JP2004364456A - Switching converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching converter with a snubber circuit for maintaining the output voltage of a rectification circuit so as to approximate the voltage of a ratio of turns of windings of a transformer. <P>SOLUTION: This switching converter includes the rectification circuit 11 and the snubber circuit 1 between an output choke Lo and a smoothing circuit 21 with the smoothing capacitor Co. The snubber circuit 1 is connected with a series circuit consisting of a first rectification element Lo and a clamping capacitor Cs, which is connected in parallel to one end of the smoothing capacitor Co. A series circuit consisting of a switch element Qs and a first resistance element Rs1 is connected with the first rectification element Lo, and one end of a second rectification element Ds2 is connected with a connection portion between the first rectification element Rs1 and the capacitor Cs. A second resistance element Rs2 is connected with the other end of the second rectification element, and the second resistance element Rs2 is connected with the other end of the smoothing capacitor Co. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a switching converter in which a primary and a secondary are insulated by a transformer and a secondary side is provided with a rectifier circuit and a smoothing circuit having an output choke and a smoothing capacitor.
[0002]
[Prior art]
FIG. 6 shows a conventional switching converter. This switching converter is provided with a bridge-type rectifier circuit 11 on the secondary side and a smoothing circuit 21 having an output choke Lo and a smoothing capacitor Co on the secondary side, with a primary-secondary insulated by a transformer T. The snubber circuit 6 is provided between the rectifier circuit 11 and the smoothing circuit 21. The snubber circuit 6 is configured by connecting a switching element Qs and a capacitor Cs in series with a smoothing capacitor Co. The switching element Qs is formed of a MOSFET, and the diode Ds connected between the drain and the source of the switching element Qs is a body diode of the switching element Qs.
[0003]
Further, in this conventional example, the snubber circuit 6 is provided on the secondary side, but the snubber circuit 6 shown in the conventional example can be provided on the primary side. In this case, for example, the main switch may be configured by a MOSFET, and the switch element Qs and the capacitor Cs may be connected in series between the drain and the source of the main switch (see Non-Patent Document 1).
[0004]
[Non-patent document 1]
J. A. Sabat, V .; Vlatkovic, R .; B. Ridley, and F.R. C. Lee "High-voltage, high-power, ZVS, full-bridge PWM converter implementing an active snubber" APEC '91 Conference Proceedings 10-15M. 1991 p. 158-163
[0005]
[Problems to be solved by the invention]
In the switching converter configured as described above, power is transmitted via the transformer T from a period (hereinafter, referred to as a “commutation period”) in which a choke current flows through the rectifier elements D1 to D4 configuring the rectifier circuit 11. (Hereinafter referred to as “power transmission period”), the diode Ds constituting the snubber circuit 6 conducts, and the voltage A on the output side of the rectifier circuit 11 is settled at the voltage of the turns ratio. By turning on Qs, the voltage of the capacitor Cs is maintained at the voltage of the turns ratio.
[0006]
[Problems to be solved by the invention]
However, in this switching converter, the resonance is caused by the resonance of the inductance Lm of the transformer T, the leakage inductance Lt, the parallel capacitors C1 to C4 of the rectifier elements D1 to D4 forming the rectifier circuit 11, and the capacitor Cs forming the snubber circuit 6. As shown in FIG. 7, the voltage A on the output side of the rectifier circuit 11 becomes higher than the voltage of the turns ratio of the transformer T, and there arises a problem that a diode with a high withstand voltage is required.
[0007]
Further, when the load is light or when the output voltage is lowered, the period during which the switch element Qs of the snubber circuit 6 is turned on is eliminated, that is, when only the rectifying element Ds and the capacitor Cs are used, as shown in FIG. In addition, the voltage A on the output side of the rectifier circuit 11 cannot be maintained at the voltage of the turns ratio, and a problem occurs that an oscillating voltage is generated.
[0008]
The present invention has been made in view of the above problems, and provides a switching converter including a snubber circuit that maintains an output voltage of a rectifier circuit at a value close to a voltage of a turns ratio of a transformer.
[0009]
[Means for Solving the Problems]
The switching converter according to the present invention can maintain the output voltage of the rectifier circuit at a value close to the voltage of the turns ratio of the transformer by the action of the first rectifier element and the first resistor element forming the snubber circuit.
[0010]
Further, even when the period during which the switch element of the snubber circuit is turned on at the time of light load or when the output voltage is lowered is eliminated, the output voltage of the rectifier circuit is reduced by the action of the second rectifier element and the second resistor element. Is maintained at a value close to the voltage of the turns ratio, and in any state, the output voltage of the rectifier circuit can be maintained at a value close to the voltage of the turns ratio of the transformer.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the switching converter of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an embodiment of the switching converter according to the present invention. This switching converter has a primary-secondary insulation with a transformer T, has rectifiers D1 to D4 on the secondary side, and connects capacitors C1 to C4 in parallel with these rectifiers D1 to D4, respectively. A rectifier circuit 11 of a type and a smoothing circuit 21 having an output choke Lo and a smoothing capacitor Co are provided. The snubber circuit 1 is provided between the rectifier circuit 11 and the smoothing circuit 21.
[0012]
Although the illustration of the primary side insulated by the transformer T is omitted, a high-frequency inverter may be provided on the primary side. In the present invention, it is optimal to use a bridge type high frequency inverter or a push-pull type high frequency inverter as the high frequency inverter.
[0013]
The snubber circuit 1 is configured as follows. A series circuit of a first rectifying element Ds and a capacitor Cs is connected in parallel with the smoothing capacitor Co. A series circuit of a switch element Qs and a first resistance element Rs1 is connected in parallel with the first rectifier element Ds. The anode of the second rectifier Ds2 is connected to the connection between the first rectifier Ds and the capacitor Cs, and the second resistor Rs2 is connected to the cathode of the second rectifier Ds2. This second resistance element Rs2 is connected to one end of the smoothing capacitor Co.
[0014]
The switching converter according to the present embodiment is configured as described above, and operates as follows. First, in the steady state, when switching from the commutation period to the power transmission period, the voltage A on the output side of the rectifier circuit 11 is clamped by the capacitor Cs via the first rectifier element Ds1. When Qs is turned on, the capacitor Cs and the inductance Lm of the transformer T, the leakage inductance Lt and the parallel capacitors C1 to C4 of the rectifiers D1 to D4 forming the rectifier circuit 11, and the capacitor Cs forming the snubber circuit 1 , The output voltage of the rectifier circuit 11 becomes higher than the voltage of the turns ratio of the transformer T. In order to prevent this, in the present invention, as shown in FIG. 3, when the switch element Qs is turned on, the electric charge charged in the capacitor Cs is discharged through the first resistance element Rs1, and the output of the rectifier circuit 11 The voltage A does not cause resonance as shown in FIG. 2 and is maintained at a voltage corresponding to the turns ratio of the transformer T.
[0015]
Subsequently, as shown in FIG. 4, when the period during which the switch element Qs is turned on has disappeared, that is, when the load is light or the output voltage is reduced, the rectifier circuit 11 only requires the rectifier element Ds and the capacitor Cs. The voltage A on the output side cannot be maintained at the voltage of the turns ratio, and an oscillation voltage is generated. Therefore, in the present invention, the electric charge charged in the capacitor Cs is caused to flow through the second rectifying element Ds2 and the second resistive element RS2 to prevent surge, and as shown in FIG. The voltage A on the output side is maintained at the voltage of the turns ratio.
[0016]
Next, another embodiment according to the switching converter of the present invention will be described. This embodiment is shown in FIG. This switching converter is provided with rectifiers D1 and D2 on the secondary side in which the primary and secondary parts are insulated by a transformer T, and is connected to capacitors C1 and C2 in parallel with the rectifiers D1 and D2, respectively. A pull-type rectifier circuit 12 and a smoothing circuit 21 having an output choke Lo and a smoothing capacitor Co are provided. The snubber circuit 1 similar to the embodiment shown in FIG. 1 is provided between the rectifier circuit 12 and the smoothing circuit 21.
[0017]
Although the illustration of the primary side insulated by the transformer T is also omitted in this embodiment, a high-frequency inverter is provided on the primary side in this embodiment, and a bridge-type high-frequency inverter or a push-pull It is best to use a type of high frequency inverter. The operation is also substantially the same as that of the embodiment shown in FIG.
[0018]
【The invention's effect】
According to the switching converter of the present invention, the output voltage of the rectifier circuit does not cause a resonance state due to the action of the first rectifier and the capacitor, the first resistor and the switch constituting the snubber circuit. There is an effect that it can be maintained at a value close to the voltage.
[0019]
Further, even when the period during which the switch element of the snubber circuit is turned on at the time of light load or when the output voltage is lowered is eliminated, the output voltage of the rectifier circuit is reduced by the action of the second rectifier element and the second resistor element. Is maintained at a value close to the voltage of the turns ratio, and in any state, the output voltage of the rectifier circuit can be maintained at a value close to the voltage of the turns ratio of the transformer.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing one embodiment of a switching converter according to the present invention.
FIG. 2 is a waveform chart showing an output voltage of a rectifier circuit in the present embodiment.
FIG. 3 is a waveform diagram of a switching gate signal at full load.
FIG. 4 is a waveform diagram of a switching gate signal under a light load.
FIG. 5 is a circuit diagram showing an embodiment of a switching converter different from that of FIG. 1;
FIG. 6 is a circuit diagram showing a conventional example of a switching converter.
FIG. 7 is a waveform diagram showing an output voltage of a rectifier circuit in a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Snubber circuit 6 Snubber circuit 11 Bridge type rectifier circuit 12 Push-pull type rectifier circuit 21 Smoothing circuit T Transformers Lm, Lm1, Lm2 Inductances Lt, Lt1, Lt2 of transformer T Leakage inductances D1 to D4 Rectifiers C1 to C4 Parallel capacitors Or, capacitance Lo in the rectifier element Output choke Co Smoothing capacitor Ds Diode Cs Capacitor Ds1, Ds2 Rectifier element Qs Switch element Rs1, Rs2 Resistance element

Claims (6)

A switching converter in which a primary and a secondary are insulated by a transformer, a rectifier circuit on a secondary side, and a smoothing circuit having an output choke and a smoothing capacitor are provided. A snubber circuit is provided therebetween, and this snubber circuit connects a series circuit of a first rectifier and a capacitor in parallel with the smoothing capacitor, and a switch element and a first resistor in parallel with the first rectifier. A series circuit of the first rectifier and a capacitor, a second rectifier is connected to the connection portion of the capacitor, a second resistor is connected to the other of the second rectifier, A switching element connected to one end of the smoothing capacitor, and the switching element is turned on during a period in which power is transmitted through the transformer. Over data. The switching converter according to claim 1, wherein the rectifier circuit is a bridge-type rectifier circuit. The switching converter according to claim 1, wherein the rectifier circuit is a push-pull rectifier circuit. 4. The switching converter according to claim 1, further comprising a high-frequency inverter on a primary side of the transformer. The switching converter according to claim 4, wherein a bridge-type high-frequency inverter is provided on a primary side of the transformer. 5. The switching converter according to claim 4, further comprising a push-pull type high frequency inverter on a primary side of the transformer.

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