JP2002354804A - Resonance type power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the efficiency decline of a current resonance type power supply device in a light load state and to obtain a highly efficient resonance type power supply device. SOLUTION: A means is provided which increases an inductance component and reduce a capacitance component of a resonating means comprising an inductor and a capacitor respectively. In a light load state, the inductance is increased and the capacitance is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device using a current resonance system, which has a high efficiency at a light load.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a conventional embodiment. FIG. 3 and FIG. 4 are waveforms of each part for explaining the operation. The operation will be described below with reference to these figures. 2
Reference numeral 01 denotes a DC voltage rectified into DC from an AC input through an input filter to a diode and a smoothing capacitor. The switching power supply unit has a half-bridge configuration, and the primary side 202a of the transformer 202 has 203, 20
4 are driven by the two switching elements. Also,
Reference numerals 205 and 206 denote parasitic diodes generated between the source and the drain of the switching elements 203 and 204. Reference numeral 207 denotes a leakage inductance that does not contribute to primary-secondary coupling in the transformer 202, and reference numeral 208 denotes a resonance capacitor that performs a resonance operation with the primary inductance 202a or the leakage inductance 207. Capacitors 209 attached to both ends of the switching element 204 are capacitors for voltage resonance. The secondary side 202b of the transformer 202 has its center connected to ground, and rectifier diodes 210 and 21 at both ends having different polarities with respect to the winding direction.
After the anode side is connected and the cathode side is connected in common, it is connected to the rectifying capacitor 212 and the output voltage 213 is output. The normal operation will be described.

[0005] 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 a 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 depends on the resonance current Ir and the exciting current I
The current having a difference from lp flows in proportion to the winding of the transformer 202, flows from the secondary winding 202b through the rectifying diode 210 to the rectifying capacitor 212, and is output. When the resonance operation proceeds and the resonance current Ir and the excitation current Ilp of the transformer 202 become equal, the transmission of the power to the secondary side ends, and the resonance operation of the leakage inductance 207, the primary inductance 202a, and the resonance capacitor 208 starts. Will be At this time, the leakage inductances 207 and 1
The energy stored in the next inductance 202a is transferred to the resonance capacitor 208. Thereafter, when the switching element 203 is turned off, the energy stored in the leakage inductance 207 and the primary inductance 202a is used as the voltage resonance capacitor 209.
To discharge. Parasitic diode 2 due to capacitor voltage
When 06 is turned on, the switching element 204 is turned on. When the switching element 204 is turned on, the leakage inductance 207 and the resonance capacitor 2
08 and a power is transmitted to the secondary side via the diode 211. The direction in which the resonance current flows at this time is opposite to the above. When the resonance operation proceeds and the resonance current Ir and the excitation current ILp of the transformer 202 become equal, the resonance operation of the leakage inductance 207, the primary inductance 202a, and the resonance capacitor 208 is performed. At this time, the energy stored in the leakage inductance 207 and the primary inductance 202a is transferred to the resonance capacitor 208. Thereafter, when the switching element 204 is turned off, the leakage inductance 207 and the primary inductance 202a
And the energy stored in the capacitor 20 for voltage resonance.
Charge 9 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, the switching elements 203, 2
04 is alternately driven to supply power to the secondary side.

FIG. 3 illustrates the above operation. This shows the waveform of each part at the time of the normal operation. From the top, the resonance current Ir, the excitation current ILp of the transformer 202, and the voltage V between the source and the drain of the switching elements 203 and 204 are shown.
ds1, Vds2, and switching loss are shown, respectively. Since the current resonance type power supply utilizes a resonance operation, zero current switching and zero voltage switching are realized in an ideal form.
Loss due to on-resistance of 4, secondary-side rectifier diode 21
Loss due to Vf of 0 and 211, loss at turn-off, and the like cannot be avoided, and switching loss occurs.
FIG. 4 shows the waveform of each part of the current resonance type power supply at the time of light load. When the load is light, the output power on the secondary side is small, so the switching frequency must be reduced. Since the number of turn-offs increases, the switching loss increases, and the output power relative to the input power increases. Since the ratio becomes small, the efficiency is deteriorated. FIG. 6 shows this state. As shown in this figure, the efficiency is high when the output power is large, but the efficiency becomes worse as the load becomes lighter.

[0005]

In the conventional current resonance type power supply, the output power on the secondary side becomes small when the load is light as described in the conventional example, so that the switching frequency must be reduced. However, since the number of turn-offs increases, the switching loss increases, and the ratio of the output power to the input power becomes relatively small, resulting in a problem that the efficiency is deteriorated.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems in the prior art, and has a resonance means for resonating at a resonance frequency determined by an inductance and a capacitor; Switching means for switching a current according to the input voltage to generate a switching current, a transforming means for transforming a voltage according to the switching means, and rectifying a switching current according to an output voltage from the transforming means. In a resonance type power supply device having a rectifier for supplying power to a load, the conventional problem can be solved by increasing the inductance component of the resonance means and decreasing the capacitor component at a light load.

[0007]

FIG. 1 is a view for explaining an embodiment of the present invention, and portions having the same functions as those of the conventional example are denoted by the same reference numerals. The difference in circuit configuration from FIG.
The inductance 101 is connected in series with the leakage inductance 207, the switching element 102 for switching operation is arranged at both ends of the inductance 101, and the capacitor 103 is connected in series with the resonance capacitor 208,
The switching element 104 for switching the operation is arranged at both ends of the capacitor 103.

Hereinafter, the operation of this circuit will be described.
Usually, the resonance frequency of the resonance circuit is calculated based on the following equation: fr = 1 / (2 × π × √ (L × C)) (1) The inductance value (L) and the capacitance of the capacitor (C) 1
One is decided.

Since the switching elements 203 and 204 normally operate the resonance circuit in the inductance region, if the load is reduced, the oscillation frequency of the resonance circuit is increased, and the impedance is increased to prevent an increase in the exciting current of the transformer and to reduce the resonance. The output power, which is the product of the difference between the current and the exciting current and the output voltage determined by the primary-secondary winding ratio, is reduced. However, in this method, it is necessary to reduce the exciting current in order to make the oscillation state commensurate with the load, so that the oscillation frequency must be increased and the switching loss increases. In the present embodiment, in order to solve this problem, the leakage inductance 207 at light load is set.
It is characterized in that an inductance 101 (Ls) is arranged in series with the capacitor 101, and a capacitor 103 (Cs) is arranged in series with the resonance capacitor 208.

According to this method, the inductance value and the capacitance of the capacitor are L → L + Ls C → (C × Cs) / (C + Cs), and the inductance value increases and the capacitance of the capacitor decreases.

The inductance 1 is set so that the resonance frequency calculated by the equation (1) is equal to or lower than that in normal operation.
By setting 01 (Ls) and the capacitor 103 (Cs), the resonance operation can be performed without increasing the oscillation frequency. The following is a calculation formula of the resonance current Ir and the transformer excitation current ILp. Ir∝√ (C / L) (2) ILp = Vin × t / L (3) From Equations (2) and (3), the inductance value increases and the capacitance of the capacitor decreases. It can be seen that both the exciting current ILp of the transformer decreases.

According to such a method, it is possible to realize an operation under a light load without increasing the oscillation frequency, so that it is possible to prevent an increase in switching loss due to a higher frequency.

The switching elements 102 and 104 are controlled so as to be on during normal operation and off when light load is applied. The other operations at the time of resonance are the same as those in the conventional example, and a description thereof will be omitted.

FIG. 5 shows waveforms of respective parts for explaining the present embodiment. From above, a resonance current Ir, a transformer excitation current Ilp, switching elements 203 and 204 are shown.
3 shows the source-drain voltages Vds1 and Vds2 of FIG. In the conventional example, as compared with the normal operation, the oscillation frequency increases at a light load, and the switching loss increases. On the other hand, according to the present invention, the resonance circuit is switched by turning off the switching elements 215 and 217 at a light load, thereby switching the resonance circuit. Current and the exciting current of the transformer,
By setting the oscillation frequency to be equal to or lower than that, it is possible to suppress an increase in the frequency of the switching elements 203 and 204 and to prevent an increase in switching loss.

FIG. 6 shows the relationship between output power and efficiency when this embodiment is realized. In the conventional circuit configuration, the efficiency decreases as the output power decreases. On the other hand, in the circuit configuration proposed in the present invention, the output power is reduced by turning off the switching elements 102 and 104 and switching the resonance circuit at a light load. It can be seen that the efficiency is improved when it is small. In this case, the switching element 20
Since the loss due to the on-resistance of the transistors 3 and 204 is smaller than that in the normal operation, the efficiency is higher than that in the normal operation. However, during normal operation, the loss due to the on-resistance of the switching elements 102 and 104 occurs, so that the efficiency during normal operation is slightly lower than when there is no means for switching the resonance circuit.

[0016]

According to the conventional circuit configuration, the efficiency decreases as the output power decreases. On the other hand, in the circuit configuration proposed in the present invention, the switching elements 102 and 104 at light load are used.
Is turned off and the resonance circuit is switched, so that the resonance current and the exciting current of the transformer are reduced, and the switching frequency does not need to be increased. Therefore, an increase in switching loss can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a resonance type 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 during normal operation of a resonance type power supply device for explaining a conventional embodiment.

FIG. 4 is a waveform diagram of each part of the resonance type power supply device for explaining the conventional embodiment when the load is light.

FIG. 5 is a waveform diagram of each part of the resonance type power supply device according to the embodiment of the present invention when the load is light.

FIG. 6 is a diagram illustrating the relationship between output power and efficiency of a resonance-type power supply device for explaining the effect of the present invention.

[Explanation of symbols]

Reference Signs List 101 Inductance 103 Capacitor 102, 104 Switching element for resonance condition switching (normally on, off at light load) 201 DC voltage rectified and smoothed from AC input 202 Transformer 202a Primary winding 202b Secondary winding 203, 204 Half bridge Of the main switching elements 205, 206 Parasitic diodes generated in the main switching elements 207 Leakage inductance not contributing to the primary-secondary coupling in the transformer 202 208 Capacitors for current resonance 209 Capacitors for voltage resonance 210, 211 Rectifier diodes 212 smoothing capacitor 213 rectifier diode, output voltage rectified and smoothed by smoothing capacitor

Claims (1)

[Claims] 1. A resonance means for resonating at a resonance frequency determined by an inductance and a capacitor; a switching means for switching a current according to an input voltage corresponding to the resonance frequency to generate a switching current; And a rectifier for rectifying a switching current corresponding to an output voltage from the transformer and supplying the rectified current to a load. Increase the ingredients,
A resonance type power supply device characterized by reducing a capacitor component.