JP2001157444A - Dc-dc conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a synchronous rectifying operation even when a current smoothing reactor current is cut off and to reduce a loss generated in a DC-DC conversion device which is constituted by using a unipolar transistor as a main switching element. SOLUTION: The rise voltage of the parasitic diode of the unipolar transistor which constitutes the DC-DC conversion device (a chopper) is made larger than an ON-voltage at a time when a current is made to flow to the unipolar transistor. The operating frequency of the parasitic diode is made high which is nearly the same as the switching frequency of a unipolar semiconductor element. As a result, a bidirectional unipolar characteristic is obtained. A current smoothing reactor is formed as a DC reactor and a saturable reactor. The cutoff of the current smoothing reactor current is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit configuration of a DC-DC converter, and more particularly, to a DC-DC converter configured using unipolar transistors.

[0002]

2. Description of the Related Art A circuit shown in FIG. 10 is a DC-DC conversion circuit widely used as a step-down chopper. FIG.
1, 1 is a high-voltage side DC power supply, 2 is a high-voltage side voltage smoothing capacitor, 3 is a semiconductor switch, 4 is a diode,
Is a current smoothing reactor, 6 is a low voltage side voltage smoothing capacitor, and 7 is a low voltage side DC power supply. The semiconductor switch of FIG. 10 is shown in the case of an IGBT which is a bipolar element.

In FIG. 10, DC-DC power conversion is performed by causing the semiconductor switch 3 to perform a high-frequency switching operation. The power conversion control is performed by switching the semiconductor switch 3 at a constant frequency and controlling the ratio of Ton / T. Here, Ton is the ON time of the semiconductor switch 3, and T is the switching cycle. FIG. 11 shows the control of the chopper shown in FIG. 10 and the operation waveform of each part. 11, (a) shows the gate-on signal of the semiconductor switch 3, (b) shows the current of the current smoothing reactor 5,
(C) shows the current of the semiconductor switch 3, (d) shows the current of the diode 4, and (e) shows the waveform of the voltage of the smoothing capacitor 6.

A bidirectional power conversion type chopper, as shown in FIG. 12, which is capable of converting power from a low voltage side to a high voltage side with the chopper shown in FIG. 10 is also well known. FIG.
2, the same components as those in FIG. 10 are denoted by the same reference numerals. FIG. 12 is obtained by adding circuit elements 3a and 4a to the circuit shown in FIG. That is, the diode 3a is connected to the semiconductor switch 3, and the semiconductor switch 4a is connected to the diode 4 as shown in the figure. FIG.
In 2, the semiconductor switch 4a can be switched to perform power conversion from the low voltage side to the high voltage side in addition to the step-down chopper operation by the switching of the semiconductor switch 3.
That is, FIG. 12 shows a chopper system capable of performing both a step-down type and a step-up type power conversion.

The operation of the step-down chopper is the same as that of FIG.
This is performed by switching a at a constant cycle and controlling the ratio of Ton / T. Here, Ton is the ON time of the semiconductor switch 4a, and T is the switching cycle. FIG.
FIG. 11 shows waveforms of respective parts of the boost chopper operation corresponding to FIG.

In FIG. 13, (a1) indicates a semiconductor switch 4a.
(B) shows the current of the current smoothing reactor 5, (f) shows the current of the semiconductor switch 4a, (g) shows the current of the diode 3a, and (h) shows the voltage waveform of the smoothing capacitor 2.

[0007]

The major problems of the bidirectional chopper are (1) miniaturization of the device, (2) higher efficiency of the device, (3) lower cost, and (4) reduction of noise.

[0008] In the bidirectional chopper, in order to realize the above-mentioned problems, (5) how to increase the switching frequency and (6) how to reduce the loss of switching loss are major issues. The device shown in FIG.
In order to reduce the weight, as shown in FIG. 14, a circuit system in which an IGBT is replaced with a MOSFET as a switch element has been proposed. The feature of this circuit resides in that the parasitic diode originally built in the MOSFET is positively utilized as an anti-parallel diode of the switch element to reduce the number of elements.

In FIG. 14, the same components as those in FIG. 12 are denoted by the same reference numerals. 30 and 40 are MOSFET switches. 31 and 41 are MOSFET transistors, and 32 and 42 are MOSFET parasitic diodes. Since the operation in FIG. 14 is the same as the operation in FIG. 12, the description will be omitted. A major problem in the chopper shown in FIG. 14 is the parasitic diode. The MOSFET is a unipolar element, and has an ON voltage-current characteristic unique to the unipolar element as shown in FIG. On the other hand, since the parasitic diode is a bipolar element, the on-voltage-current characteristic has a rising voltage as shown in FIG.

As can be seen from the characteristics shown in FIGS. 15 and 16, the voltage at the time of forward and reverse current flow when the MOSFET is on is
The current characteristics are as shown in FIG. Here, the efficiency of the unipolar characteristic element and the bipolar characteristic element will be described. FIG.
8 shows an example of the output and efficiency of a DC-DC converter such as a chopper, and FIG. 18 shows a comparison in the case of a steady-state loss without considering a switching loss.

In FIG. 18, the bold line shows the characteristics of a unipolar device, and the thin line shows the characteristics of a bipolar device. From the figure, it is understood that the efficiency of the unipolar element is higher than that of the bipolar element in the low output region. However, at present, (1) a bidirectional unipolar element is not realized. (2) A possible operation switching frequency of a parasitic diode with a built-in MOSFET is about 1/10 of that of a MOSFET, and the circuit configuration shown in FIG. The switching frequency is almost the same as the switching frequency of the circuit system shown in Fig. 12. Since the switching frequency cannot be increased by using a MOSFET, (3) the realization of a compact, lightweight, and highly efficient chopper is greatly expected. It has become. An object of the present invention is to realize a chopper that solves the above problems.

[0012]

SUMMARY OF THE INVENTION The present invention provides (1) MOS
When the gate of the FET is on, current can flow in both forward and reverse directions. (2) When the bipolar element is operated at high speed and high frequency,
Focusing on the fact that the rising voltage increases, the basics are (3) the parasitic diode of the MOSFET can be operated at the same switching frequency as the MOSFET, and (4) the rising voltage of the parasitic diode is increased. By applying a MOSFET as a switching element to a unipolar ON characteristic of a forward / reverse bidirectional flow type, and further performing synchronous rectification by a unipolar transistor, a high efficiency and high frequency chopper of a bidirectional operation type is realized. Therefore, in the first invention, one end of the first semiconductor switch is connected to one end of the first DC power supply, and one end of the second semiconductor switch is connected to the other end of the first semiconductor switch. One end of the current smoothing reactor is connected to one end of the current smoothing reactor, and one end of the second DC power supply is connected to the other end of the current smoothing reactor. And a DC-DC converter in which the other end of the second semiconductor switch is connected to the other end of the second DC power supply, wherein each of the first and second semiconductor switches has a parasitic diode. And a rising voltage of the parasitic diode is equal to or higher than an on-voltage generated when a specified current flows through the unipolar transistor.

According to a second aspect of the present invention, in the DC-DC converter according to the first aspect of the present invention, the frequency of the parasitic diode is increased so that the parasitic diode can operate at an operation switching frequency of each of the unipolar transistors. In a third aspect, in the DC-DC converter according to the first and second aspects, the unipolar transistor is a MOSF.
ET.

According to a fourth aspect of the present invention, in the DC-DC converter according to any one of the first to third aspects of the present invention,
The current of each of the first and second semiconductor switches is caused to flow through the unipolar transistor. Also,
In a fifth aspect, in the DC-DC converter according to any one of the first to fourth aspects, the first DC power supply and the second DC power supply are operated by a switching operation of the first and second semiconductor switches. And bidirectional power conversion.

According to a sixth aspect of the present invention, in the DC-DC converter according to any one of the first to fifth aspects, the current smoothing reactor is formed by a series circuit of a DC reactor and a saturable reactor. The intermittent current of the current reactor is detected based on the voltage generated in the saturable reactor when the current of the smoothing reactor is inverted.

In a seventh aspect of the present invention, in the DC-DC converter according to any one of the first to sixth aspects, the current smoothing reactor is formed by a series circuit of a primary winding of a DC reactor and a saturable reactor. The current interruption of the current smoothing reactor is detected based on a voltage generated in a secondary winding of the saturable reactor at the time of reversing the current of the current smoothing reactor.

[0017]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, and corresponds to claims 1 to 5. 1, the same components as those in FIGS. 10, 12, and 14 are denoted by the same reference numerals. In FIG. 1, reference numerals 110 and 120 denote bidirectional unipolar semiconductor switches, in which 110a and 120a denote unipolar transistors,
110b and 120b are diodes parasitic on the unipolar transistor.

FIG. 2 is a voltage-current characteristic diagram of the unipolar semiconductor switch of FIG. 1 when flowing bidirectionally. In the figure, the forward current value If and the reverse current value Ir are current flowing widths, and the corresponding voltage waveforms across the switch element are shown. In FIG. 2, the rising voltage V of the parasitic diode
Since o is larger than the on-state voltage Vof when the unipolar transistor flows in the forward direction, the voltage when the current flows in the reverse direction does not become this rising voltage.

FIG. 3 shows an example of the structure of a unipolar transistor having the characteristics shown in FIG. 2 using a MOSFET as an example. In the figure, 100a is a transistor portion, and 100b is a parasitic diode portion. The transistor section is the same as the conventional one, but the high frequency of the parasitic diode section of 100b is the same as the conventional high frequency of the diode, that is, the lifetime control of the carrier is performed by diffusing heavy metals such as platinum or irradiating an electron beam. Just do it.

In the circuit configuration shown in FIG. 1, the characteristics of the semiconductor switch are changed to the bidirectional unipolar characteristics and the synchronous rectification operation is performed with respect to the circuit configuration of the bidirectional chopper shown in FIG. FIG. 4 is an explanatory diagram of the circuit operation of FIG. 1, and shows the case of the step-down operation corresponding to FIG. here,
FIG. 4 shows a case where the current smoothing reactor current is continuous. In FIG. 4, the same operation waveforms as those shown in FIG. 11 are indicated by the same symbols.

In FIG. 4, (a1) indicates the gate-on signal of the unipolar transistor 110a, (a2) indicates the gate-on signal of the unipolar transistor 120a, (c1) indicates the current of the unipolar transistor 110a, and (d1) indicates the current of the unipolar transistor 120a. Is shown. The difference between the control of FIG. 4 and FIG. 11 is that, in FIG. 11, the smoothing reactor current is circulated by the diode 4, whereas in the example of FIG.
The same operation as the diode 4 is performed. That is, by turning on the gate of the transistor 120a in the reverse flow region operation shown in FIG. 2, the current flows to the unipolar transistor 120a without flowing the current to the parasitic diode 120b. This control method is a method called a synchronous rectification method.

In the control operation shown in FIG. 4, if the current smoothing reactor current is interrupted while the unipolar transistor 120a is in the gate-on state, as shown in FIG.
The current flows backward from the DC power supply 7. Indicates the current direction when the current is continuous. For this reason, in the synchronous rectification method, when this current interruption occurs, it is necessary to turn off the gate of the unipolar transistor 120a.

FIG. 6 is a circuit diagram showing a second embodiment of the present invention in this case, and corresponds to claim 6. 6, the same components as those in FIG. 1 are denoted by the same reference numerals.
In FIG. 6, reference numeral 200 denotes a saturable reactor, 300 denotes a current interruption detecting circuit of the current smoothing reactor, and 400 denotes a control circuit including a gate drive circuit of the semiconductor switches 110 and 120.

FIG. 7 is a diagram for explaining the operation of FIG. 7, the same operations as those shown in FIG. 4 are indicated by the same symbols. FIG. 7 is an operation diagram when the current of the current smoothing reactor is continuous. (I) is a voltage waveform generated in the saturable reactor. Here, the current smoothing reactor current is continuous. Therefore, there is no current reversal of the saturable reactor, and no voltage is generated in the saturable reactor, so that the synchronous rectifying unipolar transistor 120a remains gate-on during the gate-off period of the semiconductor switch 110a.

FIG. 8 is an operation diagram when the current of the current smoothing reactor is intermittent. Since the current smoothing reactor current is about to reverse at time, a voltage is generated in the saturable reactor 200 in the direction shown. This voltage generation is detected by the current interruption detecting circuit 300, and the gate of the unipolar transistor 120a for synchronous rectification is turned off. Since the gates of both the unipolar transistors 110a and 120a are turned off, the backflow from the DC power supply 7 does not need to occur.

Since the semiconductor switch 110a is turned on again at the time, a current starts flowing through the saturable reactor, and a voltage having a polarity opposite to the time is generated in the saturable reactor. FIG. 9 is a circuit configuration diagram of a third embodiment of the present invention, and corresponds to claim 7. 9, the same components as those in FIG. 6 are denoted by the same reference numerals. 6 is that the saturable reactor 200 of FIG. 6 is replaced with a saturable reactor 200a having a secondary winding 200b.
The current interruption of the current smoothing reactor is detected by the current interruption detection circuit 300a by the voltage generated in the secondary winding. FIG.
9 differs from FIG. 9 only in that the saturable reactor voltage detection in FIG. 8 is detected from the secondary winding in FIG. 9, and all other operations are the same. The circuit operation is also the same as in FIG. The description of the operation is omitted.

[0027]

According to the present invention, the following effects are expected because the rising voltage of the parasitic diode of the unipolar transistor is high, the high frequency operation type is used, and the bidirectional unipolar operation type switching element is used as the chopper circuit configuration. it can. (1) Since the two-way operation of the step-down operation and the step-up operation can be realized integrally, the size, weight, and cost of the device can be reduced.

(2) Even if the current smoothing reactor current is intermittent, synchronous rectification can be performed, so that high efficiency can be realized. (3) Since the switching element operates in a unipolar operation in both the forward and reverse directions, the loss of the switching element can be reduced, and a highly efficient chopper can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating characteristics of the semiconductor switch of FIG. 1;

FIG. 3 is a diagram showing an example of a sectional structural view of the semiconductor switch of FIG. 1;

FIG. 4 is a diagram illustrating the operation of FIG.

FIG. 5 is a diagram illustrating another operation of FIG. 1;

FIG. 6 is a circuit diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram illustrating the operation of FIG.

FIG. 8 is another diagram for explaining the operation of FIG. 6;

FIG. 9 is a circuit diagram showing a third embodiment of the present invention.

FIG. 10 is a circuit configuration diagram of a conventional step-down chopper.

FIG. 11 is a diagram illustrating the operation of FIG.

FIG. 12 is a circuit configuration diagram of a conventional step-up / step-down chopper.

FIG. 13 is a diagram illustrating the operation of FIG.

FIG. 14 is another circuit configuration diagram of a conventional step-up / step-down chopper.

FIG. 15 is a diagram showing characteristics of a transistor of the semiconductor switch of FIG. 14;

FIG. 16 is a diagram showing characteristics of a parasitic diode of the semiconductor switch of FIG. 14;

17 is a diagram illustrating forward / backward characteristics of the semiconductor switch of FIG. 14;

FIG. 18 is a diagram illustrating loss characteristics of a semiconductor.

[Explanation of symbols]

1, 7: DC power supply, 2, 6: voltage smoothing capacitor, 3,
4a: bipolar semiconductor switch, 3a, 4: diode, 4: current smoothing reactor, 30, 40, 110,
120: Unipolar semiconductor switch, 31, 41, 1
00a, 110a, 120a: unipolar transistor, 32, 42, 100b, 110b, 120b: parasitic diode, 200, 200a: saturable reactor, 2
00b: saturable reactor secondary winding, 300, 300a
... Current smoothing reactor current interrupt detection circuit, 400 ... Control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G065 AA08 DA07 EA01 HA02 HA03 LA02 MA03 MA10 NA03 NA04 NA05 NA06 5H006 CA02 CA07 CB03 CB07 CC08 DA04 DB01 5H730 AA15 BB13 BB14 BB57 DD04 EE13 FG01

Claims (7)

[Claims] An end of a first semiconductor switch is connected to one end of a first DC power supply, and the other end of the first semiconductor switch is connected to one end of the first semiconductor switch.
One end of the second semiconductor switch is connected to one end of the current smoothing reactor, one end of the second DC power supply is connected to the other end of the current smoothing reactor, and the other end of the first DC power supply is connected to the second end. In a DC-DC converter in which the other end of a semiconductor switch is connected to the other end of a second DC power supply, the first and second semiconductor switches are each a unipolar transistor having a parasitic diode. A DC-DC converter, wherein a rising voltage of a parasitic diode is equal to or higher than an ON voltage generated when a specified current flows through the unipolar transistor. 2. The DC-DC converter according to claim 1, wherein the frequency of the parasitic diode is increased so that the parasitic diode can operate at an operation switching frequency of each of the unipolar transistors. 3. The device according to claim 1, wherein said unipolar transistor is a MOSF.
3. The DC-DC converter according to claim 1, wherein the DC-DC converter is ET. 4. The DC-DC converter according to claim 1, wherein the current of each of the first and second semiconductor switches is passed through the unipolar transistor. 5. A bidirectional power conversion between the first DC power supply and the second DC power supply by a switching operation of the first and second semiconductor switches. The DC-DC converter according to any one of claims 1 to 4. 6. The current smoothing reactor is formed by a series circuit of a DC reactor and a saturable reactor, and detects a current discontinuity of the current reactor based on a voltage generated in the saturable reactor when the current of the current smoothing reactor is inverted. 6. The method according to claim 1, wherein
The direct-current to direct-current converter according to any one of the above. 7. The current smoothing reactor is formed by a series circuit of a DC reactor and a primary winding of a saturable reactor, and is formed by a voltage generated in a secondary winding of the saturable reactor when the current of the current smoothing reactor is inverted. 7. The DC-DC converter according to claim 1, wherein an intermittent current of the current smoothing reactor is detected.
DC converter.