JPH07107742A - Series resonance converter - Google Patents

Abstract

PURPOSE:To make it possible to prevent the occurrence of switching loss and the like with the output capacity being increased by performing conduction-width control with two auxiliary switching elements within the conducting period of a main switch when the operating frequency of the main switching element is the frequency lower than an audio frequency. CONSTITUTION:When a load resistance 24 becomes large and the operating frequency is decreased to the degree of an audio frequency region by constant voltage control, e.g. an auxiliary switching element (AS) 13 is turned ON in a first resonance current loop I1. Then the resonance current is commutated into the loop of a dotted line I1'. The loop of the resonance current I/I' is switched to the o loop of a DC power supply 10- the AS 13- a resonance capacitor 19- a resonance inductor 30- a switching element 26- the DC power supply 10. The resonance current 11 continues to flow. Therefore, the resonance current 11 can be made to flow only in the required period for the primary winding of a transformer, with the resonance current being continuously made to flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a series resonance converter applied to, for example, a switching type power supply device.

[0002]

2. Description of the Related Art FIG. 1 shows an example of a circuit configuration of a series resonance converter. A MOS-FET as well as a series circuit of two main switching elements 11 and 12 such as a MOS-FET
, A series circuit of two auxiliary switching elements 13 and 14, and a series circuit of two feedback diodes 15 and 16,
A series (2) circuit of two resonance capacitors 19 and 20 is connected to the DC power source 10, and two auxiliary switching elements 13 and 14 and two feedback diodes 15 and 16 are connected.
Are respectively connected in parallel, and the main switching elements 11, 1 are connected.
The series circuit of the primary winding of the first transformer 17 and the resonance inductor 18 is connected between the connection point of the second series circuit and the connection point of the series circuits of the resonance capacitors 19 and 20, and
A rectifying diode 21 on the secondary winding of the transformer 17 of
22 is connected to form a full-wave rectifier circuit, and a smoothing capacitor 23 and a load resistor 24 are connected to the output of the full-wave rectifier circuit.

Next, the operation of this series resonance converter will be described. When the switching element 11 is turned on, the resonance current I1 is generated by the loop of the DC power supply 10-the switching element 11-the primary winding of the transformer 17, the resonance inductor 18, the resonance capacitor 20 and the DC power supply 10 as shown by the dotted line in the figure. Flows. When the ratio of the number of primary windings to the number of secondary windings of the transformer 17 is n, a resonance current of 1 / n times flows in the secondary winding of the transformer 17, so this resonance current is rectified by the diode 2 for rectification.
It is rectified by Nos. 1 and 22, the smoothing capacitor 23 is charged, and a DC voltage is supplied to the load resistor 24. When the main switching element 11 is OFF, the electric charge stored in the resonance capacitor 20 with the polarity shown in the figure passes through the feedback diode 15 and becomes the feedback current I2 as shown by the chain line in the figure.
Be returned to. This feedback current I2 is not converted to the load side and continues to flow during the OFF period TOFF. Although this waveform is shown in FIG. 3, it goes without saying that the resonance current (primary primary current) I1 described above continues to flow in the ON period TON.

Particularly at a light load, the auxiliary switching element 13 turns on when the resonance current I1 is flowing, and the DC power supply 10-auxiliary switching element 13-resonance inductor 18-resonance capacitor 20-DC power supply 10-router-
By passing the bypass resonance current I1 'as shown by the dotted line in the figure, PWM control can be used together without impairing the resonance characteristics. The subsequent feedback current I2 flows in exactly the same route as described above (3). Incidentally, the waveform of this case is shown in FIG.

As described above, the half-bridge series resonance converter shown in FIG. 1 controls the frequency when the load is heavy,
When the load becomes light and approaches the audible frequency range (about 20 KHZ), PWM (PULSE WIDTH MODULAT)
By switching to ION) control, it can be used as a series resonance converter which does not generate noise due to switching over a wide load range and has less switching loss and switching noise.

[0006]

[Problems to be Solved by the Invention]
The hybrid system series resonance converter has the following problems. That is, as indicated by the equation P0 = K · f · C · Vin2, if the input voltage Vin is constant, the maximum output capacitance P0 is proportional to the product of the resonance frequency f and the capacitance C of the resonance capacitor. When this formula is expanded, P0 = K · C ^0.5 / L ^0.5 · Vin. Therefore, in order to increase the maximum output capacitance P0, there is a method of reducing the resonance inductor L or increasing the capacitance C of the resonance capacitor. , If the resonance inductor L is made smaller, there is a limit from the viewpoint of protection of the element during commutation,
When the capacitance C of the resonance capacitor is increased, the resonance frequency f decreases and the controllable width becomes narrow at the audible frequency of 20 KHZ or higher.

Therefore, in order to increase the output capacitance with the series resonance converter, basically, a so-called full bridge system is used in which two pairs of the half bridge series resonance converters are combined in parallel as shown in FIG. Has been adopted. However, in the conventional full bridge system, until the reverse blocking function of the feedback diode is restored, a large spike-shaped current flows through the switching element, causing problems such as increased loss and noise and increased stress on the switching element. However, problems such as an increase in the number of parts will occur in order to prevent this (4).

Therefore, the object of the present invention is to suppress the increase in the number of components while adopting the full bridge system to increase the output capacitance, to prevent the rising of the current of the switching element from becoming steep, and to reverse the feedback diode. It is an object of the present invention to provide a large-capacity series resonant converter in which a spike-shaped current does not flow even if the direction blocking function is not restored.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an embodiment of the present invention, in which parts corresponding to those in FIG. As shown in FIG. 2, according to the present invention, resonance inductors 29 and 30 are provided instead of the resonance inductor 18, and the auxiliary switching element 2 is provided.
A circuit in which the parallel circuit of 5 and the feedback diode 27, the two resonance inductors 29 and 30, the auxiliary switching element 26 and the parallel circuit of the feedback diode 28 are connected in series to the DC power supply 10 and the resonance capacitor is connected. Instead of 19, 20, a resonance capacitor 19 is connected between one end of the primary winding of the transformer 17 and the connection point of the resonance inductors 29, 30.

The operation of the series resonant converter of the present invention will be described below. When the main switching element 11 and the auxiliary switching element 26 are turned on, the DC power supply 10-the main switching element 11-the primary winding of the transformer 17-the resonance capacitor 19-the resonance inductor 30-the main switching element 26-the DC power supply 10 are connected. The resonance current I1 flows as shown by the dotted line in the figure. When this resonance current I1 has finished flowing, the charge charged in the resonance capacitor 19 with the polarity shown in the figure is the resonance capacitor 19-return diode 15-DC power supply 10-feedback diode 28-resonance inductor 30-resonance capacitor. In the loop of 19, the feedback current I2 flows as shown by the alternate long and short dash line in the figure. The current waveform at this time is exactly the same as that of the conventional method as shown in FIG. (5)

When commutating from the positive half-cycle mode to the negative half-cycle mode, the feedback diodes 15, 16 are used.
During the recovery time, it is necessary to add an inductance in series with the primary winding of the transformer 17 or another inductance to the feedback current route in order to prevent a short-circuit current during commutation. Since it is not a part, it is omitted in the figure.

When the load resistance 24 becomes large and the operating frequency is lowered to the audible frequency range (20 KHZ) by the constant voltage control, for example, the first resonance current I1
When the auxiliary switching element 13 is turned on in the loop, the resonance current is commutated to the route indicated by the dotted line I1 'in the figure. The resonance current I1 'loop is switched to the loop of the DC power supply 10-auxiliary switching element 13-resonance capacitor 19-resonance inductor 30-switching element 26-DC power supply 10 to keep the resonance current I1 flowing. Here, this is the bypass resonance current I1 'loop. Therefore,
The resonance current I1 can be made to flow only for a period required for the primary winding of the transformer 17 while continuously flowing the resonance current. Also, from the resonance current loop I1 to the bypass resonance current loop
Switching loss or switching noise does not occur when the load resistance 24 is switched to the low level I1 '.

In the conventional half-bridge type series resonant converter shown in FIG.
A voltage of 1 / 2.Vin is applied to the primary winding of the transformer 17, but in the full bridge type series resonance converter of FIG. 2 according to the present invention, the DC input voltage Vin is the same as the primary voltage of the transformer 17. Applied to the winding. Therefore, since the maximum output capacitance P0 is proportional to the square of the voltage applied to the primary winding of the transformer as described above, the full-bridge series resonant converter of the present invention is a conventional half-bridge system. 4 times the output capacity can be obtained.

[0014]

【The invention's effect】

(6) As described above, the series resonance converter according to the present invention.
As a full bridge system, the power conversion ratio is increased or PWM control is performed without increasing the output capacitance and without losing the characteristic of current resonance that switching current is not steeply generated to cause switching loss and switching noise. Can be used together.

[Brief description of drawings]

FIG. 1 A conventional half-bridge type serial resonance converter.

FIG. 2 is a full-bridge type series resonance converter of the present invention.

[Fig. 3] Main current waveform during frequency control

FIG. 4 Current waveform of main part during PWM control

[Explanation of symbols]

11, 12, 25, 26 Main switching element 15, 16 Feedback diode 17 Transformer 18, 29, 30 Resonance inductance 19, 20 Resonance capacitor 21, 22 Rectifying diode 23 Smoothing capacitor 24 Load resistance 13, 14 Auxiliary switching element I1 Transformer primary current (resonance current) I1 'Bypass resonance current I2 Feedback current T 1 cycle period (7) TON ON width period TOFF OFF width period TA PWM ON width period TB PWM OFF width period T1 Feedback current period T2 idle period

Claims (1)

[Claims] 1. A first bridge circuit in which two main switching elements are connected in series, and a parallel circuit of two main switching elements and a feedback diode in the direction of returning to a power source through respective resonance inductances. Second bridge circuit connected in series by a DC power supply, and one end of the primary winding of the transformer is connected to the connection point of the two main switching elements in series of the first bridge circuit. A series resonance converter in which one end of a resonance capacitor is connected to the other end of a winding, and the other end of the resonance capacitor is connected to a connection point of two resonance inductances forming the second bridge circuit, At the connection point between the primary winding of the transformer and the resonance capacitor, two series feedback diodes in the direction of returning to the power source and two series auxiliary switching elements in the forward direction of the power source are parallel. When connected and the operating frequency of the main switching element is lower than the audible frequency, the two auxiliary switching elements operate so as to perform conduction width control (PWM) within the conduction period of each main switching element. A series resonant converter characterized in that