JP2011239539A - Switching power supply device and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device and a control method thereof in which a power factor improvement operation is performed surely by controlling a PFC voltage and an output voltage in the switching power supply device where a half bridge type switching elements are shared and a power factor improvement part and a current resonance converter part are combined.SOLUTION: The switching power supply device 1 in which a first and second half bridge type switching element Q1 and Q2 are shared, and the power factor improvement part 2 and the current resonance converter part 3 are combined, comprises: a PFC voltage detector 4; a first reference voltage generating part 5; a first error amplifier 6; and a switching controller 7, where an output signal from the first reference voltage generating part 5 is set up as a voltage value corresponding to at least 2√2 times the actual value (Vac-in) of AC input voltage, and the first and second switching element Q1 and Q2 are controlled so that an actual value of the PFC voltage and the AC input voltage satisfies a relation: V>2√2 Vac-in.

Description

  In an AC / DC converter including a power factor correction (PFC) unit and a current resonance (LLC) converter unit that share a half-bridge type switching element, the present invention reliably performs the power factor improvement operation of the power factor improvement unit. The present invention relates to a switching power supply apparatus for controlling a PFC voltage and a control method thereof.

  2. Description of the Related Art Conventionally, a switching power supply device including an AC / DC converter for improving a power factor has been used for digital devices such as notebook computers, liquid crystal televisions, plasma televisions, game machines, and home entertainment devices. This AC / DC converter with a power factor improving function is generally composed of a full-wave rectifier bridge, a step-up type power factor improving unit, and a DC / DC converter unit.

  Examples of the DC / DC converter unit include a flyback converter, a forward converter, a current resonance (LLC) converter, and the like, and a current resonance converter is widely used in power supplies that require high efficiency.

  FIG. 9 shows a switching power supply device with a power factor improvement function disclosed in Patent Document 1, and includes a full-wave rectifier bridge 18, a power factor improvement unit 20, and a half-bridge type current resonance converter unit 30. It is configured.

  In the circuit configuration of this device, the power factor improvement unit 20 includes an inductor 21, a diode 22, a switching device between two switching elements 31 and 32 provided on the input side of the full-wave rectification bridge 18 and the current resonance converter unit 30. An active filter including the element 23 and a smoothing capacitor 26 are included.

  The current resonance converter unit 30 includes a series resonance circuit (resonance capacitor 33 and resonance inductor 34) connected between the intermediate point of the series circuit of the switching elements 31 and 32 and the primary winding of the transformer T. A predetermined output voltage is obtained by rectifying and smoothing the current flowing through the secondary winding by the rectifier diodes 35 and 36 and the capacitor 37.

  Although this switching power supply device has a high conversion efficiency of the current resonance converter unit 30, since it has a three-stage circuit configuration including the full-wave rectification bridge 18, the power factor improvement unit 20, and the current resonance converter unit 30, The overall efficiency is reduced to about 85 to 90%.

  In such a situation, as shown in FIG. 10, the present applicant eliminated the full-wave rectification bridge and shared the switching elements of the power factor improvement unit and the current resonance converter unit to improve the conversion efficiency. A bridge type switching power supply circuit was developed.

This switching power supply device has an AC / DC converter circuit composed of a power factor correction (PFC) unit 2 and a current resonance converter (LLC) unit 3.
The power factor improving unit 2 is connected in parallel with a series circuit in which the first and second diodes D1 and D2 are connected in a forward direction to the series circuit of the first and second switching elements Q1 and Q2. A step-up inductor L1 and an AC power supply Vac are connected in series between the points. The positive side of the first smoothing capacitor Ci is connected to the cathode side of the series circuit of the first and second diodes D1 and D2, and the negative side is connected to the anode side.

  The current resonance converter unit 3 includes a half-bridge circuit sharing the first and second switching elements Q1 and Q2 of the power factor improving unit 2, and a high-frequency transformer T sandwiched between the half-bridge circuit and the half-bridge circuit. A series resonant circuit 6 including a resonant inductor Lr and a resonant capacitor Cr on the primary side, and a rectifier circuit including rectifier diodes D3 and D4 and a second smoothing capacitor Co on the secondary side of the high-frequency transformer T are provided.

  The power factor improving unit 2 performs the second switching in the positive half cycle of the AC input voltage (hereinafter, when the intermediate point side of the first and second switching elements Q1, Q2 is a positive voltage). The device operates as a booster circuit that transfers energy stored in the boost inductor L1 when the element Q2 is turned on to the first smoothing capacitor Ci when the second switching element Q2 is turned off. Further, in the negative half cycle of the AC input voltage, it operates as a booster circuit that transfers the energy stored in the booster inductor L1 when the first switching element Q1 is turned on to the first smoothing capacitor Ci when the first switching element Q1 is turned off. To do.

  The current resonance converter unit 3 is constituted by the resonance capacitor Cr, the resonance inductor Lr, and the high-frequency transformer T, with the energy stored in the first smoothing capacitor Ci by the half bridge drive of the first and second switching elements Q1, Q2. To the load via a resonant circuit.

  Since this switching power supply circuit does not have a full-wave rectification bridge, it is more efficient than the switching power supply circuit disclosed in Patent Document 1 shown in FIG.

JP 2008-283818 A

  In the half-bridge type switching power supply device shown in FIG. 10 developed by the present applicant, the on-duty of the first and second switching elements Q1 and Q2 is fixed at about 50%, so the switching elements are shared. There was a problem that control of the power factor improvement unit 2 was difficult.

  For example, when the instantaneous value of the AC input voltage becomes close to the value of the PFC voltage, the energy stored in the boost inductor L1 during the ON period of the second switching element Q2 is all first smoothed during the OFF period of the first switching element Q1. The capacitor Ci cannot be discharged, the boost inductor L1 shifts to the current continuous mode, an excessive current flows, and it becomes difficult to maintain a high power factor.

  Furthermore, since the on-duty of the switching element cannot be reduced even at a light load, the PFC voltage of the power factor improvement unit 2 increases excessively, and the electrolytic capacitor and the switching element may be destroyed.

  The present invention has been made to solve the above-described problems, and its object is to control a PFC voltage of a power factor improvement unit in a half-bridge circuit with a fixed on-duty while ensuring a stable and stable power factor. It is an object of the present invention to provide a switching power supply device capable of improving operation and a control method thereof.

In order to solve the above object, according to the present invention, a series circuit in which first and second diodes are connected in a forward direction is connected in parallel to a series circuit of first and second switching elements. A step-up inductor and an AC power source are connected in series between the intermediate points, the positive side of the first smoothing capacitor is connected to the cathode side of the series circuit of the first and second diodes, and the negative side is connected to the anode side, respectively. By the on / off operation of the second switching element, the AC input voltage from the AC power source is boosted through a boost inductor while improving the power factor, and a DC PFC voltage (V _PFC ) is applied to the first smoothing capacitor. Power factor correction (PFC) unit that outputs the power, a half bridge circuit that shares the first and second switching elements, a high frequency transformer, the half bridge circuit, and the high frequency A resonance circuit including a resonance inductor and a resonance capacitor provided between the primary winding of the lance, and a rectifier diode and a second smoothing capacitor provided between the secondary winding and the load portion of the high-frequency transformer. A rectifying and smoothing circuit, and performing a soft switching operation of the first and second switching elements by a resonance operation by the resonance circuit and the high-frequency transformer, and using the PFC voltage as an input voltage via the high-frequency transformer, Current resonance for supplying a DC output voltage obtained by rectifying and smoothing a primary high-frequency voltage obtained by the on / off operation of the first and second switching elements to the load unit by the rectifying and smoothing circuit on the secondary side A switching power supply comprising: a converter unit; a PFC voltage detection unit that detects the PFC voltage; and a first reference voltage Based on an output signal from the first error amplifier, a first error amplifier that amplifies and outputs a difference between the PFC voltage and the first reference voltage A switching control unit that outputs a drive signal for on / off control of the second switching element, and the output signal from the first reference voltage generation unit is at least 2√2 times the effective value of the AC input voltage The effective value (V _ac-in ) of the PFC voltage and the AC input voltage is set to a voltage value corresponding to
V _PFC > 2√2V _ac-in
The first and second switching elements are controlled so as to satisfy the relationship.

  Further, in a preferred embodiment of the present invention, an output voltage detector that detects the output voltage output from the rectifying and smoothing circuit, a second reference voltage generator that generates a second reference voltage, the output voltage, and the A second error amplifier that amplifies and outputs a difference from the second reference voltage, and the switching control unit is configured to output the first error amplifier based on output signals from the first error amplifier and the second error amplifier. The output voltage is controlled at a constant voltage by controlling the second switching element.

  The switching control unit is installed on the secondary side of the high-frequency transformer, and transmits the output signal of the first error amplifier to the switching control unit on the secondary side via the first insulating means. The drive signal output from the switching control unit is transmitted to the first and second switching elements through the second insulating means.

  The switching control unit is installed on a primary side of the high-frequency transformer, and transmits an output signal of the second error amplifier to the switching control unit on the primary side through a third insulating unit. Yes. Further, the first, second and third insulating means are photocouplers or insulating transformers.

  The resonant inductor may be replaced with a leakage inductance of the high frequency transformer.

Further, according to the control method of the switching power supply device of the present invention, the series circuit in which the first and second diodes are connected in the forward direction is connected in parallel to the series circuit of the first and second switching elements. A step-up inductor and an AC power source are connected in series between the intermediate points of the circuit, the positive side of the first smoothing capacitor is connected to the cathode side of the series circuit of the first and second diodes, and the negative side is connected to the anode side. 1. By turning on / off the second switching element, the AC input voltage from the AC power source is boosted through the boost inductor while improving the power factor, and a DC PFC voltage ( and power factor (PFC) unit that outputs a V _PFC), and the first half-bridge circuit and the second switching element and a common, and high frequency transformer, said Hafuburi A resonant circuit including a resonant inductor and a resonant capacitor provided between a first circuit and a primary winding of the high-frequency transformer, a rectifier diode provided between a secondary winding of the high-frequency transformer and a load unit, and a first A rectifying / smoothing circuit including two smoothing capacitors, and performing a soft switching operation of the first and second switching elements by a resonance operation by the resonance circuit and the high-frequency transformer, and using the PFC voltage as an input voltage, A DC output voltage obtained by rectifying and smoothing the primary high-frequency voltage obtained by the on / off operation of the first and second switching elements through the transformer by the rectifying and smoothing circuit on the secondary side is supplied to the load unit. A method for controlling the PFC voltage of a switching power supply device comprising: The effective value (Vac-in) of the voltage and the AC input voltage is
V _PFC > 2√2Vac-in
It is characterized by being controlled so as to satisfy the relationship.

  According to another aspect of the present invention, there is provided a method for controlling a switching power supply apparatus comprising: detecting the PFC voltage; generating a first reference voltage corresponding to at least 2√2 times an effective value of the AC input voltage; Comparing a voltage with the first reference voltage and outputting a first error amplification signal obtained by amplifying the difference between the two and turning on / off the first and second switching elements based on the first error amplification signal And a step of controlling.

  Further, in a preferred embodiment, the step of detecting the output voltage output from the rectifying and smoothing circuit, the step of generating a predetermined second reference voltage, and comparing the output voltage with the second reference voltage And a step of outputting a second error amplification signal obtained by amplifying the difference between the first and second switching elements based on the first and second error amplification signals. It is characterized by.

  According to the output result of the first error amplification signal, the PFC voltage is controlled by providing a switching pause period of the first and second switching elements, and according to the output result of the second error amplification signal. The output voltage of the current resonance converter unit is controlled by changing a switching frequency of the first and second switching elements.

  Further, in the above control method of the switching power supply device of the present invention, the on-duty immediately after one of the switching pause periods of the first and second switching elements is set to a half pulse that is approximately a half of the predetermined on-duty, and the first The on-duty immediately before the other switching pause period of the second switching element is a half pulse that is approximately one half of the predetermined on-duty.

The switching power supply according to the present invention is a switching power supply in which a half-bridge type switching element is shared and a power factor correction unit and a current resonance converter unit are combined, and the PFC voltage V _PFC is 2√2Vac-in (where Vac-in is controlled to be equal to or greater than the effective value of the AC input voltage. As a result, the power factor improving operation of the switching power supply device can be reliably performed and the high power factor can be maintained.

  Further, in the present invention, the PFC voltage of the power factor correction unit is controlled independently by changing the switching rest period, and the output voltage from the current resonance converter unit is controlled by changing the switching frequency. Thereby, a predetermined output voltage can be reliably supplied to the load section while maintaining a high power factor.

  Furthermore, according to the switching element control method of the present invention, the size of the high-frequency transformer can be kept small, and an inexpensive switching power supply device can be provided.

1 is a circuit configuration diagram of a switching power supply device according to a first embodiment of the present invention. It is a figure explaining the pressure | voltage rise operation | movement of the power factor improvement part of this invention. It is a circuit block diagram of the switching power supply device which concerns on 2nd Embodiment of this invention. It is a circuit block diagram of the switching power supply device which concerns on 3rd Embodiment of this invention. It is a circuit block diagram of the switching power supply device which concerns on 4th Embodiment of this invention. In the embodiment of the present invention in FIG. 3, (a) shows a control block diagram, and (b) shows an operation waveform of a switching element in the control method. It is a figure for demonstrating one form of the half pulse control in this invention, and its effect. It is a figure for demonstrating the more suitable form and effect of the half pulse control in this invention. It is a circuit block diagram of the switching power supply device of a prior art example. It is a circuit block diagram of the half-bridge type switching power supply device which combined the power factor improvement part and current resonance converter part which are the basic composition in this invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a basic configuration of a switching power supply device 1 according to the first embodiment of the present invention.
In FIG. 1 and the following description, the same reference numerals are given to components common to the configurations described in the prior art.

  In the power factor improving unit 2, a series circuit of first and second diodes D1 and D2 and a series circuit of first and second switching elements Q1 and Q2 are connected in parallel, and a boost inductor L1 is provided between the intermediate points of both series circuits. And an AC power source Vac are connected in series, and a first smoothing capacitor Ci is connected in parallel to both ends of the series circuit of the first and second diodes D1 and D2.

  The current resonance converter unit 3 includes a half bridge circuit sharing the first and second switching elements Q1 and Q2 of the power factor improvement unit 2, and an intermediate point between the half bridge circuit and one end of the primary winding of the high frequency transformer T. The other end of the high-frequency transformer T is connected to the negative electrode side of the first smoothing capacitor Ci. A rectifier circuit including rectifier diodes D3 and D4 and a second smoothing capacitor Co is provided on the secondary side of the high-frequency transformer T.

  The power factor improving unit 2 stores energy in the boost inductor L1 when the second switching element Q2 is on when the intermediate point side of the AC power supply Vac with the first and second switching elements Q1 and Q2 is a positive half cycle. When the first switching element Q1 is on, the energy accumulated in the boost inductor L1 is boosted and stored in the first smoothing capacitor Ci. Similarly, when the AC power supply Vac has a negative half cycle, energy is stored in the boost inductor L1 when the first switching element Q1 is on, and energy accumulated in the boost inductor L1 when the second switching element Q2 is on. The first smoothing capacitor Ci accumulates while being boosted.

  The current resonance converter unit 3 performs a soft switching operation by a resonance operation of the first and second switching elements Q1 and Q2 of the half bridge type and the primary side resonance capacitor Cr and the resonance inductor Lr. Yes. The first and second switching elements Q1, Q2 are controlled by the switching control unit 7, and are turned on / off alternately. An alternating high-frequency voltage generated based on this on / off operation is applied to both ends of the primary winding of the high-frequency transformer T, and currents flowing through the secondary winding of the high-frequency transformer T are rectified by the rectifier diodes D3 and D4 and the second smoothing capacitor. A predetermined output voltage can be obtained by rectifying and smoothing at Co.

In FIG. 1, the other end of the high-frequency transformer T is connected to the negative electrode side of the first smoothing capacitor Ci, but can be changed to a connection to the positive electrode side.
The resonance capacitor is a series circuit of a capacitor Cr1 and a capacitor Cr2, and this series circuit is connected in parallel to the series circuit of the first and second switching elements Q1 and Q2, and the resonance inductor Lr and the high frequency are connected between the intermediate points of both series circuits. It is also possible to change to a configuration in which the primary winding of the transformer T is connected in series.
In addition, the present invention can be applied to a modified circuit of a similar half-bridge circuit.

In the present invention, as shown in FIG. 1, in order to control the first and second switching elements Q1 and Q2, the PFC voltage (V _PFC ) of the power factor improvement unit 2 stored in the first smoothing capacitor Ci is detected. The PFC voltage detection unit 4 that performs the control, the first reference voltage generation unit 5 that generates a reference voltage for controlling the PFC voltage to a predetermined voltage value, and the difference between the PFC voltage V _PFC and the first reference voltage is amplified. The switching control unit 7 further controls the first and second switching elements Q1 and Q2 on / off based on the output signal of the first error amplifier 6.

Here, when the effective value of the AC input voltage from the AC power supply Vac is Vac-in, the first reference voltage generator 5 has at least 2√V in order to set the PFC voltage V _PFC to 2√2Vac-in or higher. The reference voltage value corresponding to 2 Vac-in or higher is set. Here, “corresponding” includes the case where the detected PFC voltage value is detected as a divided voltage value of the actual PFC voltage. In this case, the actual reference voltage value is 2√2Vac−. The value obtained by multiplying in by the voltage division ratio.

As described above, the effect of controlling the PFC voltage V _PFC to 2√2 Vac-in or more will be described in more detail below.

  In this switching power supply device 1, the first and second switching elements Q 1, Q 2 constitute a half bridge circuit of the current resonance converter unit 3. Accordingly, the on-duty of the first and second switching elements Q1, Q2 is fixed at about 50%. On the other hand, since the first and second switching elements Q1 and Q2 also serve as a switching element of the power factor improvement unit 2, the on-duty of the switching element of the power factor improvement unit 2 is approximately 50%. Become fixed.

  On the other hand, in the continuous mode PFC and the critical mode PFC, which are general power factor correction circuits, the on-duty is changed in accordance with the phase angle of the AC power supply Vac in both cases (the former is caused by the change in the ON width and the latter In this case, the power factor correction operation is realized by changing the switching frequency. For example, in continuous mode PFC, when the phase angle of the AC power supply Vac is around 0 ° (when the instantaneous value of the AC input voltage is small), the ON width is large, and the phase angle is around 90 ° (the instantaneous value of the AC input voltage is When it is large), the on-width is controlled to be small so that the current from the AC power supply Vac is substantially proportional to the instantaneous value of the AC input voltage, thereby realizing the power factor improving operation.

However, in the present invention, since the on-duty is fixed at about 50% as described above, when the boost inductor L1 is operated in the continuous mode, the power factor improving operation by changing the ON width as in the continuous mode PFC. I can't. Therefore, in the switching power supply device 1 sharing the switching elements of the power factor improvement unit 2 and the current resonance converter unit 3 as in the present invention, it is necessary to always operate the boost inductor L1 in the discontinuous mode. If the operation in the continuous mode is performed, the choke current flowing through the step-up inductor L1 suddenly increases, which leads to deterioration of the power factor and saturation of the choke core, which is not preferable.
Therefore, in the present invention, it is necessary to perform control in the discontinuous mode so as not to cause this problem.

Furthermore, conditions for operating the boost inductor L1 in the discontinuous mode in the switching power supply device 1 of the present invention will be described. FIG. 2 shows a simplified operation of the first and second switching elements Q1 and Q2 in the switching power supply device 1 of the present invention.
The boost converter of FIG. 2 has an input voltage Vin (corresponding to an instantaneous value of an AC input voltage), and an inductor current i flowing through the boost inductor L1 is a voltage applied to the boost inductor L1, _VL , and a voltage is applied. If time is t,
i = (V _L / L1) · t
It is. Therefore, the peak current ip of the inductor when the second switching element Q2 is in the on operation is represented by Ton as the on-time of the second switching element Q2.
ip = (Vin / L1) · Ton
Also, if the off time of the second switching element Q2 is Toff,
ip = [(V _PFC −Vin) / L1] · Toff
It becomes.
In order to operate in the discontinuous mode, the inductor current i needs to be reduced to 0 A during the OFF period of the second switching element Q2.

That is, this condition is
(V _PFC -Vin) ・ Toff> Vin ・ Ton
Since the on-duty is fixed at about 50%, Toff = Ton.
(V _PFC -Vin)> Vin
It becomes. Therefore, if V _PFC > 2Vin is always set, the operation in the discontinuous mode becomes possible.

This condition is most severe when the instantaneous value Vin of the AC input voltage is the maximum. If the effective value of the AC input voltage is Vac_in, it becomes √2Vac_in. Therefore,
V _PFC > 2√2Vac_in
If the PFC voltage V _PFC satisfying the relational expression is set, the operation in the discontinuous mode becomes possible.

As described above, according to the present invention, by controlling the PFC voltage so as to satisfy V _PFC > 2√2Vac_in, in the switching power supply device 1 in which the power factor improving unit 2 and the current resonance converter unit 3 share the switching element, It becomes possible to operate the inductor L1 in the discontinuous mode. As a result, the current output from the AC power supply Vac can be set to a current value substantially proportional to the AC input voltage, and a power factor improving operation at a high power factor can be realized.

  FIG. 3 shows the configuration of the switching power supply device 1a according to the second embodiment of the present invention. In addition to the switching power supply device 1 shown in FIG. An output voltage detector 8 for detecting an output voltage output to the load unit, a second reference voltage generator 9 for setting the output voltage to a predetermined voltage value, and amplifying the difference between the output signals from both The switching control unit 7 is configured to turn on / off the first and second switching elements Q1 and Q2 based on output signals from the first error amplifier 6 and the second error amplifier 10. Turn off control.

  With the above configuration, the PFC voltage of the power factor improvement unit 2 and the output voltage of the current resonance converter unit 3 can be controlled simultaneously, and a predetermined output voltage is applied to the load unit while maintaining a high power factor. Can be supplied.

FIG. 4 shows the configuration of a switching power supply device 1b according to the third embodiment of the present invention.
In switching power supplies for personal computers and TVs, an insulating means is generally provided between a primary side circuit and a secondary side circuit for safety. Therefore, when the switching control unit 7 is arranged on the secondary side with the high-frequency transformer T interposed therebetween as shown in FIG. 4, the output signal from the first error amplifier 6 on the primary side passes through the first insulating means 11. Is transmitted to the switching control unit 7 on the secondary side. Further, the switching element drive signal output from the switching control unit 7 is transmitted to the first and second switching elements Q1 and Q2 on the primary side via the second insulating means 12.

  FIG. 5 shows the configuration of a switching power supply device 1c according to the fourth embodiment of the present invention. In this case, the switching control unit 7 is arranged on the primary side, and an output signal from the second error amplifier 10 on the secondary side is transmitted to the switching control unit 7 on the primary side via the third insulating means 13. .

  The first, second, and third insulating means described above are preferably composed of a photocoupler or an insulating transformer.

  As described above, by providing the insulating means (first, second, and third insulating means) as in the third and fourth embodiments, a safe switching power supply device can be provided.

  The resonant inductor Lr in the above description can be replaced with a leakage inductance of the high-frequency transformer T.

  Further, the first and second reference voltage generators, the first and second error amplifiers, and the switching control unit in the above description incorporate all or part of these functions into the microcomputer, and these functions are stored in the microcomputer. It is also possible to substitute by the above operation.

Next, steps of the control method of the present invention will be described below.
The control method of the switching power supply according to the first embodiment of the present invention includes a power factor improving unit 2 stored in a first smoothing capacitor Ci connected in parallel to the half bridge circuit of the first and second switching elements Q1, Q2. A step of detecting the PFC voltage, a step of generating a first reference voltage corresponding to at least 2√2 times the effective value Vac-in of the AC input voltage, and the detected PFC voltage value and the first reference voltage. A step of outputting a first error amplification signal obtained by comparing and amplifying the difference between the two, a control signal is output from the switching control unit 7 based on the output signal, and the first and second switching elements Q1, Q2 are output. Controlling on / off.

By performing these steps in sequence, first and second switching elements Q1, Q2 is turned on / off control as PFC voltage V _PFC is the voltage value of more than 2√2 times the rms value of the AC input voltage Therefore, the boost inductor L1 of the power factor improvement unit 2 can always be operated in the current discontinuous mode.
If the PFC voltage V _PFC is set lower than 2√2Vac-in, the boost inductor L1 shifts to the current continuous mode, and the AC input current waveform is distorted, so that the power factor is deteriorated. However, according to the present invention, since the PFC voltage V _PFC can be maintained at 2√2 Vac-in or higher, a high power factor can be realized.

  Furthermore, in the control method for the switching power supply device according to the second embodiment of the present invention, the step of detecting the output voltage of the current resonance converter unit 3, the step of generating a predetermined second reference voltage, and the detected output voltage A step of comparing the value and the second reference voltage and outputting a second error amplification signal obtained by amplifying the difference between the two and the switching control unit based on the output signals from the first and second error amplifiers; 2 controlling the switching elements Q1 and Q2.

By sequentially performing these steps, the PFC voltage V _PFC of the power factor improvement unit 2 and the output voltage Vo of the current resonance converter unit 3 can be controlled independently.

  In the above control method, the first and second switching elements Q1 and Q2 are shared, and the half-bridge type switching power supply devices 1 and 1a in which the power factor improving unit 2 and the current resonance converter unit 3 are combined, and the insulating means (first This is implemented in the switching power supply devices 1b and 1c provided with the first, second and third insulating means.

Furthermore, a more preferable process for independently controlling the PFC voltage _VPFC of the power factor improvement unit 2 and the output voltage Vo of the current resonance converter unit 3 will be described below with reference to FIG.

FIG. _6A shows a control block diagram for controlling the PFC voltage _VPFC of the power factor correction unit 2 and the output voltage Vo of the current resonance converter unit 3. However, for the sake of explanation, FIG. 6 shows a block diagram in which the power factor improvement unit 2 and the current resonance converter unit 3 are separated, but the first and second switching elements Q1 and Q2 are actually common to both.

That is, an AC input voltage from the AC power source Vac is input to the power factor improvement unit 2, and the PFC voltage V _PFC output from the power factor improvement unit 2 is supplied to the current resonance converter unit 3, and the PFC voltage and the first reference The difference with the voltage is amplified and output, and the period during which switching of the first and second switching elements Q1, Q2 is suspended is changed based on the output signal. Further, the difference between the output voltage Vo of the current resonance converter unit 3 and the second reference voltage is amplified and output, and the switching frequency of the first and second switching elements Q1, Q2 is changed based on the output signal.

  Next, the effect of the above control method will be described. First, regarding the control of the output voltage Vo of the current resonance converter unit 3, the output voltage Vo can be changed by changing the switching frequency as in the case of a general current resonance converter. Accordingly, as shown in FIG. 6, if the switching frequency is modulated based on the error amplification signal (second error amplification signal) between the predetermined second reference voltage and the output voltage Vo, the output voltage Vo is set to the second reference voltage value. The predetermined voltage value can be controlled.

On the other hand, regarding the control of the PFC voltage V _PFC , the on-duty of the first and second switching elements Q1, Q2 is fixed at about 50%, and therefore cannot be controlled by the change of the on-duty. Therefore, as shown in FIG. 6B, the PFC voltage V _PFC is controlled by providing a switching pause period.

  For example, as shown in FIG. 6B, (1) in the case of full load, the on-duty of the first and second switching elements Q1, Q2 is constant at about 50%, there is no idle period, and the on-duty is always on. / Off operation is maintained.

However, (2) when the load is lightened, the PFC voltage V _PFC increases without a switching pause period. Since the output signal of the first error amplifier 6 changes due to this voltage increase, the ratio of the switching pause period is changed based on the error amplification signal (first error amplification signal) so that the PFC voltage V _PFC becomes constant. Let

(3) When the load is further reduced, the ratio of the switching pause period is further increased to keep the PFC voltage V _PFC constant.

As described above, by providing the switching pause periods of the first and second switching elements Q1 and Q2 based on the error amplification signal (first error amplification signal) between the PFC voltage V _PFC and the first reference voltage, the PFC voltage On the other hand, the output voltage is changed by changing the switching frequency of the first and second switching elements Q1, Q2 based on the error amplification signal (second error amplification signal) between the output voltage Vo and the second reference voltage. Can be controlled.

  In the above description, FIG. 6B is used to describe the idle period of the switching element. However, the mode of the idle period of the switching element is not limited to this, and the scope of the present invention is not deviated. Can be changed.

  Next, the form of the control method by the more preferable idle period of a switching element is demonstrated using FIG. FIG. 7A shows respective waveforms when switching is started at an on-duty of about 50% from the beginning (without half-pulse control) when the switching element is idle and switching starts again.

  In this case, as shown in FIG. 7A, immediately after switching is started, the exciting current of the high-frequency transformer T is approximately 0 A (ampere) (point A), and is turned on with an on-duty of 50% immediately after the start of switching. Then, since the exciting current increases (point B), the number of turns must be increased to increase the size of the high-frequency transformer T, and the switching power supply device becomes expensive.

  On the other hand, as shown in FIG. 7B, when only the first switching immediately after the start of switching, the on-duty is set to a half pulse (approximately 25%) that is a half of the predetermined on-duty (approximately 50%). An increase in the excitation current of the transformer can be suppressed (D point).

  In FIG. 7, since switching is started from the second switching element Q2, only the first on-duty of the second switching element Q2 is a half pulse. However, when switching is started from the first switching element Q1, Only the first on-duty of one switching element Q1 is a half pulse.

  By performing the half pulse control as described above, the exciting current of the high-frequency transformer T can be suppressed. Therefore, the size of the high-frequency transformer T can be reduced, and the switching power supply device can be made inexpensive.

  Furthermore, a more preferable form of half pulse control will be described with reference to FIG. FIG. 8A shows the waveform of each part when half pulse control is performed only at the start of switching.

  In this case, since the second switching element Q2 is a half pulse, the sum of the on period of the first switching element Q1 and the sum of the on period of the second switching element Q2 is larger in the second switching element Q2. At this time, since both of the switching elements also serve as the switching element of the power factor improving unit 2, the current waveform from the AC power source Vac becomes asymmetrical between positive and negative as shown in FIG. There's a problem.

  On the other hand, as shown in FIG. 8B, the on-duty immediately after the switching pause period of one switching element (Q2) is a half pulse, and the on-duty immediately before the pause period of the other switching element (Q1) is also a half pulse. Then, since the sum of the ON periods of both switching elements becomes equal, the current waveform from the AC power supply Vac becomes positive and negative symmetrical as shown in FIG. 8B, and a high power factor can be maintained.

  In FIG. 8, since switching is started from the second switching element Q2, the first on-duty of the second switching element Q2 is a half pulse and the end of the first switching element Q1 is a half pulse. When switching is started from the element Q1, the first on-duty of the first switching element Q1 is a half pulse, and the end of the second switching element Q2 is a half pulse.

  As described above, by performing the half pulse control described with reference to FIG. 8, it is possible to maintain a high power factor while suppressing the excitation current of the high-frequency transformer T.

As described above, the switching power supply device of the present invention reliably performs the power factor correction operation by controlling the PFC voltage to 2√2 Vac-in (Vac-in is an effective value of the AC input voltage) or more. Can maintain a high power factor.
Also, the PFC voltage can be controlled independently by changing the switching pause period, and the output voltage can be controlled independently by changing the switching frequency, so that a predetermined output voltage can be reliably supplied to the load section while maintaining a high power factor. Can be supplied to.
Furthermore, according to the switching element control method of the present invention, the size of the high-frequency transformer can be kept small, and an inexpensive switching power supply device can be provided.

1, 1a, 1b, 1c: switching power supply device, 2: power factor improvement unit, 3: current resonance converter unit, 4: PFC voltage detection unit, 5: first reference voltage generation unit, 6: first error amplifier, 7 : Switching control unit, 8: output voltage detection unit, 9: second reference voltage generation unit, 10: second error amplifier, 11: first insulation unit, 12: second insulation unit, 13: third insulation unit, Q1: First switching element, Q2: second switching element, D1: first diode, D2: second diode, D3, D4: rectifier diode, Ci: first smoothing capacitor, Co: second smoothing capacitor, L1: boost inductor, Lr: resonant inductor, Cr: resonant capacitor, T: high frequency transformer, Vac: AC power supply, V _PFC : PFC voltage

Claims (11)

A series circuit in which the first and second diodes are connected in the forward direction is connected in parallel to the series circuit of the first and second switching elements, and the boost inductor and the AC power supply are connected in series between the intermediate points of the two series circuits. Are connected to the cathode side of the series circuit of the first and second diodes, and the negative side is connected to the anode side, respectively, and by the on / off operation of the first and second switching elements, A power factor correction (PFC) unit that boosts an AC input voltage from the AC power source through the boost inductor while improving a power factor and outputs a DC PFC voltage (V _PFC ) to the first smoothing capacitor. When,
A resonant circuit including a half-bridge circuit having the first and second switching elements in common, a high-frequency transformer, and a resonant inductor and a resonant capacitor provided between the half-bridge circuit and a primary winding of the high-frequency transformer. And a rectifying / smoothing circuit including a rectifying diode and a second smoothing capacitor provided between the secondary winding of the high-frequency transformer and the load section, and the first operation is performed by the resonance operation of the resonance circuit and the high-frequency transformer. The soft switching operation of the second switching element is performed, and the primary high-frequency voltage obtained by the on / off operation of the first and second switching elements through the high-frequency transformer with the PFC voltage as an input voltage. A DC output voltage obtained by rectifying and smoothing by the rectifying and smoothing circuit on the secondary side is supplied to the load unit. And a flow resonant converter section,
In a switching power supply device comprising:
A PFC voltage detector that detects the PFC voltage; a first reference voltage generator that generates a first reference voltage; and a first error amplifier that amplifies and outputs the difference between the PFC voltage and the first reference voltage; A switching control unit that outputs a drive signal for on / off control of the first and second switching elements based on an output signal from the first error amplifier, and the first reference voltage is input to the AC input The voltage value corresponding to at least 2√2 times the effective value (Vac- _in ) of the voltage is set, and the effective values of the PFC voltage and the AC input voltage are
V _PFC > 2√2Vac _-in
The switching power supply device is characterized in that the first and second switching elements are controlled so as to satisfy the relationship. An output voltage detector for detecting the output voltage output from the rectifying and smoothing circuit; a second reference voltage generator for generating a second reference voltage; and amplifying a difference between the output voltage and the second reference voltage. And a second error amplifier for outputting
The switching control unit performs constant voltage control on the output voltage by controlling the first and second switching elements based on respective output signals from the first error amplifier and the second error amplifier. The switching power supply device according to claim 1.   The switching control unit is installed on the secondary side of the high-frequency transformer, and the output signal of the first error amplifier is transmitted to the switching control unit on the secondary side via the first insulating means, and the switching control is performed. 3. The switching power supply device according to claim 1, wherein the drive signal output from the unit is transmitted to the first and second switching elements through a second insulating unit.   The switching control unit is installed on a primary side of the high-frequency transformer, and transmits an output signal of the second error amplifier to the switching control unit on the primary side through a third insulating unit. Item 3. The switching power supply device according to Item 2. 5. The switching power supply device according to claim 3, wherein the first, second, and third insulating means are photocouplers or insulating transformers. 6. The switching power supply circuit according to claim 1, wherein the resonant inductor is replaced with a leakage inductance of the high-frequency transformer. A series circuit in which the first and second diodes are connected in the forward direction is connected in parallel to the series circuit of the first and second switching elements, and the boost inductor and the AC power supply are connected in series between the intermediate points of the two series circuits. The positive side of the first smoothing capacitor is connected to the cathode side of the series circuit of the first and second diodes, the negative side is connected to the anode side, and the on / off operation of the first and second switching elements A power factor correction (PFC) unit that boosts an AC input voltage from the AC power source through a boost inductor while improving a power factor and outputs a DC PFC voltage (V _PFC ) to the first smoothing capacitor; ,
A resonant circuit including a half-bridge circuit having the first and second switching elements in common, a high-frequency transformer, and a resonant inductor and a resonant capacitor provided between the half-bridge circuit and a primary winding of the high-frequency transformer. And a rectifying / smoothing circuit including a rectifying diode and a second smoothing capacitor provided between the secondary winding of the high-frequency transformer and the load section, and the first operation is performed by the resonance operation of the resonance circuit and the high-frequency transformer. The soft switching operation of the second switching element is performed, and the primary high-frequency voltage obtained by the on / off operation of the first and second switching elements through the high-frequency transformer with the PFC voltage as an input voltage. A DC output voltage obtained by rectifying and smoothing by the rectifying and smoothing circuit on the secondary side is supplied to the load unit. And a flow resonant converter section,
A method for controlling the PFC voltage of a switching power supply device comprising:
The effective value (Vac- _in ) of the PFC voltage and the AC input voltage is
V _PFC > 2√2Vac _-in
And a control method for the switching power supply device, wherein the control is performed so as to satisfy the relationship. Detecting the PFC voltage, generating a first reference voltage corresponding to at least 2√2 times the effective value of the AC input voltage, comparing the PFC voltage with the first reference voltage, A step of outputting a first error amplification signal obtained by amplifying the difference; and a step of performing on / off control of the first and second switching elements based on the first error amplification signal. The control method of the switching power supply device according to claim 7.   Detecting the output voltage output from the rectifying and smoothing circuit; generating a predetermined second reference voltage; and comparing the output voltage and the second reference voltage to amplify a difference between them. 9. The method comprising: outputting an error amplification signal; and performing on / off control of the first and second switching elements based on the first and second error amplification signals. The control method described in 1. According to the output result of the first error amplification output, the PFC voltage is controlled by providing a switching pause period of the first and second switching elements, and the first error amplification output according to the output result of the second error amplification output. 10. The method of controlling a switching power supply according to claim 9, wherein the output voltage of the current resonance converter unit is controlled by changing a switching frequency of the first and second switching elements.   The on-duty immediately after one switching suspension period of the first and second switching elements is set to a half pulse that is approximately a half of a predetermined on-duty, and immediately before the other switching suspension period of the first and second switching elements. 11. The method of controlling a switching power supply device according to claim 10, wherein the on-duty is set to a half pulse that is approximately a half of the predetermined on-duty.

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