JPH1014241A - Power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance safety by connecting a first diode in the same direction as the DC output terminal of a full-wave rectifier, so that a current flows from an inductor through a second diode to a load circuit when a switching element is turned off, thereby preventing an undue input power from being fed, with respect to the output power. SOLUTION: The mode is switched when the sum (Vc1 +Vz) of the voltage Vc1 of a capacitor C1 and a load voltage Vz varies between the full-wave rectified output voltage |Vin| of an AC power supply P and the charged voltage VEC of a smoothing capacitor EC. When a switching element Q is turned off and |Vin|<Vc1 +Vz=VEC, a current flows through a path of an inductor LM, the capacitor C1, a diode D1, the smoothing capacitor EC and a diode D2 and a current also flows through a path of the inductor LM, a load circuit Z and the diode D2. According to the arrangement, an undue power is prevented from being fed with respect to the output power at the time of increasing the load, circuit current, and the safety is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply, and more particularly to a power supply in which a chopper circuit has improved input current distortion from an AC power supply.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram of a conventional power supply device. In this circuit, a boosting chopper circuit for improving input current distortion by a switching element Q1, an inductor LI and a diode D1, a switching element Q2 and an inductor LM
And a step-down chopper circuit for limiting the load current by the diode D2. Hereinafter, the circuit configuration will be described. The AC power supply P is connected via a filter circuit F to the AC input terminal of the full-wave rectifier DB. The DC output terminal of the full-wave rectifier DB is connected to a series circuit of the inductor LI and the switching element Q1. A smoothing capacitor EC is connected to both ends of the switching element Q1 via a diode D1. A load circuit Z is connected to the smoothing capacitor EC via a switching element Q2 and an inductor LM, and a diode D2 is connected to a series circuit of the inductor LM and the load circuit Z with the illustrated polarity. The switching elements Q1 and Q2 are composed of, for example, power MOSFETs, and are supplied with high-frequency drive signals from a control circuit (not shown).

The operation of the conventional circuit shown in FIG. 7 will be described with reference to FIG. First, a boost chopper circuit for improving input current distortion by the switching element Q1, the inductor LI, and the diode D1 will be described. The switching element Q1 is turned on / off at a high frequency, and when the switching element Q1 is turned on, as shown in FIG. 8A, an AC power supply P, a filter circuit F, a full-wave rectifier DB, an inductor LI, and a switching element Q1. A current flows in the path and the inductor L
Energy is stored in I. Next, when the switching element Q1 is turned off, a voltage is generated across the inductor LI due to the energy stored in the inductor LI, and this voltage is superimposed on the rectified output voltage of the full-wave rectifier DB, and is smoothed through the diode D1. Charged to EC. That is, as shown in FIG. 8B, a current flows through the path of the AC power supply P, the filter circuit F, the full-wave rectifier DB, the inductor LI, the diode D1, and the smoothing capacitor EC, and the energy of the inductor LI is released. . As a result, a high-frequency current always flows from the AC power supply P, and the waveform of the high-frequency current is shaped by the filter circuit F, whereby the input current distortion is improved. Further, a voltage higher than the peak value of the AC power supply P is obtained in the smoothing capacitor EC.

Next, a step-down chopper circuit for limiting a load current by using the switching element Q2, the inductor LM and the diode D2 will be described. Switching element Q2
Is turned on / off at a high frequency, and when the switching element Q2 is turned on, a current flows through the path of the smoothing capacitor EC, the switching element Q2, the inductor LM, and the load circuit Z as shown in FIG. The voltage of the capacitor EC is stepped down by the inductor LM and supplied to the load circuit Z. Further, energy is accumulated in the inductor LM by the current flowing through the inductor LM. When the switching element Q2 is turned off, as shown in FIG.
A regenerative current due to the energy stored in the inductor LM flows through the path of the inductor LM, the load circuit Z, and the diode D2.

In the prior art shown in FIG. 7, a boosting chopper circuit for improving input current distortion by using a switching element Q1, an inductor LI and a diode D1, and a step-down chopper circuit for limiting a load current by using a switching element Q2, an inductor LM and a diode D2. Because it has
Many circuit elements are required.

On the other hand, in the conventional example of FIG. 9, the switching elements Q1 and Q2 are shared by one switching element Q and the diodes D1 and D2 are shared by one diode D in the conventional example of FIG. The circuit configuration has been simplified. In this circuit, a series circuit of an inductor LI and a switching element Q is connected between the DC output terminals of the full-wave rectifier DB, and a smoothing capacitor EC is connected to both ends of the switching element Q via a diode D.
A load circuit Z is connected to both ends of the diode D via an inductor LM.

FIG. 10 shows the operation of the circuit shown in FIG. The switching element Q is turned on and off at a high frequency. When the switching element Q is turned on, a current flows through the path shown in FIG. 10A, and when the switching element Q is turned off, a current flows through the path shown in FIG. That is, when the switching element Q1 is turned on, a current flows through the path of the AC power supply P, the filter circuit F, the full-wave rectifier DB, the inductor LI, and the switching element Q, and energy is accumulated in the inductor LI. Further, a current flows through the path of the smoothing capacitor EC, the inductor LM, the load circuit Z, and the switching element Q, and the voltage of the smoothing capacitor EC is stepped down by the inductor LM and supplied to the load circuit Z. Next, when the switching element Q is turned off, a regenerative current due to the energy stored in the inductor LM flows through the path of the inductor LM, the load circuit Z, and the diode D. Also, a voltage is generated across the inductor LI due to the stored energy of the inductor LI, and this voltage is superimposed on the rectified output voltage of the full-wave rectifier DB,
The smoothing capacitor EC is charged via the diode D. That is, a current flows through the path of the AC power supply P, the filter circuit F, the full-wave rectifier DB, the inductor LI, the diode D, and the smoothing capacitor EC, and the energy of the inductor LI is released. As a result, a high-frequency current always flows from the AC power supply P, and the waveform of the high-frequency current is shaped by the filter circuit F, whereby the input current distortion is improved.

Next, in the conventional example of FIG. 11, a full bridge circuit composed of four switching elements Qa, Qb, Qc, Qd is added in order to invert the polarity of the power supplied to the load circuit Z. ing. Switching element Qa ~
The switching element Qa is a first set of switching elements Qa and Qd, and a second set of switching elements Qb and Qc, and is alternately turned on and off at a low frequency. The operation is shown in FIGS.
Shown in First, as shown in FIGS. 12A and 12B, while the switching element Q is turned on and off at a high frequency,
The switching elements Qa and Qd are turned on, and the switching elements Qb and Qc are turned off, thereby supplying power in one direction to the load circuit Z. Next, as shown in FIGS. 12C and 12D,
While the switching element Q is turned on and off at a high frequency, the switching elements Qa and Qd are turned off, and the switching elements Qb and Qc are turned on to supply the load circuit Z with power in the opposite direction. Thereby, the polarity of the power supplied to the load circuit Z is inverted at a low frequency.

[0009]

The conventional circuit shown in FIG. 7 has a problem that the number of circuit elements is large. In the conventional example of FIG. 9 or FIG. 11, the circuit element is also used. However, the current of the step-up chopper circuit and the current of the step-down chopper circuit are superimposed and flow through the switching element Q and the diode D which are shared. In addition, the current withstand capability increases and the cost reduction effect due to the decrease in the number of elements is reduced. Also,
Since the control signal of the switching element Q is also used,
For example, when the power is controlled by changing the on-duty of the switching element Q at a constant frequency, if the on-duty of the switching element Q is reduced, the input power is reduced in terms of the function of the boost chopper circuit. As for the function of the step-down chopper circuit, the output power is reduced. However, the characteristics of each chopper circuit with respect to the on-duty change when the input voltage or the load resistance changes. Therefore, for example, when the on-duty is controlled to keep the output power constant, the input power may be excessively large or small compared to the output power. When the input power becomes excessive with respect to the output power, surplus energy is accumulated in the smoothing capacitor EC, the voltage across the smoothing capacitor EC increases, and the voltage applied to the components increases,
In some cases, the components will be stressed.

Such a phenomenon is caused, for example, when the conventional circuit shown in FIG. 11 is applied to a lighting device for a high-pressure discharge lamp, in the process of starting the high-pressure discharge lamp, the impedance of the load is low, and This is particularly noticeable because a large current needs to flow. That is, a constant on-duty must be provided to allow the output current to flow, but the output power is small because the load impedance is low. On the other hand, since the input power is an amount corresponding to the on-duty, the input power becomes excessive.

An object of the present invention is to solve such a problem. An object of the present invention is to use not only switching elements of a step-up chopper circuit and a step-down chopper circuit but also inductors. Provided is a power supply device that achieves further cost reduction, and when the load circuit resistance is low and the load circuit current is increased, the input power is not excessive with respect to the output power, and safety can be improved. It is in.

[0012]

According to the present invention, in order to solve the above-mentioned problems, as shown in FIG. 1, a first diode D1 is connected between DC output terminals of a full-wave rectifier DB. A smoothing capacitor EC is connected, and a first electrode connected to a first diode D1 of the smoothing capacitor EC is connected to one end of an inductor LM via a switching element Q;
A load circuit Z is connected between the other end of the inductor LM and the second electrode of the smoothing capacitor EC, and a second diode D2 is connected between the one end of the inductor LM and the second electrode of the smoothing capacitor EC. , A capacitor C1 is connected between a connection point between the first diode D1 and the DC output terminal of the full-wave rectifier DB and the other end of the inductor LM,
Is connected to an AC power supply P via a filter circuit F, and a first diode D1 is connected to a full-wave rectifier DB
The second diode D2 is connected in the same direction as the DC output terminal of the second switching element Q, and is connected to a polarity that allows a current to flow from the inductor LM to the load circuit Z via the second diode D2 when the switching element Q is turned off. It is a feature.

[0013]

FIG. 1 is a circuit diagram showing a preferred embodiment of the present invention. In this circuit, not only the switching element Q but also the inductor LM is shared by the step-up chopper circuit and the step-down chopper circuit. Hereinafter, the circuit configuration will be described. The AC power supply P is a filter circuit F
To the AC input terminal of the full-wave rectifier DB. A diode D is connected to the DC output terminal of the full-wave rectifier DB.
1, a smoothing capacitor EC is connected. A series circuit of a switching element Q, an inductor LM, and a load circuit Z is connected in parallel to both ends of the smoothing capacitor EC. A diode D2 is connected to the series circuit of the inductor LM and the load circuit Z with the illustrated polarity. Also,
The series circuit of the load circuit Z and the capacitor C1 is a full-wave rectifier D
B is connected in parallel between the DC output terminals.

The operation of the circuit shown in FIG. 1 will be described with reference to FIG.
In this circuit, the sum of the voltage Vc ₁ and the load voltage of the capacitor C1 (Vc ₁ + Vz) is full-wave rectified output voltage of the AC power supply P |
The mode is switched by changing between Vin | and the charging voltage V _EC of the smoothing capacitor EC.

First, when switching element Q is on, | V
When in | <Vc ₁ + Vz <V _EC , the mode becomes the mode 1 shown in FIG. 2A, and a current flows through the path of the smoothing capacitor EC, the switching element Q, the inductor LM, and the load circuit Z.

Next, when the switching element Q is turned on, | V
in | <Vc₁+ Vz = V_ECIn the case of, as shown in FIG.
Mode 2 and smoothing capacitor EC, switching
Current flows through the path of the element Q, the inductor LM, and the load circuit Z.
It is. Vc₁+ Vz = V _ECSo the diode
D1 conducts, capacitor C1, diode D1, switch
Current also flows through the path of the switching element Q and the inductor LM.
You.

Next, when switching element Q is off, | V
When in | <Vc ₁ + Vz = V _EC , the mode 3 shown in FIG. 2C is established, and the inductor LM, the capacitor C1,
Diode D1, smoothing capacitor EC, diode D2
And the current also flows through the path of the inductor LM, the load circuit Z, and the diode D2.

Next, when switching element Q is off, | V
When in | <Vc ₁ + Vz <V _EC , the mode becomes the mode 4 shown in FIG. 2D, and current flows through the path of the inductor LM, the load circuit Z, and the diode D2, but Vc ₁ + Vz <V _EC
Therefore, the diode D1 does not conduct.

Next, when switching element Q is off, | V
When in | = Vc ₁ + Vz <V _EC , the mode 5 shown in FIG. 2E is established, and a current flows through the path of the inductor LM, the load circuit Z, and the diode D2.
Current also flows through the path of the filter circuit F, the full-wave rectifier DB, the capacitor C1, and the load circuit Z.

As described above, in the circuit of FIG. 1, the mode is switched by the sum (Vc ₁ + Vz) of the voltage Vc _{1 of the} capacitor C ₁ and the load voltage Vz. The basic operation is an operation of the step-down chopper circuit including the switching element Q, the inductor LM, and the diode D2 using the smoothing capacitor EC as a power supply.
Is turned on, the energy of the smoothing capacitor EC is supplied to the load circuit Z via the inductor LM (mode 1). When the load voltage Vz is increased, the (Vc ₁ + Vz) reaches the voltage V _EC of the smoothing capacitor EC, capacitor C1
Is transferred to the inductor LM (mode 2). Next, when the switching element Q is turned off, the energy stored in the inductor LM is supplied to the load circuit Z, and is also supplied to the smoothing capacitor EC together with the energy of the capacitor C1 (mode 3). Voltage Vc ₁ of the load voltage Vz or the capacitor C1 is reduced, (Vc ₁
+ Vz) when smaller than the voltage V _EC of the smoothing capacitor EC, inductor LM of energy is released only to the load circuit Z (mode 4). Further, when the load voltage Vz decreases and (Vc ₁ + Vz) decreases to | Vin |,
Energy is supplied from the AC power supply P to the capacitor C1 and the load circuit Z (mode 5).

In the case where the load impedance is low and a large current must be output, which is a problem in the conventional example, the load voltage Vz does not increase in the circuit of FIG. 1, so that Vc ₁ + Vz = V Do not reach _EC . As a result, Mode 2 and Mode 3 do not occur. This period is a period in which the energy stored in the capacitor C1 from the AC power supply P during the mode 5 is released to the inductor LM (mode 2) and the smoothing capacitor EC (mode 3). , Which means that the potential of the capacitor C1 is always maintained, so that energy cannot be taken from the AC power supply P during the mode 5 period. For this reason, it is possible to prevent the input power from becoming excessive,
Voltage V _EC of the smoothing capacitor EC can be prevented from being abnormally increased.

[0022]

FIG. 3 shows an embodiment of the basic circuit shown in FIG.
In order to invert the polarity of the power supplied to the load circuit Z,
It is obtained by adding a full bridge circuit composed of four switching elements Qa, Qb, Qc, and Qd. Switching elements Qa to Qd are composed of switching elements Qa and Qd.
Are the first set, and the switching elements Qb and Qc are the second set, and are turned on and off alternately at a low frequency. The operation is shown in FIG.
And FIG. First, as shown in FIG. 4, while the switching element Q is turned on and off at a high frequency, the switching elements Qa and Qd are turned on, and the switching elements Qb and Qc are turned on.
Is turned off, and supplies power in one direction to the load circuit Z.
Next, as shown in FIG. 5, while the switching element Q is turned on and off at a high frequency, the switching elements Qa and Q
d is off, switching elements Qb and Qc are on,
The power is supplied to the load circuit Z in the reverse direction. Thereby, the polarity of the power supplied to the load circuit Z is inverted at a low frequency.

Also in this circuit, the sum (Vc ₁ + | Vz |) of the voltage Vc _{1 of the} capacitor C ₁ and the load voltage is the full-wave rectified output voltage | Vin | of the AC power supply P and the smoothing capacitor EC.
By changing between the charging voltage V _EC, mode is switched.

First, when the switching element Q is turned on, | V
_{in | <Vc 1 + | Vz} | at the time of the <V _EC, as shown in FIG. 4 (a)
, The smoothing capacitor EC, the switching element Q, the inductor LM, the switching element Qa,
A current flows through the path of the load circuit Z and the switching element Qd.

Next, when the switching element Q is turned on, | V
When in | <Vc ₁ + | Vz | = V _EC , FIG.
, The smoothing capacitor EC, the switching element Q, the inductor LM, the switching element Qa,
A current flows through the path of the load circuit Z and the switching element Qd. Since Vc ₁ + Vz = V _EC , the diode D
1 conducts, and a current also flows through the path of the capacitor C1, the diode D1, the switching element Q, and the inductor LM.

Next, when switching element Q is off, | V
When in | <Vc ₁ + | Vz | = V _EC , FIG.
Mode 3 as shown in FIG.
1, a current flows through the path of the diode D1, the smoothing capacitor EC, and the diode D2, and the inductor LM, the switching element Qa, the load circuit Z, the switching element Q
d, a current also flows through the path of the diode D2.

Next, when the switching element Q is off, | V
When in | <Vc ₁ + | Vz | <V _EC , FIG.
Next mode 4 shown in, inductor LM, switching elements Qa, the load circuit Z, the switching element Qd, a current flows in a path of the diode D2, since it is Vc ₁ + Vz <V _EC, the diode D1 does not conduct.

Next, when switching element Q is off, | V
When in | = Vc ₁ + | Vz | <V _EC , FIG.
And the current flows through the path of the inductor LM, the switching element Qa, the load circuit Z, the switching element Qd, and the diode D2, and the AC power supply P, the filter circuit F, the full-wave rectifier DB, the capacitor C1, the switching element Qa , Load circuit Z, switching element Qd
Current also flows through the path.

When the polarity of the output of the load circuit Z is to be reversed, FIGS. 5 (a) to 5 (d) are used instead of FIGS. 4 (a) to 4 (d).
Operation. First, when the switching element Q is on,
_{Vin | <Vc 1 + | Vz} | < at the time of the V _EC, as shown in FIG. 5
In the mode 1 shown in (a), a current flows through the path of the smoothing capacitor EC, the switching element Q, the inductor LM, the switching element Qc, the load circuit Z, and the switching element Qb.

Next, when the switching element Q is turned on, | V
When in | <Vc ₁ + | Vz | = V _EC , FIG.
, The smoothing capacitor EC, the switching element Q, the inductor LM, the switching element Qc,
A current flows through the path of the load circuit Z and the switching element Qb. Since Vc ₁ + Vz = V _EC , the diode D
1 conducts, and a current also flows through the path of the capacitor C1, the diode D1, the switching element Q, and the inductor LM.

Next, when switching element Q is off, | V
When in | <Vc ₁ + | Vz | = V _EC , FIG.
Mode 3 as shown in FIG.
1, a current flows through the path of the diode D1, the smoothing capacitor EC, and the diode D2, and the inductor LM, the switching element Qc, the load circuit Z, the switching element Q
b, a current also flows through the path of the diode D2.

Next, when switching element Q is off, | V
_{in | <Vc 1 + | Vz} | at the time of the <V _EC, as shown in FIG. 5 (d)
Next mode 4 shown in, inductor LM, the switching element Qc, a load circuit Z, the switching element Qb, a current flows in a path of the diode D2, since it is Vc ₁ + Vz <V _EC, the diode D1 does not conduct.

Next, when switching element Q is off, | V
When in | = Vc ₁ + | Vz | <V _EC , FIG.
And the current flows through the path of the inductor LM, the switching element Qc, the load circuit Z, the switching element Qb, and the diode D2, and the AC power supply P, the filter circuit F, the full-wave rectifier DB, the capacitor C1, the switching element Qc , Load circuit Z, switching element Qb
Current also flows through the path.

The embodiment shown in FIG. 6 is an example in which the present invention is applied to a discharge lamp lighting device. A different point is that a series circuit of an inductor Lo and a discharge lamp DL is used for a load circuit Z in the circuit of FIG. And a point where a small capacity capacitor Co is connected in parallel with the input side of the full bridge circuit. The operation of the circuit is the same as that of the circuit of FIG. 3, except that the inductor Lo and the capacitor Co constitute a low-pass filter for the discharge lamp DL as the actual load, and the potential across the capacitor Co is equal to the load voltage. The difference is that the mode is switched corresponding to Vz.

[0035]

According to the present invention, the step-up chopper circuit for improving the input current distortion and the step-down chopper circuit for limiting the load current serve as both the switching element and the inductor, so that the current of the switching element is increased as compared with the prior art. Without reducing the number of inductor elements,
Further, when the load circuit has a low impedance, the voltage applied to the component can be prevented from rising.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a basic circuit configuration of the present invention.

FIG. 2 is a circuit diagram for explaining a current path of the circuit of FIG.

FIG. 3 is a circuit diagram showing one embodiment of the present invention.

FIG. 4 is a circuit diagram for explaining a current path of the circuit of FIG. 3;

FIG. 5 is a circuit diagram for explaining another current path of the circuit of FIG. 3;

FIG. 6 is a circuit diagram showing another embodiment of the present invention.

FIG. 7 is a circuit diagram showing a circuit configuration of a conventional example.

FIG. 8 is a circuit diagram for explaining a current path of the circuit of FIG. 7;

FIG. 9 is a circuit diagram showing a circuit configuration of another conventional example.

FIG. 10 is a circuit diagram for explaining a current path of the circuit of FIG. 9;

FIG. 11 is a circuit diagram showing a circuit configuration of still another conventional example.

FIG. 12 is a circuit diagram illustrating a current path of the circuit of FIG. 11;

[Explanation of symbols]

 P AC power supply DB Full-wave rectifier Q Switching element LM Inductor EC Smoothing capacitor Z Load circuit F Filter circuit C1 Capacitor D1 Diode D2 Diode

Claims (7)

[Claims] 1. A smoothing capacitor is connected between a DC output terminal of a full-wave rectifier via a first diode, and a first electrode connected to the first diode of the smoothing capacitor is connected to an inductor of the inductor via a switching element. Connected to one end, a load circuit is connected between the other end of the inductor and the second electrode of the smoothing capacitor, a second diode is connected between the one end of the inductor and the second electrode of the smoothing capacitor, A capacitor is connected between a connection point between the first diode and the DC output terminal of the full-wave rectifier and the other end of the inductor, and an AC input terminal of the full-wave rectifier is connected to an AC power supply through a filter circuit, The first diode is connected in the same direction as the DC output terminal of the full-wave rectifier, and the second diode is connected from the inductor to the load circuit via the second diode when the switching element is off. A power supply device connected to a polarity through which a current can flow. 2. The power supply device according to claim 1, wherein said load circuit is an inductive load. 3. The power supply device according to claim 2, wherein a small-capacity capacitor is connected in parallel with said inductive load. 4. The power supply device according to claim 3, wherein a diode is connected in antiparallel to said inductive load. 5. The power supply device according to claim 2, wherein the inductive load is a series circuit of an inductor and a discharge lamp. 6. The load circuit further includes a full bridge circuit formed by connecting two sets of circuits in which two switching elements are connected in series, and a connection point of the first set of switching elements and a second bridge. The load circuit is connected between connection points of a set of switching elements, and the switching elements forming the full bridge circuit are switched at a low frequency so as to alternately reverse the polarity of power supplied to the load circuit. The power supply device according to any one of claims 1 to 5, wherein 7. A smoothing capacitor is connected between a DC output terminal of the full-wave rectifier via a first diode, and a first electrode connected to the first diode of the smoothing capacitor is connected to a first electrode of the inductor via a switching element. Connected to one end, a load circuit is connected between the other end of the inductor and the second electrode of the smoothing capacitor, a second diode is connected between the one end of the inductor and the second electrode of the smoothing capacitor, A capacitor is connected between a connection point between the first diode and the DC output terminal of the full-wave rectifier and the other end of the inductor, and an AC input terminal of the full-wave rectifier is connected to an AC power supply through a filter circuit, The first diode is connected in the same direction as the DC output terminal of the full-wave rectifier, and the second diode is connected from the inductor to the load circuit via the second diode when the switching element is off. It is connected to a polarity through which a current can flow, and has control means for turning on and off the switching element at a frequency higher than the power supply frequency of the AC power supply, and the load circuit has two switching elements connected in series. A full bridge circuit comprising two sets of circuits connected in parallel is added, and the load circuit is connected between a connection point of a first set of switching elements and a connection point of a second set of switching elements constituting the full bridge circuit. A power supply device, comprising: a control unit for switching a switching element included in the full bridge circuit at a low frequency so as to alternately reverse the polarity of power supplied to the load circuit.