JP3496069B2 - AC-DC converter - Google Patents

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 that converts an alternating current into a direct current and outputs the converted direct current, and particularly to an AC-DC converter that achieves a high power factor of the input and a stable direct current output. Regarding

[0002]

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

In the figure, 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 the filtering process. A rectifying circuit 2 composed of a diode bridge circuit for rectifying, 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 rectifying circuit 2 into a high frequency AC current. Q1 and switching transistors Q3 and Q4 for controlling charging / discharging of the capacitor C8 of the charging circuit 8.
A transformer T1 for transforming the alternating current converted by the switching transistor Q1 with a difference number ratio n11: n2 to output the alternating current; and a rectifying and smoothing for rectifying and smoothing the alternating current output from the transformer T1 for output. And a circuit 60.

The switching transistors Q1, Q3,
The 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 is input to each of them, arithmetic processing is performed on the basis of each input, and a control signal is output to the switching transistors Q1, Q3 and Q4.

Next, a conventional AC-DC based on the above configuration
The AC-DC conversion operation of the converter will be described.
Input power Pi based on the input voltage Vi and the input current Ii
Is fluctuating up and down with respect to the output power Po, and 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 to 8, and the electric charge is charged.

Further, when the input power Pi is lower than the output power Po, the charge charged in the capacitor C8 is discharged, and the released charge is generated in the valley portion generated by the ripple of the output voltage Vo. Is used to reduce the ripple voltage.

[0007]

Since the conventional AC-DC converter is constructed as described above, three switching transistors Q1, Q3 and Q4 are arranged and the switching transistors Q1, Q3 and Q4 are arranged. The control circuit 9 must individually and independently control the circuit, which complicates the circuit configuration and complicates the control operation. Further, the conventional AC-DC converter does not consider surge energy generated in the transformer T1 at all, and an RC snubber or the like must be separately connected in order to prevent the influence of the surge energy.
As described above, when the surge energy is consumed by the resistance of the RC snubber or the like, there is a problem that the conversion efficiency of AC-DC is extremely reduced.

As another conventional AC-DC converter, a power factor improving converter is inserted between the rectifier circuit on the input power source side and the input capacitor, and the AC-DC converter is connected to the latter stage of the input capacitor. Although there is a two-stage type, there is a problem that the circuit configuration becomes large, the power efficiency is lowered, and the manufacturing cost becomes high. Also,
Although there is a one-stage AC-DC converter that uses a power factor correction converter, it has a problem that the output current or voltage ripple is large.

The present invention has been made in order to solve the above problems, and AC-D capable of suppressing the ripple component as much as possible and improving the conversion efficiency and the power factor with a simple circuit configuration.
An object is to provide a C converter.

[0010]

AC-DC according to the present invention
The converter converts the alternating current supplied from the power supply side into a pulsating direct current with a rectifier circuit, converts the direct current into a high frequency alternating current with a switching transistor, and steps up or down the high frequency alternating voltage with a transformer. outputs Te, the AC-DC converter that outputs a DC current to the step-up or step-down high-frequency ac through rectifying and smoothing circuit, the primary winding to the primary winding of the transformer are connected in series, the transformer The secondary winding is connected in parallel to the secondary winding of the
An auxiliary transformer that adds a frequency alternating current and outputs to the rectifying and smoothing circuit, and is connected in series to the primary winding of the auxiliary transformer and connected in parallel to the switching transistor, and the charged electric charge is pulsated at the output side. Of direct current
A capacitor that discharges to the output side through the auxiliary transformer at the valley portion, and feedback control that feedback-controls the switching transistor based on the output DC voltage value, current value, or each variation. And means.

As described above, in the present invention, the rectifier circuit is used.
Generating a high-frequency ac current Ri by the switching transistor from the DC current of the converted ripple, each of the transformer for boosting or stepping down the voltage of the AC to a predetermined <br/> value and the auxiliary transformer
Primary windings are connected in series and each secondary winding is connected in parallel.
A capacitor is connected in series with the primary winding of the auxiliary transformer and in parallel with the switching transistor, and switching is performed based on the DC current output from the transformer and the auxiliary transformer through the rectifying / smoothing circuit. Since the transistor is controlled by the feedback control means, the electric charge charged in the capacitor can be discharged to the output side through the auxiliary transformer in the valley portion of the pulsating current.
Becomes, Ru can as small as possible suppression output ripple dc current or voltage at the output. Also, with this circuit configuration,
The power factor can be improved by reducing the waveform distortion of the input current while keeping the output ripple as small as possible.

Also, 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 source, if necessary. As described above, in the present invention, the feedback control means performs feedback control on the switching transistor at a frequency higher than the frequency of the AC power source, so that the response of the output fluctuation is delayed and the peak of the DC current having the output ripple is generated. The feedback signal based on the part of Fig. 2 will drive the switching transistor to lower the peak value of the alternating current, and the feedback signal based on the part of the valley of the direct current with output ripple will drive the switching transistor to increase the alternating current. Ripple in the output DC current can be suppressed more reliably.

Further, the AC-DC converter according to the present invention may include a switching transistor and an auxiliary transistor if necessary .
Rutotomoni connected in parallel to the lance of the primary winding,
An auxiliary switching transistor that is connected in series to the capacitor and that is controlled to perform a complementary on / off operation in conjunction with the on / off operation of the switching transistor, and is connected in series to the auxiliary switching transistor. And an auxiliary capacitor connected in parallel with the primary winding of the switching transistor and the auxiliary transformer . As described above, in the present invention, the auxiliary switching transistor connected in parallel to the switching transistor is drive-controlled in a complementary manner with the switching transistor, so that the surge energy due to the parasitic inductance of the transformer and the auxiliary transformer is charged in the capacitor and the auxiliary capacitor. The charged electric charge can be regenerated to the output side through the auxiliary transformer, so that the conversion efficiency of AC-DC can be improved and the power factor can be improved.

Further, in the AC-DC converter according to the present invention, the auxiliary switching transistor is controlled to use the electric charge charged in the auxiliary capacitor so that the switching transistor is turned on by zero voltage switching, if necessary. It is what is done. As described above, in the present invention, since the auxiliary switching transistor is drive-controlled so that the switching transistor has zero voltage switching, the switching transistor can be protected from the surge voltage due to the parasitic inductance of the transformer and the auxiliary transformer and high efficiency can be achieved. Can be achieved.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment of the Invention) An AC-DC converter according to a first embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is an overall circuit configuration diagram of the 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 the low frequency region.

In each of the above drawings, the AC-
The DC converter is a noise filter 1 that removes a noise component of the AC current iin supplied from the commercial AC power supply 100.
And a rectifier circuit 2 composed of a diode bridge circuit for rectifying the AC current iin from which the noise component has been removed, and a MOS- which performs high-frequency switching so that an average value generates an AC current from the rectified pulsating current i1. A switching transistor 3 composed of an FET, a transformer T1 for stepping up / down a high frequency AC voltage generated by the switching transistor 3 to a predetermined voltage value, and a primary side winding with respect to a primary side winding n1 of the transformer T1. Auxiliary transformer T2 in which n21 is connected in series and the secondary winding n22 is connected in parallel to the secondary winding n2 of the transformer T1.
And the output current induced in the capacitor C4 connected in series with the primary winding n21 and connected in parallel with the switching transistor 3, the transformer T1 and the auxiliary transformer T2, and output. And a pulse width modulation (P) of the switching transistor 3 by a feedback signal based on the output DC voltage Vo.
WM) controlling PWM control section 7.

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

The transformer T1 steps up / down the high frequency alternating current input according to the turn ratio of the primary winding n1 and the secondary winding n2. On the other hand, the high-frequency alternating current is charged into the capacitor C4 through the primary winding of the auxiliary transformer T2, and the capacitor C4 releases the charge charged in the valley portion of the waveform in the low-frequency pulsating voltage, and the emission current. Output 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 alternating current ic21 from the auxiliary transformer T2 and the emission current i2 output from the transformer T1 (corresponding to the emission current i1 multiplied by the reciprocal of the winding ratio of the transformer T1).
And are added, and the DC voltage Vo in which the ripple component ΔVo is suppressed as much as possible is output through the rectifying / smoothing circuit 6, as shown in FIG.

(Second Embodiment of the Present Invention) Second Embodiment of the Present Invention
The AC-DC converter according to the embodiment of FIG.
It will be described based on. This FIG. 3 shows the AC according to the present embodiment.
-DC converter overall circuit configuration diagram, Fig. 4 shows an operation timing chart in the AC-DC converter described in Fig. 3.

In each of the above figures, the AC-
The DC converter includes a commercial AC power supply 1, a rectifier circuit 2, a switching transistor 3, and a transformer T, like 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, and in addition to this configuration,
A configuration including an active snubber circuit 5 which is connected in parallel to the switching transistor 3 and is controlled by a PWM control unit 7 so as to complementarily turn on / off in conjunction with a turn-on / turn-off operation of the switching transistor 3. Is.

The active snubber circuit 5 includes a MOS-
Auxiliary switching MOS consisting of FET transistor-
FETQ2 and this auxiliary switching MOS-FETQ2
And a snubber capacitor C5 connected in series on the subsequent stage side. This auxiliary switching MOS-FE
TQ2 is a parasitic capacitor Cs2 generated as a parasitic capacitance.
Are connected in parallel, and the diode Ds2 generated as a body diode is connected in parallel reverse bias.

The switching transistor 30 has an M
Main switching MO consisting of OS-FET transistor
It consists of S-FET Q1 and this main switching MOS-
Parasitic capacitor Cs generated as a parasitic capacitance in the FET Q1
1 is connected in parallel, and the diode Ds1 generated as a body diode is connected in parallel reverse bias.

As in the case of the first embodiment, the PWM control section 7 sets the PW to the set pulse width DTs.
Main switching MOS-FE with drive signal based on M control
TQ1 is driven and controlled, and this control signal is generated by a delay circuit having dead times t1, t2 and t6, t7 corresponding to a predetermined delay time, and the generated drive signal is inverted by an internal inverter. The auxiliary switching MOS-FET Q2 is controlled.

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

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

Further, when the main switching MOS-FET Q1 of the switching transistor 30 is turned off, the surge energy generated by the parasitic inductance of the transformer T1 and the auxiliary transformer T2 is charged in the snubber capacitor C5 and the capacitor C4 of the active snubber circuit 5. This charged electric charge is a high frequency AC pulse current i having the amplitude of the pulsating current output from the transformer T1.
It 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 / smoothing circuit 6.

Next, as shown in FIG. 4, the operation in the high frequency region is as follows. First, during the operation period t1, the main switching MOS-F is operated.
This is a period in which the 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 accumulated in the primary winding. At the same time, an exciting current flows through the auxiliary transformer T2 due to the energy stored in the capacitor C4, and energy is stored in the primary winding of the auxiliary transformer T2.

During the operation periods t2 and t3, the main switching MO is
S-FET Q1 and auxiliary switching MOS-FET Q2
Is the dead time period when 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 is completed, the output diode D61 is turned on, and the energy stored in the primary side of the transformer T1 is transferred to the load side. Then, the surge energy generated in the main switching MOS-FET Q1 is the auxiliary switching MOS-FET.
It passes through the body diode Ds2 of Q2 and is absorbed by the capacitors C4 and C5. On the other hand, surge energy generated by the parasitic inductance of the auxiliary transformer T2 passes through the route of the body diode Ds2-capacitor C5 and is absorbed by 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 in the off state, and the auxiliary switching M of the active snubber circuit 5 is M.
This is a period during which the OS-FET Q2 is in the ON state. During this period, the auxiliary switching M is performed while the body diode Ds2 of the auxiliary switching MOS-FET Q2 is on.
Zero voltage switching is realized by turning on the OS-FET Q2.

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

During the operation period t6, the auxiliary switching MOS
-Because the FET Q2 is kept on, the exciting current is flowing 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 of is extracted.

During the operation period t8, the main switching MOS-
When the discharge of the parasitic capacitor Cs1 of the FET Q1 is completed,
The body diode Ds1 of the main switching MOS-FET Q1 is turned on, and zero voltage switching is performed by turning on the main switching MOS-FET Q1 while the body diode Ds1 is on. In the AC-DC converter according to each of the above-described embodiments, the switching transistor is composed of MOS-FET, but it may be composed of bipolar transistor, IGBT or the like. In this case, it is necessary to connect the diodes in antiparallel.

Further, in addition to the respective polar relations in the primary and secondary windings of the auxiliary transformer T2 of the AC-DC converter according to each of the above-mentioned embodiments, arbitrary polar combinations may be adopted. Further, although the configuration is such that the switching transistor 3 of the AC-DC converter according to each of the above embodiments is driven and controlled by the PWM control unit 7 by PWM control, it may be configured to perform feedback control by another control method, for example, frequency control. it can.

Further, the AC-DC according to the second embodiment.
The active snubber circuit 5 in the converter is connected in parallel to the switching transistor 3 and is controlled by the PWM control unit 7 so as to complementarily turn on / off in conjunction with the turn-on / turn-off operation of the switching transistor 3. However, the switching transistor 3 and the capacitor C4 may be connected in parallel. Also in this case, the PWM control unit 7 controls in the same manner as described above, and the same action and effect are obtained.

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

[0037]

According to the present invention, a rectifier circuit is used for conversion.
From the pulsating DC current
Ri to generate a high frequency ac current, the primary side of the transformer and the auxiliary transformer for stepping up or stepping down the voltage of the alternating current to a predetermined value
Connect windings in series and connect each secondary winding in parallel
A capacitor is connected in series to the primary winding of the auxiliary transformer and in parallel with the switching transistor, and the switching transistor is based on the DC current output from the transformer and the auxiliary transformer through the rectifying / smoothing circuit. Is controlled by the feedback control means, the charge charged in the capacitor can be discharged to the output side through the auxiliary transformer at the valley of the pulsating current.
Ri, Ru can as small as possible suppression output ripple dc current or voltage at the output. Further, with this circuit configuration, there is an effect that the waveform distortion of the input current can be reduced and the power factor can be improved while keeping the output ripple as small as possible.

Further, in the present invention, since the feedback control means of the switching transistor performs feedback control at a frequency higher than the frequency of the AC power source, the response of the output fluctuation becomes slower and the DC current having the output ripple. The switching transistor is controlled so that the peak value of the alternating current is lowered by the feedback signal based on the peak portion and the switching transistor is increased by the feedback signal based on the valley portion of the direct current having the output ripple. This has the effect of more reliably suppressing ripples in the output DC current.

Further, in the present invention, the auxiliary switching transistor connected in parallel with the switching transistor is driven and controlled complementarily to the switching transistor, so that surge energy due to the parasitic inductance of the transformer and the auxiliary transformer is stored in the capacitor and the auxiliary capacitor. It is possible to recharge the charged electric charge to the output side via the auxiliary transformer, and
It is possible to improve the conversion efficiency and improve the power factor.

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

[Brief description of 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 the 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 the operation of the AC-DC converter shown in FIG.

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

6 is a control circuit configuration diagram for controlling the switching transistor shown in FIG.

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

[Explanation of symbols]

1 noise filter 2 rectifier circuit 3 switching transistors 5 Active snubber circuit 6,60 Rectification smoothing circuit 7 PWM control unit 8 charging circuit 9 Control circuit 71 Delay circuit 72 Inverter 100 AC power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Moriyama Nobuyuki Shimozumi Izumihonkaku 3144-1 Ricoh Keiki Co., Ltd. (56) Reference JP-A-8-294278 (JP, A) ) JP-A-2-168856 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 7/12 H02M 3/28

Claims (4)

(57) [Claims] 1. A rectifier circuit converts an alternating current supplied from a power source side into a pulsating direct current, the switching transistor converts the alternating current into a high frequency alternating current, and the high frequency alternating current voltage is boosted by a transformer or buck and outputs, in the AC-DC converter that outputs a DC current to the step-up or step-down high-frequency ac through rectifying and smoothing circuit, the primary winding to the primary winding of the transformer are connected in series, The secondary winding is connected in parallel to the secondary winding of the transformer, and each of the secondary windings is induced.
A supplementary transformer that adds high-frequency alternating current and outputs it to the rectifying / smoothing circuit, and a primary side winding of the auxiliary transformer, which is connected in series, is connected in parallel to the switching transistor, and is charged.
The charge is output at the valley of the DC current of the pulsating current on the output side.
It is characterized by comprising a capacitor for discharging to the output side via an auxiliary transformer, and feedback control means for feedback-controlling the switching transistor based on the output DC voltage value, current value or each variation. AC-DC
converter. 2. The AC-DC converter according to claim 1, wherein the feedback control means performs feedback control at a frequency higher than the frequency of the AC voltage supplied from the power source. . 3. The AC-DC converter according to claim 1, wherein the primary of the switching transistor and the auxiliary transformer.
Rutotomoni is connected in parallel to the side winding, the capacitor
Are connected in series to the support, the auxiliary switching transistor which is controlled to be complementary on-off operation in synchronization with the on-off operation of the switching transistor, Ru is connected in series with the auxiliary switching transistor
Together with the switching transistor and the auxiliary transistor
And an auxiliary capacitor connected in parallel to the primary winding of the AC-DC converter. 4. The AC-DC converter according to claim 3, wherein the auxiliary switching transistor is controlled so as to perform a zero-voltage switching turn-on operation of the switching transistor by using an electric charge charged in the auxiliary capacitor. An AC-DC converter characterized in that