CN213783142U - Power conversion circuit, DC-DC converter, and AC-DC converter - Google Patents

Abstract

Provided are a power conversion circuit, a DC-DC converter, and an AC-DC converter. A wider input voltage can be handled than a forward converter. The present disclosure relates to a power conversion circuit having a transformer, an input circuit including a primary winding of the transformer, and an output circuit including a secondary winding of the transformer. The input circuit includes a primary side winding and a switching element connected in series between one input terminal and the other input terminal. The output circuit includes a secondary winding, a 1 st current line connecting one end of the secondary winding to a negative side terminal of the output, a 2 nd current line connecting the other end of the secondary winding to a positive side terminal of the output, an output coil connected to the 1 st current line and the 2 nd current line in parallel with the output, and a commutation diode provided on at least 1 of the 1 st current line and the 2 nd current line.

Description

Power conversion circuit, DC-DC converter, and AC-DC converter

Technical Field

The utility model relates to a power conversion circuit, DC-DC converter and AC-DC converter.

Background

As one of the insulation type DC-DC converters, there is a forward converter circuit. The converter circuit achieves power conversion with relatively few components. Patent document 1 describes a single-converter type power conversion circuit that directly generates a constant voltage by a forward converter based on an input current rectified by a diode bridge. The power conversion circuit can be said to be a circuit in which a PFC circuit and a DC-DC converter circuit are integrated.

Patent document 1: japanese laid-open patent publication No. 2010-284031

The forward converter is suitable for a small and large power application as compared with the reverse converter, but on the other hand, there is a limit that only a voltage lower than the voltage obtained by multiplying the input voltage by the transformer winding ratio can be output. For example, when the transformer winding ratio is set to n: 1 and the input voltage is Vin, the maximum value of the output voltage is Vin/n. Therefore, the forward converter has a problem that it is difficult to cope with a wide input voltage, and conversion efficiency is lowered.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a compare in forward converter, can deal with the input voltage's of wider width power conversion circuit.

The utility model discloses a circuit of a mode is power conversion circuit, and it has: a transformer; an input circuit including a primary winding of the transformer; and an output circuit including a secondary side winding of the transformer, wherein the input circuit includes the primary side winding and a switching element connected in series between an input terminal on one side and an input terminal on the other side, the output circuit including: the secondary side winding; a 1 st current line connecting one end of the secondary side winding and a negative side terminal of an output; a 2 nd current line connecting the other end of the secondary side winding with a positive side terminal of an output; an output coil connected to the 1 st current line and the 2 nd current line in parallel with the output; and a commutation diode disposed on at least 1 of the 1 st current line and the 2 nd current line.

In the power conversion circuit according to the above aspect, the direction of the current flowing through the secondary winding when the switch is turned on is a direction from the other end of the secondary winding toward one end.

In the power conversion circuit according to the above aspect, the output circuit further includes a parallel line connected in parallel to the 1 st current line or the 2 nd current line, the 1 st current line or the 2 nd current line has a diode that allows conduction of a current flowing to the secondary winding but restricts conduction in an opposite direction when the switch is on, the parallel line has a diode that allows conduction of a current flowing to the secondary winding but restricts conduction in an opposite direction when the switch is off, and a voltage drop when the 1 st current line or the 2 nd current line is on is smaller than a voltage drop when the parallel line is on.

In the power conversion circuit of the above aspect, the 1 st current line or the 2 nd current line has a diode that permits conduction of a current flowing to the secondary winding when the switch is on but restricts conduction in the opposite direction, and the input circuit further includes a reset circuit that releases excitation energy stored in the transformer when the switch is on when the switch is off.

The DC-DC converter according to one aspect of the present invention includes the above-described power conversion circuit, wherein the input terminal of one side of the input circuit and the input terminal of the other side of the input circuit are input terminals connected to a DC power supply.

The AC-DC converter of one embodiment of the present invention has the above-described power conversion circuit, the input circuit further includes a rectifier circuit that rectifies alternating current outputted from the alternating current power supply, and the input terminal of one side of the input circuit and the input terminal of the other side are input terminals connected to the rectifier circuit.

According to the utility model discloses, compare in forward converter, can deal with the input voltage of wider width.

Drawings

Fig. 1 is a circuit diagram of a power conversion circuit having a basic configuration according to the present embodiment.

Fig. 2a is a circuit diagram showing the operation of the power conversion circuit when the switch is turned on. Fig. 2b is a circuit diagram showing the operation of the power conversion circuit when the switch is off. Fig. 2c is a graph showing the time variation of the coil current in the continuous current mode.

Fig. 3 is a circuit diagram of a general forward converter.

Fig. 4a to 4b are circuit diagrams of a power conversion circuit according to modification 1. Fig. 4a is a circuit diagram showing the operation of the power conversion circuit when the switch is turned on. Fig. 4b is a circuit diagram showing the operation of the power conversion circuit when the switch is off.

Fig. 5a to 5c are circuit diagrams showing changes in the circuit configuration of the power conversion circuit according to modification 1.

Fig. 6 is another circuit diagram of the power conversion circuit according to modification 1.

Fig. 7 is a circuit diagram of a power conversion circuit according to modification 2.

Fig. 8 is another circuit diagram of the power conversion circuit according to modification 2.

Fig. 9 is another circuit diagram of the power conversion circuit according to modification 2.

Fig. 10 is a circuit diagram of a power conversion circuit according to modification 3.

Fig. 11 is a circuit diagram showing an example of a control circuit of the power conversion circuit.

Description of the reference symbols

TR: a transformer; w 1: a primary side winding; w 2: a secondary side winding; ws: a secondary winding; d1: a commutation diode; d2: a diode; d3: a diode; ds: a diode; LN 1: a 1 st current line; LN 2: a 2 nd current line; l: an output coil; c: an output capacitor; PS: inputting a power supply; DC: a direct current power supply; AC: an alternating current power supply; DB: a diode bridge (rectifier circuit); SW: a switching element (switch); LD: a load (output); 10: a power conversion circuit (basic structure: DC-DC converter); 20: an input circuit; 30: an output circuit; 40: a control circuit; 60: a power conversion circuit (1 st modification: DC-DC converter); 70: a power conversion circuit (modification 2: DC-DC converter); 72: a reset circuit; 74: a reset circuit; 76: a reset circuit; 80: a power conversion circuit (modification 3: AC-DC converter).

Detailed Description

< brief summary of embodiments of the present invention >

The following describes an outline of an embodiment of the present invention. (1) The power conversion circuit of the present embodiment includes a transformer TR, an input circuit 20 including a primary winding w1 of the transformer TR, and an output circuit 30 including a secondary winding w2 of the transformer TR. The input circuit 20 includes the primary winding w1 and a switching element SW connected in series between one input terminal and the other input terminal.

The output circuit 30 includes the secondary winding w2, a 1 st current line LN1 connecting one end of the secondary winding w2 to a negative side terminal of an output, a 2 nd current line LN2 connecting the other end of the secondary winding w2 to a positive side terminal of the output, an output coil L connected to the 1 st and 2 nd current lines LN1 and LN2 in parallel to the output, and a commutation diode D1 provided on at least 1 of the 1 st and 2 nd current lines LN1 and LN 2.

(2) In the power conversion circuit of the present embodiment, the direction of the current flowing to the secondary winding w2 when the switch is turned on is, for example, a direction from the other end of the secondary winding w2 to one end.

According to the power conversion circuit of the present embodiment, since the output circuit 30 having the above-described circuit configuration is employed, when the switching element SW is controlled in the continuous current mode, the ratio of the output voltage to the input voltage can be adjusted according to the ratio of the on time to the off time. Therefore, there is no limitation in accordance with the winding ratio of the transformer TR, and it is possible to cope with a wider input voltage than the forward converter.

(3) In the power conversion circuit according to the present embodiment, it is preferable that the output circuit 30 further includes a parallel line LN3 connected in parallel to the 1 st current line or the 2 nd current lines LN1, LN2, wherein the 1 st current line or the 2 nd current line LN1, LN2 has a diode D3 that allows conduction of a current flowing through the secondary winding w2 but restricts conduction in the opposite direction when the switch is on, the parallel line LN3 has a diode D2 that allows conduction of a current flowing through the secondary winding w2 but restricts conduction in the opposite direction when the switch is off, and a voltage drop when the 1 st current line or the 2 nd current line LN1, LN2 is on is smaller than a voltage drop when the parallel line LN3 is on.

In this way, accumulation of excitation energy of transformer TR can be prevented only by using diodes D2 and D3 having relatively low cost and low withstand voltage. Therefore, the power conversion circuit 60 capable of discharging excitation energy can be manufactured at low cost.

(4) In the power conversion circuit of the present embodiment, the 1 st current line or the 2 nd current lines LN1, LN2 may have a diode D3 that permits conduction of current flowing through the secondary winding w2 during an on period of the switching element but restricts conduction in the opposite direction, and the input circuit 20 may further include reset circuits 72, 74, 76 that release excitation energy stored in the transformer when the switch is on, when the switch is off.

According to the power conversion circuit of the present embodiment, the reset circuits 72, 74, and 76 provided in the input circuit 20 release the excitation energy stored in the transformer when the switch is off, so that the magnetic saturation of the transformer can be prevented, and the operation of the power conversion circuit 70 can be stabilized.

(5) The DC-DC converter of the present embodiment includes the power conversion circuit described in any one of (1) to (4) above, and the input terminal on one side and the input terminal on the other side of the input circuit 20 are input terminals to which a direct-current power supply DC is connected.

(6) The AC-DC converter of the present embodiment includes the power conversion circuit described in any one of (1) to (4) above, the input circuit 20 further includes a rectifier circuit DB that rectifies an alternating current output from an alternating-current power supply AC, and the input terminal on one side and the input terminal on the other side of the input circuit 20 are input terminals to which the rectifier circuit DB is connected.

Detailed description of embodiments of the present invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. At least some of the embodiments described below may be arbitrarily combined.

[ Power conversion Circuit having basic Structure ]

Fig. 1 is a circuit diagram of a power conversion circuit 10 having a basic configuration according to the present embodiment. The power conversion circuit 10 having a basic configuration is constituted by an insulation type DC-DC converter that converts power by a transformer TR.

As shown in fig. 1, the power conversion circuit 10 has a transformer TR, an input circuit 20 including a primary winding w1 of the transformer TR, and an output circuit 30 including a secondary winding w2 of the transformer TR. The power conversion circuit 10 actually includes a controller CT (see fig. 11) that controls the operation of the switching element SW of the input circuit 20. The switching element SW is formed of a MOSFET, an IGBT, or the like. A configuration example of the control circuit 40 including the controller CT will be described later.

In the power conversion circuit 10, the energy accumulated in the coil L due to the forward current generated in the transformer TR during the on period of the switching element SW is discharged from the coil L to the load LD during the off period of the switching element SW, and the power is supplied to the load LD of the output circuit 30. Hereinafter, in the present embodiment, the positive side of the output circuit 30 is defined as "upper side", and the negative side (ground side) of the output circuit 30 is defined as "lower side".

The transformer TR has a primary winding w1 and a secondary winding w2 that are magnetically coupled. The primary winding w1 and the secondary winding w2 have the same polarity. In the present embodiment, the primary-side and secondary-side winding ratio is n: 1. However, the winding ratio of the transformer TR is not limited to n: 1.

The input circuit 20 includes input terminals P1 and P2 connected to the input power supply PS, a primary winding w1, and a switching element SW. The input power source PS, the primary winding w1, and the switching element SW are connected in series. The input power source PS of the power conversion circuit 10 having the basic configuration is constituted by a direct-current power source DC such as a dry battery or a battery, for example. Alternatively, a circuit that converts ac to dc by a combination of a diode bridge and a large-capacity capacitor or the like may be used.

The output circuit 30 includes output terminals P3, P4 connected to the load (output) LD, a secondary winding w2, a commutation diode D1, an output coil L, and an output capacitor C. The output circuit 30 includes a 1 st current line LN1 connecting one end (upper end in the drawing) of the secondary winding w2 to the negative-side terminal P4 of the output, and a 2 nd current line LN2 connecting the other end (lower end in the drawing) of the secondary winding w2 to the positive-side terminal P3 of the output.

The output coil L is connected to the 1 st and 2 nd current lines LN1, LN2, respectively, in parallel with the load LD. Specifically, the upper end of the output coil L is connected to the middle of the 2 nd current line LN2 communicated with the positive electrode side terminal P3, and the lower end of the output coil L is connected to the middle of the 1 st current line LN1 communicated with the negative electrode side terminal P4.

The output capacitor C is disposed between the output coil L and the load LD, and is connected to the 1 st and 2 nd current lines LN1, LN2, respectively, in parallel with the load LD. Specifically, the output capacitor C has an upper end connected to the middle of the 2 nd current line LN2 connected to the positive electrode side terminal P3, and a lower end connected to the middle of the 1 st current line LN1 connected to the negative electrode side terminal P4.

The commutation diode D1 is provided in a portion closer to the load LD than the upper end of the output coil L in the 2 nd current line LN 2. In the illustrated example, the commutation diode D1 is disposed between the upper end of the output coil L and the upper end of the output coil C. Specifically, the anode of the commutation diode D1 is connected to the upper end of the output coil L, and the cathode of the commutation diode D1 is connected to the positive-side terminal P3 via the upper end of the output capacitor C.

The commutation diode D1 may be provided in a portion closer to the load LD than the lower end of the output coil L in the 1 st current line LN 1. The orientation of the commutation diode D1 in this case is opposite to that of fig. 1.

As shown in parentheses in fig. 1, a diode D3 having an anode connected to the upper end of the secondary winding w2 may be provided on the 1 st current line LN1 to interrupt the reverse operation. However, the operation of power conversion circuit 10 in which diode D3 is not provided in 1 st current line LN1 will be described first. In the following description, the "switching element SW" is also simply referred to as "switch SW".

[ operation of Power conversion Circuit ]

Fig. 2a is a circuit diagram illustrating the operation of the power conversion circuit 10 when the switch is turned on. Fig. 2b is a circuit diagram illustrating the operation of the power conversion circuit 10 when the switch is off. Fig. 2c is a graph showing the time variation of the coil current in the continuous current mode.

As shown in fig. 2a, when the switch SW is turned on, a forward current flows to the secondary side by applying an input voltage to the primary side of the transformer TR, and a current also flows to the coil L provided on the secondary side. At this time, the secondary side of the transformer TR takes the upper side of fig. 2a as a high voltage side, and generates a forward voltage (Vin/n) corresponding to the winding ratio n: 1 of the transformer TR. Vin/n is also applied between both ends of the coil L, and a current flows to the lower side of fig. 2a as a high voltage side, and energy is stored.

During this time, energy is also accumulated in the excitation inductance of the transformer TR. Further, diode D1 is reverse biased by Vout + Vin/n, and diode D1 is non-conductive. Further, power to the load LD is supplied from the capacitor C.

When the switch SW is turned off, the current of the coil L no longer flows to the secondary side of the transformer TR, but flows to the load LD through the diode D1, as shown in fig. 2 b. That is, energy is discharged from the coil L to the capacitor C and the load LD (path (1) of fig. 2 b). Here, for the sake of simplicity, ignoring the voltage drop Vf of the diode D1, the voltage across the coil L becomes Vout with the upper side of fig. 2b being the high voltage side.

Therefore, the voltage of Vout is generated on the secondary side of the transformer TR with the lower side of fig. 2b as the high voltage side, and a current is generated downward in fig. 2b by energy release from the excitation inductance. This current also flows through diode D1 to capacitor C and load LD (path (2) of fig. 2 b).

On the primary side, the lower side of fig. 2b is set as the high voltage side, and a reverse voltage of n · Vout is generated. Therefore, a voltage of Vin + n · Vout is applied between both ends of the switch SW. Therefore, the withstand voltage of the switch SW needs to be set to withstand the voltage.

The operation of the power conversion circuit 10 will be described in more detail with reference to fig. 2 c. Here, assuming a simple model in which a voltage drop, an error, and the like during diode passage are ignored, attention is paid to increase and decrease of the current of the output coil L (hereinafter, also referred to as "coil current") in the continuous current mode. The on-time of the switch in the continuous current mode is "ton", and the off-time of the switch is "toff".

In this case, assuming that the coil current in the on period increases to Δ Ion, the following equation holds. Vin/n is L.DELTA.ion/ton

Further, assuming that the coil current during the off period is reduced to Δ Ioff, the following equation is established. Here, Vout · L · Δ Ioff/toff, in a steady state,

since Δ Ion is Δ Ioff, the following equation holds. Vout/(Vin/n) ton/toff

That is, Vout is output at toff ton (duty ratio 50%) Vin/n. In this way, since voltage conversion can be performed at the ratio of the winding ratio n, even when the step-up or step-down ratio is large, power conversion can be easily performed. In the non-insulated chopper circuit, when the voltage conversion ratio is large, the duty ratio is a maximum or minimum, and a large voltage and a large current are switched, so that the switching loss increases.

On the other hand, the power conversion circuit 10 is set to Vout < Vin/n when toff > ton, and Vout > Vin/n when toff < ton. That is, according to the power conversion circuit 10 having the basic configuration, a voltage larger than Vin/n and a voltage smaller than Vin/n can be output by the ratio of toff and ton.

[ reset of Transformer ]

As described above, the following events 1 to 3 hold true for the power conversion circuit 10 of the basic circuit. Event 1: when the switch is turned on, Vin/n (positive at the lower side of the figure) is applied across the coil. Event 2: when the switch is off, -Vout is applied across the coil. Event 3: in steady state, the ripple of the coil current increases and decreases in concert. That is, the relationship of the following expression (1) is established. Vout/(Vin/n) ═ ton/toff. (1)

Here, if attention is paid to the secondary side of the transformer TR, Vin/n is applied while the switch is on, with the upper side of fig. 2a being positive, and-Vout is applied while the switch is off, with respect to the excitation inductance of the transformer TR as viewed from the secondary side. That is, the same voltage condition as that of the coil L is established. Therefore, in the steady state, the increase and decrease of the ripple current are also the same with respect to the excitation inductance, and the relationship of the equation (1) is established. Therefore, the excitation inductor is not saturated by continuously accumulating energy.

In the power conversion circuit 10, the energy stored in the field inductance during the on-state of the switch is discharged to the secondary side by the reverse operation during the off-state, and is transmitted to the load LD via the diode D1, without particularly providing a reset circuit. Therefore, the energy of the exciting inductance can be transmitted to the secondary side without waste, and a highly efficient operation can be realized.

[ comparative example: case of a general Forward converter

Fig. 3 is a circuit diagram of a general forward converter. In fig. 3, the reset circuit is omitted, and the current path when the switch is on is indicated by a broken line, and the current path when the switch is off is indicated by a straight line.

As shown in fig. 3, when the switch is turned on, a forward voltage Vin/n is generated on the secondary side of the transformer with the upper side of fig. 3 as the high voltage side, and a current flows to the load through the diode Da and the coil L. Neglecting the voltage drop Vf of the diode, the voltage at the left end of the coil L relative to the right end at this time becomes Vin/n-Vout.

When the switch is turned off, the voltage on the secondary side of the transformer TR is inverted, a reverse bias is applied to the diode Da, and no current flows. Therefore, the coil current flows from the negative electrode of the load (GND on the secondary side) through the diode Db. Neglecting the voltage drop Vf of the diode Db, the voltage at the left end of the coil L relative to the right end at this time is-Vout.

In the steady state, the increase width and the decrease width of the ripple current generated in the coil L coincide, and therefore the following expression holds. (Vin/n-Vout)/Vout toff/ton

∴Vout/(Vin/n)＝ton/(ton+toff)

Since Vout is a value obtained by multiplying Vin/n by a duty ratio, Vout is limited to a range from 0 to Vin/n.

Therefore, in order to meet the specifications of wide input voltages, the winding ratio n must be determined so that a desired output voltage can be obtained even at the assumed lowest input voltage Vin _ min. That is, the winding ratio n needs to be determined so that Vin _ min/n > Vout. Further, in the forward converter, since the reset operation of discharging the excitation energy of the transformer TR during the off period is required, the off time of the reset operation is required, and the duty ratio cannot be set too high and cannot be set to a value close to 100%.

In consideration of such a restriction, the winding ratio n must be determined so that Vin _ min/n is sufficiently larger than Vout, and the winding ratio n cannot be made excessively large. Therefore, there is a problem that conversion efficiency is lowered when the input voltage is high. Further, since the winding ratio n cannot be increased, the duty ratio needs to be decreased accordingly in order to output a low voltage with respect to the input, and the switching current also increases. Therefore, the switching loss becomes large.

[ Effect of Power conversion Circuit ]

Unlike, for example, a flyback converter (not shown), the power conversion circuit 10 of the present embodiment does not temporarily store all of the converted power in the transformer TR, and therefore can reduce the size of the transformer TR and suppress power loss in the transformer TR. In addition, the number of parts is relatively small, and the cost is also suppressed.

As described above, the power conversion circuit 10 according to the present embodiment can cope with a wider input voltage than a general forward converter (fig. 3). Further, the present invention can also be applied to a single converter circuit in which a PFC and a DC-DC converter are integrated. Since the power conversion output can be performed even when the input voltage is low, the input conduction angle can be increased, and the input power can be increased.

When the power conversion circuit 10 of the present embodiment is a single converter system, the input power increases during a time period when the input voltage is high. Therefore, the optimum design can be performed for a high input voltage, and high-efficiency AC-DC conversion can be performed. In contrast, since the forward converter can output only an output voltage obtained by multiplying an input voltage by 1/n, it is necessary to design the forward converter to operate at the lowest possible input voltage, and it is difficult to improve the operation efficiency in a state where the input voltage is high.

[ Power conversion Circuit according to modification 1 ]

Fig. 4a to 4b are circuit diagrams of a power conversion circuit 60 according to modification 1. Fig. 4a is a circuit diagram showing the operation of the power conversion circuit 60 when the switch is turned on. Fig. 4b is a circuit diagram illustrating the operation of the power conversion circuit 60 when the switch is off.

In the above description, the voltage drop Vf when the diode D1 is turned on is ignored, but Vf is present in the actual diode D1. Therefore, even when the voltage drop Vf is taken into consideration, a countermeasure is required to release the excitation inductance when the switch is off without saturating the transformer TR. In the power conversion circuit 10 having the basic configuration, as described above, the reset operation of the transformer TR is performed in principle, but in the power conversion circuit 60 of modification 1, the reset operation of the transformer TR can be performed more reliably, even in consideration of the voltage drop Vf of the diode D1.

In the power conversion circuit 60 of modification 1, a parallel line LN3 connected in parallel to the 1 st current line LN1 is added to the output circuit 30, and diodes D3 and D2 are provided on the 1 st current line LN1 and the parallel line LN3, in comparison with the power conversion circuit 10 having the basic configuration. The anode of diode D3 of the 1 st current line LN1 is connected to the upper end of secondary winding w 2. Diode D2 and diode D3 of parallel line LN3 face opposite directions, and the cathode is connected to the upper end of secondary winding w 2.

Therefore, the diode D3 of the 1 st current line LN1 allows conduction of current to the secondary winding w2 when the switch is on, but limits conduction in the opposite direction. In contrast, diode D2 of parallel LN3 allows conduction of current to secondary winding w2 when the switch is open, but limits conduction in the opposite direction.

As shown in fig. 4a to 4b, when Vf1, Vf2, and Vf3 are set as the on-state voltage drops of diodes D1, D2, and D3, respectively, Vf2 > Vf3 is set. According to the power conversion circuit 60 of fig. 4a to 4b, the energy stored in the excitation inductance can be appropriately released when the switch is off only by adding two diodes D2, D3 to the power conversion circuit 10 of the basic configuration (fig. 1). The reason for this will be described below.

As shown in fig. 4a, when the switch is turned on, a forward voltage of Vin/n is generated at the secondary side of the transformer. At this time, the current flows rightward to the diode D3 of the 1 st current line LN1, generating a voltage drop of Vf 3. Thus, a voltage of Vin/n-Vf3 is generated across the coil L. Further, Vin/n voltage is applied to the secondary side of the excitation inductance of the transformer TR.

As shown in fig. 4b, when the switch is turned off, the current of the coil L flows to the load LD through the diode D1. Therefore, the voltage across the coil L becomes Vout + Vf 1. Hereinafter, this is referred to as Vout'. That is, Vout' ═ Vout + Vf 1. On the secondary side of the transformer, a reverse current flows downward. Since this current flows through diode D2 of parallel line LN3, the voltage generated at the secondary side of the transformer becomes Vout' + Vf 2.

When stable, the current ripple of the coil L increases and decreases uniformly, so toff/ton is (Vin/n-Vf 3)/Vout'. Here, if attention is paid to the current ripple of the magnetizing inductance Lm as seen from the secondary side of the transformer, the following is given.

The current increase Δ Im _ on at the time of turn-on is (Vin/n) ton/Lm

The current decrease Δ Im _ off at the time of off becomes (Vout' + Vf2) · toff/Lm

ΔIm_off/ΔIm_on＝(Vout’+Vf2)·(toff/ton)/(Vin/n)＝(Vout’+Vf2) ·(Vin/n－Vf3)/(Vout’·Vin/n)＝(1+Vf2/Vout')·(1－Vf3/(Vin/n))

Here, if diodes D2, D3 such as Vf2 > Vf3 are employed, Δ Im _ off > Δ Im _ on, i.e., Δ Im _ off/Δ Im _ on > 1. Therefore, during the off period of the switch SW, the energy release from the field inductance of the transformer TR is completed, and the field current behaves in a discontinuous mode. In this case, the transformer TR can be reliably reset without accumulating excitation energy, and therefore, the transformer TR can be made small and inexpensive and can be stably operated.

Fig. 5a to 5c are circuit diagrams showing changes in the circuit configuration of the power conversion circuit 60 according to modification 1. The power conversion circuit 60 in fig. 5a has the same circuit configuration as the power conversion circuit 60 in fig. 4 a. That is, in addition to commutating diode D1, two diodes D2 and D3 are included, diode D3 is provided on 1 st current line LN1, and diode D2 is provided on parallel line LN 3.

As described above, in this case, if the two types of diodes D2, D3 having the relationship of Vf2 > Vf3 are used, the accumulation of excitation energy can be prevented. However, as for a circuit that provides a difference in voltage drop when the 1 st current line LN1 and the parallel line LN3 are turned on, the following various measures can be adopted in addition to the 2 kinds of diodes D2 and D3.

For example, in the example of fig. 5b, 3 diodes D0 (voltage drop Vf0) are used, 1 diode D0 is disposed on the 1 st current line LN1, and 2 diodes D0 connected in series are disposed on the parallel line LN 3. In this case, a difference can be provided between the voltage drops of the 1 st current line LN1 and the parallel line LN3 only by the diode D0 of the same kind, which has an advantage that the passive element can be easily selected.

In the example of fig. 5c, 2 diodes (voltage drop Vf0) and 1 resistor R0 are used, 1 diode D0 is disposed on the 1 st current line LN1, and 1 diode D0 and resistor R0 connected in series are disposed on the parallel line LN 3. In this case, a difference can be provided between the voltage drops of the current line LN1 and the parallel line LN3 only by the diode D0 of the same type, which is advantageous in that the passive element can be easily selected.

In any of the circuits of fig. 5a to 5c, since a large potential difference does not occur between both ends of the diodes D0, D2, and D3, an element having a low withstand voltage may be used. In this way, according to the power conversion circuit 60 of modification 1, only by using the relatively inexpensive diodes D0, D2, and D3 having a low withstand voltage, it is possible to prevent the accumulation of the excitation energy of the transformer TR. Therefore, the power conversion circuit 60 capable of discharging excitation energy can be manufactured at low cost.

Fig. 6 is another circuit diagram of the power conversion circuit 60 according to modification 1. As shown in fig. 6, a parallel line LN3 connected in parallel to the 2 nd current line LN2 may be added to the output circuit 30, and diodes D3 and D2 may be provided in the 2 nd current line LN2 and the parallel line LN 3. The cathode of the diode D3 of the 2 nd current line LN2 is connected to the lower end (negative pole in the drawing) of the secondary winding w 2. Diode D2 and diode D3 of parallel line LN3 face opposite directions, and the anode is connected to the lower end (negative pole in the drawing) of secondary winding w 2.

In this case, the diode D3 of the 2 nd current line LN2 allows conduction of current flowing to the secondary winding w2 when the switch is on, but restricts conduction in the opposite direction. In contrast, diode D2 of parallel LN3 allows conduction of current to secondary winding w2 when the switch is open, but limits conduction in the opposite direction.

In the case of the power conversion circuit 60 shown in fig. 6, a difference may be given to the voltage drop when the 2 nd current line LN2 and the parallel line LN3 are turned on by using a plurality of diodes D0 of the same type as in fig. 5b and 5 c.

[ Power conversion Circuit according to modification 2 ]

Fig. 7 is a circuit diagram of a power conversion circuit 70 according to modification 2. In the power conversion circuit 70 of modification 2, a diode D3 for backflow prevention and a 1 st reset circuit 72 are added to the power conversion circuit 10 having the basic configuration. In the power conversion circuits 10 and 60, the secondary side of the transformer is operated in the reverse direction to reset the exciting current when the switch is turned off. That is, the excitation energy is released by causing a current to flow to the secondary winding w2 of the transformer TR while the switch is off.

The present embodiment includes not only the power conversion circuits 10 and 60 described above but also a diode D3 for preventing reverse operation and the power conversion circuit 70 of the 2 nd modification example using the 1 st reset circuit 72. In the example of fig. 7, the diode D3 is provided on the 1 st current line LN1, but as shown by a broken line in fig. 7, the diode D3 may be provided on the 2 nd current line LN 2.

The 1 st reset circuit 72 is formed of an RC circuit provided in the input circuit 20, and includes a resistance element and a capacitor connected in parallel to the primary winding w 1. The cathode of the primary winding w1 and the capacitor are connected through a diode. In this case, after the switch SW is turned off, the current flowing through the exciting inductance flows into the capacitor through the diode.

The control circuit (not shown) of the power conversion circuit 70 detects completion of the reset from, for example, a voltage across the secondary winding (not shown) provided in the transformer TR, and performs the next turn-on at a timing after the reset detection. The electric charge accumulated in the capacitor is discharged through the resistance element.

Fig. 8 is another circuit diagram of the power conversion circuit 70 according to modification 2. In the power conversion circuit 70 of fig. 8, the 2 nd reset circuit 74 is employed. As shown in fig. 8, the 2 nd reset circuit 74 is constituted by an active clamp type reset circuit provided in the input circuit 20. The 2 nd reset circuit 74 includes a series connection of a switch SW2 composed of a capacitor and a PMOS transistor between the drain (using NMOS or the like) of the switch SW1 and the primary side ground.

According to the 2 nd reset circuit 74, after the switch SW1 is turned off, the exciting current of the transformer TR flows into the capacitor through the diode of the switch SW 2. During this period, the switch SW2 is turned on. When the field current is finally discharged, this time, in the opposite direction, a regenerative current is generated from the charged capacitor toward the input + terminal through the field inductance of the transformer TR.

When the switch SW2 is turned off during generation of the regenerative current, a current flows to the parallel diode of the switch SW1 due to a current flowing upward in fig. 8. By turning on the switch SW1 in this state, soft switching can be realized, and high-efficiency operation can be performed while suppressing switching loss.

Fig. 9 is another circuit diagram of the power conversion circuit 70 according to modification 2. In the power conversion circuit 70 of fig. 9, a 3 rd reset circuit 76 is employed. As shown in fig. 9, the 3 rd reset circuit 76 includes a secondary winding ws added to the primary side of the transformer TR and a diode Ds having a cathode connected to the upper end of the secondary winding ws and an anode connected to ground. According to the 3 rd reset circuit 76, after the switch is turned off, the energy of the exciting inductance flows to the secondary winding ws through a path indicated by a broken line in fig. 9, and is regenerated at the positive electrode of the input power source PS.

[ Power conversion Circuit according to modification 3 ]

Fig. 10 is a circuit diagram of a power conversion circuit 80 according to modification 3. The power conversion circuit 80 of the modification 3 is composed of an AC-DC converter having a basic configuration in which a rectifier circuit DB is added to the power conversion circuit 10.

That is, the input circuit 20 of the power conversion circuit 80 is provided with a rectifier circuit DB that rectifies alternating current output from an input power supply PS composed of an alternating current power supply AC. Specifically, the input terminal P1 on the positive side of the input circuit 20 is connected to the cathode-side terminal of the rectifier circuit DB, and the input terminal P2 on the negative side of the input circuit 20 is connected to the anode-side terminal of the rectifier circuit DB.

The power conversion circuit 80 according to modification 3 is configured to receive an input obtained by rectifying an ac input through the diode bridge DB, control the input so as to obtain a desired output voltage, and control the duty ratio so as to obtain an input current proportional to the absolute value of the ac input voltage, thereby obtaining a single converter circuit in which a PFC and a DCDC converter are integrated. According to the power conversion circuit 80 of the modification 3, since the input voltage is not only a voltage lower than the winding ratio n: 1 but also a voltage higher than that, the operation can be performed up to a low voltage close to the zero crossing of the ac voltage, and a high power can be obtained.

On the other hand, when the forward converter is of the single-converter type, as disclosed in, for example, japanese patent laid-open nos. 4-138506, 10-150769, and 2010-284031, the forward converter cannot output a voltage higher than the input winding ratio. Therefore, if the operation is performed until the vicinity of the zero cross point, the winding ratio n cannot be increased.

On the other hand, if the switch is designed to operate even when the input voltage is low, the duty ratio is reduced when the input voltage is high, and a large current must be supplied to the switch in a short time. Therefore, the switching current increases, and the power loss increases. The input power also becomes large in a period in which the input voltage is high, and thus the loss becomes further large.

The power conversion circuit 80 of the modification 3 has the same circuit configuration as the power conversion circuit 10 having the basic configuration, and therefore can output an output voltage equal to or higher than Vin/n with respect to the input voltage Vin. Therefore, n can be set to be large. Therefore, the duty ratio in the high voltage/high power input can be increased. Therefore, the switching current can be suppressed, and the switching loss can be suppressed.

[ control Circuit of Power conversion Circuit ]

Fig. 11 is a circuit diagram showing an example of the control circuit 40 of the power conversion circuit 80. As shown in fig. 11, the control circuit 40 of the power conversion circuit 80 includes a controller CT, a current sensor Si, an input voltage sensor Sv1, and an output voltage sensor Sv 2. The controller CT is formed by an integrated circuit such as an ASIC or FPGA.

The current sensor Si is a sensor for detecting a current flowing through the lower end of the switch SW, and is composed of, for example, a shunt resistor. The input voltage sensor Sv1 is a sensor that detects the rectified voltage in the input circuit 20. The output voltage sensor Sv2 is a sensor that detects the voltage of the positive electrode of the load LD. The sensing detection method of the output voltage sensor Sv2 may be, for example, a method of transmitting the output voltage value divided by the voltage dividing resistor to the controller CT through an isolation amplifier, a method of combining a shunt regulator and a photo coupler, or the like. The controller CT may monitor the voltage of an auxiliary winding (not shown) provided in the transformer TR to indirectly detect the output voltage.

The controller CT monitors the input voltage and the input current, and adjusts the duty ratio of the control signal input to the switch SW so that the input current and the input voltage are proportional. In this case, since the input current intermittently flows by the on/off of the switch SW, it is preferable to use a current value averaged over a period longer than the on/off period of the switch SW.

This can improve the power of the input current (PFC control). The control is performed by a relatively high speed feedback loop. The controller CT also monitors the output voltage and performs duty ratio adjustment (constant voltage control) to achieve a desired voltage. This feedback control is performed in a cycle slower than the PFC control.

In the control circuit 40 of fig. 11, if a control method is adopted in which the ratio of the on-time ton and the off-time toff is determined according to the magnitude of the input current, PFC control can be performed without monitoring the input voltage. For example, ton may be set to be constant, and toff may be determined based on the input current. However, since the input current intermittently flows by the on/off of the switch SW, it is preferable to use a current value averaged over a period longer than the on/off period of the switch SW.

For example, if the voltage drop Vf of the diode D1 is ignored, the coil current increases when the switch is on to become Δ I (Vin/n) · ton/L, and the coil current decreases when the switch is off to become Δ I (Vout · toff/L). When the balance is increased and decreased, (Vin/n) · ton ═ Vout · toff, that is, toff/ton ∈ (Vin/n)/Vout, the relationship toff/ton ∈ Vin is obtained.

Therefore, if toff/ton is determined so as to be the input current Iin ∈ toff/ton, Iin ∈ Vin can be realized. Namely, PFC control can be realized. Ton may be constant and toff may be determined to be proportional to Iin. In this case, the offset or the like may be appropriately set in consideration of the error amount, instead of a simple ratio.

[ other modifications ]

The embodiments disclosed herein are illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the appended claims, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.

Claims (6)

1. A power conversion circuit, comprising:

a transformer;

an input circuit including a primary winding of the transformer; and

an output circuit including a secondary side winding of the transformer,

it is characterized in that the preparation method is characterized in that,

the input circuit includes the primary-side winding and a switching element connected in series between an input terminal on one side and an input terminal on the other side,

the output circuit includes:

the secondary side winding;

a 1 st current line connecting one end of the secondary side winding and a negative side terminal of an output;

a 2 nd current line connecting the other end of the secondary side winding with a positive side terminal of an output;

an output coil connected to the 1 st current line and the 2 nd current line in parallel with the output; and

a commutation diode disposed on at least 1 of the 1 st current line and the 2 nd current line.

2. The power conversion circuit according to claim 1,

the direction of the current flowing to the secondary winding when the switch is turned on is a direction from the other end of the secondary winding toward one end.

3. The power conversion circuit according to claim 1 or 2,

the output circuit further includes a parallel line connected in parallel with the 1 st current line or the 2 nd current line,

the 1 st current line or the 2 nd current line has a diode that permits conduction of current flowing to the secondary side winding but limits conduction in the opposite direction when the switch is turned on,

the parallel line has a diode that permits conduction of current to the secondary winding but limits conduction in the opposite direction when the switch is off,

the voltage drop of the 1 st current line or the 2 nd current line at the time of conduction is smaller than the voltage drop of the parallel line at the time of conduction.

4. The power conversion circuit according to claim 1 or 2,

the 1 st current line or the 2 nd current line has a diode that permits conduction of current flowing to the secondary side winding but limits conduction in the opposite direction when the switch is turned on,

the input circuit further includes a reset circuit that releases excitation energy accumulated in the transformer when the switch is turned on, when the switch is turned off.

5. A DC-DC converter is characterized in that,

the DC-DC converter has the power conversion circuit according to any one of claims 1 to 4,

the input terminal on one side and the input terminal on the other side of the input circuit are input terminals connected to a direct current power supply.

6. An AC-DC converter is characterized in that,

the AC-DC converter has the power conversion circuit according to any one of claims 1 to 4,

the input circuit further includes a rectifying circuit for rectifying an alternating current output from the alternating current power source,

the input terminal on one side and the input terminal on the other side of the input circuit are input terminals connected to the rectifier circuit.

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