JPH0828969B2 - Complex resonance type converter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a forward resonance type composite resonance type converter in which resonance circuits are provided on a primary side and a secondary side of a transformer.

A resonant converter is capable of reducing switching loss by performing switching during the period when the resonant voltage or the resonant current is zero, and a resonant circuit is provided on the primary side or secondary side of the transformer. is there.
It is desired to further improve the efficiency of such a resonant converter.

[Conventional technology]

The conventional resonant converter has, for example, the configuration shown in FIG. 3, in which 31 is a transformer, 32 is a switching transistor, 33 is a rectifying diode, 34 is a flywheel diode, and Reference numeral 35 is a smoothing circuit composed of an inductance 40 and a capacitor 41, 36 is a frequency control circuit that controls the frequency by detecting the difference between the output voltage of the smoothing circuit and the set voltage, and 37 is a resonance circuit on the primary side. A capacitor, 38 is a power supply, 39 is an output capacitance between the source and drain of the switching transistor 32, and 42 is a load.

A resonant circuit is constituted by the exciting inductance of the primary winding of the transformer 31, the capacity of the capacitor 37 and the output capacity 39 of the switching transistor 32, and the frequency control circuit 36
The switching signal of the switching transistor 32 is controlled by the output signal of, and current is supplied from the power supply 38 to the primary winding of the transformer 31 while the switching transistor 32 is on, and the induced voltage of the secondary winding of the transformer 31 is supplied. Is rectified by the rectifier diode 33, the rectified output is smoothed by the smoothing circuit 35 and supplied to the load 42, and the output voltage of the smoothing circuit 35 and the set voltage are compared in the frequency control circuit 36,
The switching frequency of the switching transistor 32 is controlled according to the difference to stabilize the output voltage.

FIG. 4 is a diagram for explaining the operation of the resonant converter shown in FIG. 3, in which (a) is a gate-source voltage applied from the frequency control circuit 36 to the gate of the switching transistor 32.
V _GS , (b) shows the drain-source voltage V _DS of the switching transistor 32, and E shows the voltage of the power supply 38.
(C) is the drain current of the switching transistor 32
I _D , (d) is the voltage V _D1 applied to the rectifying diode 33,
(E) shows the current I _D1 flowing through the rectifying diode 33.

When the gate-source voltage V _GS goes low, the switching transistor 32 turns off and the transformer 31
The resonance voltage of the half wave of the sine wave by the resonance circuit of the primary side is
It is applied to the switching transistor 32 as shown in (b). The rectifier diode 33 has a flywheel
A voltage as shown in (d) is applied through the diode 34.

When the gate-source voltage V _GS becomes high level,
The switching transistor 32 is turned on, and the current _ID shown in (c) flows. As a result, the current I _D1 shown in (e) flows through the rectifying diode 33.

In such a voltage resonance, the OFF width of the switching transistor 32 is made constant, and the ON width is varied to control the output power. Therefore, when the output voltage of the smoothing circuit 35 rises above the set voltage, The frequency control circuit 36 raises the switching frequency of the switching transistor 32. Conversely, when the output voltage of the smoothing circuit 35 drops below the set voltage, the frequency control circuit 36 lowers the switching frequency to reduce the output voltage. Will be stabilized.

[Problems to be Solved by the Invention]

In the resonance type converter of the above-mentioned conventional example, the voltage resonance of the primary side allows the switching transistor 32 to perform zero voltage switching to reduce the switching loss. The current I _D1 flowing in the rectifier diode 33 becomes a square wave as shown in FIG. 4 (e), which causes switching loss and noise in the rectifier diode 33.

It is an object of the present invention to reduce the switching loss on the secondary side, improve efficiency, and realize a low noise converter.

[Means for solving the problem]

The composite resonance type converter of the present invention is such that the primary side of the transformer is voltage resonance and the secondary side is current resonance.
It will be described with reference to the drawings.

The switching transistor 2 is connected to the transformer 1 and the primary winding, and the rectifying diode 3 is connected to the secondary winding of the transformer 1.
And a flywheel diode 4 are connected to each other, and a smoothing circuit 5 for smoothing the rectified output by the rectifying diode 3 is connected. The difference between the output voltage of the smoothing circuit 5 and the set voltage is detected to detect the switching transistor 2 A frequency control circuit 6 for controlling the switching frequency is connected, and a resonance circuit is formed by the exciting inductance of the primary winding of the transformer 1, the output capacitance of the switching transistor 2 and the capacitance of the capacitor 7, and the switching transistor 2 has a sine wave. In a resonant converter to which a half-wave resonant voltage of a wave is applied, the leakage inductance of the secondary winding of the transformer 1 and the flywheel. A resonant circuit is configured by the capacitor 8 connected in parallel with the diode 4, and a half-wave resonant current of a sine wave is passed through the rectifying diode 3.

[Action]

A resonant circuit is formed by the exciting inductance of the primary winding of the transformer, the capacitor 7 and the output capacitance 9 of the switching transistor 2, and the switching transistor 2
Of the secondary winding of the transformer 1 and the capacitor 8 to form a resonance circuit, and a half-wave resonance current of a sine wave is passed through the rectification diode 3 to reduce the zero voltage of the rectification diode 3. It enables current switching. In this case, the sine wave half-wave resonance current is set to flow at the maximum load, whereby the loss and noise due to the rectifying diode 3 at the maximum load can be reduced.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a main part of an embodiment of the present invention, in which a switching transistor 2 such as a field effect transistor is connected to the primary winding of a transformer 1 and the exciting inductance of the primary winding of the transformer 1 and switching・ Output capacitor 9 between drain and source of transistor 2 and capacitor 7
And constitute a resonance circuit, and the frequency control circuit 6 controls ON / OFF of the switching transistor 2 to turn on / off the current supplied from the power supply 13 to the primary winding of the transformer 1.

In addition, the rectifier diode 3 and the flywheel diode 4 are connected to the secondary winding of the transformer 1,
The rectified output of is smoothed by the smoothing circuit 5 including the inductance 10 and the capacitor 11, and a DC voltage is applied to the load 12. A capacitor 8 is connected in parallel with the flywheel diode 4, and the capacitor 8 and the leakage inductance of the secondary winding of the transformer 1 form a resonance circuit.

The frequency control circuit 6 detects the difference between the output voltage of the smoothing circuit 5 and the set voltage, and controls the switching frequency of the switching transistor 2 so that the output voltage becomes the set voltage, as in the conventional example. is there.

FIG. 2 is a diagram for explaining the operation of the embodiment of the present invention.
Is the gate-source voltage V _GS of the switching transistor 2, (b) is the drain-source voltage V _DS of the switching transistor 2, (c) is the drain current I _D of the switching transistor 2, and (d) is rectified The current I _D1 flowing through the diode 3 (e) represents the voltage V _D1 applied to the rectifying diode 3.

When the gate-source voltage V _GS of the switching transistor 2 is at a low level, the switching transistor 2 is turned off, the drain current I _D and the rectifying diode 3
The current I _D1 flowing through is zero as shown in (c) and (d). Further, due to the resonance circuit formed by the exciting inductance of the primary winding of the transformer 1 and the output capacitance 9 of the switching transistor 2 and the capacitance of the capacitor 7, the drain-source voltage V _DS of the switching transistor 2 is
As shown in (b), a half-wave resonant voltage of a sine wave is obtained. That is, the zero voltage switching of the switching transistor 2 can be performed.

Further, when the gate-source voltage V _GS is at high level, the switching transistor 2 is turned on and the drain current I _D flows as shown in (c). Switching
The drain-source voltage V _DS of the transistor 2 is
As shown in (b), it becomes almost zero. When the load 12 is set to a state where the maximum allowable load current is supplied, the current I _D1 flowing through the rectifier diode 3 is (d) due to the leakage circuit of the secondary winding of the transformer 1 and the resonance circuit formed by the capacitor 8. As shown in, a half-wave resonant current of a sine wave is obtained. _That is, the voltage V _D1 applied to the rectifying diode 3 when the current I _D1 is zero is a sinusoidal half-wave voltage as shown in (e).

Since the current I _D1 flowing through the rectifying diode 3 becomes a half-wave resonant current of a sine wave, the rectifying diode 3 can be switched when the current I _D1 is zero. Therefore, the present invention capable of reducing switching loss and noise is not limited to the above-mentioned embodiment, but various additions and modifications can be made.

〔The invention's effect〕

As described above, according to the present invention, a resonant circuit is configured by the exciting inductance of the primary winding of the transformer 1, the output capacitance 9 of the switching transistor 2 and the capacitance of the capacitor 7, and the secondary winding of the transformer 1 is formed. A resonant circuit is formed by the leakage inductance and the capacitance of the capacitor 8 connected in parallel with the flywheel diode 4,
In the composite resonance type converter, the primary side of the transformer 1 is operated by voltage resonance and the switching transistor 2 is operated by zero voltage switching, and the secondary side of the transformer 1 is operated by current resonance and the rectifying diode 3 is operated by zero current switching. It can be operated. Therefore, since switching loss can be reduced, efficiency can be improved, a low noise converter can be realized, a switching frequency of several MHz can be easily achieved, and miniaturization can be achieved by increasing the frequency. .

[Brief description of drawings]

FIG. 1 is a circuit diagram of an essential part of an embodiment of the present invention, FIG. 2 is an operation explanatory diagram of an embodiment of the present invention, FIG. 3 is a circuit diagram of an essential part of a conventional example,
FIG. 4 is an operation explanatory diagram of a conventional example. 1 is a transformer, 2 is a switching transistor, 3 is a rectifying diode, 4 is a flywheel diode, 5
Is a smoothing circuit, 6 is a frequency control circuit, 7 is a capacitor of the primary side resonance circuit, and 8 is a capacitor of the secondary side resonance circuit.

Claims (1)

[Claims] 1. A switching transistor (2) for turning on and off a current supplied from a DC power supply to a primary winding of a transformer (1), and a rectifying diode () connected to a secondary winding of the transformer (1). 3) and a flywheel diode (4), a smoothing circuit (5) for smoothing a rectified output by the rectifying diode (3), and detecting a difference between an output voltage of the smoothing circuit (5) and a set voltage. The switching
A frequency control circuit (6) for controlling the switching frequency of the transistor (2), an exciting inductance of the primary winding of the transformer (1) and an output capacitance of the switching transistor (2) form a resonance circuit. A converter (7) for applying a half-wave sinusoidal resonance voltage to the switching transistor (2), wherein the transformer (7) is connected in parallel with the flywheel diode (4). A resonance circuit is formed including the leakage inductance of the secondary winding of 1), and a capacitor (8) for flowing a half-wave sinusoidal resonance current is connected to the rectifying diode (3). Complex resonance type converter.