JP3723947B2 - High power factor switching power supply - Google Patents

Description

[0001]
[Industrial application fields]
The present invention is a switching power supply that uses an AC power supply as an input and outputs a predetermined DC power to a load. When the power is turned on, no inrush current flows, and the power factor correction switching that can maintain the waveform of the input current as a sine wave regardless of load fluctuations It relates to the power supply.
[0002]
[Prior art]
As a conventional example of a power source in which an inrush current does not flow when an AC power source is turned on, a capacitorless switching power source shown in FIG. 13 is known. In FIG. 13, Vac is an AC power source, LPF is a low-pass filter, DB is a rectifier circuit, T1 has a first terminal (1) and a second terminal (2) on the primary side, and the first terminal ▲ A transformer T1, M1 having a primary winding N1 and a secondary winding N3 provided between 1 and the second terminal (2) is a switching transistor (hereinafter referred to as a switch M1), C11, C12 Is a snubber circuit capacitor, R11 and R12 are snubber circuit resistors, and D11 is a snubber circuit diode. A rectifying / smoothing circuit including a diode D1 and a smoothing capacitor C3 is connected to the secondary side.
[0003]
The rectifier circuit DB connected to the AC power source, the positive output terminal of the rectifier circuit DB and the first terminal (1) of the transformer T1 are connected, the second terminal (2) of the transformer T1 and the rectifier circuit DB A switch M1 is connected between the negative output terminal, a CRD snubber circuit of a capacitor C12, a resistor R12, and a diode D11 is connected in parallel to the winding N1 of the transformer T1, and a CR of a capacitor C11 and a resistor R11 is connected in parallel to the switch M1. Snubber circuit is connected.
[0004]
The secondary winding N3 and the diode D1 of the transformer T1 are connected in a flyback form to store power when the switch M1 is on and supply the power stored when the switch M1 is off to the load, and a pair of DC output terminals Are connected to both ends of the capacitor C3. These snubber circuits of the circuit of FIG. 13 are connected to reduce the voltage applied to the switch M1 when the switch M1 is switched or to reduce dv / dt of the switch M1. However, these snubber circuits absorb the transient spike voltage generated in the switch M1 and the transformer T1 in the capacitors C11 and C12 and consume the electric power as heat. For this reason, if the switching noise is well absorbed in the design, there is a problem that power consumption increases and efficiency is lowered.
[0005]
Further, during the period in which the AC voltage is high, the voltage fluctuation at the first terminal (1) of the transformer T1 is large due to the switching of the switch M1, so that the AC input current flows into the rectifier circuit DB. During the period when the AC voltage passing through the AC is low, the voltage fluctuation at the first terminal {circle around (1)} of the transformer T1 does not become so large as to draw current from the rectifier circuit DB, so that the AC input current hardly flows into the rectifier circuit DB.
[0006]
As a conventional example of a power source in which a smoothing capacitor is connected to the primary side, the power source shown in FIG. 14 (Japanese Patent Laid-Open No. 9-93946) is known. In FIG. 14, substantially the same parts as those in FIG. 13 are denoted by the same reference numerals. The rectifier circuit DB connected to the AC power source, the positive output terminal of the rectifier circuit DB and the first terminal (1) of the first transformer T1 are connected, and the second terminal (2) of the first transformer T1. Is connected to one terminal of the second transformer (hereinafter referred to as transformer T2), and a switch M1 is connected between the other terminal (3) of the second transformer T2 and the negative output terminal of the rectifier circuit DB. The smoothing capacitor C13 and the diode D11 in the reverse direction are connected in series from the terminal (2) of the first transformer T1 to the negative output terminal of the rectifier circuit DB, and the terminal (3) of the second transformer T2 and the diode D11 are connected. A reverse diode D12 is connected to the cathode.
[0007]
A diode D1 and a smoothing capacitor C3 are connected to the secondary side of the first transformer T1, and a rectifying and smoothing circuit of the diode D2 and the smoothing capacitor C3 is connected to the secondary side of the second transformer T2. The secondary winding N3 and diode D1 of the first transformer T1 and the secondary winding N22 and diode D2 of the second transformer T2 store power while the switch M1 is on, and are off. The power stored in is connected to the load in a flyback type, and the pair of DC output terminals are connected to both ends of the capacitor C3.
[0008]
Since the smoothing capacitor C13 on the primary side and the diode D11 in the reverse direction are connected in series between the terminal {circle around (2)} of the first transformer T1 and the negative output terminal of the rectifier circuit DB, the negative electrode of the smoothing capacitor C13 is connected. Is not fixed to the potential (0 V) of the negative output terminal of the rectifier circuit DB, but changes every time the switch M1 is turned on or off. Further, since the capacitor C13 is not a resonance capacitor but a smoothing capacitor, the first and second transformers T1 and T2 and the smoothing capacitor C13 do not resonate when the switch M1 is turned on and off. Therefore, when the switch M1 is turned on, the rise of the on-current to the switch M1 cannot be suppressed, and when the switch M1 is turned off, the rise of the off-voltage of the switch M1 cannot be suppressed. Accordingly, a large switching loss is generated when the switch M1 is turned on / off, so that the efficiency is lowered. During the period when the AC voltage is low, there is a problem that the power factor is low because the current drawn from the rectifier circuit DB of the smoothing capacitor C13 is small.
[0009]
[Problems to be solved by the invention]
In the present invention, in view of the above-described problems of the prior art, the switch M1 performs soft switching so as to suppress the generation of transient spike voltage and the switching loss in the switch M1 and the transformer T1, and the electric power stored at the time of soft switching is 2 The efficiency is increased by outputting to the next side, and at the same time, the transformers T1 and T2 are stably resonated, so that the AC input current flows through the rectifier circuit even during a period of low AC voltage, and the power factor becomes a sine wave close to 1. Another object of the present invention is to provide a high power factor switching power supply device in which an inrush current does not flow when a power input is turned on even without an inrush current prevention resistor.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a primary winding of a first transformer, a primary winding of a second transformer, and a switch are connected in series between positive and negative output terminals of an AC voltage rectifier circuit. And connecting one terminal of the resonance capacitor to a connection point between the primary winding of the first transformer and the primary winding of the second transformer, and connecting the other terminal to the negative output terminal of the rectifier circuit, When the switch is switched, the first transformer, the second transformer, and the resonance capacitor resonate, and the switch soft-switches due to the resonance, and from the rectifier circuit even in a period of low AC voltage. This realizes a high power factor switching power supply with high efficiency by drawing current strongly.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Details of embodiments of the present invention will be described below with reference to the drawings.
(Embodiment 1) A first embodiment of the present invention will be described with reference to FIG. However, in FIG. 1, the same reference numerals are given to substantially the same parts as those of the prior art example of FIG. Also, circuits such as AC input voltage detection, DC output voltage detection, and switching control are not shown. The transformers T1 and T2 start winding the dots shown in the figure. The rectifier circuit DB connected to the AC power source, the positive output terminal of the rectifier circuit DB and the first terminal (1) of the first transformer T1 are connected, and the second terminal (2) of the transformer T1 and the rectifier circuit DB are connected. A series circuit of the winding N21 of the second transformer T2 and the switch M1 is connected between the negative output terminal of the second transformer T2, and a resonance capacitor C1 is connected in parallel with the series circuit of the transformer T2 and the switch M1. A terminal connected to the switch M1 of the transformer T2 is defined as a terminal (3). The secondary winding N3 and the first diode D1 of the transformer T1, and the secondary winding N22 and the second diode D2 of the transformer T2 store power while the switch M1 is on, and are off. Is connected to both ends of the capacitor C3 in a flyback manner for supplying the power stored in the capacitor to the load. FIG. 2 shows the voltage and current characteristics of each part of the circuit of FIG. 1 over time (sections T0,..., T5). Each waveform in FIG. 2 shows its characteristics as a representative example for helping understanding. (A) is the current IDB of the positive output terminal of the rectifier circuit. (B) is the charge / discharge current IC1 of the capacitor C1. (C) is the current IM1 of the switch M1. (D) is the voltage VM1 of the switch M1. (E) is the voltage V (2) of the second terminal (2) of the transformer T1. (F) is a current IN3 output to the secondary side from the winding N3 of the transformer T1. (G) is a current IN22 output to the secondary side from the winding N22 of the transformer T2.
[0012]
When the switch M1 is turned on, the voltage at the first terminal {circle around (1)} of the transformer T1 is lowered, and the AC input current is drawn from the positive output terminal of the rectifier circuit DB. Since the current drawn from the positive output terminal of the rectifier circuit DB and flowing through the winding N1 of the transformer T1 flows through the primary winding N21 of the transformer T2, the current flowing through the switch M1 becomes zero current switching (ZCS) that rises gently. (Section T0-T1). Then, with a slight delay, the discharge current of the capacitor C1 is added to the current flowing from the winding N1 and flows through the switch M1 (section T1-T2). When the secondary side voltage of the transformer T2 reaches the output voltage of the capacitor C3, the electric power stored in the transformer T2 is output from the N22 to the secondary side (section T2-T5). At this time, the discharge of the capacitor C1 ends, and the current flowing through the capacitor C1 stops. A current that flows through the winding N1 of the transformer T1 from the positive output terminal of the rectifier circuit DB continues to flow through the switch M1 (section T2-T3).
[0013]
Next, when the current flowing through the switch M1 stops when the switch M1 is turned off, the current drawn from the positive output terminal of the rectifier circuit DB flows into the capacitor C1 and charges (section T3-T4). When the voltage of the secondary winding N3 of the transformer T1 reaches the output voltage of the capacitor C3, the energy stored in the transformer T1 is output from the secondary side (section T4-T5). At this time, the current flowing through the winding N1 of the transformer T1 stops, and the charging of the capacitor C1 ends. As shown in FIG. 3, there is a period during which the AC input current hardly flows through the rectifier circuit during a period in which the AC voltage passing through the voltage zero point is low, but an AC input current close to a sine wave can flow.
[0014]
When the switch M1 is turned off, the voltage VM1 applied to both ends of the switch M1 gradually increases as the capacitor C1 is charged, and thus becomes zero voltage switching (ZVS). As a result, the switch M1 is turned on by zero current switching and turned off by zero voltage switching, so that soft switching with little switching loss can be performed. Then, the electric power stored in the transformer T2 by the action of the soft switching when the switch M1 is turned on is output from the secondary winding N22. Since the electric power stored in the transformer T1 is also output from the secondary winding N3 due to the current to be charged, the conversion efficiency can be increased to 95% or more.
[0015]
The adjustment of the DC output voltage is carried out by detecting the DC output voltage and comparing it with a reference voltage, so that the DC output voltage becomes constant. This can be achieved by frequency control that varies with the off time.
[0016]
In a period higher than the period in which the AC voltage is low, fluctuations in voltage at the first and second terminals of the transformer T1 due to resonance of the transformer T1, the capacitor C1, the transformer T2, and the switch M1 become larger. For this reason, the charge / discharge current of the capacitor C1 is larger, the charge / discharge time is longer, the resonance period is longer, and the time for the current to flow through the switch M1 is longer in the period higher than the period in which the AC voltage is low. On the contrary, during the period when the AC voltage is low, the charging / discharging current of the capacitor C1 is small, the charging / discharging time is short, the resonance period is short, and the time for the current to flow through the switch M1 is short.
[0017]
Therefore, when the AC input voltage is detected and the period during which the AC voltage is lower than the period during which the AC voltage is high, frequency control is performed to shorten the time of one switching cycle while maintaining a constant ON / OFF time ratio of the switch M1. Alternatively, during the low AC voltage period, the ON time in one switching cycle of the switch M1 is made constant, the OFF time is shortened, or the ON time ratio is increased in the ON / OFF time ratio. By performing duty control and increasing the pull-in of the AC input current during a period in which the AC voltage is low, the AC input current can be a sine wave having a power factor close to 1. Further, the DC output voltage can be made constant by adding the control by the DC output voltage detection to the control by the AC input voltage detection.
[0018]
The capacity of the capacitor C1 is a capacity suitable for causing resonance with the transformers T1 and T2 so that the switch M1 performs soft switching.
[0019]
(Embodiment 2) A second embodiment will be described with reference to FIG. However, in FIG. 4, the same parts as those in FIG. In FIG. 4, the transformer T1 in FIG. 1 is provided with a third terminal (4), a second primary winding N2 is provided between the first terminal (1) and the third terminal (4). The configuration is the same as that shown in FIG. 1 except that a second resonance capacitor C2 is connected between the third terminal (4) and the negative output terminal of the rectifier circuit DB.
[0020]
FIG. 5 shows the voltage and current characteristics of each part of the circuit of FIG. 4 over time (sections T0,..., T5). Each waveform in FIG. 5 shows its characteristics as a representative example for helping understanding. (A) is the current IDB of the positive output terminal of the rectifier circuit. (B) is a current IN1 flowing through the winding N1 of the transformer T1. (C) is the charge / discharge current IC2 of the capacitor C2. (D) is the charge / discharge current IC1 of the capacitor C1. (E) is the current IM1 of the switch M1. (F) is the voltage VM1 of the switch M1. (G) is the voltage V (2) of the second terminal (2) of the transformer T1. (H) is a current IN3 output to the secondary side from the winding N3 of the transformer T1. (I) is a current IN22 output to the secondary side from the winding N22 of the transformer T2.
[0021]
When the switch M1 is turned on, the current drawn through the positive output terminal of the rectifier circuit DB and flowing through the winding N1 of the transformer T1 flows through the primary winding N21 of the transformer T2, so that the current flowing through the switch M1 is moderate. Stand up (section T0-T1). Slightly behind, the discharge current of the capacitor C1 is added to the current flowing from the winding N1 and flows through the switch M1. At the same time, the charging current of the capacitor C2 flows through the winding N2 of the transformer T1 (section T1-T2). When the voltage on the secondary side of the transformer T2 reaches the output voltage of the capacitor C3, the energy stored in the transformer T2 is output from N22 to the secondary side (section T2-T5). At this time, the discharge of the capacitor C1 is finished, the charging of the capacitor C2 is also finished, and the current flowing through the capacitors C1, C2 is stopped. A current that flows through the winding N1 of the transformer T1 from the positive output terminal of the rectifier circuit DB continues to flow through the switch M1 (section T2-T3).
[0022]
Next, when the current flowing through the switch M1 is stopped when the switch M1 is turned off, the current drawn from the positive output terminal of the rectifier circuit DB is also stopped. When the current from the positive output terminal of the rectifier circuit DB stops, the transformer T1 causes the discharge current of the capacitor C2 to flow as the charging current of the capacitor C1. As a result, the capacitor C2 is discharged and the capacitor C1 is charged (section T3-T4). When the voltage of the secondary winding N3 of the transformer T1 reaches the output voltage of the capacitor C3, the electric power stored in the transformer T1 is output to the secondary side (section T4-T5).
[0023]
The capacitances of the capacitors C1 and C2 and the transformer T2 are determined by adjusting the switch M1 so that the transformer T1 causes stable resonance.
[0024]
switch M Capacitor after 1 turns off C 2 discharges into a discharged state, and the capacitor C 1 is charged and charged, the transformer T 1, T 2 and capacitor C 1, C 2 resonance ends, then switch M Capacitor when 1 is turned on C 2 draws alternating current as charging current,By switching the switch M1 so as to cause stable resonance in the circuit of the capacitor C2, the transformer T1, the capacitor C1, and the transformer T2, including the circuit of the transformer T2 and the switch M1, the AC voltage is high in the low period as well as in the low period. Also, an alternating current can be drawn from the positive output terminal of the rectifier circuit DB, and a sine wave alternating current input with a power factor close to 1 is obtained as shown in FIG.
[0025]
The number of windings of the winding N3 of the transformer T1 is a value adjusted according to the output in relation to the winding N1. The number of windings N2 is smaller than that of the winding N1, and the winding N2 is adjusted so that the winding N1 and the capacitor C1 resonate stably even when the AC voltage is low. Therefore, since the number of windings of the winding N2 is small, the loss in the winding N2 is very small. By charging / discharging the capacitor C2 by the winding N2 of the transformer T1, the resonance between the winding N1 and the capacitor C1 can be stabilized even during a period in which the AC voltage is low. The winding direction of the winding N2 of the transformer T1 can be the same or opposite to the winding direction of the winding N1, and the same effect can be obtained by adjusting the capacity and switching time of each part.
[0026]
(Embodiment 3) A third embodiment will be described with reference to FIG. However, in FIG. 7, the same parts as those in FIG. The circuit of FIG. 7 is a forward type of the output circuit on the secondary side of the transformer T1 of the circuit of FIG. 1 that supplies power to the load while the switch M1 is on. The secondary winding N3 of the first transformer T1 is connected to the smoothing capacitor C3 via the diode D1 and the smoothing choke coil L1, and the pair of DC output terminals are connected to both ends of the smoothing capacitor C3. A diode D3 having a flywheel action is connected between the other terminal of the secondary winding N3 and a connection point between the diode D1 and the choke coil L1. FIG. 8 shows voltage and current characteristics of each part of the circuit of FIG. 7 along time (sections T0,..., T5). Each waveform in FIG. 8 shows its characteristics as a representative example for helping understanding. (A) is the current IDB of the positive output terminal of the rectifier circuit. (B) is the charge / discharge current IC1 of the capacitor C1. (C) is the current IM1 of the switch M1. (D) is the voltage VM1 of the switch M1. (E) is the voltage V (2) of the second terminal (2) of the transformer T1. (F) is a current IN3 output to the secondary side from the winding N3 of the transformer T1. (G) is a current IN22 output to the secondary side from the winding N22 of the transformer T2.
[0027]
When the switch M1 is turned on, the discharge current of the capacitor C1 flows through the primary winding N21 of the transformer T2, so that the current flowing through the switch M1 rises gently (section T0-T1). Next, the discharge of the capacitor C1 ends, the voltage at the second terminal {circle around (2)} of the transformer T1 drops, and the AC input current is drawn from the positive output terminal of the rectifier circuit DB. When the current drawn from the positive output terminal of the rectifier circuit DB flows through the primary winding N1 of the transformer T1, power is output from the secondary winding N3 to the secondary load (section T1-T3). When the secondary side voltage of the transformer T2 reaches the output voltage of the capacitor C3, the electric power stored in the transformer T2 is output from the winding N22 to the secondary side (section T1-T5). When the current flowing through the switch M1 stops when the switch M1 is turned off, the current drawn from the positive output terminal of the rectifier circuit DB flows into the capacitor C1 and charges (section T2-T3).
[0028]
When the output from the secondary winding N3 of the transformer T1 is finished, a flywheel current flows through the diode D3 (section T3-T4). Next, a current is gently drawn from the positive output terminal of the rectifier circuit DB to charge the capacitor C1 (section T4-T5). As shown in FIG. 3, there is a period during which the AC input current hardly flows through the rectifier circuit during a period in which the AC voltage passing through the voltage zero point is low, but an AC input current close to a sine wave can flow.
[0029]
Since the transformer T2 of this circuit is connected in a flyback manner so as to store power when the switch M1 is on and supply the power stored during the off period to the load, as in the circuit of FIG. When the switch M1 is turned off, the voltage applied to both ends of the switch gradually increases as the capacitor C1 is charged. Therefore, the turn-off loss of the switch M1 is small. As a result, the switch M1 can perform soft switching with little turn-on loss and turn-off loss.
[0030]
(Embodiment 4) The circuit of FIG. 9 has both terminals of a switch M1 (hereinafter referred to as a main switch M1) in order to more reliably stabilize soft switching when the switch M1 of the circuit of FIG. 1 is on. In the meantime, the resonance coil L21 and the auxiliary switch M2 are connected in series. Description of the circuit portion of FIG. 1 is omitted. First, the operation of the resonance coil L21 and the auxiliary switch M2 will be described. FIG. 10 shows voltage and current characteristics of each part of the circuit of FIG. 9 along time (sections T0,..., T5). Each waveform in FIG. 10 shows its characteristics as a representative example to help understanding. (A) is the current IDB of the positive output terminal of the rectifier circuit. (B) is the charge / discharge current IC1 of the capacitor C1. (C) is the current IM1 of the main switch M1. (D) is the current IM2 of the auxiliary switch M2. (E) is the voltage VM1 of the main switch M1. (F) is the voltage V (2) of the second terminal (2) of the transformer T1. (G) is a current IN3 output to the secondary side from the winding N3 of the transformer T1. (H) is a current IN22 output to the secondary side from the winding N22 of the transformer T2.
[0031]
By turning on the auxiliary switch M2 before the main switch M1, the voltage at the terminal (3) of the transformer T2 (the voltage VM1 of the main switch M1) is reduced to zero volts (0V), and immediately after that, the main switch M1 is turned on. Thus, zero voltage switching (ZVS) can be performed. When the auxiliary switch M2 is turned on, the voltage at the first terminal {circle around (1)} of the transformer T1 drops, current is drawn from the positive output terminal of the rectifier circuit DB, and the winding N1 of the transformer T1 and the winding of the transformer T2 N21 flows through the resonance coil L21 to the auxiliary switch M2. Since it passes through the resonance coil L21, a small current flows through the auxiliary switch M2 without inrush current. Then, after the voltage VM1 of the main switch M1 becomes 0V, the main switch M1 is turned on to perform zero voltage switching (ZVS). Immediately after turning on the main switch M1, the auxiliary switch M2 is turned off. (Section T0-T1). Slightly behind, the discharge current of the capacitor C1 is added to the current flowing from the winding N1 and flows through the main switch M1 (section T1-T2). After the section T2, it is the same as the description of the circuit of FIG.
[0032]
When the auxiliary switch M2 is turned on before the main switch M1 and the voltage VM1 of the main switch M1 becomes zero volts (0V), the main switch M1 is turned on, so that the main switch M1 is surely stable in zero voltage switching. (ZVS). Further, since the on-time of the auxiliary switch M2 is very short compared to the on-time of the main switch M1, the loss in the resonance coil L21 and the auxiliary switch M2 is very small. The resonance coil L21 can also be formed using the leakage inductance of the transformer T2.
[0033]
Since the main switch M1 reliably performs zero voltage switching (ZVS), even if the AC input voltage fluctuates greatly in the range of 60V to 280V, the load on the output side is 10% to 100%. Even if the range fluctuates greatly, the switching time of the main switch M1 can be controlled to make the DC output voltage constant, and, as with the circuit of FIG. Can do. Of course, by changing and adjusting the transformer, coil, capacitor, switch and the like of the circuit so as to correspond to the high voltage, it is possible to make the power supply usable in a wide range of voltages of 500V and 1000V.
[0034]
When electrical equipment is not used, that is, when the power is on standby, the main switch M1 is switched at a low frequency by making the duty ratio of the on / off time extremely small, so that the very small power required on the secondary side The above power is supplied and wasteful power is consumed. Then, harmonic noise appears on the AC side due to intermittent switching of the main switch M1. However, when the power is on standby, the main switch M1 is turned off and only the auxiliary switch M2 is switched to the minimum necessary, so that only the necessary power can be supplied on the secondary side. Consumption can be reduced very much, and switching can be performed without generating harmonic noise on the AC side.
[0035]
(Embodiment 5) FIG. 11 shows an embodiment comprising one transformer as a fifth embodiment. In the circuit of FIG. 11, the two transformers T1 and T2 of the circuit of FIG. 9 are replaced with one transformer T5 so that characteristics close to those of the circuit of FIG. 9 are obtained. However, in FIG. 11, the same reference numerals are given to substantially the same parts as in FIG. In FIG. 11, Vac is an AC power source, LPF is a low-pass filter, DB is a rectifier circuit, T5 has first, second, third and fourth terminals on the primary side, and the first terminal (5). And the second terminal {circle around (6)} between the first primary winding N51 and the second terminal {circle around (6)} and the third terminal {circle around (7)}. And a transformer T5 having a third primary winding N53 and a secondary winding N58 between the second terminal (6) and the fourth terminal (8), a main switch M1, an auxiliary switch M2, The resonance capacitor C1 and the resonance coil L21. A rectifying / smoothing circuit including a diode D1 and a smoothing capacitor C3 is connected to the secondary side.
[0036]
The rectifier circuit DB connected to the AC power supply, the positive output terminal of the rectifier circuit DB and the first terminal (5) of the transformer T5 are connected, the third terminal (7) of the transformer T5 and the negative terminal of the rectifier circuit DB. A switch M1 is connected between the output terminal, a resonance capacitor C1 is connected between the fourth terminal (8) of the transformer T5 and the negative output terminal of the rectifier circuit DB, and between both terminals of the switch M1, The resonance coil L21 and the auxiliary switch M2 are connected in series. The secondary winding N58 and the diode D1 of the transformer T5 are connected in a flyback form to store power when the switch M1 is on and supply the power stored during the off period to the load, and a pair of DC output terminals Are connected to both ends of the capacitor C3.
[0037]
First, the operation of the transformer T5 will be described. Based on FIG. 12, the voltage and current characteristics of each part of the circuit of FIG. 11 are shown along time (sections T0,..., T5). Each waveform in FIG. 12 shows its characteristics as a representative example to help understanding. (A) is the current IDB of the positive output terminal of the rectifier circuit. (B) is the charge / discharge current IC1 of the capacitor C1. (C) is the current IN52 of the winding N52 of the transformer T5. (D) is the current IM1 of the main switch M1. (E) is the current IM2 of the auxiliary switch M2. (F) is the voltage VM1 of the main switch M1. (G) is a current IN58 output to the secondary side from the winding N58 of the transformer T5.
[0038]
When the auxiliary switch M2 is turned on, the voltage at the first terminal {circle around (5)} of the transformer T5 is lowered, current is drawn from the positive output terminal of the rectifier circuit DB, and flows through the windings N51 and N52 of the transformer T5 to resonate. Flows to the auxiliary switch M2 through the coil L21. Since it passes through the resonance coil L21, a current that rises gently without any inrush current flows through the auxiliary switch M2. (Section T0-T1). When the capacitor C1 is discharged with a slight delay, the voltage at the terminal (5) of the transformer T5 rises and the current from the positive output terminal of the rectifier circuit DB stops. When the discharge of the capacitor C1 ends and the voltage at the terminals (6) and (7) of the transformer T5 drops, current is again drawn from the positive output terminal of the rectifier circuit DB and flows through the windings N51 and N52 of the transformer T5. Immediately after the voltage at the terminal (7) of the transformer T5 (the voltage VM1 of the main switch M1) has dropped to zero volts, the main switch M1 is turned on to pass the current from the winding N52 to the negative output terminal of the rectifier circuit DB. Immediately thereafter, the auxiliary switch M2 is turned off. (Section T1-T2). The main switch M1 is turned off by passing a current for a certain time. (Section T2-T3). When the main switch M1 is turned off, the current flowing from the positive output terminal of the rectifier circuit DB to the winding N51 is charged by the capacitor C1 and stopped. When the main switch M1 is turned off, the voltage VM1 of the main switch M1 rises gently. (Section T3-T4). The electric power stored in the transformer T5 is output from the winding N58 to the secondary side. (Section T4-T5).
[0039]
The electric power stored on the primary side by the windings N51, N52, and N53 of the transformer T5 is discharged from the winding N58 to the secondary side. The important operation of each winding will be described. The winding N51 is a main winding that transmits primary power to the secondary side. The winding N53 acts to strengthen the discharge of the resonance capacitor C1 when the auxiliary switch M2 is turned on, and to reliably reduce the voltage at the terminal (7) of the transformer T5 to zero volts in a short time. Therefore, the ON time of the auxiliary switch M2 can be shortened, and the power consumption in the auxiliary switch M2 and the resonance coil L21 can be minimized. Further, when the main switch M1 is turned off, the resonance capacitor C1 is charged by the current flowing from the positive output terminal of the rectifier circuit DB to the winding N51, so that charging takes a short time. . As a result, the rise of the voltage VM1 of the main switch M1 becomes gentle, and the main switch M1 is turned off by zero voltage switching. When the auxiliary switch M2 and the main switch M1 are turned on, the winding N52 controls the magnitude of the peak value of the current flowing through each switch to the magnitude of the current necessary for the power supply. Since the current is not limited by the resistance but is controlled by the inductance of the winding N52, power can be stored in the transformer T5 and discharged to the secondary side, so that power consumption can be reduced. Further, the resonance of the winding N53 and the capacitor C1 can draw a current from the positive output terminal of the rectifier circuit DB, and can draw a current effectively even during a period of low AC voltage. Current can flow. The resonance coil L21 can also use the leakage inductance of the transformer T5.
[0040]
As described above, the configuration of the present invention has been described as the case of the AC power supply input. However, even when the DC voltage power supply is connected by removing the portion that rectifies the AC voltage into the DC in the circuit of the above embodiment, the DC-DC is highly efficient. It is obvious that a converter can be constructed.
【The invention's effect】
As described above, by performing soft switching with this circuit, switching loss can be reduced and generation of noise and overvoltage inside the power supply can be suppressed. Further, the efficiency can be further improved by outputting the power during soft switching from the transformer T2 to the secondary load. The AC input current is a sine wave with a power factor of less noise and higher harmonics close to 1, and at the same time, a stable DC voltage can be output. Also, even if the load on the output side changes greatly, the output voltage can be made constant by maintaining a sine wave AC input current with a power factor close to 1. In addition, since no smoothing capacitor is used on the primary side of the power supply, no inrush current flows when the power is turned on. Therefore, no resistor for preventing inrush current is required. Since an inrush current does not flow even during a momentary interruption, transient stress on circuit elements inside the power supply is reduced, and a stable and stable DC output voltage can be recovered quickly. It is also possible to perform high-power factor soft switching with high efficiency close to the characteristics of the configuration of two transformers with the configuration of one transformer.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a configuration of a first embodiment of a switching power supply device according to the present invention;
FIG. 2 is a current and voltage waveform diagram for explaining the operation of the first embodiment of the switching power supply device of the present invention;
FIG. 3 is a waveform diagram of an AC input current of the switching power supply device according to the first embodiment of the present invention.
FIG. 4 is a circuit diagram showing a configuration of a second embodiment of the switching power supply device of the present invention;
FIG. 5 is a current and voltage waveform diagram for explaining the operation of the second embodiment of the switching power supply apparatus of the present invention;
FIG. 6 is a waveform diagram of an AC input current of the second embodiment of the switching power supply device of the present invention.
FIG. 7 is a circuit diagram showing a configuration of a third embodiment of the switching power supply unit according to the present invention;
FIG. 8 is a current and voltage waveform diagram for explaining the operation of the third embodiment of the switching power supply apparatus of the present invention;
FIG. 9 is a circuit diagram showing a configuration of a fourth embodiment of the switching power supply unit of the present invention;
FIG. 10 is a current and voltage waveform diagram for explaining the operation of the fourth embodiment of the switching power supply apparatus of the present invention;
FIG. 11 is a circuit diagram showing a configuration of a fifth embodiment of the switching power supply unit of the present invention;
FIG. 12 is a current and voltage waveform diagram for explaining the operation of the fifth embodiment of the switching power supply apparatus of the present invention;
FIG. 13 is a diagram illustrating an example of a configuration of a conventional switching power supply device;
FIG. 14 is a diagram showing an example of the configuration of another conventional switching power supply device.
[Explanation of symbols]
C1, C2 ... Resonance capacitors
C3: Smoothing capacitor
DB: Rectifier circuit
D1, D2 ... Diode
L1, L21 ... Choke coil
M1 ... Transistor switch (main switch)
M2 ... Transistor switch (auxiliary switch)
T1, T2, T5 ... Transformer

Claims (1)

  A first primary winding N1 having a first terminal, a second terminal, and a third terminal on a primary side, and provided between the first terminal and the second terminal; A first transformer T1 having a second primary winding N2, a secondary winding N3, a primary winding N21 and a secondary winding provided between the first terminal and the third terminal A second transformer T2 having N22; a rectifying circuit DB that rectifies an AC voltage and has a positive output terminal connected to the first terminal of the first transformer T1; and a second transformer T1. And the other end of the primary winding N21 is connected to one end of the switching means M1, and the other end of the switching means M1 is connected to the other end of the primary winding N21. Connected to the negative output terminal of the rectifier circuit DB, the second terminal of the first transformer T1 and the negative output of the rectifier circuit DB. A charge / discharge circuit of the first resonance capacitor C1 connected between the first transformer T1 and the third output terminal of the first transformer T1 and a negative output terminal of the rectifier circuit DB. A charging / discharging circuit of the second resonance capacitor C2, a first rectifying / smoothing circuit in which the secondary winding N3 of the first transformer T1 is connected to the smoothing capacitor C3 via the diode D1, and the second transformer. A secondary winding N22 of T2 is connected to the smoothing capacitor C3 via a diode D2, and the same polarity of each of the first rectifying and smoothing circuit and the second rectifying and smoothing circuit. A high power factor switching power supply device comprising an output terminal commonly connected to the terminal.

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