JPH11356045A - Direct current-direct current conversion device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce loss and noise produced due to discharge of a snubber capacitor at the time of turn-on, by regenerating the energy of the snubber capacitor to a direct- current power supply, and, at the point when it becomes zero, turning on MOSFET. SOLUTION: The positive pole side of a direct-current power supply 1, the positive pole side of the first primary winding 21 of a transformer, and the negative pole side of the second primary winding 23 of the transformer are connected. The negative pole side of the first primary winding 21 of the transformer and one end of a first semiconductor switch element 31 are connected, and the positive pole side of the second primary winding 23 of the transistor and one end of a second semiconductor switch element 41 are connected. The negative pole side of the direct-current power supply 1, the other end of the first semiconductor switch element 31, the second semiconductor switch element 31 and a snubber capacitor 51 are parallel-connected, and the secondary winding 22 of the transformer is connected to the input of a rectifier circuit 3. When MOSFET 41 is turned on, the transformer 2 is excited in the negative direction. When the MOSFET is turned off, the exciting current of the transformer 2 is regenerated from the snubber capacitor 51 to the first primary winding 21 to the direct-current power supply 1, and when the energy becomes zero, MOSFET 31 is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a DC-DC converter for extracting insulated DC power from a DC power supply.

[0002]

2. Description of the Related Art FIG. 13 shows a single-pole forward type DC-DC converter as a conventional example of a DC-DC converter. As shown in FIG. 1, the single-pole forward DC-DC converter includes a DC power supply 1, a transformer 2, a rectifier circuit 3, a smoothing filter 4, a MOSFET 31 as a semiconductor switch, and a diode 71. The rectifier circuit 3 includes diodes 61 and 62, and the smoothing filter 4 includes a reactor 63 and a capacitor 64. The operation of the single-pole forward DC-DC converter will be described below with reference to the operation waveforms shown in FIG.

When the MOSFET 31 is turned on during the period, the transformer 2 is excited in the positive direction via the first primary winding 21, and at the same time, is connected to the load connected to the output terminal via the rectifier circuit 3 and the smoothing filter 4. DC power is supplied. MOSFET 31 turns off during the period
The voltage across the terminal 31 rises, and the diode 7
1 conducts, the diode 71, the second primary winding 23
, The excitation energy of the transformer 2 is regenerated to the DC power supply 1. When the excitation energy of the transformer 2 becomes 0, the reset of the transformer 2 is completed, and the period shifts.

FIG. 15 shows a dual DC-DC converter as a conventional DC-DC converter. As shown in the figure, a two-pole forward type DC-DC converter includes a DC power supply 1, a transformer 2, a rectifier circuit 3, a smoothing filter 4, MOSFETs 31 and 32 as semiconductor switches,
It is composed of diodes 71 and 72. Rectifier circuit 3
Is composed of diodes 61 and 62, and the smoothing filter 4 is composed of a reactor 63 and a capacitor 64. This 2
The operation of the stone-forward DC-DC converter will be described below with reference to the operation waveforms shown in FIG.

When the MOSFETs 31 and 32 are turned on during the period, the transformer 2 is excited in the positive direction via the primary winding 21, and at the same time, the DC voltage is applied to the load connected to the output terminal via the rectifier circuit 3 and the smoothing filter 4. Power is supplied. When the MOSFETs 31 and 32 are turned off during the period, the MOS
When the voltage across the FET 31 increases and the diodes 71 and 72 conduct during the period, the diodes 71 and 72
The excitation energy of the transformer 2 is regenerated to the DC power supply 1 via the primary winding 21. When the excitation energy of the transformer 2 becomes 0, the reset of the transformer 2 is completed, and the period shifts.

In the circuits shown in FIGS. 13 and 15, the snubber capacitors 51 and 32 are connected in parallel to the MOSFETs 31 and 32, respectively, in order to suppress the voltage rise rate when the MOSFETs 31 and 32 are turned off during the period and to reduce switching loss and noise. 52 are connected.

[0007]

In the case of the above-mentioned conventional example, the energy absorbed by the snubber capacitor is equal to that of the MOSFET.
Is discharged at the time of turn-on, and becomes a loss. Here, the capacitance of the snubber capacitors 51 and 52 is C, the voltage between both ends of the DC power supply 1 is Ed, and the first primary winding 21 and the second 1
The turns ratio of the secondary winding 23 is 1: 1 and the switching frequency is f
Then, the loss P generated by the snubber capacitor
In the circuit of FIG. 13, P = (１ ／) × C × (2Ed) ² × f, and in the circuit of FIG. 15, P = C × (Ed) ² × f.

For this reason, when the switching frequency increases, the loss generated by the snubber capacitor increases,
The conversion efficiency of the device decreases. Further, since the energy of the snubber capacitor is rapidly discharged when the MOSFET is turned on, an increase in noise is also a problem. An object of the present invention is to reduce switching loss and noise of a DC-DC converter.

[0009]

To achieve the above object, a first invention is directed to a positive electrode of a DC power supply, a positive electrode of a first primary winding of a transformer, and a negative electrode of a second primary winding of a transformer. The first side of the first primary winding of the transformer is connected to one end of the first semiconductor switch element, and the second side of the first primary winding of the transformer is connected to the second semiconductor switch element. One end is connected, the negative side of the DC power supply is connected to the other end of the first semiconductor switch element and the other end of the second semiconductor switch element, and the first semiconductor switch element and the snubber capacitor are connected in parallel. The secondary winding of the transformer is connected to the input of a rectifier circuit, and the output of the rectifier circuit is connected to the input of a smoothing filter to provide a DC-DC converter. A second invention is a DC-DC converter in which a snubber capacitor and a third semiconductor switch element are connected in series instead of the snubber capacitor of the first invention.

According to a third aspect of the present invention, one end of the first semiconductor switch element is connected to one end of the third semiconductor switch element and the negative electrode of the primary winding of the transformer, and one end of the second semiconductor switch element is connected to the fourth end of the fourth semiconductor switch element. One end of the semiconductor switch element is connected to the positive side of the primary winding of the transformer, and the other end of the first semiconductor switch element is connected to the other end of the fourth semiconductor switch element and the negative side of the DC power supply. Connecting the other end of the second semiconductor switch element, the other end of the third semiconductor switch element, and the positive electrode side of the DC power supply, and connecting the first semiconductor switch element and the first snubber capacitor in parallel; Connecting the second semiconductor switch element and a second snubber capacitor in parallel,
A DC-DC converter in which the transformer secondary winding is connected to the input of a rectifier circuit and the output of the rectifier circuit is connected to the input of a smoothing filter.

According to a fourth invention, a first snubber capacitor and a fifth semiconductor switch element are connected in series instead of the first snubber capacitor of the third invention, and the second snubber capacitor is replaced with the second snubber capacitor. A DC-DC converter in which a second snubber capacitor and a sixth semiconductor switch element are connected in series.

In a fifth aspect based on the first aspect, a capacitor is inserted between the positive electrode of the first primary winding of the transformer and the second semiconductor switch, and the secondary winding of the transformer is provided. Is connected to the input of the rectifier circuit via the separately installed inductance or the leakage inductance of the transformer, and the output of the rectifier circuit is connected to the input of the smoothing filter.

In a sixth aspect based on the third aspect, a first capacitor is connected between the positive side of the primary winding of the transformer and the fourth semiconductor switch, and a negative side of the primary winding of the transformer is provided. A second capacitor is inserted between the third semiconductor switch and the third semiconductor switch, respectively, and the transformer secondary winding is connected to an input of a rectifier circuit through a separately installed inductance or a transformer leakage inductance; A DC-DC converter in which the output of the rectifier circuit is connected to the input of the smoothing filter.

[0014]

FIG. 1 is a circuit diagram showing an embodiment of the first invention. This is a single-pole forward type DC-DC converter shown in FIG.
The configuration is such that a MOSFET 41 as a semiconductor switch is connected. The operation of the circuit of FIG. 1 will be described below with reference to the operation waveforms shown in FIG.

The operation during the period is the same as that shown in FIG. When the MOSFET 41 is turned on during the period, the transformer 2 is excited in the negative direction via the second primary winding 23. When the MOSFET 41 is turned off during the period, the exciting current of the transformer 2 recirculates through the path of the snubber capacitor 51 → the first primary winding 21 → the DC power supply 1, and the energy of the snubber capacitor 51 is regenerated to the DC power supply 1. When the energy of the snubber capacitor 51 becomes 0, the MOSFET 31 is turned on, and the period shifts.

FIG. 3 is a circuit diagram showing an embodiment of the second invention. This is a configuration in which the snubber capacitor 51 and the MOSFET 43 as a semiconductor switch are connected in series instead of the snubber capacitor 51 in the circuit diagram of FIG. The operation of the circuit of FIG. 3 will be described below with reference to the operation waveforms shown in FIG.

The operation during the period 1 is the same as that shown in FIG. When the MOSFET 41 is turned on during the period, the transformer 2 is excited in the negative direction via the second primary winding 23. At this time, recharging of the snubber capacitor 51 is prevented by turning off the MOSFET 43. When the MOSFET 41 is turned off during the period, the transformer 2
Excitation current of MOSFET 43 → snubber capacitor 51
→ The first primary winding 21 → returns on the path of the DC power supply 1, and the energy of the snubber capacitor 51 is regenerated to the DC power supply 1. When the energy of the snubber capacitor 51 becomes 0, the MOSFET 31 is turned on, and the period shifts.

FIG. 5 is a circuit diagram showing an embodiment of the third invention. This is because, instead of the diodes 71 and 72, in the dual forward DC-DC converter shown in FIG.
The configuration is such that MOSFETs 41 and 42 as semiconductor switches are connected. The operation of the circuit of FIG. 5 will be described below with reference to the operation waveforms shown in FIG.

The operation during the period 1 is the same as that shown in FIG. When the MOSFETs 41 and 42 are turned on during the period, the transformer 2 is excited in the negative direction via the primary winding 21. When the MOSFETs 41 and 42 are turned off during the period, the exciting current of the transformer 2
1 → primary winding 21 → snubber capacitor 52 → DC power supply 1
And the energy of the snubber capacitors 51 and 52 is regenerated to the DC power supply 1. Snubber capacitor 51
When the energy of the MOSFET becomes 0, the MOSFETs 31, 3
2 is turned on, and the period shifts.

FIG. 7 is a circuit diagram showing an embodiment of the fourth invention. This is because in the circuit diagram of FIG. 5, instead of snubber capacitor 51, snubber capacitor 51 and MOSFET 43 as a semiconductor switch are connected in series, and instead of snubber capacitor 52, snubber capacitor 52 and MOSFET 44 as a semiconductor switch are connected in series. The configuration is as follows. The operation of the circuit of FIG. 7 will be described below with reference to operation waveforms shown in FIG.

The operation during the period 1 is the same as that shown in FIG. When the MOSFETs 41 and 42 are turned on during the period, the transformer 2 is excited in the negative direction via the primary winding 21. At this time, the recharge of the sun capacitors 51 and 52 is prevented by turning off the MOSFETs 43 and 44. When the MOSFETs 41 and 42 are turned off during the period, the exciting current of the transformer 2 is changed from the MOSFET 43 → the snubber capacitor 51 → the primary winding 21 → the MOSFET 44 →
When the energy flows back from the snubber capacitor 51 to the DC power supply 1 and the energy of the snubber capacitors 51 and 52 becomes 0, the MOSFET 31 is turned on and the period shifts.

FIG. 9 is a circuit diagram showing an embodiment of the fifth invention. This is a conventional example of a single-pole forward DC-DC converter shown in FIG. 13 in which a MOSFET 12 and a capacitor 6 are connected in series instead of a diode 71, and a transformer secondary winding 22 and a rectifier circuit 3 are connected via an inductance 7. Connected.

The operation of the circuit shown in FIG. 9 when the winding ratio of the transformer primary winding 21 to the tertiary winding 23 is 1: 1 will be described below with reference to waveforms. Here, the voltage across the MOSFET is positive on the drain side, the current is positive on the direction from the drain side to the source, and the capacitance of the capacitor 6 is sufficiently large.
The voltage between both ends is almost constant.

The operation during the period is the same as that shown in FIG. When the MOSFET is turned on during the period, the difference voltage Er between the voltage Ed across the DC power supply 1 and the voltage Vc across the capacitor 6 is applied in the opposite direction to the tertiary winding 23, and the transformer 2 is reset. Where Er
Is represented by Er = Ed−Vc.

When the average value of the current of the MOSFET 12 becomes positive, Er decreases due to the increase in Vc, and when the average value becomes negative, Er increases due to the decrease in Vc. With respect to D, the relationship Ed × D = Er × (1−D) is established, and the average value of the current of the MOSFET 12 flowing in the period becomes 0.

When the MOSFET 12 is turned off during the period, the exciting current of the transformer 2 flowing in the reverse direction during the period flows back through the path of the capacitor 51 → the primary winding 21 → the DC power supply 1, and the energy of the capacitor 51 is changed to the DC power supply. Regenerated to 1 If the MOSFET 31 is turned on when the energy of the capacitor 51 becomes zero or the minimum, the period starts.

In the conventional example shown in FIG. 13, when the secondary winding 22 and the rectifier circuit 3 are connected without passing through the inductance 7,
When the voltage across the MOSFET 31 becomes lower than Ed, the diode 61 becomes forward-biased, so that the exciting current of the transformer flows back through the secondary winding → the diode 61 → the diode 62, and the voltage across the MOSFET 31 is higher than the Ed. It does not fall. Therefore, during the period MOSFET
In order to lower the voltage at 31 from Ed, it is necessary to connect the secondary winding 22 and the rectifier circuit 3 via the inductance 7 as shown in FIG. The same effect can be obtained by using the leakage inductance of the transformer 2 as the inductance 7.

FIG. 11 is a circuit diagram showing an embodiment of the fifth invention. This is a conventional example of a two-pole forward type DC-DC converter shown in FIG.
The configuration is such that the secondary circuit of the transformer 22 and the rectifier circuit 3 are connected via the inductance 7 at the same time as the series circuit of the FET 12a and the capacitor 6a and the diode 72 are replaced with the series circuit of the MOSFET 12b and the capacitor 6b. .

The operation of the circuit shown in FIG. 11 will be described below with reference to the operation waveforms shown in FIG. Here, MOSFE
The voltage across T is positive on the drain side, the current is positive in the direction from the drain side to the source, and the capacitances of the capacitors 6a and 6b are sufficiently large and equal.

The operation during the period is the same as that in FIG. MOSFET12 in the period
a, When the MOSFET 12b is turned on, the difference voltage Er between the voltage Ed across the DC power supply 1 and the voltage Vc across the capacitors 6a and 6b is applied to the primary winding 21 in the reverse direction, and the transformer 2 is reset. Here, Er is represented by Er = Ed−2Vc.

When the average value of the currents of the MOSFETs 12a and 12b becomes positive, Er decreases due to an increase in Vc, and when the average value becomes negative, Er increases due to a decrease in Vc.
With respect to the duty ratio D of a, 11b, the relationship of Ed × D = Er × (1-D) is established, and the MOSFETs 12a,
The average value of the current of 2b is 0.

During the period, the MOSFETs 12a and 12a
When b is turned off, the transformer 2 flowing in the opposite direction during the period
The excitation current flows through the path of the capacitor 51 → the primary winding 21 → the capacitor 52 → the DC power supply 1, and the capacitor 51,
The energy of 52 is regenerated to the DC power supply 1. When the MOSFETs 31 and 32 are turned on when the energy of the capacitors 5a and 5b becomes zero or minimum, the period shifts to the period.

In the conventional example shown in FIG. 15, when the secondary winding 22 and the rectifier circuit 3 are connected without passing through the inductance 7,
Since the diode 61 becomes forward biased when the voltage across the MOSFETs 31 and 32 becomes lower than Ed / 2,
The exciting current of the transformer returns in the path of secondary winding → diode 61 → diode 62, and the voltage across MOSFETs 31 and 32 does not fall below Ed / 2. Therefore, it is necessary to connect the secondary winding 22 and the rectifier circuit 3 via the inductance 7 as shown in FIG. Also,
The same effect can be obtained by using the leakage inductance of the transformer 2 as the inductance 7.

[0034]

According to the present invention, the following effects can be obtained. First, since the energy of the snubber capacitor is regenerated to the DC power supply and the MOSFET is turned on when the power becomes zero, the loss and noise generated by the snubber capacitor discharge at turn-on can be reduced. . Further, according to the second and fourth aspects of the present invention, it is possible to prevent the snubber capacitor from being recharged during the period, thereby reducing the loss that occurs at the time of recharging.

As a result, the conversion efficiency of the device is improved, and the size of the cooling device for heat radiation can be reduced. In addition, there is an advantage that the filter can be downsized due to low noise. Further, according to the fifth and sixth aspects of the present invention, by inserting an inductance on the secondary winding side, the voltage of the MOSFET can be made lower than the DC power supply voltage during the period.
It is easy to make the voltage across T close to zero.

[Brief description of the drawings]

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

FIG. 2 is an operation waveform diagram of the embodiment of the first invention.

FIG. 3 is a circuit diagram showing an embodiment of the second invention.

FIG. 4 is an operation waveform diagram of the embodiment of the second invention.

FIG. 5 is a circuit diagram showing an embodiment of the third invention.

FIG. 6 is an operation waveform diagram of the embodiment of the third invention.

FIG. 7 is a circuit diagram showing an embodiment of the fourth invention.

FIG. 8 is an operation waveform chart of the embodiment of the fourth invention.

FIG. 9 is a circuit diagram showing an embodiment of the fifth invention.

FIG. 10 is an operation waveform diagram of the fifth embodiment of the present invention.

FIG. 11 is a circuit diagram showing an embodiment of the sixth invention.

FIG. 12 is an operation waveform chart of the embodiment of the sixth invention.

FIG. 13 is a circuit diagram showing a conventional example of a single-stone forward type DC-DC converter.

FIG. 14 is an operation waveform diagram of a conventional example of a one-stone forward type DC-DC converter.

FIG. 15 is a circuit diagram showing a conventional example of a dual-forward DC-DC converter.

FIG. 16 is an operation waveform diagram of a conventional example of a dual-forward DC-DC converter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Transformer, 3 ... Rectifier circuit, 4 ... Smoothing filter, 5, 6, 6a, 6b ... Capacitor, 7 ... Inductance, 21 ... Transformer first primary winding, 22 ... Transformer Secondary winding, 23... Transformer second primary winding, 31, 32,
... MOSFET as main semiconductor switch element, 41
Reference numerals 42, 43, 44, 12, 12a, 12b: MOSFETs as auxiliary semiconductor switches; 51, 52: snubber capacitors; 61, 62: diodes constituting a rectifier circuit; 63: reactors constituting a smoothing filter;
Capacitors constituting a smoothing filter, 71, 72 ... diodes

Claims (6)

[Claims] 1. A negative electrode of a first primary winding of a transformer, wherein a positive electrode of a DC power supply, a positive electrode of a first primary winding of a transformer and a negative electrode of a second primary winding of the transformer are connected. Side and one end of a first semiconductor switch element, the transformer second primary winding positive side and one end of a second semiconductor switch element are connected, and the negative side of the DC power supply and the The other end of the first semiconductor switch element is connected to the other end of the second semiconductor switch element, the first semiconductor switch element and a snubber capacitor are connected in parallel, and the secondary winding of the transformer is connected to a rectifier circuit. A rectifier circuit connected to an input of a smoothing filter. 2. A negative terminal of the first primary winding of the transformer, wherein a positive terminal of the DC power supply is connected to a positive terminal of the first primary winding of the transformer and a negative terminal of the second primary winding of the transformer. Side and one end of a first semiconductor switch element, the transformer second primary winding positive side and one end of a second semiconductor switch element are connected, and the negative side of the DC power supply and the The other end of the first semiconductor switch element is connected to the other end of the second semiconductor switch element, and a series circuit of a snubber capacitor and a third semiconductor switch is connected in parallel to the first semiconductor switch element. A DC-DC converter, wherein the secondary winding of the transformer is connected to an input of a rectifier circuit, and an output of the rectifier circuit is connected to an input of a smoothing filter. 3. One end of a first semiconductor switch element, one end of a third semiconductor switch element, and a negative electrode side of a primary winding of a transformer are connected, and one end of a second semiconductor switch element and a fourth semiconductor switch are connected. Connecting one end of an element to the positive electrode side of the transformer primary winding, connecting the other end of the first semiconductor switch element, the other end of the fourth semiconductor switch element, and the negative electrode side of the DC power supply, The other end of the second semiconductor switch element, the other end of the third semiconductor switch element, and the positive side of the DC power supply are connected, and the first semiconductor switch element and the first snubber capacitor are connected in parallel. The second semiconductor switch element and a second snubber capacitor are connected in parallel, the secondary winding of the transformer is connected to the input of a rectifier circuit, and the output of the rectifier circuit is connected to the input of a smoothing filter. DC-DC conversion characterized by Location. 4. One end of a first semiconductor switch element, one end of a third semiconductor switch element, and a negative electrode of a primary winding of a transformer are connected, and one end of a second semiconductor switch element and a fourth semiconductor switch are connected. Connecting one end of an element to the positive electrode side of the transformer primary winding, connecting the other end of the first semiconductor switch element, the other end of the fourth semiconductor switch element, and the negative electrode side of the DC power supply, The other end of the second semiconductor switch element, the other end of the third semiconductor switch element, and the positive side of the DC power supply are connected, and a first snubber capacitor and a second snubber capacitor are connected to the first semiconductor switch element. 5, a series circuit of a second snubber capacitor and a sixth semiconductor switch is connected in parallel to the second semiconductor switch element, and the secondary winding of the transformer To the input of the rectifier circuit DC output of the rectifier circuit, characterized in that connected to the input of the smoothing filter - DC converter. 5. The DC-DC converter according to claim 1, wherein a capacitor is inserted between a positive electrode of the first primary winding of the transformer and the second semiconductor switch. A DC-DC converter wherein a winding is connected to an input of a rectifier circuit via an inductance provided separately or a leakage inductance of a transformer, and an output of the rectifier circuit is connected to an input of a smoothing filter. 6. The DC-DC converter according to claim 3, wherein a first capacitor is provided between a positive electrode of the primary winding of the transformer and the fourth semiconductor switch, and the primary winding of the transformer is formed. A second capacitor is inserted between the negative electrode side and the third semiconductor switch, and is connected to an input of a rectifier circuit via an inductance in which the transformer secondary winding is separately installed or a leakage inductance of the transformer. And an output of the rectifier circuit is connected to an input of the smoothing filter.