JP4617025B2 - Resonant power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a resonant power supply device, and more particularly to a resonant power supply device that achieves high efficiency at light loads.
[0002]
[Prior art]
FIG. 2 is a circuit diagram showing a conventional embodiment. 3 and 4 are waveforms of respective parts for explaining the operation. The operation will be described below with reference to these drawings.
Reference numeral 201 denotes a DC voltage rectified from an AC input to a direct current by a diode and a smoothing capacitor via an input filter. The switching power supply unit has a half-bridge configuration, and the primary winding 202 a of the transformer 202 is driven by two switching elements 203 and 204. Reference numerals 205 and 206 denote parasitic diodes generated between the source and drain of the switching elements 203 and 204. Reference numeral 207 denotes a leakage inductance that does not contribute to the primary-secondary coupling in the transformer 202, and 208 denotes a resonant capacitor that performs a resonance operation with the primary winding 202a or the leakage inductance 207. Capacitors 209 attached to both ends of the switching element 204 indicate capacitors for voltage resonance. The secondary winding 202b of the transformer 202 has a center portion connected to the ground, the anode sides of the rectifying diodes 210 and 211 are connected to both ends having different polarities with respect to the winding direction, and the cathode side is connected in common. The output voltage 213 is output to the rectifying capacitor 212.
A normal operation will be described.
[0003]
First, the switching element 203 is turned on while a current flows through the parasitic diode 205. When the switching element 203 is turned on, the leakage inductance 207 and the resonance capacitor 208 perform a resonance operation, and the resonance current Ir flows. At this time, since energy is supplied to the secondary side, the primary winding 202a of the transformer does not contribute to the resonance operation. The power supplied to the secondary side is rectified by the difference between the resonance current Ir and the exciting current Ilp of the transformer 202 from the secondary winding 202b via the rectifying diode 210 in proportion to the winding of the transformer 202. It flows to the capacitor 212 and is output. When the resonance operation progresses and the resonance current Ir and the excitation current Ilp of the transformer 202 become equal, the transmission of power to the secondary side ends, and the resonance operation between the leakage inductance 207, the primary winding 202a, and the resonance capacitor 208 starts. Done. At this time, the energy stored in the leakage inductance 207 and the primary winding 202a is transferred to the resonance capacitor 208. Thereafter, when the switching element 203 is turned off, the voltage resonance capacitor 209 is discharged with the energy stored in the leakage inductance 207 and the primary winding 202a. When the parasitic diode 206 is turned on by the voltage of the capacitor, the switching element 204 is turned on. When the switching element 204 is turned on, resonance operation between the leakage inductance 207 and the resonance capacitor 208 is performed again, and power is transmitted to the secondary side via the diode 211. At this time, the direction in which the resonance current flows is opposite to the above. When the resonance operation proceeds and the resonance current Ir and the exciting current ILp of the transformer 202 become equal, the resonance operation of the leakage inductance 207, the primary winding 202a and the resonance capacitor 208 is performed. At this time, the energy stored in the leakage inductance 207 and the primary winding 202a is transferred to the resonance capacitor 208. Thereafter, when the switching element 204 is turned off, the voltage resonance capacitor 209 is charged with the energy stored in the leakage inductance 207 and the primary winding 202a. When the parasitic diode 205 is turned on by the voltage of the capacitor, the switching element 203 is turned on again. As described above, power is supplied to the secondary side while the switching elements 203 and 204 are alternately driven.
[0004]
FIG. 3 illustrates the above operation. This shows the waveform of each part during normal operation, and shows the resonance current Ir, the excitation current ILp of the transformer 202, the source-drain voltages Vds1, Vds2, and switching loss, respectively, from the top. . Since the current resonance type power supply uses resonance operation, zero current switching and zero voltage switching are realized in an ideal form. However, the loss due to the on-resistance of the switching elements 203 and 204, the secondary side rectifier diodes 210 and 211, and the like. Loss due to Vf, loss at turn-off, etc. cannot be avoided, and switching loss occurs. FIG. 4 shows the waveform of each part of the current resonance type power supply at light load. Since the output power on the secondary side becomes small at light loads, the switching frequency must be lowered, the number of turn-offs increases, switching loss increases, and the output power relative to the input power is relatively high. Since the ratio is small, the efficiency deteriorates. This is shown in FIG. As shown in this figure, the efficiency is high when the output power is large, but the efficiency decreases as the load becomes lighter.
[0005]
[Problems to be solved by the invention]
In the conventional current resonance type power supply, as explained in the previous example, the output power on the secondary side becomes small at light load, so the switching frequency must be lowered and the number of turn-offs increases. As a result, the switching loss increases, and the ratio of the output power to the input power becomes relatively small, so that the efficiency is deteriorated.
[0006]
[Means for Solving the Problems]
The present invention has been made in view of the problems in the conventional example described above, and a resonance means that resonates at a resonance frequency determined from an inductance and a capacitor, and a current corresponding to an input voltage corresponding to the resonance operation of the resonance means. Switching means for generating a switching current by switching, transformer means for outputting a voltage corresponding to the switching current from the switching means to the primary winding to the secondary winding, and rectifying the output voltage from the transformer means In the resonance type power supply device having the rectifying means for supplying to the load, the inductance value and the capacitor capacity of the resonance means can be switched, and the inductance value of the resonance means is increased and the capacitor capacity is decreased at a light load. This is to solve the conventional problems.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a view for explaining an embodiment of the present invention, and parts having the same functions as those of the conventional example are given the same symbols. The difference in circuit configuration from FIG. 2 for explaining the conventional example is that the inductance 101 is connected in series with the leakage inductance 207 of the transformer 202, the switching elements 102 for switching operation are arranged at both ends of the inductance 101, and the resonant capacitor The capacitor 103 is connected in series with 208, and the switching element 104 for switching the operation is arranged at both ends of the capacitor 103.
[0008]
The operation of this circuit will be described below. Normally, the resonant frequency of the resonant circuit is calculated based on the following formula:
fr = 1 / (2 × π × √ (L × C)) (1)
One is determined by the inductance value (L) and the capacitor capacity (C).
[0009]
Since the switching elements 203 and 204 operate the resonance circuit in the normal inductance region, if the load is lightened, the oscillation frequency of the resonance circuit is increased and the impedance is increased to prevent an increase in the excitation current of the transformer. The output power, which is the product of the difference between the excitation current and the output voltage determined by the primary-secondary winding ratio, is reduced. However, in this method, since an oscillation state suitable for the load is required, it is necessary to reduce the excitation current. Therefore, the oscillation frequency must be increased, resulting in an increase in switching loss. In order to solve this problem, the present embodiment is characterized in that the inductance 101 (Ls) is arranged in series with the leakage inductance 207 and the capacitor 103 (Cs) is arranged in series with the resonance capacitor 208 at light load.
[0010]
By this method, the inductance value and the capacitor capacity are L → L + Ls C → (C × Cs) / (C + Cs)
Thus, the inductance value increases and the capacitor capacity decreases.
[0011]
By setting the inductance 101 (Ls) and the capacitor 103 (Cs) so that the resonance frequency calculated by the equation (1) is the same as or lower than that at the normal time, without increasing the oscillation frequency, Resonant operation can be performed. The following is a calculation formula for the resonance current Ir and the transformer excitation current ILp.
Ir∝√ (C / L) (2)
ILp = Vin × t / L (3)
From equations (2) and (3), it can be seen that both the resonance current Ir and the excitation current ILp of the transformer decrease because the inductance value increases and the capacitance of the capacitor decreases.
[0012]
Since it is possible to realize an operation at a light load without increasing the oscillation frequency by such a method, an increase in switching loss due to a higher frequency can be prevented.
[0013]
The switching elements 102 and 104 are controlled to be turned on during normal operation and to be turned off at light loads. Other operations at the time of resonance are the same as those in the conventional example, and will be omitted.
[0014]
FIG. 5 shows waveforms of respective parts for explaining the present embodiment. From the top, the resonance current Ir, the transformer excitation current Ilp, the source-drain voltages Vds1, Vds2 of the switching elements 203 and 204, and the switching loss are shown. Is shown. In the conventional example, the oscillation frequency is increased and the switching loss is increased at a light load as compared with the normal operation. On the other hand, in the present invention, the resonance circuit is switched by turning off the switching elements 215 and 217 at the light load, thereby resonating. By reducing the current and the exciting current of the transformer so that the oscillation frequency is equal to or lower than that, the high frequency of the switching elements 203 and 204 can be suppressed, and an increase in switching loss can be prevented.
[0015]
FIG. 6 shows the relationship between output power and efficiency when this embodiment is realized. In the conventional circuit configuration, when the output power decreases, the efficiency decreases. On the other hand, in the circuit configuration proposed in the present invention, the output power is reduced by switching off the switching elements 102 and 104 and switching the resonance circuit at light load. It can be seen that the efficiency is increased when it is small. At this time, since the loss due to the on-resistance of the switching elements 203 and 204 is smaller than that in the normal operation, the efficiency is higher than that in the normal operation. However, since the loss due to the on-resistance of the switching elements 102 and 104 occurs during normal operation, the efficiency during normal operation is slightly lower than when there is no switching means for the resonance circuit.
[0016]
【The invention's effect】
In the conventional circuit configuration, when the output power decreases, the efficiency decreases. On the other hand, according to the present invention, the inductance value and the capacitor capacity of the resonance means can be switched to increase the inductance value at light load. By switching the resonance means so as to reduce the capacitance, the resonance current and the excitation current of the transformer are lowered and the switching frequency does not need to be increased, so that an increase in switching loss can be prevented.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of a resonant power supply device illustrating an embodiment of the present invention.
FIG. 2 is a circuit configuration diagram of a resonance type power supply device illustrating a conventional embodiment.
FIG. 3 is a waveform diagram of each part at the time of normal operation of a resonance type power supply device for explaining a conventional embodiment;
FIG. 4 is a waveform diagram of each part at the time of a light load of a resonance type power supply device illustrating a conventional embodiment.
FIG. 5 is a waveform diagram of each part at the time of light load of the resonance type power supply device according to the embodiment of the invention.
FIG. 6 is a relationship diagram between output power and efficiency of a resonance type power supply device for explaining the effect of the present invention.
[Explanation of symbols]
101 Inductance 103 Capacitors 102, 104 Switching element for switching resonance conditions (normally on, light load off)
201 DC voltage rectified and smoothed from AC input 202 Transformer 202a Primary winding 202b Secondary winding 203, 204 Main switching element 205, 206 constituting half bridge 1 Parasitic diode 207 generated in main switching element 1 Leakage inductance 208 that does not contribute to next-secondary coupling 208 Current resonance capacitor 209 Voltage resonance capacitor 210, 211 Rectification diode 212 Smoothing capacitor 213 Output voltage rectified and smoothed by rectification diode, smoothing capacitor

Claims (1)

A resonance means that resonates at a resonance frequency determined from an inductance and a capacitor;
Switching means for generating a switching current by switching a current corresponding to an input voltage corresponding to a resonance operation of the resonance means;
Transformer means for outputting to the secondary winding a voltage corresponding to the switching current from the switching means to the primary winding;
In a resonance type power supply device having rectifying means for rectifying the output voltage from the transformer means and supplying the rectified voltage to a load,
A resonance type power supply apparatus, wherein the resonance means is configured to be switchable between an inductance value and a capacitor capacity, the inductance value of the resonance means is increased at a light load, and the capacitor capacity is decreased.

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