JPH09201052A - Dc power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of a DC power supply by stopping the power factor improving operation of a power factor improving circuit when the output current value of a DC-DC converter is smaller than a preset value. SOLUTION: An AC power supply 1 is connected to the input terminal of a rectifier circuit 2 and the input terminal of an active filter 3 which works as a power factor improving circuit is connected to the positive-and negative-side output terminals (a) and (b) of the rectifier circuit 2. A current detecting circuit 10 usually detects the output current value of a DC-DC converter 4 and compares the detected value with a preset reference value by means of a comparator circuit 11. When the detected value is smaller than the reference value, an on/off circuit 12 stops the operation of the control circuit 5 of the filter 3 by outputting a signal Vo so as to set a switching element Q1 to a nonoperating state while the element Q1 is turned off. In such a way, the power loss of a DC power unit is reduced by stopping the operation of the filter 3 when the output current of the converter 4 is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device used for OA equipment and the like, and more particularly to a DC power supply device provided with a power factor correction circuit for an input current from an AC power supply.

[0002]

2. Description of the Related Art In recent years, there has been a problem that a harmonic current generated from an electronic device flows out to a power system and adversely affects not only the electronic device but also other devices sharing the power source. This is because most DC power supplies except large power supplies or some special power supplies employ a capacitor input type rectifier circuit, so the AC input current has a narrow pulse-like waveform, This is due to the inclusion of many harmonic currents.

An active filter is one of the effective means for suppressing the harmonic current and improving the power factor. This active filter is inserted between the input rectifier circuit and the DC / DC converter of the conventional switching power supply, and the power factor is controlled by controlling the input current waveform from the rectifier circuit to be a smooth waveform close to a sine wave. It is known as a circuit for improving and reducing the harmonic component of the input current.
Various types of active filters such as a boost type, a step-down type, and a step-up / down type have been proposed. Here, a DC power supply device equipped with the most common boost type will be described as an example.

FIG. 6 is a schematic circuit diagram of a conventional DC power supply device equipped with this step-up type active filter. This DC power supply device includes a rectifier circuit 2 configured by a diode bridge for full-wave rectifying the AC input from an AC power supply 1, a step-up chopper-type active filter 3 as a power factor correction circuit, and an active filter 3 thereof. It is composed of a DC / DC converter 4 which forms a circuit which receives an output voltage and outputs a predetermined DC voltage between output terminals 8 and 9.

The DC / DC converter 4 forms a drive power supply circuit for the control circuit 5 of the active filter 3 and its own control circuit 6 on the winding mn side of the transformer T1. Further, the voltage detection circuit 7 is provided between the output terminals 8 and 9, and the control circuit 6 is controlled according to the detected voltage so that the output voltage becomes a predetermined voltage.

In the operation of this DC power supply device, when the AC power supply 1 is turned on, the input voltage is full-wave rectified by the rectification circuit 2 to become a pulsating current voltage. This pulsating voltage is applied to the series circuit of the starting resistors R2 and R3, the resistance-divided voltage is smoothed by the driving power supply smoothing capacitor C3, and when the voltage exceeds a predetermined value, the control circuit 5 of the active filter 3 and DC
The control circuit 6 of the DC / DC converter 4 starts to operate, and the switching elements Q1 and Q2 by the respective FETs are started.
A pulse for driving is output to.

The active filter 3 turns on / off the switching element Q1 so that the input current waveform from the rectifier circuit 2 (detected by the voltage between both ends d and e of the resistor R4) is the input voltage from the AC power source 1. The output voltage (voltage between g and e) that is approximated to be similar to the waveform (voltage waveform between f and d) and is rectified and smoothed by the diode D5 and the smoothing capacitor C1 is stabilized.

On the other hand, in the DC / DC converter 4, the control circuit 6 turns on / off the switching element Q2 to interrupt the current flowing through the primary winding h-j of the transformer T1, and thereby the secondary winding k. An alternating voltage is induced on the −p side. The AC voltage is applied to the diodes D9 and D1.
0, inductor L3, and smoothing capacitor C4 are rectified and smoothed, and a DC voltage is output between terminals 8 and 9.

The voltage detection circuit 7 detects the output voltage and controls the control circuit 6 so that the voltage becomes a predetermined value. An AC voltage is also induced on the winding m-n side of the transformer T1, and the AC voltage is induced by the diodes D7 and D8 and the inductor L.
2, and rectifying and smoothing by the driving power supply smoothing capacitor C3, and the voltage thereof is supplied to the control circuit 6 as a driving power supply to bring the DC / DC converter 4 into a continuous operation state, and also to the control circuit 5 of the active filter 3. The drive power is supplied to enter the continuous operation state.

[0010]

However, in the circuit of the conventional DC power supply device described above, when the AC power supply 1 is turned on, the magnitude of the load connected between the output terminals 8 and 9 of the DC / DC converter 4 is increased. Since the active filter 3 and the DC / DC converter 4 unconditionally start continuous operation regardless of fluctuations or fluctuations, the DC / DC converter 4
When the load connected between the output terminals 8 and 9 is light and the output power is small, the efficiency is extremely reduced as compared with the case where the load is heavy and the output power is large.

The cause of the decrease in efficiency is a loss in which neither the active filter 3 nor the DC / DC converter 4 is proportional to the output power. Specifically, the remarkable ones are the power consumption of the control circuits 5 and 6 and the switching element. The drive power and switching loss of Q1 and Q2, the power consumption of the voltage detection circuit 7 and the like can be mentioned, because the ratio of these power loss to the input power increases.

That is, the DC power supply device shown in FIG.
Since the step-up chopper type active filter 3 is installed to reduce the harmonic current, compared to the DC power supply device that does not have the active filter 3, the power loss increases as the switching circuit is added. However, there is a problem that the efficiency of the power supply device is reduced. In other words, the DC power supply device including the AC input current power factor correction circuit and the DC / DC converter that is the load of the AC input current is used when there is no need for power factor improvement or when there is little need for power factor improvement. The power factor correction circuit is continuously operating, which increases power loss and reduces the efficiency of the power supply device.

The present invention has been made in view of the above points, and in a DC power supply device having a power factor correction circuit such as an active filter between such a rectifier circuit and a DC / DC converter, an input current When there is no need to reduce the harmonic current of
The purpose is to improve efficiency by reducing the power loss due to the power factor correction circuit.

[0014]

As shown in FIG. 1 which is a block diagram showing the basic structure of a direct current power supply device according to the present invention, a rectifier circuit 2 for rectifying alternating current input from an alternating current power source 1 and its rectifier circuit. Output from the power factor improving circuit 3 and the power factor improving circuit 3 such as an active filter for inputting the pulsating current output from the circuit 2 and controlling the input current waveform so that it becomes a waveform close to a sine wave and then rectifying and smoothing. In the DC power supply device 5 including the DC / DC converter 4 for converting the generated DC voltage into a predetermined voltage and supplying the same to the load 20, the output current value of the DC / DC converter 4 is achieved in order to achieve the above object. And a current stop means for stopping the power factor improving operation of the power factor improving circuit 3 when the current value detected by the current detecting means 14 is smaller than a preset value. 5 and in which the provided.

The current detecting means 14 outputs the value of the output current of the rectifier circuit 2 as shown by the broken line in FIG. 1 or the value of the input current from the AC power source 1 as a current proportional to the output current of the DC / DC converter 4. May be detected.
According to this configuration, on the output side or the input side of the DC power supply device 5, the current detection means 14 detects the output current of the DC / DC converter or the value of the current proportional thereto, and the operation stop control means 15 detects it. The current value is compared with a preset value, and when it is smaller than the preset value, the power factor improving operation of the power factor improving circuit 3 is stopped and the power factor improving circuit 3 is stopped.
Reduce power loss due to.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 2 is a schematic circuit diagram showing the configuration of a DC power supply device according to an embodiment of the present invention, and the same or corresponding portions as those in FIGS. 1 and 6 are designated by the same reference numerals.

The DC power supply device shown in FIG. 2 is similar to the conventional DC power supply device shown in FIG. 6, and has a rectifier circuit 2 formed of a diode bridge connected to an AC power supply 1, and an output terminal of the rectifier circuit 2. Is connected to the input current waveform to improve the power factor by controlling the input current waveform to be a sine wave, and the booster chopper active filter 3 which is a power factor correction circuit for reducing the harmonic component of the input current, and the DC output. It is composed of a forward type DC / DC converter 4 for generating a voltage and a driving power source.

A current detection circuit for detecting the output current is provided on the secondary side of the transformer T1 in the DC / DC converter 4, and a comparison circuit for comparing the current value detected by the current detection circuit 10 with an arbitrary value. 11 and an on / off circuit 12 that activates or deactivates the active filter 3 according to the comparison result are different from the conventional DC power supply device shown in FIG. And this Figure 2
The current detection circuit 10 in FIG. 1 corresponds to the current detection means 14 in FIG. 1, and the comparison circuit 11 and the on / off circuit 12 correspond to the operation stop control means 15 in FIG.

Explaining the circuit configuration of this DC power supply device in more detail, the AC power supply 1 is connected to the input terminal of the rectifier circuit 2 and is connected to the positive output terminal a and the negative output terminal b of the rectifier circuit 2. , Active filter 3 which is a power factor correction circuit
The input terminal of is connected. The active filter 3 includes a series circuit of an inductor L1 connected to the positive output terminal a of the rectifier circuit 2 and a diode D5, a capacitor C1 connected between the positive and negative output lines 3a and 3b, an inductor L1 and a diode D5. A switching element Q1 formed by an FET connected between the connection point with the anode and the negative output line 3b, and the switching element Q1 being turned on / off.
The control circuit 5 controls the off state.

The control circuit 5 has a voltage between terminals f and d for detecting a pulsating voltage input from the rectifier circuit 2,
Resistor R4 for detecting the input current value from the rectifier circuit 2
The voltage between both ends d and e and the voltage between g and e for detecting the output voltage of the active filter 3 are input.

The output lines 3a and 3b of the active filter 3 are connected to the input lines 4a and 4b of the DC / DC converter 4. The first primary winding h-j of the transformer T1 is provided between the positive and negative input lines 4a and 4b.
And a switching element Q2 composed of an FET are connected in series. An anode of a diode D6 is connected to the j side of the primary winding, and a resistor R1 and a capacitor C2 are connected to its cathode.
Connect one end of the parallel circuit with and connect the other end to the primary winding h
The snubber circuit is formed by connecting to the side (the positive side input line 4a). The gate of the switching element Q2 is connected to the control circuit 6 that controls the on / off thereof.

Further, the anode of the diode D7 is connected to the m side of the winding m-n of the transformer T1, the one end of the inductor L2 is connected to the cathode thereof, and the cathode of the diode D8 is connected to the connection point between the diode D7 and the inductor L2. And the anode and one end of the capacitor C3 are wound m-
It is connected to the n side of n (negative input line 4b), and the other end of the capacitor C3 is connected to the other end of the inductor L2 to form a rectifying / smoothing circuit.

A series circuit of starting resistors R2 and R3 is also connected between the output terminals of the rectifying circuit 2, and the resistor R
The voltage divided by 2 and R3 is applied between both terminals of the drive circuit in the control circuits 5 and 6 and the capacitor C3.

On the other hand, the configuration of the secondary side of the transformer T1 in the DC / DC converter 4 is the same as that of the conventional DC power supply device shown in FIG.
9, D10, inductor L3, and capacitor C4 are connected, the voltage detection circuit 7 is connected between the output terminals 8 and 9, and the detection voltage is input to the control circuit 6. Then, the current detection circuit 10 is inserted between the anode connection point of the diode D10 of the negative output line connecting the p-side of the secondary winding of the transformer T1 and the output terminal 9 and the p-side of the secondary winding. , The value of the output current of the DC / DC converter 4 is detected. Further, the provision of the comparison circuit 11 for inputting the output signal of the current detection circuit 10 and the ON / OFF circuit 12 for inputting the comparison output and controlling the control circuit 6,
As described above.

Next, the operation of the DC power supply device thus constructed will be described. The normal operation when the active filter is in the operating state is the same as that of the conventional DC power supply device described with reference to FIG. Therefore, the description thereof will be omitted. The current detection circuit 10 constantly detects the value of the output current of the DC / DC converter 4, and compares the detected value with the comparison circuit 1.
1 is compared with a preset reference value. When the detected value is smaller than the reference value, the comparison result causes the on / off circuit 12 to stop the operation of the control circuit 5 of the active filter 3 by the output signal Vo, thereby turning off the switching element Q1. Leave it as is.

As described above, when there is no need to reduce the harmonic current of the input current from the AC power source 1, or when the need is small, that is, when the output current of the DC / DC converter 4 is small, the active filter 3 The operation of the control circuit 5 is stopped. Thereby, the power loss in the active filter 3 can be reduced and the efficiency of the DC power supply device can be improved.

FIG. 3 shows a current detection circuit 10 and a comparison circuit 1.
1, a specific circuit example of the on / off circuit 12 will be shown. To briefly explain this, in FIG. 3, the current detection circuit 10 uses a current transformer CT to detect an alternating current. Then, the DC / D shown in FIG.
The primary winding of the current transformer CT is connected in series between the p side of the secondary winding side of the transformer T1 of the C converter 4 and the anode side of the diode D10.

As a result, this current transformer CT
A current that is inversely proportional to the turn ratio with respect to the current flowing through the primary winding flows through the secondary winding. The current is converted into a voltage by the resistor R5, and the detected voltage Vd, that is, a voltage having a value proportional to the output current of the DC / DC converter 4, is input to the + side input terminal of the comparator 30 of the comparison circuit 11, and 5 V The power supply voltage is divided by resistors R6 and R7, and a predetermined reference voltage Vr is input to its-side input terminal as a comparison voltage.

When the detected voltage Vd becomes higher than the reference voltage Vr, the comparator 30 outputs the + side saturated output voltage (high level output) to the on / off circuit 12 via the diode D12. The output voltage causes a base current to flow in the transistor TR1 of the on / off circuit 12, and the transistor TR1 is turned on. for that reason,
Due to the voltage drop of the resistor R7, a low level output signal Vo
Is output to the control circuit 5 of the active filter 3 to turn on the operation of the control circuit 5.

On the contrary, when the detection voltage Vd becomes lower than the reference voltage Vr, the output of the comparator 30 becomes low level (0
V) and the transistor TR1 of the on / off circuit 12
Is turned off, the output signal Vo becomes high level,
The operation of the control circuit 5 of the active filter 3 is turned off. The capacitor C6 of the on / off circuit 12 is provided to give some delay (time constant) to the on / off of the transistor TR1.

In place of the current transformer CT and the current-voltage conversion circuit of FIG. 3, a resistor for current detection is connected in series between the p side of the secondary winding side of the transformer T1 and the anode side of the diode D10. Alternatively, the voltage value that is proportional to the output current of the DC / DC converter 4 may be detected by connecting the two terminals of the resistor. Further, the location where such a current detection circuit 10 is inserted is also a DC such as a current supply circuit to the load on the front side of the output terminal 8 or 9, the primary side of the transformer T1, the output side or the input side of the rectifier circuit 2, Any location may be used as long as it can detect a current value proportional to the output current of the / DC converter 4. It is also possible to substitute the switch current by the switching element Q1.

Next, another embodiment of the DC power supply device according to the present invention is shown in FIG. In this figure, FIG. 2 and FIG.
The same parts as those in are denoted by the same reference numerals, and the description thereof will be omitted. In this embodiment, the DC / DC converter 4 is the same as the conventional example shown in FIG. 6, and no current detection circuit or the like is provided. Then, the resistor R4 for detecting the input current from the rectifier circuit 2 in the active filter 3
Instead of, the current detection circuit 10 'is inserted between d and e of the negative side output line 3b, and the detected current value is input to the control circuit 5 and also to the comparison circuit 11'. The operation and stop of the control circuit 5 are controlled by the output signal Vo of the ON / OFF circuit 12 'which inputs the output of'.

FIG. 5 shows a current detection circuit 10 'and a comparison circuit 1
1'and a specific circuit example of the on / off circuit 12 'are shown. This example is also an example in which a current transformer is used for the current detection circuit. That is, this current detection circuit 10 '
The primary winding of the current transformer CT is inserted in series between d and e in FIG. 4, and a current corresponding to the current (pulsating current) flowing therethrough is generated in the secondary winding. Then, the current is converted into a voltage by the resistor R8 via the diode bridge DB, and DC /
A detection voltage proportional to the output current of the DC converter 4 is output.

This detection voltage is input to the control circuit 5 and applied to the cathode of the diode D14 of the comparison circuit 11 '. As a result, the peak value of this detection voltage is level-detected by the diode D14, and when it is below a predetermined voltage, the diode D14 becomes conductive and the resistance R9 having a large resistance value.
The base voltage of the transistor TR2 lowers due to the voltage drop in the transistor TR2, the base current stops flowing, and the transistor TR2 is turned off.

As a result, the capacitor C7 is charged,
Since the base voltage is applied to the transistor TR3 of the on / off circuit 12 ', the transistor TR3 is turned on, and thus the transistor TR4 is also turned on. Therefore, the output signal Vo to the control circuit 5 becomes high level, the operation of the control circuit 5 is stopped, and the switching element Q
1 is kept in the OFF state and remains inactive.

On the contrary, when the peak value of the detection voltage across the resistor R8 exceeds a predetermined voltage, the diode D14 stops conducting, the transistor TR2 is turned on, and the charging voltage of the capacitor C is discharged. / OFF circuit 1
The base voltage is not applied to the 2'transistor TR3, and the transistor TR3 is turned off. This also turns off the transistor TR4.

Therefore, the output signal Vo to the control circuit 5 is
Becomes a low level, the control circuit 5 is operated, and the switching element Q1 is turned on / off. Also in this circuit, the capacitor C7 turns on the transistors TR3 and TR4.
It is provided to give some delay (time constant) to off.

Also in this example, when the output current of the DC / DC converter 4 is small and there is no need to reduce the harmonic current of the input current from the AC power source 1, or when the need is small, the active filter 3 is not activated. The operation of the control circuit 5 can be stopped. Thereby, the power loss in the active filter 3 at that time can be reduced and the efficiency of the DC power supply device can be improved.

The current detection circuit 10 'shown in FIG.
The current detection circuit 10, the comparison circuit 11, and the on / off circuit 12 shown in FIG. 3 may be used instead of the comparison circuit 11 'and the on / off circuit 12'. Or,
The resistor R4 in FIG. 2 is connected to the current detection circuit 10 or 1
Alternatively, the voltage generated between both ends d-e of the resistor R4 may be input to the comparison circuit 11 or 11 '.

In each of the above embodiments, DC / D
Although the C converter is the forward type, it can be applied to other types such as a flyback type, a half bridge type, and a chopper type. Further, as means for stopping the operation of the control circuit 5 of the active filter 3,
It is possible to use the ON / OFF function of the control IC used in the control circuit 5, cut off the drive power supply of the control IC, or cut off the drive signal of the switching element by any means.

[0041]

As described above, according to the present invention, there is no need to reduce the harmonic current of the input current in the DC power supply device having the power factor correction circuit such as the active filter 3. Alternatively, when the necessity is small, the operation of the power factor correction circuit can be stopped to reduce power loss and improve the efficiency of the DC power supply device.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a DC power supply device according to the present invention.

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

FIG. 3 is a current detection circuit 10 and a comparison circuit 1 in FIG.
1 is a diagram showing a specific circuit example of an ON / OFF circuit 12.

FIG. 4 is a circuit diagram showing another embodiment of the DC power supply device according to the present invention.

5 is a current detection circuit 10 'and a comparison circuit 1 in FIG.
It is a figure which shows the specific circuit example of 1 ', and an on / off circuit 12'.

FIG. 6 is a circuit diagram of a conventional DC power supply device equipped with an active filter as a power factor correction circuit.

[Explanation of symbols]

 1: AC power supply 2: Rectifier circuit 3: Power factor correction circuit, active filter 4: DC / DC converter 5: Active filter control circuit 6: DC / DC converter control circuit 7: Voltage detection circuit 8, 9: DC / Output terminal of DC converter 4, 10 ': current detection circuit 11, 11': comparison circuit 12, 12 ': on / off circuit 14: current detection means 15: operation stop control means 20: load

Claims (2)

[Claims] 1. A rectifying circuit for rectifying an alternating current input from an alternating current power source, and a pulsating current output from the rectifying circuit are input, and the input current waveform is controlled so as to be a waveform close to a sine wave, and then rectifying and smoothing. And a DC / DC for converting a DC voltage output from the power factor correction circuit into a predetermined voltage
In a DC power supply device including a converter, current detection means for detecting an output current of the DC / DC converter or a current value proportional to the current, and a current value detected by the current detection means is a preset value. A DC power supply device, comprising: an operation stop control means for stopping the power factor correction operation of the power factor correction circuit when it is smaller. 2. The DC power supply device according to claim 1, wherein the power factor correction circuit is an active filter having a switching element connected between positive and negative lines between the rectifier circuit and the DC / DC converter, The direct-current power supply device, wherein the operation stop control means is means for putting the switching element in a non-operating state while being kept off.