JPH1066335A - Converter circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the usage of a diode with little forward voltage drop and improve the efficiency. SOLUTION: A switching circuit 1 converts an inputted DC power into a pulse wave and outputs the pulse wave. An output rectifying circuit 2 converts the pulse wave outputted from the switching circuit 1 into a DC power and outputs the DC power. Snubber circuits 31 and 32 include capacitors 311 and 321, switching devices 312 and 322 and discharge circuits 313 and 323. The capacitors 311 and 321 are charged in one direction by reverse voltages applied to output rectifying diodes 21 and 22. The switching devices 312 and 322 convert charge stored in the capacitors 311 and 321 into pulse waves and discharge through the discharge circuits 313 and 323. A pulse generating circuit 4 generates a pulse wave which does not depend upon the switching operation of the switching circuit 1 and the generated pulse waves are supplied to the switching devices 312 and 322.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching type converter circuit.

[0002]

2. Description of the Related Art A switching type converter circuit comprises:
The DC input voltage is switched by a switching circuit, converted into a high-frequency pulse wave, and output. This high-frequency pulse wave is converted into a direct current by an output rectifier circuit and supplied to a load. In this type of converter circuit, the forward loss generated by the output rectifier diode included in the output rectifier circuit accounts for a large proportion of the total loss, and particularly, a large output current at a low voltage is supplied to the load. The case is remarkable. In order to reduce the forward loss of the output rectifier diode as much as possible, a Schottky barrier diode having a small forward voltage drop may be used. Withstand voltage becomes lower. Moreover, the reverse breakdown voltage decreases as the forward voltage drop decreases.

Therefore, when the loss is to be reduced by using a Schottky barrier diode having a low forward loss, how the reverse voltage applied to the Schottky barrier diode is reduced An important point is to keep the value lower than the withstand voltage.

As a means for achieving this, a circuit design technique for designing a circuit so that the voltage required to supply power to the load is equal to or less than the reverse withstand voltage of the output rectifier diode is required. In this case, a surge voltage is generated due to the leakage inductance of the transformer, the parallel capacitance of the diode itself, and the recovery characteristics, and a surge voltage is applied to the output rectifier diode. For this reason, it is difficult to solve the problem regarding the reverse withstand voltage of the output rectifier diode only by the circuit design technique.

Therefore, a snubber circuit has been proposed as a means for absorbing a surge voltage. The snubber circuit is
In this case, the voltage applied to the output rectifier diode is maintained at a value equal to or lower than the reverse withstand voltage of the rectifier diode. Further, by removing the surge voltage by the snubber circuit, the generation of noise can be reduced.

A typical snubber circuit has a structure in which a capacitor having a sufficiently large capacity to serve as a constant voltage source for a pulse wave voltage generated in an output rectifier diode is output via the diode. Connect in parallel with the rectifier diode. In this case, even if a surge voltage occurs, the reverse voltage applied between the terminals of the output rectifier diode is clamped to the voltage charged in the capacitor. However, in order to keep the charging voltage of the capacitor at a constant value,
It is necessary to discharge the same amount of energy as the energy charged by clamping the surge voltage per unit time. As a means for discharging energy, a method of connecting a resistor in parallel with a capacitor has been conventionally known.

However, when the voltage of the capacitor is Vc (capacity is
If it is large enough, it will be DC voltage)
If the resistance value of the resistor connected in parallel to the c^Two/ R [W] is consumed entirely by the resistor,
And the efficiency of the converter is reduced. Also clan
The voltage value to be switched depends on the generated surge voltage and the
To be determined by the correlation between the capacitance value and the resistance value of the resistor,
The value of each element is not found in the calculation, and the optimum value is
There is a hassle of having to decide. Only
If the withstand voltage of the output rectifier diode becomes lower, surge
Since the voltage must be kept lower, the snubber
The energy that must be absorbed by the circuit
As a result, the heat generated by the resistor is further increased, and the efficiency is reduced.

As means for solving the above-mentioned problems, a capacitor voltage is switched by a switching element to convert it into a pulse wave, and the converted energy is temporarily stored in an inductor and then released, so that different voltages can be transmitted. Such a snubber circuit has been proposed. According to this snubber circuit, resistance heating can be avoided, and absorbed energy can be supplied to a load or an input voltage source without losing energy, thereby preventing a reduction in efficiency. The snubber circuit having such a configuration is disclosed in Japanese Patent Application Laid-Open Nos.
-271275.

The snubber circuits disclosed in these known documents drive a switch element for switching a capacitor voltage to convert it into a pulse wave by a pulse wave synchronized with a drive pulse wave of a switching element of a power conversion circuit. Has taken. However, since the duty ratio of the drive pulse wave of the switching element of the power conversion circuit changes depending on conditions such as input and load, the voltage of the clamp capacitor included in the snubber circuit changes accordingly. Under these conditions, when the switch element of the snubber circuit is driven by a pulse wave synchronized with the drive pulse wave of the switching element of the power conversion circuit to convert the capacitor voltage into a pulse wave, the capacitor voltage value does not become constant . For this reason, the difference between the withstand voltage and the transmission voltage is small, and a low breakdown voltage diode with a narrow allowable range of the clamp voltage is used.
It becomes difficult to maintain the clamp voltage within this allowable voltage range in the range of fluctuation of the input voltage and the load current.

[0010]

The main objects of the present invention are as follows.
Enables the use of a diode with a small forward voltage drop,
An object of the present invention is to provide a converter circuit with improved efficiency.

Another object of the present invention is to provide an unnecessary rectifier superimposed on an original transmission voltage generated in an output rectifier diode.
An object of the present invention is to provide a converter circuit capable of absorbing a voltage.

Still another object of the present invention is to provide a converter circuit in which a loss is reduced by regenerating energy stored when a voltage is clamped.

Still another object of the present invention is to provide a converter circuit capable of holding a capacitor clamp voltage at a constant value which does not change due to a change in input voltage or load current.

Still another object of the present invention is to maintain a clamp voltage within this allowable voltage range even in a low breakdown voltage diode having a small difference between the withstand voltage and the transmission voltage and a narrow allowable range of the clamp voltage. To provide a converter circuit that can be used.

[0015]

To solve the above-mentioned problems, a converter circuit according to the present invention includes a switching circuit, an output rectifier circuit, a snubber circuit, and a pulse generation circuit. The switching circuit converts the input DC voltage into a high-frequency pulse wave and outputs the high-frequency pulse wave. The output rectifier circuit converts the high-frequency pulse wave output from the switching circuit into a direct current and outputs the direct current.

[0016] The snubber circuit includes a capacitor, a switching element, and a discharge circuit. The capacitor is charged in one direction by a reverse voltage applied to an output rectifier diode included in the output rectifier circuit. The switching element converts the charge stored in the capacitor into a pulse wave and discharges the pulse wave through the discharge circuit.

The pulse generation circuit generates a pulse wave independent of the switching operation of the switching circuit, and supplies the generated pulse wave to the switching element.

As described above, the converter circuit according to the present invention has the switching circuit and the output rectifier circuit, and the switching circuit converts the input DC voltage into a pulse wave and outputs the pulse wave, and Since the circuit converts the pulse wave output from the switching circuit into direct current and outputs the direct current, a converter circuit that obtains a different output DC voltage from one input DC voltage can be realized.

The converter circuit according to the present invention has a snubber circuit, and the snubber circuit includes a capacitor. The capacitor is charged in one direction by a reverse voltage applied to an output rectifier diode included in the output rectifier circuit. The capacitor has a sufficiently large capacity to serve as a constant voltage source for the pulse wave voltage generated in the output rectifier diode. Therefore, even if a surge voltage that is a reverse voltage occurs to the output rectifier diode, the reverse voltage applied to the output rectifier diode is clamped to the voltage charged in the capacitor. That is, an unnecessary surge voltage superimposed on the original transmission voltage generated in the output rectifier diode can be absorbed.

The snubber circuit includes a switching element and a discharge circuit. The switching element converts the charge stored in the capacitor into a pulse wave and discharges the pulse wave through the discharge circuit. Therefore, it is possible to employ a circuit that temporarily stores the converted energy in the inductor and then discharges the converted energy, and can transmit the converted energy to different voltages. Further, it is possible to avoid the resistance heat generation and supply the absorbed energy to the load and the input voltage source without losing the absorbed energy, thereby avoiding a decrease in efficiency.

In the converter circuit according to the present invention, the pulse generation circuit generates a pulse wave independent of the switching operation of the switching circuit, and supplies the generated pulse wave to the switching element. According to this configuration, unlike the related art in which the switch element that switches the capacitor voltage and converts it into a pulse wave is driven by the pulse wave synchronized with the drive pulse wave of the switching element of the power conversion circuit, the clamp voltage Can be maintained at a constant value that does not change due to changes in the input voltage or the load current.

Further, the difference between the withstand voltage and the transmission voltage is small,
Even in a low breakdown voltage diode having a narrow allowable range of the clamp voltage, the clamp voltage can be maintained within this allowable voltage range.

Therefore, according to the present invention, it is possible to use a diode having a small forward voltage drop, and to realize a converter circuit with improved efficiency.

This type of converter circuit usually includes a control circuit for controlling the switching operation of the switching circuit. The pulse generation circuit may be independent of the control circuit, or may have a configuration in which a signal for generating a pulse wave is obtained from an oscillator normally provided in the control circuit.

Other objects, features and advantages of the present invention will be described in more detail with reference to the accompanying drawings which are embodiments.

[0026]

FIG. 1 is an electric circuit diagram of a converter circuit according to the present invention. The converter circuit according to the present invention includes a switching circuit 1, an output rectifier circuit 2, snubber circuits 31, 32, and a pulse generation circuit 4. Reference numeral 5 denotes a conversion transformer, and reference numeral 6 denotes a control circuit. The switching circuit 1 converts the input DC voltage E1 into a high-frequency pulse wave and outputs it. In the embodiment, the switching circuit 1
Is adapted to transmit the converted pulse wave via the conversion transformer 5 and is connected to the primary winding 51 of the conversion transformer 5. The conversion transformer 5 has two secondary windings 52 and 53 that are electromagnetically coupled to the primary winding 51.

The output rectifier circuit 2 converts a pulse wave output from the switching circuit 1 into a direct current and outputs the direct current. The output rectifier circuit 2 shown in the embodiment has a diode 2 which is in a forward direction with respect to a voltage generated in the secondary winding 52 of the conversion transformer 5.
1, a diode 22 having a forward direction with respect to a voltage generated in a secondary winding 53, and a choke coil 23 which is in series with the power transmission line and an output smoothing capacitor 24 which is in parallel with the power transmission line. Prepare. Diode 21,
Preferably, 22 is constituted by a Schottky barrier diode. This is because, as described above, the Schottky barrier diode has a low forward voltage drop and can contribute to reduction of loss and improvement of efficiency.

Of the snubber circuits 31 and 32, the snubber circuit 31 includes a capacitor 311 and a switching element 312.
And a discharge circuit 313. Capacitor 311
Is an output rectifier diode 21 included in the output rectifier circuit 2.
Is charged in one direction by the reverse voltage applied to the. As a means for charging the capacitor 311 in one direction with a reverse voltage, in the embodiment, one end of the capacitor 311 is
Connected to the anode of the output rectifier diode 21,
The cathode of the output rectifier diode 21 and the capacitor 31
The diode 310 is connected to the other end of the first diode.
The switching element 312 converts the electric charge accumulated in the capacitor 311 into a pulse wave, and discharges the electric wave through a discharge circuit 313.

The discharge circuit 313 shown in the embodiment includes a transformer 316 having a first winding 314 and a second winding 315. The switching element 312 is a three-terminal element having one control electrode and two main electrodes, for example, a field effect transistor.
11 and the diode 310, and the other of the main electrodes is connected to one end of the first winding 314 of the transformer 316. The other end of the first winding 314 is connected to the capacitor 3
11 and a connection point of the output rectifier diode 21.

The second winding 315 is connected to a power transmission line via a diode 317 oriented to have the same polarity with respect to the DC output voltage Vo.

Similarly, the snubber circuit 32 includes a capacitor 3
21, a switching element 322, and a discharge circuit 323. The capacitor 321 is charged in one direction by a voltage applied to the output rectifier diode 22 included in the output rectifier circuit 2. As a means for charging the capacitor 321 in one direction, one end of the capacitor 321 is connected to the anode of the output rectifier diode 22 and between the cathode of the output rectifier diode 22 and the other end of the capacitor 321. Diode 320 is connected. The switching element 322 converts the charge stored in the capacitor 321 into a pulse wave, and
Discharge through 3.

The discharge circuit 323 has basically the same circuit configuration as the discharge circuit 311. Specifically, the discharge circuit 323 includes the first winding 324 and the second winding 32
5 including a transformer 326. The switching element 322 is a three-terminal element having one control electrode and two main electrodes.
1 and the diode 320, and the other of the main electrodes is connected to one end of the first winding 324 of the transformer 326. The other end of the first winding 324 is connected to the capacitor 32
1 and the connection point of the output rectifier diode 22.

The second winding 325 is connected to a power transmission line via a diode 327 oriented to have the same polarity with respect to the DC output voltage Vo.

The pulse generating circuit 4 includes the switching circuit 1
Generates a pulse wave that does not depend on the switching operation of the switching elements 312 and 322
Is supplied to the control electrode. The pulse generation circuit 4 includes a control circuit 6
, Or a signal for generating a pulse wave may be obtained from an oscillator included in the control circuit 6.

The control circuit 6 can be widely used as long as it has a configuration used in this type of converter circuit. In general, the main switch included in the switching circuit 1 is controlled based on a signal obtained by detecting a DC output voltage Vo by a built-in or external voltage detection circuit and comparing the detection signal with a reference voltage. And stabilizes the DC output voltage Vo. Examples of the control method include frequency control, pulse width control, and a combination thereof.

When the control circuit 6 having such a configuration is used, the pulse generation circuit 4 generates a sawtooth wave having a constant amplitude generated by a control IC (for example, MC34067) used in the control circuit 6. By utilizing this, a pulse wave having a constant time ratio can be generated, and the switching elements 312 and 322 of the snubber circuits 31 and 32 can be driven.

As described above, the converter circuit according to the present invention has the switching circuit 1 and the output rectifier circuit 2, and the switching circuit 1 receives the input DC voltage E1.
Is converted to a pulse wave and output, and the output rectifier circuit 2 converts the pulse wave output from the switching circuit 1 to DC and outputs it. Therefore, a converter circuit that obtains a different output DC voltage Vo from one input DC voltage E1 Can be realized.

Assuming that the switching circuit 1 is of a type (such as a push-pull circuit) that operates with a first on-period and a second on-period, during the first on-period of the switching circuit 1, Secondary winding 52 of transformer 5
Then, a voltage is generated in the forward direction with respect to the output rectifier diode 21, and the rectifier diode 21 performs rectification. The rectified output is subjected to a smoothing action by the choke coil 23 and the smoothing capacitor 24, and its DC output voltage Vo is supplied to a load (not shown). During the first ON period of the switching circuit 1, the secondary winding 53 of the transformer 5
Occurs in the opposite direction to the output rectifier diode 22.

During the second ON period of the switching circuit 1, a voltage is generated in the secondary winding 53 of the transformer 5 in a forward direction with respect to the output rectifier diode 22, and the rectification by the output rectifier diode 22 is performed. . The rectified output is subjected to a smoothing action by the choke coil 23 and the smoothing capacitor 24, and its DC output voltage Vo is output to the output terminals 71, 7
2 to the load.

The converter circuit according to the present invention has snubber circuits 31, 32, and the snubber circuits 31, 32
Capacitors 311, 321 are included. Capacitor 3
11 and 321 are charged in one direction by a reverse voltage applied to the output rectifier diodes 21 and 22 included in the output rectifier circuit 2. The capacitors 311 and 321 have a sufficiently large capacity to serve as a constant voltage source for the pulse wave voltage generated in the output rectifier diodes 21 and 22 in the reverse direction. Therefore, even if a surge voltage occurs in the reverse direction with respect to the output rectifier diodes 21 and 22, the reverse voltage applied to the output rectifier diodes 21 and 22 is not changed by the capacitor 31.
1, 321 is clamped to the charged voltage. That is, unnecessary surge voltages can be absorbed by the capacitors 311 and 321.

The snubber circuits 31 and 32 include switching elements 312 and 322 and discharge circuits 313 and 323. The switching elements 312 and 322 convert electric charges accumulated in the capacitors 311 and 321 into pulse waves. And discharges through the discharge circuits 313 and 323.
In an embodiment, the discharge circuit 313 includes a transformer 316, and the converted energy is discharged through a first winding 314 and a second winding 315 of the transformer 316.
Similarly, the discharge circuit 323 includes a transformer 326, and the converted energy is supplied to the first winding 32 of the transformer 326.
4 and the second winding 325. Therefore, the converted energy can be transmitted to different voltages in an insulated state. Further, it is possible to avoid heat generation due to the resistance and supply the absorbed energy to the load without losing the energy, thereby avoiding a decrease in efficiency.

In the case of the embodiment, the switching element 312,
When the 322 is turned on, the transformers 316, 3
The windings 314 and 324 are excited. At this time, the voltages generated in the windings 315 and 325 are diodes 317 and 3
27, the energy that has excited the windings 314, 324 is not released, and
5, 325. And the switching element 3
The diodes 317 and 327 are turned on by the flyback voltage generated when the switches 12 and 322 are turned off.
It is discharged to 72.

In the converter circuit according to the present invention, the pulse generation circuit 4 generates a pulse wave independent of the switching operation of the switching circuit 1 and supplies the generated pulse waves to the switching elements 312 and 322. According to this configuration, unlike the related art in which the switch element that switches the capacitor voltage and converts it into a pulse wave is driven by the pulse wave synchronized with the drive pulse wave of the switching element of the power conversion circuit, the clamp voltage V
c can be held at a constant value that does not change due to changes in the input voltage or the load current.

FIG. 2 is a circuit diagram illustrating the operation of snubber circuit 31 shown in FIG. The same applies to the snubber circuit 32. In the figure, the clamp voltage Vc of the capacitor 311 can be expressed by the relational expression of Vc = {(1-D) / D} (Vo + Vf), where the winding ratio of the transformer 316 is 1. Here, D: duty ratio, the on time of the switching element 312 is ton, and the cycle is T.
D = ton / T Vo: DC output voltage Vf: forward voltage drop of diode 317 However, when the switching element 312 is turned on, the voltage drop across the switching element 312 is zero.

As is apparent from the above equation, the relationship between the DC output voltage Vo and the clamp voltage Vc is determined by the duty ratio, and is independent of the cycle (frequency) of the pulse wave.

Also, when a low breakdown voltage Schottky barrier diode is used as the output rectifier diodes 21 and 22, the difference between the withstand voltage and the transmission voltage is reduced, and the allowable range of the clamp voltage is reduced. Also, the clamp voltage Vc can be maintained within this allowable voltage range. Therefore, according to the present invention, a low-loss Schottky barrier diode
And a converter circuit with improved efficiency can be realized.

FIG. 3 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. The feature of this embodiment is that the windings 315 and 325 of the transformers 316 and 326 constituting the discharge circuits 313 and 323 are connected to the DC power supply E1 via the diodes 317 and 327. Therefore, in the case of this embodiment, the energy absorbed by the capacitors 311 and 321 can be returned to the DC power supply E1 side without causing a loss, and a decrease in efficiency can be avoided.

FIG. 4 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. This embodiment shows a specific example of the circuit configuration of the switching circuit 1. The switching circuit 1 has a circuit configuration called a resonance type. Other components are almost the same as those of the embodiment shown in FIG. The switching circuit 1 has two switch elements 11 and 12 and a resonance circuit 13. The switch elements 11 and 12 are field-effect transistors, and main circuits each including a source and a drain are connected in series with each other and in series with the DC power supply E1. The resonance circuit 13 is connected between a connection point of the switch elements 11 and 12 and the primary winding 51 of the conversion transformer 5. The resonance circuit 13 forms a series resonance circuit having a resonance capacitor 131 and a resonance inductor 132 as main elements. The switch elements 11 and 12 are controlled by a pulse supplied from the control circuit 6.

FIG. 5 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention, and shows an effective circuit configuration when the clamp voltage Vc is higher than the DC output voltage Vo. In the drawings, the same components as those in FIGS. 1 to 4 are denoted by the same reference numerals. The switching circuit 1 is of the resonance type described with reference to FIG.

In the snubber circuit 3, an inductor 318 is used instead of the transformer used in FIG. The switching element 312 which is a three-terminal element has one of the main electrodes connected to one end of the capacitor 311. The discharge circuit 313 includes an inductor 318 and a commutation diode 319. The inductor 318 is
One end is connected to the other main electrode of the switching element 312, and the other end is connected to the output end 71 of the output rectifier circuit 2. The commutation diode 319 is connected to the switching element 31.
2 and the connection point between the inductor 318 and the connection point between the output terminal 72 and the other end of the capacitor 311.

According to this embodiment, the circuit configuration can be significantly simplified as compared with the embodiment of FIG.

During the second ON period when the switch element 12 of the switching circuit 1 is turned on (the switch element 11 is turned off), the voltage generated in the secondary winding 52 of the conversion transformer 5 is applied to the diode 21. In the opposite direction. At the timing when a voltage in the reverse direction is applied to the diode 21, the diode 310 conducts, and electric charge is accumulated in the capacitor 311 through the diode 310. Therefore, even if a surge voltage is generated in the reverse direction with respect to the output rectifier diode 21, the reverse voltage generated in the output rectifier diode 21 is clamped to the voltage charged in the capacitor 311.
That is, an unnecessary surge voltage can be absorbed by the capacitor 311.

During the first ON period when the switch element 11 of the switching circuit 1 is turned on (the switch element 12 is turned off), a voltage generated in the secondary winding 53 of the conversion transformer 5 is applied to the diode 22. In the opposite direction. At the timing when a reverse voltage is applied to the diode 22, the diode 320 conducts, and charges are accumulated in the capacitor 311 through the diode 320. Therefore, even if a surge voltage occurs in the reverse direction with respect to the output rectifier diode 22, the reverse voltage generated in the output rectifier diode 22 is clamped to the voltage charged in the capacitor 311.
That is, an unnecessary surge voltage can be absorbed by the capacitor 311.

When the switching element 312 conducts, the electric charge accumulated in the capacitor 311 is transferred to the switching element 312.
12, and energy is stored in the inductor 318. Next, when the switching element 312 is turned off, the energy stored in the inductor 318 is discharged to the output terminals 71 and 72 of the converter circuit through the diode 319 as a flyback voltage.

FIG. 6 is an electric circuit diagram showing the snubber circuit 3 shown in FIG. In the circuit of FIG. 6, the clamp voltage can be determined from the relationship of Vc = Vo / D + ｛(1-D) / D｝ Vf. The duty ratio D is as described above, and the voltage Vf is the diode 31.
9, and the voltage Vo is a DC output voltage. As shown in the above equation, also in the case of this embodiment, the relationship between the DC output voltage Vo and the clamp voltage Vc is determined by the duty ratio, and is independent of the cycle (frequency) of the pulse wave.

FIG. 7 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention. In the figure, the same components as those in FIG. 5 are denoted by the same reference numerals. In this embodiment, the conversion transformer 5 has only one secondary winding 52. The output rectifier circuit 2 includes an output rectifier diode 21,
22 are connected in series and connected between the terminals of the secondary winding 52, and two output choke coils 231 and 232 are connected in series and connected between the terminals of the secondary winding 52. The connection points 21 and 22 and the connection point of the output choke coils 231 and 232 are led to output terminals 71 and 72, and a smoothing capacitor 24 is connected between the output terminals 71 and 72.

The configuration and operating characteristics of the snubber circuit 3 are shown in FIG.
This is the same as the snubber circuit 3 in the embodiment shown in FIG. According to this embodiment, the circuit configuration can be further simplified as compared with the embodiment of FIG.

FIG. 8 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention. In the figure, the same components as those of the embodiment described above are denoted by the same reference numerals. This embodiment shows an effective circuit configuration when the clamp voltage Vc is lower than the DC output voltage Vo. The discharge circuit 313 has an output terminal 73 different from the output terminal 71 of the rectification output circuit 2. The other output terminal 74 is connected to the output terminal 72 of the rectification output circuit 2.

The discharge circuit 313 includes a series connection circuit of an inductor 318 and a diode 319. The series connection circuit of the inductor 318 and the diode 319 is connected between one end of the capacitor 311 and the output terminal 73. The switching element 312, which is a three-terminal element, has a main electrode connected between the connection point of the inductor 318 and the diode 319 and the connection point of the output terminal 74 and the other end of the capacitor 311.

Also in this embodiment, the voltage clamping action by the capacitor 311 is substantially the same as in the above-described embodiments. The difference is in the discharge action.

FIG. 9 is a circuit diagram illustrating the operation of snubber circuit 3 shown in FIG. At the timing when a reverse voltage is applied to the diode 21, electric charge is accumulated in the capacitor 311 through the diode 310. When the switching element 312 conducts, energy is stored in the inductor 318. Next, when the switching element 312 is turned off, the voltage Vc of the capacitor 311 and the inductor 31
8 is discharged to the output terminals 73 and 74 through the diode 319.

In this case, in the circuit of FIG. 9, the clamp voltage Vc can be determined from the relationship of Vc = (1−D) (Vo + Vf).
The duty ratio D is as described above, the voltage Vf is the forward voltage drop of the diode 319, and the voltage Vo is the DC output voltage. As is clear from the above equation, also in the case of this embodiment, the relationship between the DC output voltage Vo and the clamp voltage Vc is determined by the duty ratio and is independent of the cycle (frequency) of the pulse wave.

Next, the actual data will be described. FIG.
7 shows the voltage (Vr in FIG. 7) generated in the output rectifier diode 21 and the current flowing in the forward direction (I in FIG. 7) when the snubber circuit is not connected in the circuit of FIG.
It is a measured waveform of f). The operating conditions are the input voltage DC24
0V, output voltage 5V, load current 30A (output power 150
W).

As shown in FIG. 10, the voltage Vr is oscillating, and a surge voltage of 45.8 V is generated at the maximum.

FIG. 11 shows waveforms of the voltage Vr and the current If of the output rectifier diode 21 of the converter circuit according to the present invention shown in FIG. Operating conditions are input voltage DC240V
Output voltage 5V, load current 30A (output power 150W)
It is.

As shown in FIG. 11, when the voltage Vr is about 22V
It can be seen that it is clamped to In addition, since a part of the output current passes through the snubber circuit, the current If flowing through the output rectifier diode 21 is not connected to the snubber circuit.
It is smaller than the data of 0. At this time, 8.6 W of electric power was being supplied from the snubber circuit 3 to the load.

[0067]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to use a diode having a small forward voltage drop and provide a converter circuit with improved efficiency. (B) It is possible to provide a converter circuit capable of absorbing an unnecessary surge voltage superimposed on an original transmission voltage generated in an output rectifier diode. (C) It is possible to provide a converter circuit that eliminates an increase in loss by regenerating energy accumulated when the voltage is clamped. (D) It is possible to provide a converter circuit capable of holding a clamp voltage at a constant value that does not change due to a change in an input voltage or a load current. (E) It is possible to provide a converter circuit capable of maintaining a clamp voltage within this allowable voltage range even in a low breakdown voltage diode having a small difference between the withstand voltage and the transmission voltage and a narrow allowable range of the clamp voltage. .

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of a converter circuit according to the present invention.

FIG. 2 is an electric circuit diagram showing a snubber circuit of the converter circuit shown in FIG.

FIG. 3 is an electric circuit diagram showing another embodiment of the converter circuit according to the present invention.

FIG. 4 is an electric circuit diagram showing still another embodiment of the converter circuit according to the present invention.

FIG. 5 is an electric circuit diagram showing still another embodiment of the converter circuit according to the present invention.

6 is an electric circuit diagram showing a snubber circuit of the converter circuit shown in FIG.

FIG. 7 is an electric circuit diagram showing still another embodiment of the converter circuit according to the present invention.

FIG. 8 is an electric circuit diagram showing still another embodiment of the converter circuit according to the present invention.

9 is an electric circuit diagram showing a snubber circuit of the converter circuit shown in FIG.

FIG. 10 is a diagram showing actually measured waveforms of a voltage and a current generated in an output rectifier diode when a snubber circuit is not connected in the circuit of FIG. 7;

11 is a diagram showing actually measured waveforms of the voltage and current of the output rectifier diode of the converter circuit according to the present invention shown in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching circuit 2 Output rectifier circuit 21, 22 Output rectifier diode 3, 31, 32 Snubber circuit 310, 320 Diode 311, 321 Capacitor 312, 322 Switching element 313, 323 Discharge circuit 4 Pulse generation circuit

Claims (6)

[Claims] 1. A switching circuit, an output rectifier circuit,
A converter circuit including a snubber circuit and a pulse generation circuit, wherein the switching circuit converts an input DC voltage into a pulse wave and outputs the pulse wave, and the output rectifier circuit outputs the pulse output from the switching circuit. The pulse wave is converted into direct current and output, the snubber circuit includes a capacitor, a switching element, and a discharge circuit, and the capacitor is applied to an output rectifier diode included in the output rectifier circuit. The switching element converts the charge stored in the capacitor into a pulse wave and discharges the same through the discharge circuit, and the pulse generation circuit performs a switching operation of the switching circuit. A converter for generating an independent pulse wave and supplying the generated pulse wave to the switching element Road. 2. The converter circuit according to claim 1, further comprising a control circuit that controls a switching operation of the switching circuit, wherein the pulse generation circuit is independent of the control circuit. . 3. The converter circuit according to claim 1, further comprising a control circuit for controlling a switching operation of said switching circuit, wherein said pulse generation circuit generates a signal for generating a pulse wave. From the control circuit. 4. The converter circuit according to claim 1, wherein the discharge circuit includes a transformer having at least a first winding and a second winding, and the switching element is a single circuit. A three-terminal element having a control electrode and two main electrodes, wherein one of the main electrodes is connected to one end of the capacitor, and the other of the main electrodes is connected to one end of the first winding of the transformer. A converter circuit in which the other end of the first winding is connected to the other end of the capacitor, and the second winding is connected to an output end of the output rectifier circuit via a rectifier diode. . 5. The converter circuit according to claim 1, wherein said switching element is a three-terminal element having one control electrode and two main electrodes, wherein one of said main electrodes is said one. Connected to one end of a capacitor, the discharge circuit includes an inductor and a commutating diode, one end of the inductor is connected to the other of the main electrodes of the switching element, and the other end is the output rectifier. The commutation diode is connected to one of the output terminals of the circuit, and the commutation diode is connected between a connection point of the switching element and the inductor and a connection point of the other output terminal and the other end of the capacitor. Converter circuit. 6. The converter circuit according to claim 1, wherein the discharging circuit includes a series connection circuit of an inductor and a diode, wherein the series connection circuit of the inductor and the diode includes:
The switching element is connected to one end of the capacitor, the switching element is a three-terminal element having one control electrode and two main electrodes, and the main electrode is connected to a connection point of the inductor and the diode, and is connected to the other end of the capacitor. A converter circuit connected between the ends.