60 Hz) as shown by the dotted line in FIG.
The pulsating current W1 has twice the frequency.

This pulsating current W1 is smoothed by the capacitor C1 to obtain a DC smoothing voltage.
Get W2. Then, the smoothed voltage is chopped in a pulse shape by a transistor Tr that repeats on / off at a predetermined frequency according to a control signal from the control circuit 12 and transmitted to the secondary side via a transformer T, where the diodes D5, D6, The rectifier circuit is configured by a choke coil L2 and a capacitor C2, and is converted into DC to obtain a DC output voltage V _O.

However, the charging current for charging the capacitor C1, as shown by the waveform W3 in FIG. 6, does not flow during the entire period of the AC cycle but flows in a pulse shape, so that the apparent power factor of the power supply device is reduced. I have.

Here, the power factor is defined as the cosine COSφ of the phase difference φ between the current and the voltage in the electric circuit theory, and is a formula that is satisfied only when the load of the sine wave AC power supply is a pure resistance. However, in general, the apparent power factor in the rectifier circuit is not the cosine of the phase difference φ but the ratio of the effective power W to the apparent power VA. Then, in the ordinary capacitor input type rectification method, the charging current W3 flows in a pulse shape and the conduction angle tl is narrow, so that the peak value of the charging current W3 increases, and the apparent power increases.

 Therefore, the power factor is about W / (VA) ≒ 0.6 (1), which is a considerably bad value.

 When the power factor is deteriorated, the following adverse effects occur.

In other words, the ripple current of the smoothing capacitor C1 increases, the service life is shortened by the temperature rise due to the internal loss, and the reliability decreases.

Since the apparent power becomes large and the power obtained from the outlet of a general commercial power supply (rated at 15 A) becomes apparently small, there is a restriction on the device configuration of electronic devices such as a computer.

For example, assuming that the power factor COSφ = 0.6 and the efficiency η = 0.7, the device input current I becomes I = W / (η × V × COSφ) = 2.4 × W / V (2) By approaching “1”, the value of the input current I becomes I = W / (η × V × COSφ) = 1.4 × W / V (3) If the power factor is not improved, the same output power and input voltage In this case, the value of the input current also becomes 1.7 times.
Therefore, the components (for example, a disk device, a floppy device, an additional memory, and the like) in the device must be limited, and the performance and function are inferior to those of the device with improved power factor.

Therefore, it is required to improve the power factor, and various measures have been taken to cope with this.

Conventionally, there are a choke input type rectification method and an active smoothing filter method as methods for improving the power factor.

(1) Choke input type rectification method The simplest method for improving the input current waveform and increasing the power factor of the capacitor input type rectification method is the choke input type rectification method as shown in the principle diagram in FIG. .

In this configuration, the choke coil L1 is connected between the bridge rectifier 11 and the smoothing capacitor C1.With this configuration, the charging current to the capacitor C1 is limited by the impedance of the choke coil L1 and the conduction angle t1 is increased. ,
Power factor is improved.

However, in the case of this method, when the output current is small, the impedance of the choke coil L1 is hardly effective, and the operation is the same as in the case of the capacitor input rectification method. Because they are large and heavy, they are rarely used except for large equipment.

(2) Active Smoothing Filter Method Therefore, an active smoothing filter method has been devised as a method for improving the power factor while enabling downsizing.

The active smoothing filter system improves a power factor by controlling an input current waveform in a sine wave shape.

FIG. 8 shows the principle diagram. The circuit configuration of the active smoothing filter system includes a boost chopper 20 and its control circuit 30.
Consists of

The step-up chopper 20 is a type of a non-insulated switching regulator that raises the output voltage higher than the input voltage and is well known.

The control circuit 30 converts the sine wave voltage V _IN of the commercial power supply into a transformer T ₁
And the current I _CIN is input by the current transformer CT. The sine wave voltage is used as a reference sine wave when controlling the current in a sine wave shape.
Current I _CIN obtained from the current transformer CT is used to recognize the current input current value.

The control circuit 30 monitors the reference sine wave and the input current, and controls the step-up chopper so that the input current becomes a sine wave.
On / off control of the 20 main transistors Tr is performed.

In the active smoothing filter system, as shown in FIG.
At a frequency of several tens KHz or more. Waveform W6 of the input current I _IN is a sinusoidal in macroscopically since the average value of the switching current waveform W5.

Therefore, in principle, the power factor is “1”. Also,
It is sufficient to supply a current to the smoothing capacitor C3 every switching cycle, and the average is a sinusoidal ripple current, so the ripple current is reduced compared to the capacitor input rectification method, and high reliability can be obtained with a small capacitor. Can be.

However, in the case of this method, since the boost chopper 20 is used, the output voltage must be always higher than the input voltage. Therefore, if an output voltage lower than the input voltage is required, the voltage must be reduced by using a DC-DC converter after the active smoothing filter, which is inefficient.

Further, since the output of the active smoothing filter is not insulated from the primary circuit, it cannot be used safely for general logic circuits and the like.

[Problems to be solved by the invention]

As described above, in the present invention, a line-operated switching power supply device employing a capacitor input rectification method has a low power factor because a current for charging a smoothing capacitor has a spire shape, and this power factor is improved. In order to improve the power factor, those using the choke input rectification method require a large choke coil inductance, so that the shape becomes large and the weight becomes heavy. Since the output voltage is higher than the input voltage because the method that uses the method uses a boost chopper, if an output voltage lower than the input voltage is required, use a DC-DC converter after the active smoothing filter. The voltage must be lowered to reduce efficiency, and the output of the active smoothing filter is insulated from the primary circuit. Since it is not connected, it is made to solve each disadvantage that it can not be used safely for general logic circuits etc.It is possible to reduce the size and weight while improving the power factor, and also DC-DC It is an object of the present invention to provide a power supply device that can obtain a voltage lower than an input voltage without adding a converter and that can obtain a safe output insulated from a primary circuit.

[Means for solving the problem]

FIG. 1 is a diagram for explaining the present invention in principle.
That is, in order to achieve the above object, the power supply device of the present invention includes a rectifier 11 for rectifying an AC supplied from an AC power supply 10.
A switching means 2 for switching the output of the rectifier 11 at a predetermined frequency, and an output of the rectifier 11 switched by the switching means 2 to a primary side, performing a predetermined conversion and outputting to a secondary side. Transformer 3, smoothing means 4 for smoothing the secondary output of transformer 3, and smoothing means 4
Detecting means 5 for detecting a current flowing through the power supply, and control means 1 for generating a signal for switching the switching means 2 at a predetermined frequency in accordance with the current detected by the detecting means 5 and the frequency of the AC power supply 10. It is characterized by having.

[Action]

In the conventional active smoothing filter system, the power factor is improved by controlling the input current in a sinusoidal waveform, but in the present invention, the power factor is improved by controlling the input current in a rectangular waveform.

The power factor improvement according to the present invention is performed by a circuit including a general forward converter and its control unit without using a boost chopper. However, there is no smoothing circuit after the bridge rectifier as the rectifier 11.

The control means 2 monitors the sine wave voltage of the commercial power supply 10 and the charging current of the output capacitor C on the secondary side by the detection means 5,
On / off control of the switch means 2 on the primary side of the forward converter is performed so that the charging current has a sine wave shape.

Here, the forward converter means the switch means 2
Is an insulation type switching regulator that transmits energy to the secondary side while the switch is on.

In the present invention, as shown in the principle explanatory diagram of FIG. 1 and the waveform diagram of FIG. 2, the charging current I _CIN flowing into the output capacitor C on the secondary side is changed by the switch means 2 at a frequency of, for example, several tens KHz or more. Switching is performed such that the average value becomes a sine wave (see FIG. 2 (c)). The power W _CIN required to charge this capacitor C is: W _CIN = I _CIN × V _O (1) Since the output voltage V _O is constant (controlled to be constant) ( 2 (b)), that the current I _CIN is sinusoidal means that the power W _CIN is controlled to be sinusoidal (see FIG. 2 (d)).

Here, in the present invention, as shown in FIG.
Since there is no smoothing circuit in the subsequent stage, there is no place to store electric energy at all during the conversion of input power to output power. Therefore, the fact that the power W _CIN is sinusoidal means that the input power W _IN is also sinusoidal (see FIG. 2 (e)). Since the input power W _IN is W _IN = I _IN × V _IN and the input voltage V _IN is sinusoidal (see FIG. 2 (d)), the fact that the power W _IN is sinusoidal means that the input current is This means that I _IN is a square wave (second
FIG. (F)).

Thereby, the conduction angle of the input current is widened, and the power factor can be approximated to “1”.

Moreover, the choke for large choke coil, such as input system is required, along with it can be reduced in size and weight, the output voltage V _O does not use step-up chopper as active smoothing filter method, the input voltage V _IN
It is also possible to make it lower.

Further, safety can be ensured because an output insulated from the primary side can be obtained by the forward converter system.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram showing the configuration of the embodiment of the present invention. In the figure, the same or corresponding parts as those shown in FIG.

In the figure, 1 is a control circuit as control means,
The details will be described later.

Reference numeral 2 denotes a main transistor as switching means, for example, a MOS-FET is employed. The on / off state of the main transistor 2 is controlled by a drive signal S1 from the control circuit 1. The main transistor does not need to be a MOS-FET, but may be an ordinary transistor or another switching element.

Reference numeral 3 denotes a transformer which inputs a pulsating current rectified by the bridge rectifier 11 into a signal switched by the main transistor 2 on the primary side, performs a predetermined voltage transformation, and outputs it to the secondary side.

Reference numeral 4 denotes a smoothing circuit, which includes diodes D5 and D6, a coil L and a capacitor C. This smoothing circuit 4
Is output to the outside as an output DC voltage V _O of the power supply device. The output of the smoothing circuit 4 is supplied to the control circuit 1 as an output voltage detection signal S2.

Reference numeral 5 denotes a current detecting resistor as a detecting means, which has a very small resistance value. This current detection resistor 5
Then, a predetermined voltage drop occurs due to the flow of the charging current _ICIN for charging the capacitor C, and this is supplied to the control circuit 1 as a current detection signal S3.
The control circuit 1 uses the current detection signal S3 to output the capacitor C
The inflow current into the device is detected. Note that a current transformer may be used as a means for detecting a current.

Reference numeral 10 denotes an AC power supply for supplying 100 VAC commercial power.

Reference numeral 11 denotes a bridge rectifier as a rectifier, which is formed by connecting four diodes D1 to D4 in a bridge.

T ₁ is a trans, once insulate the signal from the AC power source 10 and supplies to the control circuit 1 as a reference sine wave signal S4.

Next, the control circuit 1 will be described. An operational amplifier 51 calculates the difference between the signals S3 at both ends of the current detection resistor 5 and outputs the difference as a detection signal S5 of the current _ICIN flowing into the capacitor C. This signal S5 is supplied to the operational amplifier 57 of the input current control unit 56.

An output voltage control unit 52 includes an operational amplifier 53 and a reference voltage generation circuit (not shown) that generates a reference voltage _Vref . The operational amplifier 53 compares the output voltage detection signal S2 with the reference voltage _Vref, and outputs the difference (DC) as an output voltage control signal S6. The output voltage control signal S6 is an output voltage V _O becomes higher becomes the low voltage signal. This signal S6 is supplied to the multiplier 55.

54 is a bridge rectifier, and generates a reference sine wave signal S7 by rectifying the reference sine wave signal S4 obtained through the transformer T _1. This signal S7 is also supplied to the multiplier 55.

The multiplier 55 multiplies the output voltage control signal S6 by the reference sine full-wave signal S7 and outputs the result as a current command signal S8. This signal S8 is used as the operational amplifier of the input current control unit 56.
It is supplied to 57.

Reference numeral 56 denotes an input current control unit, which includes operational amplifiers 57 and 59 and a sawtooth wave generator 58.

The operational amplifier 57 receives the current command signal S8 and the detection signal
S5 is calculated and supplied to the operational amplifier 59. The sawtooth wave generator 58 is a well-known sawtooth wave generator. The operational amplifier 59 compares the output signal of the operational amplifier 57 with the output signal of the saw-tooth wave generator 58 to generate a pulse-shaped drive signal S1.

The multiplier 55 will be described in more detail. The multiplier 55 is
As shown in FIG. 4, the circuit comprises an operational amplifier 61, a switch 62, a low-pass filter 63, and a sawtooth wave generator (not shown).

The operational amplifier 61 is supplied with the output voltage control signal S6 and a sawtooth wave signal generated from a sawtooth wave generator (not shown).

The operational amplifier 61 functions as a PWM comparator, and outputs a rectangular wave pulse having a duty proportional to the level of the output voltage control signal S6.

That is, when the output voltage V _O increases, the output voltage control signal S6
Is reduced, and the sawtooth signal is sliced at a lower level, so that a rectangular pulse having a wide significant width is generated,
When the output voltage V _O decreases, the level of the output voltage control signal S6 increases, and the sawtooth signal is sliced at a high level, so that a rectangular pulse having a narrow significant width is generated. The square-wave pulse signal output from the operational amplifier 61 is
And used to control its opening and closing time.

The switch 62 is formed of, for example, a semiconductor switching element, and the reference sine full-wave signal S7 is supplied to a side of the switch 62 once. The reference the reference sine wave signal S7 is passed through a switch 62 to open and close in response to the rectangular wave pulses supplied from the operational amplifier 61, or by blocking the passage, which is switched to reflect the output voltage V _O By generating a full sine wave and passing it through a low-pass filter 63, only the fundamental wave component is extracted and output as a current command signal S8.

 Next, the operation of the above configuration will be described.

In this embodiment, the control circuit 1 has two feedback loops to make the inflow current I _CIN into the capacitor C sinusoidal.

In the first loop, the current I is adjusted so that the output voltage V _O is constant.
_{This is} a main loop (analog control loop) for slowly controlling the average value of _CIN , and includes a smoothing circuit 4 (output voltage V _O ) → an output voltage control section 52 → a multiplier 55 → an input current control section 56 → a main transistor 2 loop. is there. The second loop is a minor loop (instantaneous control loop) that instantaneously follows a reference sine wave (AC input voltage) in order to convert the waveform of the average-controlled input current into a sine wave. The loop includes the operational amplifier 51, the input current controller 56, and the main transistor 2.

The on / off operation of the main transistor 2 is controlled by control signals obtained from each loop.

That is, first, in order to stabilize the output voltage V _O, the output voltage control unit 52, amplifies the difference between the output voltage V _O to a reference voltage V _ref as a reference for obtaining a desired output voltage V _O ,
Generate the output voltage control signal S6.

The output voltage control signal S6, as described above, decreases the output voltage V _O increases, a DC signal, such as up the output voltage V _O decreases.

Next, a multiplier 55 _generates a reference sine full-wave signal S7, which is a full-wave rectified waveform of an AC input voltage waveform serving as a template of a waveform of the current _ICIN , and an output voltage control signal, which is an output of the output voltage control unit 52.
The current command signal S8 is generated by multiplying the current command signal with S6.

The operation of the multiplier 55 will be described in more detail.
As shown in the drawing, the level of the output voltage control signal S6 and the level of the sawtooth wave signal are compared by the operational amplifier 61 as a PWM comparator, and a rectangular wave pulse train having a duty proportional to the magnitude of the output voltage control signal S6 is obtained.

Next, the rectangular wave pulse train and the reference sine full wave signal S7 are synthesized. That is, when the rectangular wave pulse train is "H level", the switch 62 is closed to output the reference sine full-wave signal S7 as it is, and when it is "L level", an amplitude-modulated pulse train having a value of zero is created.

From this amplitude-modulated pulse train, a low-pass filter 63
When the basic component is extracted at, a current command signal S8, which is a product signal of the reference sine full-wave signal S7 and the output voltage control signal S6, is obtained. In order for the current I _CIN to follow the current command signal S8 as a reference value, the operational
The drive signal S1 of the main transistor 2 is obtained by amplifying the error between S8 and the current _ICIN and comparing the amplified signal with the sawtooth wave by the operational amplifier 59 to perform PWM conversion.

This keeps the output voltage V _O constant and the current I
_CIN can be a full sine wave synchronized with the AC input voltage.

As described above, the conduction angle is widened, and the power factor can be set to a value close to “1”.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to reduce the size and weight while improving the power factor, and to obtain a voltage lower than the input voltage without adding a DC-DC converter. A power supply device capable of obtaining a safe output insulated from a primary circuit can be provided.

[Brief description of the drawings]

1 is a diagram for explaining the principle of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the present invention, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is a multiplication shown in FIG. 5 is a diagram showing an example of a conventional capacitor input rectifier circuit, FIG. 6 is a waveform diagram for explaining the operation of FIG. 5, and FIG. 7 is a conventional choke input rectifier. FIG. 8 is a diagram showing an example of a circuit, FIG. 8 is a diagram for explaining a conventional active smoothing filter system, and FIG. 9 is a waveform diagram for explaining the operation of FIG. In the drawing, 1 ... control means (control circuit), 2 ... switch means (main transistor), 3 ... transformer, 4 ... smoothing means (smoothing circuit), 5 ... detection means (current detection resistor), 10 …
... AC power supply, 11 ... Rectifier (bridge rectifier), C ...
Capacitors. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (5)

(57) [Claims] 1. A rectifier (11) for rectifying an alternating current supplied from an AC power supply (10), a switch means (2) for switching the output of the rectifier (11) at a predetermined frequency, and the switch means (2). A transformer (3) for inputting the output of the rectifier (11) switched in step (1) to the primary side, performing a predetermined conversion and outputting the output to the secondary side, and smoothing the secondary side output of the transformer (3). Means (4); detecting means (5) for detecting a current flowing through the smoothing means (4); current detected by the detecting means (5) and the AC power supply (10).
And a control means (1) for generating a signal for switching the switch means (2) at a predetermined frequency according to the frequency of the power supply. 2. The power supply device according to claim 1, wherein said switch means (2) comprises a semiconductor switching element. 3. The power supply device according to claim 1, wherein said detection means (5) detects a charging current for charging a capacitor (C) constituting said smoothing means (4). . 4. The power supply device according to claim 3, wherein said control means (1) controls said switching means (2) in accordance with a current detected by said detection means (5), and said capacitor (C). A power supply device, wherein the charging current of the power supply is controlled to have a sine wave shape. 5. The power supply device according to claim 3, wherein the control means (1) sets a waveform of the AC power supply (10) to a reference sine wave, and controls the capacitor (C) so as to follow the reference sine wave. A power supply device for controlling a charging current of the power supply.