JPH0686553A - Power supply circuit - Google Patents

Abstract

PURPOSE:To improve the power factor of a rectifier circuit at low cost. CONSTITUTION:A choke coil is connected in series with a line 11 whereby one of input terminals 10a, 10a of a bridge rectifier circuit 10 and a single-phase AC power supply are connected. Also, lines 13, 14, whereby two output terminals 10b, 10b of the bridge rectifier circuit 10 for supplying a rectified voltage to the outside and the two input terminals of a switching regulator Y are connected respectively, are connected by the series circuit comprising a capacitor C2 and the parallel circuit which comprises a transistor Q1 and a discharge diode D1. Further, a rectifier diode D2 is connected in series with the line 13, wherewith one end of the capacitor C2 is connected, and the charge current to the capacitor C2 is switched on and off by the switching transistor Q1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for rectifying an AC input and smoothing the rectified output to obtain a DC output.

[0002]

2. Description of the Related Art A conventional power supply circuit will be described with reference to FIG.

In FIG. 15, reference numeral 1 denotes a bridge rectifier circuit in which diodes are connected in a bridge shape, and has two input terminals 1a and output terminals 1b. An AC power supply is connected to the two input terminals 1a, one output terminal 1b of the two output terminals 1b is connected to a collector of a chopping transistor 3 via a choke coil 2, and the other output terminal 1b is connected. Is connected to the emitter of the transistor 3.

A reverse current blocking diode 4 is connected between the collector of the transistor 3 and one of the two output terminals of the power supply circuit, and further the two output terminals of the power supply circuit are connected. A smoothing capacitor 5 is connected between them. The choke coil 2, the transistor 3 and the smoothing capacitor 5 form an active filter.

In the conventional power supply circuit thus constructed, when the transistor 3 is switching-controlled so that the AC line voltage and the load current are proportional, the filter circuit seen from the AC line operates as a constant resistance. As a result, the power factor can be improved, and the ripple filter circuit can be downsized as compared with the case where no transistor is used.

[0006]

However, in the conventional power supply circuit as described above, the output voltage of the bridge rectifier circuit 1 is directly chopped by the transistor 3, so that the power factor is greatly improved, but the chopping by the transistor 3 is performed. Therefore, a choke coil having a relatively large inductance must be used, which causes a problem of high cost.

Further, since the output voltage increases due to the increase in the inductance of the choke coil, it is necessary to use a high withstand voltage when connecting the switching regulator to the latter stage of the power supply circuit.

Therefore, it is conceivable to insert a reactor into the input line to suppress the current flowing in the choke coil. However, this reactor must also have a relatively large inductance, and the reactor is large and heavy. There is a problem to turn.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a power supply circuit capable of improving the power factor at low cost.

[0010]

In order to achieve the above object, the present invention according to claim 1 has two input terminals to which an AC voltage is applied and two outputs for supplying a rectified voltage to the outside. A bridge rectification circuit having a terminal, a coil connected to one input terminal of the bridge so that the bridge AC voltage passes, a capacitor connected between two output terminals of the rectification circuit, and a switching element in series And a circuit.

The present invention according to claim 2 is the same as claim 1
Where the coil is a choke coil or LF
It is assumed to be composed of T.

Further, the present invention according to claim 3 is the same as claim 1 or 2, wherein a discharging diode connected in parallel with the switching element and connected in series with the capacitor, a discharging voltage of the capacitor, and the discharging voltage of the capacitor. A rectifying diode connected to the connection portion between the capacitor and one output terminal of the bridge rectifier circuit is further provided so that a voltage supplied from one output terminal of the bridge rectifier circuit can pass through.

Further, the present invention according to claim 4 is a bridge rectification circuit having two input terminals to which an AC voltage is applied and two output terminals for supplying a rectified voltage to the outside. It is characterized by including a capacitor connected between two output terminals of the bridge rectifier circuit, a series circuit of a coil and a switching element.

Further, the present invention according to claim 5 provides the discharge diode connected to the switching element in parallel and connected in series with the capacitor, the discharge voltage of the capacitor, and the bridge rectification. As the voltage supplied from one output terminal of the circuit passes,
A rectifying diode connected to a connecting portion between the capacitor and one output terminal of the bridge rectifying circuit is further provided.

Further, the present invention according to claim 6 is a bridge rectifier circuit having two input terminals to which an AC voltage is applied and two output terminals for supplying a rectified voltage to the outside, and A series circuit of a capacitor connected between two output terminals of the bridge rectifier circuit, a primary side of the pulse transformer, and a switching element, a secondary side of the pulse transformer connected in parallel to the series circuit, and a discharging diode. And a series circuit of.

Further, the present invention according to claim 7 is the drive control circuit according to claim 1, 4 or 6, wherein the drive control circuit for the switching element is soft-started so that the level of the drive power supply voltage is gradually increased with time when the power is turned on. A power supply unit is provided.

[0017]

According to the present invention of claims 1 to 3, the charge current to the smoothing capacitor rectified by the bridge rectifier circuit is switched by the switching element, and is generated in the coil when the switching element is switched from ON to OFF. The reverse power that does is superimposed on the input voltage of the bridge rectifier circuit. This expands the current conduction angle of the bridge rectifier circuit and limits the peak current by the coil, improving the power factor of the bridge rectifier circuit.

According to the present invention of claims 4 to 6,
Since the charge current to the smoothing capacitor rectified by the bridge rectifier circuit is switched by the switching element, the current conduction angle of the bridge rectifier circuit is expanded and its power factor is improved.

Further, according to the present invention of claim 7, when the power supply is turned on, the drive pulse whose voltage level increases with time is output to the switching element, so that the switching element operates in the linear operation region and the switching element is overloaded. No current flows.

[0020]

[First Embodiment] The first embodiment of the present invention will be described with reference to FIG. In FIG. 1, X is a power supply circuit according to an embodiment of the present invention, and a switching regulator (constant voltage circuit) Y is connected to the subsequent stage.

In the power supply circuit X shown in FIG. 1, the bridge rectifier circuit 10 is configured to connect diodes in a bridge shape to perform full-wave rectification, and has two input terminals 10a and an output terminal 10b. The two input terminals 10a are connected to a single-phase AC power source.
A noise removing capacitor C1 is connected in parallel to the two lines 11 and 12 that connect to the single-phase AC power supply.

A choke coil L1 is connected in series to the line 11 of the two lines 11 and 12, and a line 13 connecting the output terminal 10b of the bridge rectifier circuit 10 and the switching regulator Y is connected to the line 11. , A resistor R1 for preventing inrush is connected in series.

Further, the line 1 in the subsequent stage of the resistor R1
3, one end of the capacitor C2 is connected to the capacitor C
The other end of 2 is connected to the collector of a transistor Q1 corresponding to a switching element. The emitter of the transistor Q1 is connected to the line 14 from the other output terminal 10b of the bridge rectifier circuit 10 to the switching regulator Y, and the discharging diode D1 is connected in parallel between the collector and the emitter of the transistor Q1. .

Furthermore, a rectifying diode D2 is connected in series to the line 13 in the subsequent stage of the capacitor C2, and the line 1 in the subsequent stage of the rectifying diode D2 is connected.
A capacitor C3 is connected in parallel between 3 and the line 14.

Next, the operation of the power supply circuit X of the present embodiment configured as described above will be described with reference to the waveform diagram of FIG.

Both input terminals 10a of the bridge rectifier circuit 10
In the meantime, when the AC voltage Vin having the waveform shown in FIG. 2A is input, the AC voltage Vin is full-wave rectified by the bridge rectifier circuit 10. In addition, 2 of the bridge rectification circuit 10
The rectified output that is output from the one output terminal 10b is smoothed by the capacitor C2 in the subsequent stage and becomes a DC voltage,
It is supplied to the switching regulator Y. In the switching regulator Y, the DC voltage supplied to the load is controlled to be constant.

During operation of the power supply circuit X, the drive pulse S1 having a frequency considerably higher than the frequency of the AC power supply.
Is supplied to the base of the transistor Q1 to cause the transistor Q1 to perform a switching operation.

Since the bridge rectifier circuit 10 is a circuit in which diodes are connected in a bridge shape, the voltage which can be originally supplied by the bridge rectifier circuit 10 is a so-called sine wave negative voltage portion of the AC voltage Vin. It is a full-wave rectified waveform.

On the other hand, in the steady operation state of the power supply circuit X, a predetermined voltage slightly fluctuating according to the charged electric charge is generated between both terminals of the capacitor C2.
Therefore, while the voltage that can be supplied by the bridge rectifier circuit 10 does not reach the voltage between both terminals of the capacitor C2 (20 period in FIG. 2), the switching operation of the transistor Q1 starts with the choke coil L1. It has no effect on any other factor and therefore need not be considered.

On the other hand, if the voltage that can be supplied by the bridge rectifier circuit 10 rises and exceeds the voltage between both terminals of the capacitor C2 as the AC voltage Vin changes sinusoidally (period 22 in FIG. 2). , The switching operation of the transistor Q1 affects other elements such as the choke coil L1.

That is, when the transistor Q1 is turned on, the current for charging the capacitor C2 in addition to the current supplied to the switching regulator Y also flows, so that the counter electromotive force (Eon) flows in the choke coil L1.
Occurs, and the supply voltage from the bridge rectifier circuit 10 decreases (Vin-Eon). Therefore, the capacitor C2 is not charged rapidly, but is gradually charged each time the transistor Q1 is repeatedly turned on.

When the transistor Q1 is turned off, the charging current to the capacitor C2 is rapidly stopped, so that the choke coil L1 generates a high electromotive force (Eoff) to some extent, and the bridge rectifier circuit 10 is generated by this voltage. The supply voltage from the device rises (Vin + Eoff).

Therefore, the current supplied to the switching regulator Y through the discharging diode D2 also increases, and the increase in this current contributes to the improvement of the power factor of the power supply device 1 as a whole. At this time, the capacitor C
The potential at the point A in FIG. 1 to which the positive terminal of 2 is connected is a considerably high value of Vin + Eoff−R1 · I1, but since the transistor Q1 is in the off state, this voltage causes the capacitor C2 Will never be charged.

As described above, while the voltage that can be supplied by the bridge rectifier circuit 10 is higher than the voltage between both terminals of the capacitor C2, the operation when the transistor Q1 is in the ON state as described above is performed. The operation in the off state is repeated.

If the AC voltage Vin changes further in a sinusoidal manner and the voltage that can be supplied by the bridge rectifier circuit 10 becomes lower than the voltage between both terminals of the capacitor C2 again (period 24 in FIG. 2). As in the state described above, the switching operation of the transistor Q1 has no effect on other elements again.

The current is no longer supplied from the bridge rectifier circuit 10, but instead of this, the capacitor C2 is used.
However, the charge charged when the transistor Q1 is turned on in the period 22 is supplied to the switching regulator Y via the discharging diodes D1 and D2. That is, at this time, the capacitor C2 functions as a smoothing capacitor.

By switching the transistor Q1 in this manner, the voltage having the waveform shown in FIG. 2B is applied to the two input terminals 10a of the bridge rectifier circuit 10. Then, the capacitor C2 and the transistor Q1
The voltage shown in FIG. 2C appears at both ends of the series circuit of and. In addition, as shown in FIG.
The voltage of the waveform shown in (d) appears. Further, the waveform of the current I1 flowing through the bridge rectifier circuit 10 is as shown in FIG.

In the power supply circuit X of the present embodiment, the current of the rectifier circuit, which conventionally flows only when the output voltage of the rectifier circuit exceeds the voltage across the smoothing capacitor, is shown in FIG. ), The current conduction angle of the bridge rectifier circuit 10 becomes large, and the current is limited by the choke coil L1. as a result,
The power factor of the power supply circuit X can be improved. Incidentally, in this example, it was confirmed that the power factor was 0.85.

Further, with the circuit configuration as described above, the choke coil L1 need only have an inductance of about 10 μH to 20 μH, which allows the choke coil to be made smaller and have a smaller capacity, and at the same time cost reduction. can do. Moreover, since the output voltage does not become too high, it is possible to use an inexpensive low withstand voltage switching regulator Y.

[Second Embodiment] The second embodiment of the present invention will be described with reference to FIG.
An example will be described. 3 is different from FIG. 1 in that an LFT (low frequency transformer) 16 is inserted on the input side of the bridge rectification circuit 10, and other configurations are the same as those in FIG.

Also in the second embodiment, the same effect as in the first embodiment can be obtained by the leakage inductance of the LFT 16.

[Third Embodiment] FIG. 4 shows a third embodiment of the present invention.
An example will be described. 4 is different from FIG. 1 in that the line 13 connecting one output terminal 10b of the bridge rectifier circuit 10 and the switching regulator Y is
The choke coil L1 is connected in series.

Also in the third embodiment, the same effect as that of the first embodiment can be obtained.

[Fourth Embodiment] An embodiment of the present invention will be described with reference to FIG. 5 is different from FIG. 1 in that the choke coil L1 is connected in series between the capacitor C2 and the collector of the transistor Q1.

In the fourth embodiment, the AC voltage Vin input to the bridge rectifier circuit 10 is constant, and accordingly, the capacitor C2 when the transistor Q1 is on.
Is charged with Vin-Eon, and transistor Q
1 is off, the potential at the point A in FIG. 1 to which the positive terminal of the capacitor C2 is connected is Vin-Eon.
-Vq1sat. Therefore, the same effect as the first embodiment can be obtained.

[Fifth Embodiment] The fifth embodiment of the present invention will be described with reference to FIG.
An example will be described. 6 is different from FIG. 1 in that the choke coil L1 is connected in series between one end of the capacitor C2 and the line 13.

In the fourth and fifth embodiments, when there is no backflow of current from the switching regulator Y side, the rectifying diode D2 may be omitted as shown in FIGS. 7 and 8. .

[Sixth Embodiment] The sixth embodiment of the present invention will be described with reference to FIG.
An example will be described. In FIG. 9, between the two output terminals 10b of the bridge rectifier circuit 10, a capacitor C2, a primary side of the pulse transformer T, and a switching element MO.
A series circuit with the S-type field effect transistor Q2 is connected. Further, a series circuit of the secondary side of the pulse transformer T and the discharging diode D3 is connected in parallel to this series circuit.

A constant voltage Vcc is supplied to the drive control circuit 11, and the drive control circuit 11 outputs a drive pulse to the gate terminal of the MOS field effect transistor Q2.

In the above structure, the bridge rectifier circuit 10
The rectified output rectified by is charged in the capacitor C2 when the MOS field effect transistor Q2 is turned on, and an electromotive force is generated in the pulse transformer T by this, and is discharged through the discharging diode D3. When the MOS field effect transistor Q2 is off, the current charged in the capacitor C2 is discharged.

Here, when connected to a power source having a sufficiently low impedance and turned on, a large current flows in the rectified output of the bridge rectifier circuit 10. Then, the capacitor C2
Since an excessive charging current flows to the MOS field effect transistor Q2, the MOS type field effect transistor Q2 is instantly destroyed by the overcurrent. In order to prevent the destruction of the MOS field effect transistor Q2, a slow start of a pause period control system is usually used.

In the slow start of this pause period control method, as shown in FIG. 10B, the pulse width of the drive pulse is initially narrowed and gradually widened with time. However, as shown in part A of FIG. 10, the drain current of the MOS field effect transistor Q2 is extremely small at a portion where the rectified output is low, and a large drain current flows at the time of the next driving, so that an excessive current is sufficiently supplied. I can't control it. Therefore, in order to solve this, the drive control circuit 1
1 was improved as follows.

[First Improved Example of Drive Control Circuit] A first improved example of the drive control circuit 11 will be described with reference to FIGS. 11 and 12.

In FIG. 11, the drive control circuit 11 is MO
It is for driving an S-type field effect transistor or an IGBT, and has a pulse generator 12, and the pulse generator 12 is supplied with a constant voltage Vcc at the same time when the power is turned on. Pulse generator 1
2 turns on / off the transistor Q3 by a pulse internally generated, and the drive power supply voltage Vc of the transistor Q3 is supplied from the soft start power supply unit 13.

The soft start power supply unit 13 is composed of a series circuit of a time constant resistor R2 and a capacitor C4, and the common connection point voltage of the time constant resistor R2 and the capacitor C4 is supplied as a drive power source voltage Vc of the transistor Q3. There is. The drive pulse of the transistor Q3 is output via the turn-off time shortening circuit 14.

In the above structure, when the power is turned on, the pulse generator 12 is immediately supplied with the constant voltage Vcc, but the transistor Q3 is supplied with the drive power supply voltage Vc which gradually increases with time as shown in FIG. To be done. Therefore, the drive pulse of the transistor Q3 has a constant pulse width as shown in FIG. 10D, but its voltage level gradually increases with time. Therefore, the switching element which is turned on / off by this drive pulse operates in a linear region, and its drain current (or collector current) gradually increases with time and flows to some extent even in a portion where the rectified output of the bridge rectifier circuit is small.
Therefore, a large drain current does not flow during the next driving, so that an excessive current can be sufficiently suppressed.

[Second Modified Example of Drive Control Circuit] A second modified example of the drive control circuit 11 will be described with reference to FIG. Figure 1
In FIG. 3, the drive control circuit 11 is for driving a MOS field effect transistor or an IGBT, and a totem pole circuit 15 is used to generate a drive pulse. Therefore, the turn-off time shortening circuit as in the first improved example is unnecessary. The second modified example also has substantially the same action and effect as the first modified example.

[Third Improvement Example of Drive Control Circuit] A third improvement example of the drive control circuit 11 will be described with reference to FIG. Figure 1
4, the drive control circuit 11 is the most suitable for driving a bipolar transistor, and the pulse transformer T
Create a drive pulse using ₁ . Incidentally, 16 is a differentiating circuit. The third modified example also has substantially the same actions and effects as the first modified example.

[0059]

As described above, according to the present invention, a bridge rectifier circuit having two input terminals to which an AC voltage is applied and two output terminals for supplying a rectified voltage to the outside. A coil connected to one input terminal of the bridge so that the AC voltage passes, and a series circuit of a capacitor and a switching element connected between two output terminals of the bridge rectifier circuit. .

Therefore, by switching the charge current from the bridge rectifier circuit to the capacitor by the switching element, even if the output voltage of the bridge rectifier circuit drops to the voltage across the capacitor, the current flows through the bridge rectifier circuit. The current conduction angle of the bridge rectifier circuit can be widened, and the power factor of the bridge rectifier circuit can be improved with a coil having a small capacity. Therefore, it is possible to reduce the size and cost of the parts, and it is possible to use an inexpensive and low withstand voltage switching regulator or the like.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram of voltage and current appearing in each part in the power supply circuit of FIG.

FIG. 3 is a main part configuration diagram of a power supply circuit according to a second embodiment of the present invention.

FIG. 4 is a main part configuration diagram of a power supply circuit according to a third embodiment of the present invention.

FIG. 5 is a main part configuration diagram of a power supply circuit according to a fourth embodiment of the present invention.

FIG. 6 is a main part configuration diagram of a power supply circuit according to a fifth embodiment of the present invention.

FIG. 7 is a main part configuration diagram showing a modified example of the power supply circuit according to the fourth embodiment of the present invention.

FIG. 8 is a main part configuration diagram showing a modified example of the power supply circuit according to the fifth embodiment of the invention.

FIG. 9 is a main part configuration diagram of a power supply circuit according to a sixth embodiment of the present invention.

FIG. 10 is a time chart.

FIG. 11 is a circuit diagram of a drive control circuit of a first improved example.

FIG. 12 is a graph showing characteristics of a drive power supply voltage and a drive current of a switching element.

FIG. 13 is a circuit diagram of a drive control circuit of a second improved example.

FIG. 14 is a circuit diagram of a drive control circuit of a third improved example.

FIG. 15 is a configuration diagram of a conventional power supply circuit.

[Explanation of symbols]

 10 ... Bridge rectification circuit 16 ... LFT C2 ... Capacitor D1 ... Discharge diode D2 ... Rectification diode L1 ... Choke coil Q1 ... Transistor (switching element) X ... Power supply circuit T ... Pulse transformer 11 ... Drive control circuit 13 ... Soft start power supply Department

Claims (7)

[Claims] 1. A bridge rectifier circuit having two input terminals to which an AC voltage is applied, and two output terminals for supplying a rectified voltage to the outside, and the bridge rectifier to allow the AC voltage to pass therethrough. A power supply circuit comprising: a coil connected to one input terminal of the circuit; and a series circuit of a capacitor and a switching element connected between two output terminals of the bridge rectifier circuit. 2. The power supply circuit according to claim 1, wherein the coil is a choke coil or an LFT. 3. A discharge diode connected in parallel with the switching element and connected in series with the capacitor, a discharge voltage of the capacitor and a voltage supplied from one output terminal of the bridge rectifier circuit. 3. The power supply circuit according to claim 1, further comprising a rectifying diode connected to a connection portion between the capacitor and one output terminal of the bridge rectifying circuit. 4. A bridge rectifier circuit having two input terminals to which an AC voltage is applied and two output terminals for supplying a rectified voltage to the outside, and between two output terminals of this bridge rectifier circuit. A power supply circuit comprising a series circuit including a capacitor, a coil, and a switching element connected to the power supply circuit. 5. A discharge diode connected in parallel with the switching element and connected in series with the capacitor, a discharge voltage of the capacitor and a voltage supplied from one output terminal of the bridge rectifier circuit. 5. The power supply circuit according to claim 4, further comprising: a rectifying diode connected to a connecting portion between the capacitor and one output terminal of the bridge rectifying circuit. 6. A bridge rectifier circuit having two input terminals to which an AC voltage is applied and two output terminals for supplying a rectified voltage to the outside, and between two output terminals of this bridge rectifier circuit. And a series circuit of a capacitor connected to the primary side of the pulse transformer and a switching element, and a series circuit of the secondary side of the pulse transformer and a discharging diode connected in parallel to the series circuit. Characteristic power supply circuit. 7. The power supply according to claim 1, 4 or 6, wherein the drive control circuit for the switching element is provided with a soft start power supply section for gradually increasing the level of the drive power supply voltage when the power is turned on. circuit.