WO2020027290A1

WO2020027290A1 - One-converter-type insulated switching power source

Info

Publication number: WO2020027290A1
Application number: PCT/JP2019/030311
Authority: WO
Inventors: 羽田　正二
Original assignee: Ntn株式会社
Priority date: 2018-08-03
Filing date: 2019-08-01
Publication date: 2020-02-06

Abstract

Provided is a one-converter-type insulated switching power source wherein spike voltage is suppressed and switching control is simplified. This one-converter-type insulated switching power source comprises: a transformer, a primary-side switching element, at least one reactor connected to the secondary side of the transformer, and a smoothing capacitor connected to the secondary side of the transformer, wherein one end of the reactor is connected to one end of a secondary coil. The one-converter-type insulated switching power source further comprises: a first rectification element connected between the one end of the reactor and a reference potential end; a second rectification element connected between the other end of the reactor and an output end; a third rectification element connected between the other end of the secondary coil and the reference potential end; and a secondary-side switching element that is controlled with the same timing as the primary-side switching element so as allow or block conduction on a current path between the other end of the reactor and the reference potential end.

Description

One converter type isolated switching power supply

The present invention relates to a one-converter type insulated switching power supply.

2. Description of the Related Art As a switching power supply that converts AC power into DC power, a two-converter isolated switching power supply including a non-insulated boost converter as a power factor correction circuit and an isolated DC / DC converter at a subsequent stage is known. Typical methods of the isolated DC / DC converter at the subsequent stage include a forward method and a flyback method. The forward method is suitable for a large output power supply.

On the other hand, as in

Patent Documents

1 and 2, etc., a one-converter type switching power supply in which a non-insulated boost converter and an insulated DC / DC converter at the subsequent stage are integrated into one is also known.

The number of switching elements on the primary side of the insulated switching power supply may be one in principle. However, in order to increase the output and reduce the withstand voltage characteristics of the switching elements, a plurality of switching elements as disclosed in Patent Document 3 and the like are used. Are known.

JP-A-5-236747 JP-A-2002-300780 JP-A-2015-70716

The conventional one-converter isolated switching power supply described above has several problems. When the flyback method for improving the power factor is adopted, a large spike voltage is added to the flyback voltage generated when the switching element is turned off, so that the switching element on the primary side is required to have a breakdown voltage characteristic.

When the forward method is used to increase the output of the switching power supply, the output current is only generated when the electromotive voltage generated in the secondary coil of the transformer when the switching element is turned on exceeds the voltage of the smoothing capacitor at the output end. Flows. Therefore, no current is output in a range where the electromotive voltage of the secondary coil is small, which deteriorates the power factor.

Furthermore, when the full bridge method and / or the synchronous rectification method are adopted, precise and complicated control such as adjustment of the switching timing of the primary side and the secondary side and dead time control are required.

From the above situation, the present invention provides a one-converter isolated switching power supply that suppresses a spike voltage generated when a switching element is turned off, simplifies switching control between a primary side and a secondary side, and improves power factor. The purpose is to do.

In order to achieve the above object, the present invention provides the following configurations.
An aspect of the present invention, a transformer having a primary coil and a secondary coil wound in the same polarity,
At least one primary side switching element controlled to conduct or cut off a current path including the primary coil;
At least one reactor connected to the secondary side of the transformer,
A smoothing capacitor connected between an output terminal on the secondary side of the transformer and a reference potential terminal;
One end of the reactor is connected to one end of the secondary coil, and further,
A first rectifying element connected between one end of the reactor and the reference potential end;
A second rectifying element connected between the other end of the reactor and the output end;
A third rectifying element connected between the other end of the secondary coil and the reference potential end;
And at least one secondary-side switching element controlled at the same timing as the primary-side switching element to conduct or cut off a current path between the other end of the reactor and the reference potential end.
In a first preferred form, the at least one primary-side switching element is reciprocally controlled to conduct or interrupt the current of the primary coil, respectively, in at least one first group of primary-side switching. An element and at least one second group of primary switching elements;
A second reactor having one end connected to the other end of the secondary coil;
A fourth rectifying element connected between the other end of the second reactor and the output end;
A second secondary-side switching element that is controlled to conduct or cut off a current path between the other end of the second reactor and the reference potential end,
One of the secondary switching elements is controlled at the same timing as the primary switching element of the first group, and the other secondary switching element is controlled at the same timing as the primary switching element of the second group. Is done.
-In the first preferred embodiment, further preferably, further comprising a third reactor and a fifth rectifying element, one end of the third reactor is connected to one end of the secondary coil, A fifth rectifying element is connected between the other end of the third reactor and the output end, and
Furthermore, a fourth reactor and a sixth rectifier element are provided, one end of the fourth reactor is connected to the other end of the secondary coil, and the sixth rectifier element is connected to the other of the fourth reactor. Terminal and the output terminal.
-In the second preferred embodiment, the power supply apparatus further includes a fourth rectifying element connected between the other end of the secondary coil and an output end.
In the second preferred embodiment, more preferably, the third rectifying element is a switching element controlled in synchronization with the primary-side switching element.
In the second preferred embodiment, further preferably, further comprising a second reactor and a fifth rectifying element, one end of the second reactor is connected to one end of the secondary coil, A fifth rectifying element is connected between the other end of the second reactor and the output end.

(4) The one-converter isolated switching power supply according to the present invention can suppress the spike voltage generated when the switching element is turned off, simplify the switching control between the primary side and the secondary side, and improve the power factor.

FIG. 1 is a schematic configuration diagram of a circuit example of a first embodiment of the insulated switching power supply of the present invention. FIG. 2 is a timing chart in the circuit of FIG. FIGS. 3A and 3B schematically show currents flowing during the modes Ia and IIa in the circuit of FIG. FIGS. 4A and 4B schematically show currents flowing during the modes Ib and IIb in the circuit of FIG. FIG. 5 is a diagram schematically illustrating a circuit example of a second embodiment of the insulated switching power supply of the present invention. FIG. 6 is a timing chart in the circuit of FIG. FIGS. 7A and 7B schematically show currents flowing during the modes I and II in the circuit of FIG. FIG. 8 is a schematic configuration diagram of a circuit example of a third embodiment of the insulated switching power supply of the present invention. FIG. 9 is a timing chart in the circuit of FIG. FIGS. 10A and 10B schematically show currents flowing during the modes Ia and IIa in the circuit of FIG. FIGS. 11A and 11B schematically show currents flowing during the modes Ib and IIb in the circuit of FIG. FIG. 12 is a diagram schematically showing a circuit example of a fourth embodiment of the insulated switching power supply of the present invention. FIG. 13 is a timing chart of the circuit of FIG. FIGS. 14A and 14B schematically show currents flowing during the modes I and II in the circuit of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings shown as examples. In the drawings, the same or similar components in each embodiment are denoted by the same or similar reference numerals. In this specification, description common to each embodiment may be made only in the first embodiment.

ワン The one-converter isolated switching power supply of the present invention is preferably an AC / DC converter. Thus, a typical input voltage is a rectified sine wave AC voltage. However, the switching power supply of the present invention can similarly function when the input voltage is a square wave or a triangular wave voltage other than a sine wave, or a constant voltage.

(1) First Embodiment (1-1) Circuit Configuration of First Embodiment FIG. 1 schematically illustrates a circuit example of a first embodiment of a one-converter insulated switching power supply of the present invention. ing.

<Configuration of primary side of transformer T>
In the insulated switching power supply of FIG. 1, for example, an input voltage obtained by full-wave rectifying a sine wave AC voltage is input to input

terminals

1 and 2. The AC voltage here is, for example, a sine wave having a frequency of several Hz to several tens Hz generated by a system power supply or various power generation devices. However, the waveform of the input voltage is not limited to a sine wave, and may be any waveform having a positive potential. Also, an input voltage that has been half-wave rectified instead of full-wave rectification may be used. Since a rectifying unit for rectifying an AC voltage is well known, its illustration and description are omitted.

The transformer T is a transformer in which the primary coil N1 and the secondary coil N2 are wound in the same polarity (the winding start end of the coil is indicated by a black circle). This is a so-called forward transformer. On the primary side of the transformer T, there is provided a switching unit including a plurality of switching elements, each of which is on / off controlled to conduct or cut off a current flowing through the primary coil N1 by an input voltage.

スイッチング The switching unit in FIG. 1 forms a full bridge circuit. This full bridge circuit has four switching elements A1, A2, B1, and B2, and here is an N-channel MOSFET as an example. The full bridge circuit is suitable for a high-output switching power supply. The switching elements A1 and A2 constitute a first group (hereinafter, referred to as “group A”) that is simultaneously controlled on and off, and the switching elements B1 and B2 are simultaneously controlled on and off (second group) (hereinafter, “group B”). ").

Each switching element of the switching unit is controlled on / off by a control voltage applied to a gate which is a control terminal. The control voltage is preferably a PWM signal (here, a case where the control voltage is a PWM signal will be described as an example). The frequency of the PWM signal is higher than the frequency of the input AC, for example, several tens to several hundreds of kHz. Each switching element of the group A is on-off controlled by a control voltage V _A, the switching elements of group B, on-off controlled by a control voltage V _B.

Although not shown, the control voltage V _A, generates a predetermined PWM signal as V _B, the control unit outputs are separately provided.

<Configuration on the secondary side of transformer T>
One end of the secondary coil N2 of the transformer T (the winding start end) is connected to one end of the first reactor LA and the cathode of the diode D1. The anode of the diode D1 is connected to a ground terminal n which is a negative output terminal. The ground terminal n is a reference potential terminal on the secondary side. The other end of the first reactor LA is connected to the anode of the diode D2. The cathode of the diode D2 is connected to the positive output terminal p (hereinafter, simply referred to as "output terminal" means the positive output terminal p).

The switching element A3 is connected between the other end of the reactor LA and the ground end n. The switching element A3 is, for example, an N-channel MOSFET, and has a drain connected to the other end of the reactor LA and a source connected to the ground end n. Gate of the switching element A3 is on-off controlled by a control voltage V _a.

一端 One end of the second reactor LB and the cathode of the diode D3 are connected to the other end of the secondary coil N2 of the transformer T. The anode of the diode D3 is connected to the ground terminal n. The other end of the second reactor LB is connected to the anode of the diode D4. The cathode of the diode D4 is connected to the output terminal p.

The switching element B3 is connected between the other end of the reactor LB and the ground end n. The switching element B3 is, for example, an N-channel MOSFET, and has a drain connected to the other end of the reactor LB and a source connected to the ground end n. The gate of the switching element B3 is on / off controlled by the control voltage _Vb .

平滑 A smoothing capacitor C is connected between the output terminal p and the ground terminal n.

Control voltage V _a of the switching device A3 is basically the PWM signal for turning on and off at the same timing as the control voltage V _A of the switching element on the primary side of the A group. Similarly, the control voltage V _b of the switching element B3 is basically a PWM signal for turning on and off at the same timing as the control voltage V _B of the switching element on the primary side of the B group.

However, in order to ensure the insulation of the primary side and the secondary side of the transformer T, the control voltage V _A of the switching element on the primary _side, directly V _B, it is not preferable to be applied to the gate of the switching element A3, B3. Therefore, when used as a control voltage _V a, _{V b} of the control voltage _V A, the switching element of the _{V B} secondary A3, B3 transmits those voltage signals via an insulating means. As another example, the control voltage _V A, the same timing as _{V B} independent control voltage _V a, _{V b} was generated respectively, is transmitted to the switching elements A3, B3. The securing of insulation between the primary side and the secondary side with respect to this control voltage is the same in each embodiment described later.

(1-2) Circuit Operation of First Embodiment The operation of the circuit of the first embodiment shown in FIG. 1 will be described with reference to FIGS. 2, 3, and 4.

2 (a) to 2 (d) schematically show ON / OFF control signals of each switching element in the circuit of FIG.

Figure 2 (a) is a control voltage V _A of the switching elements of the group A of the full bridge circuit. Figure 2 (b) is a control voltage V _B of the switching elements of the group B of the full bridge circuit.

As shown in FIGS. 2A and 2B, the switching elements of group A and the switching elements of group B are on / off controlled reciprocally. That is, the control voltage V _A and V _B have the same frequency and duty ratio, the phase difference therebetween is 180 °. However, if the switching elements of group A and group B are turned on at the same time, a short circuit occurs, so a dead time (a period during which both are turned off) is provided.

Figure 2 (c) is a control voltage _{V a} of the switching element A3 of the secondary side. FIG. 2D shows the control voltage _Vb of the secondary-side switching element B3.

2) As shown in FIGS. 2 (c) and 2 (d), the switching elements A3 and B3 on the secondary side are basically turned on and off at the same timing as the switching elements in the A and B groups on the primary side. Therefore, the switching element A3 and the switching element B3 are also turned on and off contrary to each other.

2 (e) (f) (g) (h) is a timing chart showing an example of a waveform of a current flowing through each component. 2 (e), (f), (g), and (h) show the current in the discontinuous mode, the current may be in the critical mode or the continuous mode depending on the load of the load (see the following). The same applies to the timing chart of each embodiment.)

に関して As shown in FIG. 2, regarding the circuit operation, the on period of the switching elements of the A group is referred to as mode Ia, and the off period is referred to as mode IIa. Further, the on period of the switching elements in the B group is referred to as mode Ib, and the off period is referred to as mode IIb. As shown in the figure, the two modes (for example, mode IIa and mode Ib) may overlap in time, but the circuit operation in each mode is performed independently.

<Operation of Mode Ia>
FIG. 3A shows the current in the mode Ia (the flow of the current is indicated by a solid line with an arrow, and so on). Referring to FIG. 3A, when the switching elements A1 and A2 are turned on on the primary side, a current ia1 flows through the primary coil N1 due to the input voltage (see FIG. 2E).

(4) When the current ia1 flows through the primary coil, an electromotive voltage is generated in the secondary coil N2 by mutual induction, and the current ia2 flows through the secondary coil N2 through the diode D3 which becomes forward biased (see FIG. 2 (f)). At this time, since the switching element A3 is also on, the output terminal of the reactor LA is at the ground potential. The diodes D1 and D2 are reverse biased. Therefore, the current ia2 flows through the path of the diode D3 → the secondary coil N2 → the reactor LA → the switching element A3 → the ground end n (see FIGS. 2 (f) and 2 (g)). The current ia2 is not supplied to the load, but the reactor LA is excited by the current ia2 to store magnetic energy.

Here, the smoothing capacitor C in the steady state is charged with a substantially constant voltage except for ripple fluctuations. A forward current in a general forward power supply flows only when the electromotive voltage of the secondary coil N2 exceeds the voltage of the smoothing capacitor C. When a sine wave input voltage is applied to the

input terminals

1 and 2, for example, in a small input voltage range, the forward voltage cannot flow because the secondary coil N2 also has a small electromotive voltage. This causes a decrease in the power factor in a general forward type power supply.

In contrast, in the circuit of FIG. 1, the current ia2 can flow through the reactor LA regardless of the magnitude of the electromotive voltage of the secondary coil N2. Therefore, regardless of the magnitude of the input voltage, power is transmitted from the primary side to the secondary side of the transformer T during the ON period of the switching element, and the power is stored in the reactor LA. This contributes to a good power factor.

<Operation of Mode IIa>
FIG. 3B shows the current in the mode IIa. When the switching elements A1 and A2 are turned off on the primary side, the current ia1 on the primary side is cut off, and the current ia2 on the secondary side is also cut off (see FIGS. 2E and 2F). A counter electromotive voltage is generated in the primary coil N1, the secondary coil N2, and the reactor LA of the transformer T. The diodes D1 and D2 are forward biased. Therefore, the current ia3 flows through the path of the diode D1, the reactor LA, the diode D2, and the output terminal p (see FIG. 2G). The magnetic energy accumulated in the reactor LA in the mode Ia is released by the current ia3. The diode D1 functions as a freewheeling diode.

<Operation of Mode Ib and Mode IIb>
FIGS. 4A and 4B show currents in the mode Ib and the mode IIb, respectively. The circuit operations in the modes Ib and IIb have the opposite polarities and are almost symmetrical to the circuit operations in the modes Ia and IIa, respectively, but are substantially the same.

電流 As shown in FIG. 4A, in the mode Ib, a current ib2 symmetrical to the current ia2 in the mode Ia flows (see FIG. 2F). Further, as shown in FIG. 4B, in the mode IIb, a current ib3 symmetrical to the current ia3 in the mode IIa flows.

<Characteristics of circuit operation>
In this circuit, regardless of the magnitude of the input voltage, when a current flows in the primary coil of the transformer T, a current can flow in the secondary coil N2, and the reactor connected in series to the secondary coil N2 by the current. Magnetic energy is stored in LA and LB. As a result, regardless of the magnitude of the input voltage, power is always transmitted from the primary side to the secondary side of the transformer T by mutual induction. Therefore, almost no magnetic energy is stored in the transformer T. As a result, since no spike voltage is generated on both the primary side and the secondary side of the transformer T, a spike suppressing means such as a snubber circuit or a magnetic flux resetting means becomes unnecessary, or they are made extremely small. Can be. For the same reason, almost no return current to the input side in the full bridge circuit is generated. As a result, power loss is reduced, and power conversion efficiency can be improved.

Furthermore, the on / off of the switching elements A3 and B3 on the secondary side is basically the same timing as the on / off of the switching elements of the A group and the B group on the primary side, but it is not necessary to strictly synchronize them. As a result, the configuration for on / off control of the switching element can be simplified.

For example, referring to FIGS. 2 (a) and 2 (c), than the time t _A of the switching element on the primary side of the A group is turned off, the time t _a when the switching element A3 of the secondary side becomes off Suppose it was a little faster. In that case, at the time t _a when the switching element A3 is turned off, only the current ia2 in FIG. 3 (a), commutated by magnetic energy from the reactor LA current ia3 in FIG. 3 (b) is discharged as soon as possible It is.

Conversely, the switching element on the primary side of the A group than the time t _A turns off, the switching element A3 of the secondary side when t _a turns off was slow somewhat. In this case, the current ia2 in FIG. 3A becomes zero, but the magnetic energy is held in the reactor LA until the switching element A3 is turned off, and when the switching element A3 is turned off, the current ia2 in FIG. Current ia3 flows, and magnetic energy is released from reactor LA.

As described above, even if the on / off timing of the switching element A3 slightly deviates from the on / off of the switching elements of the primary A group, the short circuit of the switching element A3 does not occur.

Further, for example, FIG. 2 (b) With reference to FIG. 2 (d), the a time t _B of the switching element on the primary side of the B group is turned on, and the time point t _b of the switching element B3 is on the secondary side However, the current ib2 shown in FIG. 4A only starts to flow from the point when both are turned on even if they are slightly different.

において In the present specification, regarding the on / off control of the switching element on the secondary side, the “same timing” as that of the switching element on the primary side has the same meaning as described above. On the other hand, "synchronous" means that the on / off timing is strictly controlled so as not to cause a short circuit of the switching element as in, for example, the synchronous rectification method (for example, one is turned off first and then the other is turned off). Means that.

(2) Second Embodiment (2-1) Circuit Configuration of Second Embodiment FIG. 5 schematically shows a circuit example of a second embodiment of a one-converter type insulated switching power supply of the present invention. I have.

<Configuration of primary side of transformer T>
In the insulated switching power supply of FIG. 5, for example, an input voltage obtained by full-wave rectifying a sine wave AC voltage is input to input

terminals

1 and 2. The input voltage is the same as in the first embodiment. Further, a transformer T having a primary coil N1 and a secondary coil N2 is a forward transformer similar to that of the first embodiment. The input terminal 1 is connected to one end (starting end) of the primary coil N1 of the transformer T.

In the second embodiment, on the primary side of the transformer T, there is one switching element Q1 that is on / off controlled to conduct or cut off the current flowing through the primary coil N1 by the input voltage. The switching element Q1 is, for example, an N-channel MOSFET here. The drain is connected to the other end of the primary coil N1, and the source is connected to the input terminal 2 which is the primary-side reference potential end (ground end). The switching element Q1 is on-off controlled by a control voltage V _Q which is applied to the gate is the control terminal. The control voltage _VQ is preferably a PWM signal, and is the same as in the first embodiment.

Although not shown, it generates a predetermined PWM signal as the control voltage V _Q, the control unit outputs are separately provided.

<Configuration on the secondary side of transformer T>
One end of the secondary coil N2 of the transformer T (the winding start end) is connected to one end of the reactor L and the cathode of the diode D1. The anode of the diode D1 is connected to a ground terminal n which is a negative output terminal. The ground terminal n is a reference potential terminal on the secondary side. The other end of the reactor L is connected to the anode of the diode D2. The cathode of the diode D2 is connected to an output terminal p which is a positive output terminal.

The switching element Q2 is connected between the other end of the reactor L and the ground end n. The switching element Q2 is, for example, an N-channel MOSFET, and has a drain connected to the other end of the reactor L and a source connected to the ground end n. Gate of the switching element Q2 is on-off controlled by a control voltage V _q. Control voltage V _q of the switching element Q2 is basically a PWM signal for turning on and off at the same timing as the control voltage V _Q of the switching element Q1 on the primary side.

カソード The other end of the secondary coil N2 of the transformer T is connected to the cathode of a diode D3. The anode of the diode D3 is connected to the ground terminal n. Further, the other end of the secondary coil N2 is also connected to the anode of the diode D4. The cathode of the diode D4 is connected to the output terminal p.

In a preferred example, a switching element Q3 shown in a portion surrounded by a chain line can be provided instead of the diode D3. The switching element Q3 is, for example, an N-channel MOSFET, and has a drain connected to the other end of the secondary coil N2 and a source connected to the ground end n. Gate of the switching element Q3 is on-off controlled by a control voltage V _q3 synchronized with the control voltage V _Q of the switching element Q1 on the primary side. The use of the switching element Q3 is advantageous in that there is no loss due to the forward voltage drop of the diode when the diode D3 is used.

In each embodiment of the present invention, a diode is used as a typical example of the rectifying element. However, an element that functions like a diode by control, such as the switching element Q3, is also included in the category of the rectifying element.

(2-2) Circuit Operation of Second Embodiment The operation of the circuit of the second embodiment shown in FIG. 5 will be described with reference to FIGS.

FIGS. 6A and 6B schematically show ON / OFF control signals of each switching element in the circuit of FIG.

6 (a) is a control voltage V _Q of the primary side of the switching element Q1. 6 (b) is a control voltage _{V q} of the secondary side of the switching element Q2. The switching element Q2 on the secondary side is basically turned on and off at the same timing as the switching element Q1 on the primary side. In the circuit of FIG. 5, when the switching element Q3 is used instead of the diode D3, on / off control is performed so as to synchronize with the switching element Q1 on the primary side.

6 (c), (d) and (e) are timing charts showing an example of a waveform of a current flowing through each component.

As shown in FIG. 6, regarding the circuit operation, the ON period of the switching element is referred to as mode I, and the OFF period is referred to as mode II. Mode I and mode II are repeated alternately.

<Operation of Mode I>
FIG. 7A shows a current flow in the mode I. When the switching element Q1 is turned on on the primary side, a current i1 flows through the primary coil N1 due to the input voltage (see FIG. 6C). When the current i1 flows through the primary coil, an electromotive force is generated in the secondary coil N2 by mutual induction, and the current i2 flows through the secondary coil N2 through the diode D3 (or the switching element Q3) that becomes forward biased (FIG. 6D). reference). At this time, since the switching element Q2 is on, the output side terminal of the reactor L is at the ground potential. The diodes D1, D2, D4 are reverse biased. Therefore, the current i2 flows through the path of the diode D3 (or the switching element Q3) → the secondary coil N2 → the reactor L → the switching element Q2 → the ground terminal n (see FIGS. 6D and 6E). Although the current i2 is not supplied to the load, the reactor L is excited by the current i2 and magnetic energy is accumulated.

(5) In the circuit of FIG. 5, similarly to the circuit of FIG. 1, the current ia2 can flow through the reactor L regardless of the magnitude of the electromotive voltage of the secondary coil N2. Therefore, power is transmitted from the primary side to the secondary side of the transformer T during the ON period of the switching element, regardless of the magnitude of the input voltage, and the power is stored in the reactor L. This contributes to a good power factor.

<Mode II operation>
FIG. 7B shows the current in mode II. When the switching element Q1 is turned off on the primary side, the current i1 of the primary coil N1 is cut off, and the current i2 on the secondary side is also cut off (see FIGS. 6C and 6D). A counter electromotive voltage is generated in the primary coil N1, the secondary coil N2, and the reactor L of the transformer T. The diodes D1 and D4 become forward-biased, and a current i4 flows through a path from the diode D1, the secondary coil N2, the diode D4, and the output terminal p (see FIG. 6D). Thereby, the magnetic energy remaining in the transformer T is emitted to the secondary side.

On the other hand, when the switching element Q2 is turned off and the terminal on the output side of the reactor L becomes high potential, the diode D2 becomes forward biased. Therefore, the current i3 flows through the path from the diode D1, the reactor L, the diode D2, and the output terminal p (see FIG. 6E). The magnetic energy accumulated in the reactor L in the mode I is released by the current i3. The diode D1 functions as a freewheeling diode.

<Characteristics of circuit operation>
In this circuit, regardless of the magnitude of the input voltage, when a current flows in the primary coil of the transformer T, a current can flow in the secondary coil N2, and the reactor connected in series to the secondary coil N2 by the current. Magnetic energy is stored in L. As a result, regardless of the magnitude of the input voltage, power is always transmitted from the primary side to the secondary side of the transformer T by mutual induction. Therefore, almost no magnetic energy is stored in the transformer T. As a result, since no spike voltage is generated on both the primary side and the secondary side of the transformer T, a spike suppressing means such as a snubber circuit or a magnetic flux resetting means becomes unnecessary, or they are made extremely small. Can be. As a result, power loss is reduced, and power conversion efficiency can be improved.

Furthermore, the on / off of the switching element Q2 on the secondary side is at the same timing as the on / off of the switching element Q1 on the primary side, but it is not necessary to strictly synchronize them. As a result, the configuration for on / off control can be simplified. This is as described in the first embodiment with reference to the symbols tA and ta and the symbols tB and tb in FIGS. 2A to 2D.

(4) Synchronous control is required for the switching element Q3 functioning as a rectifying element to avoid a short circuit. The switching element Q3 must be turned off before the switching element Q1 is turned off.

(3) Third Embodiment The third embodiment is a modification of the first embodiment, and therefore only the parts different from the first embodiment will be described.

(3-1) Circuit Configuration of Third Embodiment FIG. 8 schematically shows a circuit example of a third embodiment of a one-converter insulated switching power supply of the present invention.

<Configuration of primary side of transformer T>
The configuration of the primary side of the transformer T is the same as that of the first embodiment.

<Configuration on the secondary side of transformer T>
The third embodiment has all of the components of the first embodiment on the secondary side of the transformer T. Furthermore, the third embodiment has additional components on the secondary side of the transformer T. As an additional component, it has a reactor LA1 and a diode D5, one end of the reactor LA1 is connected to one end of the secondary coil N2 of the transformer T, and the diode D5 is connected between the other end of the reactor LA1 and the output end p. It is connected. As a further additional component, it has a reactor LB1 and a diode D6, one end of the reactor LB1 is connected to the other end of the secondary coil N2 of the transformer T, and the diode D6 is connected between the other end of the reactor LB1 and the output end p. It is connected to the.

(3-2) Circuit Operation of Third Embodiment The operation of the circuit of the third embodiment shown in FIG. 8 will be described with reference to FIGS. 9, 10, and 11.

FIGS. 9A to 9D schematically show ON / OFF control signals of each switching element in the circuit of FIG. These are exactly the same as FIGS. 2 (a) to 2 (d).

電流 The current of the primary coil N1 of the transformer T shown in FIG. 9E is substantially the same as that of FIG. 2E with respect to timing and waveform (change in increase and decrease).

電流 In the current of the secondary coil N2 of the transformer T shown in FIG. 9 (f), the currents ia4 and ib4 flowing through the reactor LA1 may be added to the currents ia2 and ib2 shown in FIG. 2 (f). However, the currents ia4 and ib4 may or may not flow depending on the magnitude of the input voltage, and are shown in parentheses.

The currents flowing through the reactors LA and LB shown in FIGS. 9 (g) and 9 (h) are the same as the currents ia2, ia3, ib2 and ib3 shown in FIGS. 2 (g) and 2 (h).

FIGS. 9 (i) and (j) show currents flowing through the added reactors LA1 and LB1. Since the currents ia5 and ib5 flow only when the currents ia4 and ib4 flow, they are shown in parentheses.

9, also in FIG. 9, as in FIG. 2, regarding the circuit operation, the ON period of the switching element of Group A is referred to as mode Ia, and the OFF period is referred to as mode IIa. Further, the on period of the switching elements in the B group is referred to as mode Ib, and the off period is referred to as mode IIb.

<Operation of Mode Ia>
FIG. 10A shows the current in the mode Ia. When the switching elements A1 and A2 are turned on on the primary side, a current ia1 flows through the primary coil N1 due to the input voltage (see FIG. 9E).

(4) When the current ia1 flows through the primary coil, an electromotive force is generated in the secondary coil N2 by mutual induction, and the current ia2 flows through the secondary coil N2 through the diode D3 that becomes forward-biased (see FIG. 9F). The current ia2 flows through a path from the diode D3, the secondary coil N2, the reactor LA, the switching element A3, and the ground terminal n (see FIGS. 9F and 9G). The current ia2 is not supplied to the load, but the reactor LA is excited by the current ia2 to store magnetic energy. The current ia2 flows regardless of the magnitude of the electromotive voltage of the secondary coil N2.

(4) When the electromotive voltage of the secondary coil N2 exceeds the voltage of the smoothing capacitor C, a current ia4 can flow to the output terminal p through the reactor LA1 and the diode D5. The current ia4 flows through a path from the diode D3 → the secondary coil N2 → the reactor LA1 → the diode D5 → the output terminal p (see FIG. 9 (i)). The current ia4 corresponds to a forward current in a forward switching power supply. The current ia4 is supplied to the load, and the reactor LA1 is excited by the current ia4 to store magnetic energy. On the other hand, when the electromotive voltage of the secondary coil N2 does not exceed the voltage of the smoothing capacitor C, the current ia4 does not flow. Whether the current ia4 flows depends on the magnitude of the input voltage.

<Operation of Mode IIa>
FIG. 10B shows the current in the mode IIa. When the switching elements A1 and A2 are turned off on the primary side, the current ia1 on the primary side is cut off, and the current ia2 on the secondary side is also cut off (see FIGS. 9E and 9F). A counter electromotive voltage is generated in the primary coil N1, the secondary coil N2, and the reactor LA of the transformer T. The diodes D1 and D2 are forward biased. Therefore, the current ia3 flows through the path of the diode D1, the reactor LA, the diode D2, and the output terminal p (see FIG. 9G). The magnetic energy accumulated in the reactor LA in the mode Ia is released by the current ia3. The diode D1 functions as a freewheeling diode.

場合 When the current ia4 flows in the mode Ia described above, the current ia5 flows in the mode IIa. The current ia5 flows through a path from the diode D1, the reactor LA1, the diode D5, and the output terminal p (see FIG. 9 (i)). When the current ia5 flows, the magnetic energy accumulated in the reactor LA1 in the mode Ia is released. When the current ia4 does not flow in the mode Ia, the current ia5 does not naturally flow in the mode IIa.

<Operation of Mode Ib and Mode IIb>
FIGS. 11A and 11B show currents in the mode Ib and the mode IIb, respectively. The circuit operation in the mode Ib and the mode IIb has a polarity opposite to that of the circuit operation in the mode Ia and the mode IIa and is almost symmetric, but is substantially the same.

電流 As shown in FIG. 11A, in the mode Ib, currents ib2 and ib4 symmetric to the currents ia2 and ia4 in the mode Ia flow (see FIGS. 9F and 9J). In addition, as shown in FIG. 11B, in the mode IIb, currents ib3 and ib5 symmetric to the currents ia3 and ia5 in the mode IIa flow (FIGS. 9F and 9J). However, ib4 and ib5 can flow only when the electromotive voltage of the secondary coil N2 exceeds the voltage of the smoothing capacitor C.

<Characteristics of circuit operation>
In the third embodiment, when the input voltage is large, that is, when the electromotive voltage of the secondary coil N2 of the transformer T exceeds the voltage of the smoothing capacitor C, the forward voltage is passed through the reactor LA1 and the diode D5 or through the reactor LB1 and the diode D6. A current can be output. Therefore, the third embodiment has the same features as those described above with respect to the first embodiment, and can output higher power than the first embodiment.

(4) Fourth Embodiment The fourth embodiment is a modification of the second embodiment, and therefore, only different points from the second embodiment will be described.

(4-1) Circuit Configuration of Fourth Embodiment FIG. 12 schematically shows a circuit example of a fourth embodiment of a one-converter insulated switching power supply of the present invention.

<Configuration of primary side of transformer T>
The configuration of the primary side of the transformer T is the same as that of the second embodiment.

<Configuration on the secondary side of transformer T>
The fourth embodiment has all of the components of the second embodiment on the secondary side of the transformer T. Furthermore, the fourth embodiment has a reactor L1 and a diode D5 as additional components on the secondary side of the transformer T. One end of reactor L1 is connected to one end of secondary coil N2 of transformer T, and diode D5 is connected between the other end of reactor L1 and output end p.

(4-2) Circuit Operation of Fourth Embodiment The operation of the circuit of the fourth embodiment shown in FIG. 12 will be described with reference to FIGS.

FIGS. 13A and 13B schematically show ON / OFF control signals of each switching element in the circuit of FIG. These are exactly the same as FIGS. 6 (a) and 6 (b).

The current of the primary coil N1 of the transformer T shown in FIG. 13C is basically the same as that of FIG. 6C with respect to timing and waveform (increase / decrease of current).

電流 In the current of the secondary coil N2 of the transformer T shown in FIG. 13D, a current i5 flowing through the reactor L1 may be added to the current i2 shown in FIG. 6D. However, the current i5 is shown in parentheses because it may or may not flow depending on the magnitude of the input voltage.

電流 The current flowing through reactor L shown in FIG. 13 (e) is the same as currents i2 and i3 shown in FIG. 6 (e).

FIG. 13 (f) shows a current flowing through the reactor L1. Since the current i6 also flows only when the current i5 flows, it is shown in parentheses.

13, in FIG. 13, as in FIG. 6, regarding the circuit operation, the ON period of the switching element is referred to as mode I, and the OFF period is referred to as mode II.

<Operation of Mode I>
FIG. 14A shows the current in the mode I. When the switching element Q1 is turned on on the primary side, a current i1 flows through the primary coil N1 due to the input voltage (see FIG. 13C).

(4) When the current i1 flows through the primary coil, an electromotive force is generated in the secondary coil N2 by mutual induction, and the current i2 flows through the secondary coil N2 through the diode D3 that becomes forward biased (see FIG. 13D). The current i2 flows through a path from the diode D3, the secondary coil N2, the reactor L, the switching element Q2, and the ground terminal n (see FIGS. 13D and 13E). Although the current i2 is not supplied to the load, the reactor L is excited by the current i2 and magnetic energy is accumulated. The current i2 flows regardless of the magnitude of the electromotive voltage of the secondary coil N2.

(4) Further, when the electromotive voltage of the secondary coil N2 exceeds the voltage of the smoothing capacitor C, the current i5 can flow to the output terminal p through the reactor L1 and the diode D5. The current i5 flows through a path from the diode D3, the secondary coil N2, the reactor L1, the diode D5, and the output terminal p (see FIG. 13E). The current i5 corresponds to a forward current in a forward-type switching power supply. The current i5 is supplied to the load, and the reactor L1 is excited by the current i5 to store magnetic energy. On the other hand, when the electromotive voltage of the secondary coil N2 does not exceed the voltage of the smoothing capacitor C, the current i5 does not flow. Whether the current i5 flows depends on the magnitude of the input voltage.

<Mode II operation>
FIG. 14B shows the current in mode II. When the switching element Q1 is turned off on the primary side, the current i1 on the primary side is cut off, and the current i2 on the secondary side is also cut off (see FIGS. 13C and 13D). A counter electromotive voltage is generated in the primary coil N1, the secondary coil N2, and the reactor L of the transformer T. The diodes D1 and D2 are forward biased. Therefore, the current i3 flows through the path of the diode D1, the reactor L, the diode D2, and the output terminal p (see FIG. 13E). The magnetic energy accumulated in the reactor L in the mode I is released by the current i3. The diode D1 functions as a freewheeling diode.

When the current i5 flows in the mode I described above, the current i6 flows in the mode II. The current i6 flows through a path from the diode D1, the reactor L1, the diode D5, and the output terminal p (see FIG. 13E). When the current i6 flows, the magnetic energy stored in the reactor L1 in the mode I is released. When the current i5 does not flow in the mode I, the current i6 naturally does not flow in the mode II.

<Characteristics of circuit operation>
In the fourth embodiment, when the input voltage is large, that is, when the electromotive voltage of the secondary coil N2 of the transformer T exceeds the voltage of the smoothing capacitor C, a forward current can be output through the reactor L1 and the diode D5. Therefore, the fourth embodiment has the same features as those described above with respect to the second embodiment, and can output higher power than the second embodiment.

(5) Other Embodiments Although not shown, a push-pull circuit or a half-bridge circuit can be applied as another configuration of the primary-side switching unit in the circuit of the above-described first or third embodiment.

In each of the above embodiments, the switching element in the switching unit may be an IGBT or a bipolar transistor other than the MOSFET.

In each of the above embodiments, each diode is an example of a rectifying element that can conduct current in one direction and block current in the opposite direction. Therefore, another element or circuit having a similar function can be used.

絶縁 The above-described insulated switching power supply of the present invention is not limited to the configuration example shown in the drawings, but can be variously modified within the scope of the gist of the present invention.

p Positive output terminal n Ground terminal T Transformer LA, LB, L, LA1, LB1, L, L1 Reactor N1 Primary coil N2 Secondary coil A1, A2, A3, B1, B2, B3, Q1, Q2, Q3 Switching element (MOSFET)
D1, D2, D3, D4, D5, D6 Diode C Smoothing capacitor

Claims

A transformer having a primary coil and a secondary coil wound in the same polarity,
At least one primary side switching element controlled to conduct or cut off a current path including the primary coil;
At least one reactor connected to the secondary side of the transformer,
A smoothing capacitor connected between an output terminal on the secondary side of the transformer and a reference potential terminal;
One end of the reactor is connected to one end of the secondary coil, and further,
A first rectifying element connected between one end of the reactor and the reference potential end;
A second rectifying element connected between the other end of the reactor and the output end;
A third rectifying element connected between the other end of the secondary coil and the reference potential end;
And at least one secondary-side switching element controlled at the same timing as the primary-side switching element to conduct or cut off a current path between the other end of the reactor and the reference potential end. One-converter isolated switching power supply.
The at least one first group of primary switching elements and the at least one second group of at least one first group, wherein the at least one primary side switching element is reciprocally controlled to conduct or block the current of the primary coil, respectively; It is composed of a primary side switching element,
A second reactor having one end connected to the other end of the secondary coil;
A fourth rectifying element connected between the other end of the second reactor and the output end;
A second secondary-side switching element that is controlled to conduct or cut off a current path between the other end of the second reactor and the reference potential end,
One of the secondary switching elements is controlled at the same timing as the primary switching element of the first group, and the other secondary switching element is controlled at the same timing as the primary switching element of the second group. Characterized to be
Furthermore, a third reactor and a fifth rectifying element are provided, one end of the third reactor is connected to one end of the secondary coil, and the fifth rectifying element is connected to the other end of the third reactor. And the output terminal, and
Furthermore, a fourth reactor and a sixth rectifier element are provided, one end of the fourth reactor is connected to the other end of the secondary coil, and the sixth rectifier element is connected to the other of the fourth reactor. The one-converter type insulated switching power supply according to claim 2, wherein the one-converter type switching power supply is connected between an output terminal and the output terminal.
The one-switching type insulated switching power supply according to claim 1, further comprising a fourth rectifying element connected between the other end of the secondary coil and an output end.
5. The one-converter type insulated switching power supply according to claim 4, wherein the third rectifying element is a switching element controlled in synchronization with the primary-side switching element.
Furthermore, a second reactor and a fifth rectifying element are provided, one end of the second reactor is connected to one end of the secondary coil, and the fifth rectifying element is connected to the other end of the second reactor. 6. The one-converter type insulated switching power supply according to claim 4, wherein the switching power supply is connected between the power supply and the output terminal.