JP2002058249A - Ac-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an AC-DC converter which can improve conversion efficiency and power factor by suppressing the ripple components to the utmost with a simple constitution. SOLUTION: An auxiliary transformer T2 is connected in parallel to a transformer T1 which boosts or steps down the AC current generated by a switching transistor 3 to a predetermined value, and a capacitor is connected in series to the primary winding of this auxiliary transformer T2 and besides in parallel with the above switching transistor 3, and a feed back control means controls the switching transistor, based on the DC current outputted through a rectifying and smoothing circuit from the above transformer, so this AC-DC converter discharges the charge charged in the capacitor at the section of its trough, so this can suppress the output ripple in the DC current or voltage of the output to the utmost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC-DC converter for converting an AC current into a DC current and outputting the same, and more particularly to an AC-DC converter for increasing the input power factor and stabilizing the output DC current. About.

[0002]

2. Description of the Related Art Conventionally, there has been an AC-DC converter of this type shown in FIGS. 5 is an overall circuit configuration diagram of a conventional AC-DC converter, FIG. 6 is a configuration diagram of a control circuit for controlling the switching transistor shown in FIG. 5, and FIG. 7 is a timing chart of the AC-DC converter shown in FIG. Is shown.

In FIG. 1, a conventional AC-DC converter includes an AC power supply 100 for supplying a commercial AC current iin, a noise filter 1 for filtering a noise component of the AC current iin, and an AC current after filtering. A rectifier circuit 2 comprising a bridge circuit of a rectifying diode; a charging circuit 8 for charging the rectified DC current at a predetermined timing; and a switching transistor for converting the DC current output from the rectifier circuit 2 into a high-frequency AC current Q1 and switching transistors Q3 and Q4 for controlling charging and discharging of the capacitor C8 of the charging circuit 8.
A transformer T1 that transforms the AC current converted by the switching transistor Q1 with a difference ratio n11: n2 and outputs an AC current; and a rectifier smoother that rectifies and smoothes the AC current output from the transformer T1 and outputs the rectified smoothed current. And a circuit 60.

The switching transistors Q1, Q3,
A control circuit 9 controls the turn-on / turn-off operation of Q4. The control circuit 9 controls the input voltage Vi of the AC power supply 100, the charging voltage of the capacitor C8 of the charging circuit 8, the current iLi of the inductance L8, and the output voltage. Vo are respectively input, and arithmetic processing is performed based on each input to output a control signal to the switching transistors Q1, Q3, Q4.

Next, a conventional AC-DC based on the above configuration is described.
The AC-DC conversion operation of the converter will be described.
An input power Pi based on the input voltage Vi and the input current Ii
Fluctuates up and down with respect to the output power Po. When the input power Pi is higher than the output power Po, FIG.
The capacitor C of the charging circuit 8 controlled as shown in FIG.
The current ics flows through 8, and the electric charge is charged.

When the input power Pi is lower than the output power Po, the electric charge charged in the capacitor C8 is released, and the valley generated by the ripple of the output voltage Vo is discharged. To reduce the ripple voltage.

[0007]

Since the conventional AC-DC converter is constructed as described above, three switching transistors Q1, Q3, Q4 are provided, and these switching transistors Q1, Q3, Q4 are connected. The control circuit 9 must control each of them individually and independently, so that the circuit configuration is complicated and the control operation is also complicated. Further, in the conventional AC-DC converter, no consideration is given to surge energy generated in the transformer T1, and an RC snubber or the like must be separately connected in order to prevent the influence of this surge energy.
When the surge energy is consumed by the resistance of the RC snubber or the like, there is a problem that the AC-DC conversion efficiency is extremely reduced.

As another conventional AC-DC converter, a power factor improving type converter is inserted between a rectifier circuit on an input power supply side and an input capacitor, and an AC-DC converter is connected to a stage subsequent to the input capacitor. Although there is a two-stage type, there is a problem that the circuit configuration becomes large, the power efficiency decreases, and the manufacturing cost increases. Also,
Although there is a single-stage AC-DC converter using a power factor correction type converter, there is a problem that the output current or voltage ripple is large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an AC-D capable of improving the conversion efficiency and the power factor by suppressing the ripple component with a simple circuit configuration as much as possible.
It is intended to provide a C converter.

[0010]

Means for Solving the Problems An AC current supplied from a power supply side is converted into a DC current by a rectifier circuit, and the DC current is converted into a high-frequency AC current by a switching transistor.
In an AC-DC converter that boosts or steps down the high-frequency AC current with a transformer and outputs the boosted or stepped-down high-frequency AC current through a rectifying and smoothing circuit, outputs a DC current to a primary winding of the transformer. An auxiliary transformer in which a side winding is connected in series, a secondary winding is connected in parallel to a secondary winding of the transformer, and an auxiliary transformer is connected in series to a primary winding of the auxiliary transformer; A capacitor connected in parallel with the switching transistor;
Feedback control means for performing feedback control of the switching transistor based on the output DC voltage value, current value, or each of the changes.

As described above, in the present invention, the auxiliary transformer is connected in parallel to the transformer for boosting or stepping down the alternating current generated by the switching transistor to a predetermined value, and the auxiliary transformer is connected in series with the primary winding of the auxiliary transformer. Since a capacitor is connected in parallel to the switching transistor, and the feedback control means controls the switching transistor based on a DC current output from the transformer via a rectifying / smoothing circuit, the capacitor is charged. Since the electric charge is released at the valley of the pulsating flow, the output ripple in the output DC current or voltage can be suppressed as small as possible. Further, with this circuit configuration, it is possible to improve the power factor by reducing the waveform distortion of the input current while keeping the output ripple as small as possible.

Further, in the AC-DC converter according to the present invention, the feedback control means performs feedback control at a frequency higher than the frequency of the AC voltage supplied from the power supply, if necessary. As described above, in the present invention, since the feedback control means controls the switching transistor at a frequency higher than the frequency of the AC power supply, the response of the output fluctuation becomes slow, and the peak of the DC current having the output ripple is reduced. The switching transistor is controlled so as to lower the peak value of the AC current by the feedback signal based on the portion of the above, and to increase the AC current by the feedback signal based on the valley portion of the DC current having the output ripple. Ripple in the output DC current can be more reliably suppressed.

Further, the AC-DC converter according to the present invention is connected in parallel with the switching transistor as necessary, and the ON / OFF of the switching transistor is turned on.
An auxiliary switching transistor that is controlled so as to perform complementary ON / OFF operations in conjunction with an OFF operation, and an auxiliary capacitor connected in series to the auxiliary switching transistor and connected in parallel to the switching transistor It is. As described above, in the present invention, the surge energy due to the parasitic inductance of the transformer and the auxiliary transformer is charged to the capacitor and the auxiliary capacitor by controlling the driving of the auxiliary switching transistor connected in parallel with the switching transistor in a complementary manner to the switching transistor. This allows the charged electric charge to be regenerated to the output side via the auxiliary transformer, thereby improving the AC-DC conversion efficiency and improving the power factor.

In the AC-DC converter according to the present invention, if necessary, the auxiliary switching transistor controls the switching transistor to turn on at zero voltage switching by using the charge charged in the auxiliary capacitor. Is what is done. As described above, in the present invention, since the auxiliary switching transistor is drive-controlled so that the switching transistor performs zero voltage switching, the switching transistor can be protected from a surge voltage due to the parasitic inductance of the transformer and the auxiliary transformer, and the efficiency can be increased. Can be achieved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment of the Present Invention) Hereinafter, an AC-DC converter according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an overall circuit configuration diagram of an AC-DC converter according to the present embodiment,
FIG. 2 shows a timing chart of the operation of the AC-DC converter shown in FIG. 1 in a low frequency region.

In each of the drawings, the AC-
The DC converter includes a noise filter 1 that removes a noise component of the AC current iin supplied from the commercial AC power supply 100.
A rectifier circuit 2 comprising a bridge circuit of a diode for rectifying the AC current iin from which the noise component has been removed; A switching transistor 3 comprising an FET; a transformer T1 for increasing / decreasing a high-frequency AC voltage generated by the switching transistor 3 to a predetermined voltage value; and a primary winding n1 with respect to a primary winding n1 of the transformer T1. n21 is connected in series, and an auxiliary transformer T2 is connected in parallel with a secondary winding n22 of the secondary winding n2 of the transformer T1.
And a capacitor C4 connected in series to the primary winding n21 and connected in parallel to the switching transistor 3, and rectifies and smoothes the output current induced in the transformer T1 and the auxiliary transformer T2. Rectifying / smoothing circuit 6 and a feedback signal based on the output DC voltage Vo modulates switching transistor 3 by pulse width modulation (P
WM) and a PWM control unit 7 for performing the control.

The PWM control unit 7 includes a commercial AC power supply 10
The feedback control is performed at a frequency higher than the commercial frequency of the AC voltage Vin supplied from 0 (e.g., 600 Hz for 60 Hz), so that P is inversely proportional to the increase or decrease of the DC voltage Vo.
This is a configuration for executing WM control. Next, an AC-DC conversion operation of the AC-DC converter according to the present embodiment will be described. First, an AC voltage Vi is supplied from the commercial AC power supply 100.
n, an AC current iin is input, and the rectifier circuit 2 rectifies the AC current iin to generate a low-frequency pulsating voltage. The low-frequency pulsating voltage is input to the switching transistor 3 and the transformer T1, and the switching transistor 3
Is a high frequency level (for example, a switching frequency of 20 kHz).
z), a high-frequency alternating current is generated from the low-frequency pulsating voltage.

The transformer T1 steps up / down the input high-frequency alternating current according to the turns ratio of the primary winding n1 and the secondary winding n2. On the other hand, the high-frequency alternating current is charged to the capacitor C4 through the primary winding of the auxiliary transformer T2, and the capacitor C4 discharges the electric charge charged at the valley of the waveform in the low-frequency pulsating voltage, and the discharge current Outputs ic2.

The emission current ic2 is input to the primary winding of the auxiliary transformer T2, and the auxiliary transformer T2 outputs an alternating current induced in the secondary winding by the emission current ic2. The AC current ic21 from the auxiliary transformer T2 and the emission current i2 output from the transformer T1 (corresponding to a current obtained by multiplying the emission current i1 by the reciprocal of the turns ratio of the transformer T1).
Are added, and the DC voltage Vo with the ripple component ΔVo suppressed as much as possible is output via the rectifying / smoothing circuit 6 as shown in FIG.

(Second Embodiment of the Present Invention) The second embodiment of the present invention
FIGS. 3 and 4 show an AC-DC converter according to the embodiment of FIG.
It will be described based on. FIG. 3 shows the AC according to this embodiment.
FIG. 4 is a timing chart showing the operation of the AC-DC converter shown in FIG.

In each of the drawings, the AC-
The DC converter includes a commercial AC power supply 1, a rectifier circuit 2, a switching transistor 3, and a transformer T as in the AC-DC converter according to the first embodiment shown in FIG.
1, auxiliary transformer T2, capacitor C4, rectifying and smoothing circuit 6
And a PWM control unit 7 in common. In addition to this configuration,
A configuration including an active snubber circuit 5 connected in parallel to the switching transistor 3 and controlled by a PWM control unit 7 to turn on / off in a complementary manner in conjunction with the turn-on / off operation of the switching transistor 3 It is.

The active snubber circuit 5 has a MOS-
Auxiliary switching MOS- consisting of FET transistors
FET Q2 and this auxiliary switching MOS-FET Q2
And a snubber capacitor C5 connected in series to the subsequent stage. This auxiliary switching MOS-FE
TQ2 is a parasitic capacitor Cs2 generated as a parasitic capacitance.
Are connected in parallel, and a diode Ds2 generated as a body diode is connected in parallel reverse bias.

The switching transistor 30 has an M
Main switching MO composed of OS-FET transistor
The main switching MOS-
A parasitic capacitor Cs generated as a parasitic capacitance in the FET Q1
1 are connected in parallel, and a diode Ds1 generated as a body diode is connected with a parallel reverse bias.

As in the case of the first embodiment, the PWM control unit 7 sets the pulse width DTs to the set pulse width DTs.
Main switching MOS-FE with drive signal based on M control
TQ1 is driven and controlled. Further, this control signal is generated by a delay circuit incorporating dead times t1, t2 and t6 and t7 corresponding to a predetermined delay time, and the generated drive signal is inverted by a built-in inverter. This is a configuration for controlling the auxiliary switching MOS-FET Q2.

Next, the AC-DC conversion operation of the AC-DC converter according to the present embodiment based on the above configuration will be described by dividing into the operation in the low frequency region and the operation in the high frequency region. First,
In the operation in the low frequency region, as shown in FIG. 2, the commercial low frequency AC current iin supplied from the commercial AC power supply 100.
(AC voltage Vin) is the noise filter 1 and the rectifier circuit 2
And rectified into a pulsating voltage.

The pulsating voltage is input to the transformer T1 and the switching transistor 30, and the main switching MOS-FET Q1 of the switching transistor 30 performs a switching operation at a high-frequency level (for example, 20 kHz or more) timing, and a high-frequency pulse current i1 Convert to The converted high-frequency AC pulse current i1 having the amplitude of the pulsating current is stepped up and down to a predetermined voltage by the transformer T1, and the DC voltage Vo is output to the load (not shown) through the rectifying and smoothing circuit 6.

When the main switching MOS-FET Q1 of the switching transistor 30 is turned off, surge energy generated by the parasitic inductance of the transformer T1 and the auxiliary transformer T2 charges the snubber capacitors C5 and C4 of the active snubber circuit 5. This charged electric charge is a high-frequency AC pulse current i having a pulsating amplitude output from the transformer T1.
The signal is output from the primary winding of the auxiliary transformer T2 so as to compensate for the valley portion of the waveform in 1 and is output to the load side via the rectifying and smoothing circuit 6.

Next, as for the operation in the high frequency region, as shown in FIG.
This is a period during which ETQ1 is turned on and the auxiliary switching MOS-FET Q2 of the active snubber circuit 5 is turned off. In this case, an exciting current flows through the transformer T1, and energy is stored in the primary winding. At the same time, the exciting current flows through the auxiliary transformer T2 by the energy stored in the capacitor C4, and the energy is stored in the primary winding of the auxiliary transformer T2.

The operation periods t2 and t3 are the main switching MO
S-FET Q1 and auxiliary switching MOS-FET Q2
Are dead time periods in which both are off. A charging current flows through the parasitic capacitor Cs of the main switching MOS-FET Q1, and when the charging of the parasitic capacitor Cs ends, the output diode D61 turns on, and the energy stored on the primary side of the transformer T1 is transferred to the load side. Subsequently, the surge energy generated in the main switching MOS-FET Q1 is
It is absorbed by the capacitors C4 and C5 through the body diode Ds2 of Q2. On the other hand, surge energy generated by the parasitic inductance of the auxiliary transformer T2 is absorbed by the capacitor C5 through the route of the body diode Ds2 and the capacitor C5. Therefore, the main switching MO
The voltage across the S-FET Q1 will be clamped.

During the operation periods t4 and t5, the main switching MOS-FET Q1 of the switching transistor 30 is turned off and the auxiliary switching M of the active snubber circuit 5 is turned off.
This is the period when the OS-FET Q2 is in the ON state. During this period, while the body diode Ds2 of the auxiliary switching MOS-FET Q2 is on, the auxiliary switching M
By turning on OS-FET Q2, zero voltage switching is realized.

In the secondary winding of the transformer T1, the output diode D61 continues to be turned on, and the energy continues to be transmitted to the load side. During this period, the diode D62 is turned on, and the energy (energy due to the charge of the capacitor C4) stored in the auxiliary transformer T2 is output to the load side. The surge energy stored in the capacitor C5 is also output to the load during this period. Since the energy output from the auxiliary transformer T2 during this period compensates for the low-frequency ripple, the low-frequency ripple of the output voltage is reduced.

During the operation period t6, the auxiliary switching MOS
-Since the ON state of the FET Q2 continues, an exciting current flows through the auxiliary transformer T2. By turning off the auxiliary switching MOS-FET Q2 after this period, the main switching MOS-FET Q1 is turned on during the operation period t7.
The energy stored in the parasitic capacitor Cs1 is extracted.

During the operation period t8, the main switching MOS-
When the discharge of the parasitic capacitor Cs1 of the FET Q1 ends,
The body diode Ds1 of the main switching MOS-FET Q1 is turned on. Zero voltage switching is performed by turning on the main switching MOS-FET Q1 during the ON period of the body diode Ds1. In the AC-DC converter according to each of the embodiments, the switching transistor is configured by a MOS-FET, but may be configured by a bipolar transistor, an IGBT, or the like. In this case, it is necessary to connect the diodes in anti-parallel.

Also, any combination of polarities other than the respective polarities in the primary and secondary windings of the auxiliary transformer T2 of the AC-DC converter according to each of the above embodiments may be used. Further, although the driving control of the switching transistor 3 of the AC-DC converter according to each of the above embodiments is performed by the PWM control by the PWM control unit 7, the feedback control may be performed by another control method, for example, the frequency control. it can.

The AC-DC according to the second embodiment
An active snubber circuit 5 in the converter is connected in parallel with the switching transistor 3 and is controlled by a PWM control unit 7 to turn on and off in a complementary manner in conjunction with the turning on and off operations of the switching transistor 3. However, a configuration in which the switching transistor 3 and the capacitor C4 are connected in parallel may be employed. Also in this case, the same operation and effect are achieved by being controlled by the PWM control unit 7 in the same manner as described above.

The diodes D61 and D62 connected to the output side of the transformer T1 and the auxiliary transformer T2 are MOS-F
Instead of an ET transistor, a synchronous rectification method can be used.

[0037]

According to the present invention, an auxiliary transformer is connected in parallel to a transformer for boosting or stepping down an alternating current generated by a switching transistor to a predetermined value, and the auxiliary transformer is connected in series with the primary winding of the auxiliary transformer. Connect a capacitor in parallel to the switching transistor,
Since the feedback control means controls the switching transistor based on the DC current output from the transformer via the rectifying and smoothing circuit, the electric charge charged in the capacitor is discharged at the valley of the pulsating flow. The output ripple in the output DC current or voltage can be suppressed as small as possible. Further, with this circuit configuration, there is an effect that the power factor can be improved by reducing the waveform distortion of the input current while keeping the output ripple as small as possible.

Further, in the present invention, since the feedback control means controls the switching transistor at a frequency higher than the frequency of the AC power supply, the response of the output fluctuation is delayed, and the DC current having the output ripple is reduced. The switching transistor is driven and controlled such that the switching transistor lowers the peak value of the AC current by the feedback signal based on the peak portion of the DC current and increases the AC current by the feedback signal based on the valley portion of the DC current having the output ripple. This has the effect that ripples in the output DC current can be suppressed more reliably.

Further, in the present invention, the surge energy due to the parasitic inductance of the transformer and the auxiliary transformer is supplied to the capacitor and the auxiliary capacitor by controlling the driving of the auxiliary switching transistor connected in parallel with the switching transistor in a complementary manner to the switching transistor. After charging, the charged electric charge can be regenerated to the output side via the auxiliary transformer.
This has the effect of improving the conversion efficiency and improving the power factor.

Further, in the present invention, since the auxiliary switching transistor is driven and controlled so that the switching transistor performs zero voltage switching, the switching transistor can be protected from a surge voltage due to the parasitic inductance of the transformer and the auxiliary transformer, and can have high efficiency. This has the effect that the conversion can be achieved.

[Brief description of the drawings]

FIG. 1 is an overall circuit configuration diagram of an AC-DC converter according to a first embodiment of the present invention.

FIG. 2 is a timing chart of an operation of the AC-DC converter shown in FIG. 1 in a low frequency region.

FIG. 3 is an overall circuit configuration diagram of an AC-DC converter according to a second embodiment of the present invention.

FIG. 4 is a timing chart of an operation in the AC-DC converter shown in FIG. 3;

FIG. 5 is an overall circuit configuration diagram of a conventional AC-DC converter.

6 is a configuration diagram of a control circuit that controls the switching transistor shown in FIG.

7 is a timing chart of the AC-DC converter shown in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 noise filter 2 rectifier circuit 3 switching transistor 5 active snubber circuit 6, 60 rectifying smoothing circuit 7 PWM control unit 8 charging circuit 9 control circuit 71 delay circuit 72 inverter 100 AC power supply

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Nobuyuki Moriyama 3144-1, Ippongi Shimoizumi, Kuboizumicho, Saga City, Saga Prefecture F term (reference) 5H006 AA01 AA02 AA07 CA01 CA07 CA12 CB01 CB03 CC02 DA02 DA04 DC05 5H730 AA01 AA18 AS01 BB43 BB57 CC01 DD04 DD32 DD41 EE44 FG05 XX12

Claims (4)

[Claims] An AC current supplied from a power supply side is converted into a DC current by a rectifier circuit, the DC current is converted into a high-frequency AC current by a switching transistor, and the high-frequency AC current is boosted or stepped down by a transformer and output. In the AC-DC converter for outputting the DC current through the rectifying and smoothing circuit of the stepped-up or stepped-down high-frequency AC current, a primary winding is connected in series to a primary winding of the transformer, and An auxiliary transformer in which a secondary winding is connected in parallel to a secondary winding; a capacitor connected in series to a primary winding of the auxiliary transformer, and connected in parallel to the switching transistor; And a feedback control unit that performs feedback control of the switching transistor based on the DC voltage value, the current value, or the respective changes. Characteristic AC-DC
converter. 2. The AC-DC converter according to claim 1, wherein said feedback control means performs feedback control at a frequency higher than a frequency of an AC voltage supplied from said power supply. . 3. The AC-DC converter according to claim 1, wherein said AC-DC converter is connected in parallel to said switching transistor, and is turned on complementaryly in conjunction with the on / off operation of said switching transistor. An auxiliary switching transistor controlled to be turned off, and connected in series to the auxiliary switching transistor;
An AC-DC converter, comprising: an auxiliary capacitor connected in parallel to the switching transistor. 4. The AC-DC converter according to claim 3, wherein the auxiliary switching transistor controls the switching transistor to turn on with zero voltage switching by using a charge charged in the auxiliary capacitor. AC-DC converter characterized by being performed.