JP6305492B1 - DC-DC converter - Google Patents

Abstract

A DC-DC converter that suppresses a recovery surge voltage of a secondary diode using an inductance component of a current transformer while using the current transformer for current detection. By connecting a current transformer 3 that detects current in series with a transformer 4, the inductor component of the current transformer 3 suppresses di / dt during switching of semiconductor switching elements Q1, Q2, Q3, and Q4. The energy of surge caused by the recovery current of the first rectifier diode 5 and the second rectifier diode 6 is bypassed by the first surge suppression diode 1 and the second surge suppression diode 2. [Selection] Figure 1

Description

  The present invention relates to a DC-DC converter, and more particularly to an isolated DC-DC converter that transmits a large amount of power by stepping down from a high voltage to a low voltage.

  In recent years, electric vehicles and hybrid vehicles have been developed as environmentally friendly vehicles. Such an automobile has a driving battery for operating a traveling motor by the electric power in addition to an auxiliary battery for operating a control circuit like a conventional automobile. For this reason, it is necessary to charge the driving battery in addition to the auxiliary battery. For example, there is an insulated step-down DC-DC converter (hereinafter referred to as a step-down converter) as a direct-current converter required for charging an auxiliary battery from a driving battery for supplying electric power to an electric motor of an electric vehicle. .

  Miniaturization and cost reduction of step-down converters are desired by car manufacturers. To reduce the size and cost of step-down converters, it is essential to reduce the size of magnetic components such as transformers and reactors. Higher frequency is desired. However, with high frequency driving, problems such as increased recovery loss of the diode and increased surge voltage occur. For this reason, there is a concern that the breakdown voltage of the element will increase, the loss will increase, and electromagnetic incoherence and resistance, that is, EMC (Electro-Magnetic Compatibility) will deteriorate, and the surge voltage generated in the secondary side rectifier circuit of the step-down converter will be suppressed. It is required to do.

  Therefore, as disclosed in, for example, International Publication WO2007 / 000830 (Patent Document 1), an insulation transformer and a resonance coil for zero voltage switching connected in series to a primary winding of the insulation transformer. DC-DC converter that suppresses surge voltage by connecting first and second regenerative diodes between an isolation transformer and a resonance coil in a full-bridge switching circuit driven by phase shift control It has been known.

International Publication No. WO2007 / 000830

  However, since the prior art disclosed in Patent Document 1 is based on the premise of phase shift control, a resonant reactor is required. When this circuit is applied in a hard switching configuration, the cost and size of the resonant reactor increase. Further, the converter circuit requires a current detection sensor circuit for overcurrent protection. When a current transformer is used as the primary current sensor, it is necessary to consider the inductance component of the current transformer.

  For example, when the current transformer is provided in the front stage of the full bridge circuit, a surge voltage due to the inductance component of the current transformer is generated when the switching element is turned off. This is also the case with the prior art circuit disclosed in Patent Document 1. Surge voltage must be taken into account. For this reason, as the frequency increases, the surge voltage due to the current transformer cannot be ignored, and it is necessary to increase the breakdown voltage of the primary side element, which increases the cost. On the other hand, as a method other than the current transformer, a Hall type element type current sensor can be considered, but it is expensive.

  The present invention has been made to solve the above-described problems, and suppresses the recovery surge voltage of the secondary diode using the current transformer's inductor component while using the current transformer for current detection. It is an object to obtain a DC-DC converter.

The DC / DC converter according to the present invention includes an input power supply, an insulating transformer having a primary winding and a secondary winding, a current transformer connected in series to the primary winding and detecting a current, and the primary winding. In a DC-DC converter having a full-bridge semiconductor switching circuit connected to a series circuit of a line and the current transformer, and a rectifier circuit connected to the secondary winding,
The DC-DC converter includes a first surge suppression diode and a second surge suppression diode connected to the primary winding,
An anode terminal of the first surge suppression diode and a cathode terminal of the second surge suppression diode are connected to a connection point between the current transformer and the primary winding,
The cathode terminal of the first surge suppression diode is connected to the positive side of the input power supply, and the anode terminal of the second surge suppression diode is connected to the negative side of the input power supply. To do.

Further, DC / DC converter according to the present invention, an input power source, a transformer having a primary winding and a secondary winding, connected in series with the primary winding, a current transformer for detecting a current, the A DC-DC having a half-bridge type semiconductor switching circuit having two semiconductor switching elements connected to a series circuit of a primary winding and the current transformer, and a rectifier circuit connected to the secondary winding In the converter
The DC-DC converter, Rutotomoni comprises a first surge suppression diode and the second surge suppression diode connected to the primary winding, one end of the current transformer is connected between the two semiconductor switching elements The other end is connected to the primary winding,
An anode terminal of the first surge suppression diode and a cathode terminal of the second surge suppression diode are connected to a connection point between the current transformer and the primary winding,
The cathode terminal of the first surge suppression diode is connected to the positive side of the input power supply, and the anode terminal of the second surge suppression diode is connected to the negative side of the input power supply. To do.

  According to the DC / DC converter according to the present invention, the current transformer can have a surge suppression function while maintaining a current detection function, and the parts can be simplified. As a result, conversion efficiency can be reduced with lower loss. It is possible to obtain a DC-DC converter that can simplify the heat dissipation means such as a cooling device and can be downsized.

It is a schematic block diagram of the DC-DC converter which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows operation | movement of the semiconductor switching element of the DC-DC converter which concerns on Embodiment 1 of this invention. It is explanatory drawing which shows each voltage current waveform at the time of operation | movement of the DC-DC converter which concerns on Embodiment 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a general DC-DC converter composed of a full-bridge semiconductor switching element, a capacitor, and a diode for explaining DC-DC according to Embodiment 1 of the present invention; FIG. 5 is an explanatory diagram showing a current path when each semiconductor switching element in FIG. 4 is turned on / off. FIG. 5 is an explanatory diagram showing a current path when each semiconductor switching element in FIG. 4 is turned on / off. FIG. 5 is an explanatory diagram showing a current path when each semiconductor switching element in FIG. 4 is turned on / off. FIG. 5 is an explanatory diagram showing temporal changes in current and voltage of the rectifying diode in FIG. 4. It is explanatory drawing which shows a current pathway when each semiconductor switching element of the DC-DC converter which concerns on Embodiment 1 of this invention is turned on / off. It is explanatory drawing which shows the time-dependent change of the electric current and voltage of the rectifier diode of the DC-DC converter which concerns on Embodiment 1 of this invention. It is a schematic block diagram of the DC-DC converter which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows operation | movement of the semiconductor switching element of the DC-DC converter which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows a current pathway when each semiconductor switching element of the DC-DC converter which concerns on Embodiment 2 of this invention is turned on / off. It is a schematic block diagram which shows the modification of the DC-DC converter which concerns on Embodiment 2 of this invention.

  Preferred embodiments of a DC-DC converter according to the present invention will be described below with reference to the drawings. In the description of the drawings, the same portions are denoted by the same reference numerals, and redundant description is omitted.

Embodiment 1 FIG.
1 is a schematic configuration diagram of a DC-DC converter according to Embodiment 1 of the present invention. As shown in FIG. 1, a DC-DC converter according to the first embodiment, the voltage of the input voltage _{V i} is insulated by the DC-DC converter, and outputs any output voltage _{V o.} In an electric vehicle or a hybrid vehicle, a driving battery is connected to the input side, and an auxiliary battery is connected to the output side.

  The DC-DC converter detects four semiconductor switching elements (hereinafter referred to as switching elements) Q1 to Q4, two surge suppression diodes, that is, a first surge suppression diode 1 and a second surge suppression diode 2, and a current. Current transformer 3, a transformer 4 having a center tap, two rectifier diodes, that is, a first rectifier diode 5 and a second rectifier diode 6, a smoothing reactor 7, and a smoothing capacitor 8. Yes.

  Next, the voltages detected by the input voltage detection circuit 11 and the output voltage detection circuit 12 are input to the control circuit unit 9 through the signal lines 10a and 10b, respectively. Further, the current transformer 3 is configured with a turns ratio of 1: n, the secondary side is connected to the control circuit unit 9, and outputs current information to the control circuit unit 9 as voltage information. The control unit 13 acquires the voltage information of the input voltage detection circuit 11 and the output voltage detection circuit 12 and the current information by the current transformer 3 from the control circuit unit 9 through the communication line 14a. Further, the control unit 13 outputs a control command to the control circuit unit 9 through the communication line 14b. Based on a control command from the control unit 13, the control circuit unit 9 performs on / off control of the switching elements Q1 to Q4 with a predetermined dead time by the gate drive signal lines 15a to 15d.

The subsequent stage of the input voltage _{V i,} 4 one has switching elements Q1 to Q4 are connected, for example, as the switching elements Q1 to Q4, it is possible to use MOSFET. The drain of the switching element Q1, Q3 is connected to the positive side of the input voltage V _i, the source of the switching elements Q2, Q4 is connected to the negative side of the input voltage V _i.

  One end of the primary winding of the transformer 4 is connected to the current transformer 3, and the other end is connected to a connection point between the source of the switching element Q1 and the drain of the switching element Q2. The other end of the current transformer 3 is connected to a connection point between the source of the switching element Q3 and the drain of the switching element Q4.

The connection point of the current transformer 3 and the transformer 4, a first anode terminal of the surge suppressor diode 1 is connected, a first cathode terminal of the surge suppression diode 1 is connected to the positive side of the input voltage V _i. Further, the connection point of the current transformer 3 and the transformer 4, a second cathode terminal of the surge suppression diode 2 is connected, a second anode terminal of the surge suppression diode 2 is connected to the negative side of the input voltage V _i ing.

The secondary winding of the transformer 4 includes a first rectifier diode 5 and a second rectifier diode 6, and an intermediate tap provided in the secondary winding of the transformer 4 has a negative output voltage V _o . Connected to the side. The anode terminals of the first rectifier diode 5 and the second rectifier diode 6 are connected to both ends of the secondary winding of the transformer 4, respectively. The positive side of the first cathode terminal of the cathode terminal and the second rectifying diode 6 of the rectifier diode 5 are connected respectively, the output voltage V _o and the connection point is connected.

  Next, the basic operation of the DC-DC converter according to Embodiment 1 will be described with reference to FIGS. Note that the DC-DC converter exemplified in the first embodiment is a DC-DC converter having a general full-bridge configuration, and adopts a switching system that is a hard switching system.

FIG. 2 is an explanatory diagram illustrating operations of the switching elements Q1 to Q4 of the DC-DC converter according to the first embodiment. In FIG. 2, T _dc indicates a switching period, and t _d indicates a dead time.

  As shown in FIG. 2, when switching elements Q1 and Q4 are turned on, the current flowing through the primary winding (primary side) of transformer 4 is switching element Q1 → transformer 4 (primary side) → current transformer 3 → switching element. Each route flows in the order of Q4. The transformer 4 transmits power from the primary side to the secondary side. Subsequently, the current flowing through the secondary winding (secondary side) of the transformer 4 flows through each path in the order of the transformer 4 (secondary side) → the second rectifier diode 6 → the smoothing reactor 7.

  Similarly, when the switching elements Q2 and Q3 are turned on, the current flowing to the primary side of the transformer 4 flows through each path in the order of the switching element Q3 → the current transformer 3 → the transformer 4 (primary side) → the switching element Q2. Subsequently, the current flowing through the secondary winding of the transformer 4 flows through each path in the order of the transformer 4 (secondary side) → the first rectifier diode 5 → the smoothing reactor 7.

FIG. 3 is an explanatory diagram showing voltage and current waveforms during the operation of the DC-DC converter according to the first embodiment. Here, the symbols in FIG. 3 are defined as follows.
V _tr1 : Transformer 4 primary side voltage I _tr1 : Transformer 4 primary side current V _tr2 : Transformer 4 secondary side voltage I _out : Current flowing through the smoothing reactor 7

Next, a mechanism for generating a surge due to recovery of the first rectifier diode 5 and the second rectifier diode 6 will be described with reference to FIGS.
FIG. 4 is a circuit diagram of a general conventional DC-DC converter for explaining the DC-DC converter according to the first embodiment. FIG. 4 shows switching elements Q1 to Q4 having a full bridge configuration and the first rectification. 3 is a circuit diagram including a diode 5 and a second rectifier diode 6. FIG. Here, the leakage inductance component of the transformer 4 and the inductance component of the wiring are collectively referred to as a reactor 40, and the other parts that are the same as in FIG.

5 to 7 are explanatory diagrams showing current paths when the switching elements Q1 to Q4 in FIG. 4 are turned on / off. FIGS. 5A to 7E are diagrams showing the change over time of the current path flowing through the circuit of the DC-DC converter in FIG. 4, and FIG. 8 is the first rectifier diode 5 in FIG. It is explanatory drawing which shows the time-dependent change of the electric current (≒ _ID5 ) and voltage (≒ _VD5 ).

  At time t0, when the switching elements Q2 and Q3 are on and the switching elements Q1 and Q4 are off, the path of each current flowing through the primary side and the secondary side of the transformer 8 is a path indicated by an arrow in FIG. It becomes.

When all the switching elements Q1 to Q4 are turned off at time t1, no current flows on the primary side of the transformer 4 (actually an exciting current etc. flows but is ignored here).
On the other hand, the current in the same direction as immediately before (before time t1) continues to flow on the secondary side of the transformer 4 by the smoothing reactor 7. This is due to Lenz's law that when a change in the magnetic flux occurs in the coil, the magnetic flux is generated in a direction that prevents the change in the magnetic flux and an induced electromotive force is generated, and the switching elements Q1 to Q4 are all turned off. In the instant, the smoothing reactor 7 corresponds to a constant current source. Further, since all the switching elements Q1 to Q4 are off and no voltage is generated on the primary side of the transformer 4, no voltage is generated on the secondary side of the transformer 4. Therefore, the path of the current flowing through the smoothing reactor 7 is a path indicated by an arrow in FIG.

Further, as shown in FIG. 8, at time t = t1, the magnitude of the current I _D5 (hereinafter, current I _D5 ) of the first rectifier diode 5 is _IF , and the voltage V of the first rectifier diode 5 _D5 (hereinafter, voltage _{V D5)} the size of which is _{V F.}

  At time t2, when the switching elements Q1 and Q4 are turned on, a voltage is generated on the primary side of the transformer 4, so that a voltage is also generated on the secondary side of the transformer 4. However, since the current flowing through the smoothing reactor 7 flows through the first rectifier diode 5 and the second rectifier diode 6 (corresponding to the broken-line arrow in FIG. 6C), the fact is present on the secondary side of the transformer 4. The top will be short-circuited. In such a case, the path of the current flowing on the secondary side of the transformer 4 is a path indicated by a solid arrow shown in FIG. In FIG. 6C, as time elapses from time t2, the current flowing through the second rectifier diode 6 gradually increases while the current flowing through the first rectifier diode 5 decreases. .

Further, as shown in FIG. 8, at time t2, similarly to the time t1, the magnitude of the current _{I D5} is _{I F,} the magnitude of the voltage _{V D5} is _{V F.}

  As time elapses from time t2, the current of the first rectifier diode 5 decreases, and at the moment when the forward current becomes 0 A or less, the first rectifier diode 5 has a recovery current (or reverse recovery current). Flowing. The path of the recovery current flowing through the first rectifier diode 5 is the path indicated by the solid line arrow in FIG. Note that the first rectifier diode 5 can be energized by accumulated carriers even when a reverse bias is applied by changing the bias direction (polarity) from the ON state in which the forward bias is applied. .

Further, as shown in FIG. 8, in accordance with a lapse of time from the time t2, the magnitude of the current I _D5 is gradually decreased from I _F, becomes zero. In such a case, since the recovery current flows, the magnitude increases from 0 as time elapses from the time when the magnitude of the current _ID5 becomes 0, and becomes maximum at time t3. Further, according to the lapse of time from the time t2, the magnitude of the voltage _{V D5} gradually decreases from _{V F,} a 0 at time t3.

This recovery current also flows to the primary side of the transformer 4. Here, in the first rectifier diode 5, in the recovery operation process, as the accumulated carriers decrease, the recovery current decreases and finally does not flow. However, the surge voltage V _L (= L × di / dt) is generated by the reduction rate of the recovery current (= di / dt) and the inductance component (= L) of the reactor 40. For this reason, the surge voltage V _L is applied to the transformer voltage V _{tr1 in addition} to the input voltage (≈V _i ).
V _i : Input voltage di / dt: Decreasing rate of rectifying diode recovery current di ′ / dt: Decreasing rate of rectifying diode recovery current flowing on the primary side of transformer 4 N: Transformer winding ratio (N: 1: 1)
L: Assuming that the inductance component of the reactor 40 is used, the voltage V _tr1 applied to the primary side of the transformer 4 when recovery occurs is expressed by the following equation (1).

For this reason, the voltage V _tr2 generated on the secondary side of the transformer 4 is expressed by the following equation (2).

At this time, since the transformer 4 has a center tap structure, a voltage twice as large as the transformer secondary side voltage is applied to the first rectifier diode 5. For this reason, the voltage V _D5 of the first rectifier diode 5 is expressed by the following equation (3).

The primary voltage V _tr1 of the transformer 4 is applied with a total voltage V _tr1 (= V _i + V _L ) obtained by summing the surge voltage V _L due to the inductance component of the reactor 40 and the input voltage V _i . the secondary voltage V _tr2, the primary voltage of the transformer 4 1 / N times the voltage is generated twice the voltage of the first secondary voltage V _tr2 of the transformer 4 to the rectifying diode 5 is applied Is done. For example, at time t4, as shown in FIG. 7E, the surge voltage V _L and the voltage (V _i / 2) of the smoothing capacitor 8 are 2 × 1 / N at both ends of the first rectifier diode 5. Doubled voltage is generated.

Further, as shown in FIG. 8, as time elapses from time t3, the magnitude of current _ID5 decreases and finally becomes 0 after time t4. Furthermore, as time elapses from time t3, the voltage V _D5 increases from 0, and at time t4, the magnitude of the surge voltage V _L becomes maximum, so that the voltage V _D5 increases to the maximum. Become. Then, gradually decreases the magnitude of the voltage V _D5 at time t4, the final input voltage V _i becomes equal to 2 × 1 / N those times. The above is the mechanism of surge generation.

  As described above, an excessive surge voltage is generated in the first rectifier diode 5 and the second rectifier diode 6 of the DC-DC converter, so that a circuit for suppressing the surge voltage is generally required. However, if a snubber circuit is used, the efficiency deteriorates due to heat generated by resistance. Further, as described above, as described in the prior art, it is expensive to separately provide a resonance snubber circuit.

  Therefore, as shown in FIG. 1, in the DC-DC converter according to the first embodiment, the current transformer 3 that detects current is inserted in series with the transformer 4, so that the primary side (main circuit side) of the current transformer 3. ), The change of the transformer current at the turn-off and turn-on of the switching elements Q1 and Q4 and the switching elements Q2 and Q3 is moderated. Then, the surge voltage of the current transformer 3 generated by the recovery current of the first rectifier diode 5 and the second rectifier diode 6 is the first surge suppression diode 1 inserted at the connection point between the current transformer 3 and the transformer 4 and Surge is suppressed and prevented by the second surge suppression diode 2.

Next, a mechanism in which surge is suppressed in the DC-DC converter according to Embodiment 1 will be described with reference to FIG.
FIG. 9 is an explanatory diagram illustrating a current path when the switching elements Q2 and Q3 or Q1 and Q4 of the DC-DC converter according to Embodiment 1 are on / off. FIGS. 9A and 9B are diagrams showing a change with time of a current path flowing through the circuit of the DC-DC converter.

FIG. 9A illustrates a current path when the switching elements Q2 and Q3 are turned on and the switching elements Q1 and Q4 are turned off. As described above, the switching elements Q2 and Q3 are turned on, and the recovery current flows through the second rectifier diode 6. However, due to the inductance component of the current transformer 3, the reduction rate of the recovery current (= di / dt) is It is suppressed. On the other hand, the surge voltage V _L is generated by the reduced rate of recovery current (= di / dt) and the inductance component (= L) of the current transformer 3, and the generated surge voltage V _L is the first surge suppression diode. When the voltage _Vf of 1 is exceeded, the first surge suppression diode 1 is turned on. That is, during the period in which the surge voltage of the current transformer 3 is _VL > _Vf , the current path that always flows through the current transformer 3 → the first surge suppression diode 1 → the switching element Q3 (broken arrow in FIG. 9A) Exists. Therefore, since not only the DC voltage of the input voltage V _i is the voltage of the primary winding of the transformer 4 is applied, the surge is not generated in the secondary voltage of the transformer 4.

FIG. 9B illustrates a current path when the switching elements Q1 and Q4 are turned on and the switching elements Q2 and Q3 are turned off. When a surge voltage is generated in the current transformer 3, the second surge suppression diode 2 is turned on. That is, during the period in which the surge voltage of the current transformer 3 is V _L > V _f , current always flows through the path of the current transformer 3 → the switching element Q4 → the second surge suppression diode 2 (the broken line in FIG. 9B). Arrow). In this case, since not only the DC voltage of the input voltage V _i to the primary side of the transformer 4 is applied, the surge is not generated in the secondary voltage of the transformer 4. Therefore, as shown in FIG. 10, the current I _D5 and the voltage V _D5 of the first rectifier diode 5 have time-varying characteristics as indicated by the solid line.

  From the above, the DC-DC converter according to the first embodiment does not require a special snubber circuit at low cost, and the inductance component of the current transformer 3, the first surge suppression diode 1 and the second surge suppression diode 2 are provided. By providing, it possesses a current detection function and a surge suppression function.

  In the first embodiment, the current transformer 3 is inserted between the connection point between the switching elements Q3 and Q4 and the transformer 4. However, the present invention is not limited to this. For example, the current transformer 3 includes the switching elements Q1 and Q2. It may be inserted between the connection point and the transformer 4.

  In the first embodiment, the switching method is hard switching. However, the switching method is not limited to this, and a soft switching method, for example, phase shift control may be used. In this case, not only the same effect but also soft switching is achieved. It is possible to supplement the necessary resonance reactor with the exciting inductance component of the current transformer 3.

Embodiment 2. FIG.
Next, a DC-DC converter according to Embodiment 2 of the present invention will be described.
FIG. 11 is a schematic configuration diagram of a DC-DC converter according to the second embodiment. As shown in FIG. 11, the DC-DC converter according to the second embodiment is a DC-DC converter having a half bridge configuration using two switching elements and two capacitors. With this configuration, the number of switching elements that are active elements can be reduced, leading to low cost and downsizing.

  The DC-DC converter according to the second embodiment includes two capacitors, that is, a first capacitor 90 and a second capacitor 91, two switching elements Q3 and Q4, and two surge suppression diodes, that is, a first capacitor. Surge suppressor diode 1 and second surge suppressor diode 2, current transformer 3 for detecting current, transformer 4 having a center tap, and two rectifier diodes, that is, first rectifier diode 5 and second rectifier A diode 6, a smoothing reactor 7, and a smoothing capacitor 8 are provided.

  Next, the voltages detected by the input voltage detection circuit 11 and the output voltage detection circuit 12 are input to the control circuit unit 9 through the signal lines 10a and 10b, respectively. The current transformer 3 is configured with a turns ratio of 1: n, and the secondary side is connected to the control circuit unit 9 and outputs current information to the control circuit unit 9 as voltage information. The control unit 13 acquires the voltage information of the input voltage detection circuit 11 and the output voltage detection circuit 12 and the current information by the current transformer 3 from the control circuit unit 9 through the communication line 14a. Further, the control unit 13 outputs a control command to the control circuit unit 9 through the communication line 14b. Based on a control command from the control unit 13, the control circuit unit 9 performs on / off control of the switching elements Q3 and Q4 with a predetermined dead time by the gate drive signal lines 15c and 15d.

The subsequent stage of the input voltage _{V i,} 2 two switching elements Q3, Q4 are connected, for example, as the switching elements Q3, Q4, it is possible to use MOSFET. The drain of the switching element Q3 is connected to the positive side of the input voltage V _i, the source of the switching element Q4 is connected to the negative side of the input voltage V _i. Similarly, a first capacitor 90 and a second capacitor 91 are connected to the subsequent stage of the input voltage V _i , and one end of the first capacitor 90 is connected to the positive side of the input voltage V _i , one end of the capacitor 91 is connected to the negative side of the input voltage V _i.

  One end of the primary winding of the transformer 4 is connected to the current transformer 3, and the other end is connected to a connection point between the first capacitor 90 and the second capacitor 91. The other end of the current transformer 3 is connected to a connection point between the source of the switching element Q3 and the drain of the switching element Q4.

The connection point of the current transformer 3 and the transformer 4, a first anode terminal of the surge suppressor diode 1 is connected, a first cathode terminal of the surge suppression diode 1 is connected to the positive side of the input voltage V _i. On the other hand, the connection point of the current transformer 3 and the transformer 4, a second cathode terminal of the surge suppression diode 2 is connected, a second anode terminal of the surge suppression diode 2 is connected to the negative side of the input voltage V _i ing.

  Next, the basic operation of the DC-DC converter according to Embodiment 2 will be described with reference to FIGS. Note that the DC-DC converter exemplified in the second embodiment is a DC-DC converter having a general half-bridge configuration, and adopts a switching system that is a hard switching system.

  FIG. 12 is an explanatory diagram showing the operation of the switching element of the DC / DC converter according to the second embodiment. As shown in FIG. 12, when the switching element Q3 is turned on, the current flowing through the primary winding (primary side) of the transformer 4 is the first capacitor 90 → the switching element Q3 → the current transformer 3 → the transformer 4 (primary side). ) → first capacitor 90 in this order. The transformer 4 transmits power from the primary side to the secondary side. Subsequently, the current flowing through the secondary winding (secondary side) of the transformer 4 flows through each path in the order of the transformer 4 (secondary side) → the first rectifier diode 5 → the smoothing reactor 7.

  When the switching element Q4 is turned on, the current flowing on the primary side of the transformer 4 flows through each path in the order of the second capacitor 91 → the transformer 4 → the current transformer 3 → the switching element Q4 → the second capacitor 91. Subsequently, the current flowing through the secondary winding of the transformer 4 flows through each path in the order of the transformer 4 (secondary side) → the second rectifier diode 6 → the smoothing reactor 7.

  Next, the mechanism by which surge is suppressed in the DC-DC converter according to Embodiment 2 will be described with reference to FIG. FIG. 13 is an explanatory diagram showing a current path when the switching elements Q3 and Q4 of the DC-DC converter according to the second embodiment are on / off. FIGS. 13 (a) and 13 (b) are diagrams showing changes over time in the current path flowing through the circuit of the DC-DC converter.

FIG. 13A illustrates a current path when the switching element Q3 is turned on and the switching element Q4 is turned off. As described above, the switching element Q3 is turned on, and the recovery current flows through the second rectifier diode 6, but the reduction rate (= di / dt) of the recovery current is suppressed by the inductance component of the current transformer 3. The On the other hand, the surge voltage V _L is generated by the reduced rate of reduction of the recovery current (= di / dt) and the inductance component (= L) of the current transformer 3, but the generated surge voltage V _L is the first.
When exceeding the voltage V _F of the surge suppression diode 1, a first surge suppression diode 1 is turned on. In other words, the period surge voltage of the current transformer 3 is a V _L> V _F is always current transformer 3 → first surge suppression diode 1 → current path through the switching element Q3 (broken line in FIG. 13 (a)) is Exists. For this reason, since only the DC voltage of the first capacitor 90 is applied to the primary side of the transformer 4, no surge occurs in the secondary side voltage of the transformer 4.

FIG. 13B shows a current path when the switching element Q4 is turned on and the switching element Q3 is turned off. When a surge voltage is generated in the current transformer 3, the second surge suppression diode 2 is turned on. In other words, the period surge voltage of the current transformer 3 is a V _L> V _F is always broken line of the current transformer 3 → switching element Q4 → the current flows in the second path of the surge suppression diode 2 (FIG. 13 (b) Arrow). Also at this time, since only the DC voltage of the second capacitor 91 is applied to the primary side of the transformer 4, no surge occurs in the secondary side voltage of the transformer 4. Therefore, as shown in FIG. 10 described in the first embodiment, the current I _D5 and the voltage V _D5 of the first rectifier diode 5 have the time-varying characteristics as indicated by solid arrows, and the surge voltage due to recovery is It is suppressed.

In the DC-DC converter according to the second embodiment, one end of the current transformer 3 is connected to a connection point between the source of the switching element Q3 and the drain of the switching element Q4, and the other end is connected to the transformer 4. One end of the current transformer 3 cannot be connected to the connection point between the first capacitor 90 and the second capacitor 91. This means that when the switching element Q3 or Q4 is turned on, the voltage _{V F} of the voltage (≒ _V i / 2) + diode of the surge voltage _{V L} of the current transformer 3 is first capacitor 90 or the second capacitor 91 Since the first surge suppression diode 1 or the second surge suppression diode 2 is not turned on until the voltage exceeds, a surge voltage at least up to the voltage of the first capacitor 90 or the second capacitor 91 is applied to the transformer 4. That is, in the half-bridge configuration of the second embodiment, the insertion location of the current transformer 3 needs to be connected between the connection point of the switching elements Q3 and Q4 and the transformer 4.

  From the above, the DC-DC converter according to the second embodiment not only has the same effect as the first embodiment, but also can reduce the number of switching elements, so that the drive circuit can be reduced, and the cost and size can be reduced. Can be achieved.

  In the second embodiment, the half bridge configuration uses two switching elements and two capacitors. However, the present invention is not limited to this. For example, as shown in FIG. You may make it the structure inserted. The configuration shown in FIG. 14 not only provides the same surge suppression effect, but also reduces the number of parts.

In the above embodiments, is connected to the negative side of the intermediate tap output voltage V _o of the secondary winding of the transformer 4, a first rectifier diode 5 respectively on both ends of the secondary winding of the transformer 4, the The anode terminals of the two rectifier diodes 6 are connected, but the present invention is not limited to this. Intermediate tap is connected to the positive side of the output voltage V _o, the first rectifying diode 5 at both ends of the secondary winding of the transformer 4, the cathode terminal of the second rectifying diode 6 may be a configuration that is connected . The anode terminal of the first rectifier diode 5 and are respectively connected anode terminals of the second rectifier diode 6, the negative side of the connection point output voltage V _o is connected.

In each of the above embodiments, the semiconductor switching element used in the DC-DC converter is not limited to a switching element made of a silicon (Si) semiconductor. For example, the semiconductor switching element has a band gap wider than that of a Si semiconductor. It may be made of a semiconductor material. Examples of the wide band gap semiconductor that is a non-Si semiconductor material include silicon carbide, a gallium nitride-based material, and diamond.

  A switching element made of a wide band gap semiconductor can be used in a high voltage region where it is difficult to perform a unipolar operation with a Si semiconductor, greatly reducing the switching loss generated during switching, and greatly reducing the power loss. In addition, since power loss is small and heat resistance is high, when a power module is configured with a cooling unit, the heat sink fins can be downsized and the water cooling unit can be air-cooled. Miniaturization is possible.

  In addition, switching elements made of wide band gap semiconductors are suitable for high-frequency switching operations, and when applied to converter circuits where high frequency requirements are high, the switching frequency increases, so that reactors and capacitors connected to the converter circuit are added. It can also be miniaturized. Therefore, the same effect can be obtained when the semiconductor switching element in each of the above embodiments is a switching element made of a wide gap semiconductor such as silicon carbide.

  In addition, in the case of a transistor made of a gallium nitride material among wide gap semiconductors, for example, GAN-HEMT, the parasitic capacitance between the drain and the source (generally called Coss) is sufficiently smaller than that of the Si semiconductor. By using this, the dead time to be secured can be shortened, which leads to improvement of effective duty and higher frequency.

  By using GAN-HEMT, the switching frequency is increased and the magnetic component can be miniaturized. On the other hand, the rising and falling speeds (≈di / dt) at the time of switching become steep due to high-frequency driving and the surge voltage increases, so that it is necessary to increase the breakdown voltage of the element and add a snubber circuit. However, in each of the above embodiments, by inserting the current transformer 3 in series with the transformer 4, the rise of the current flowing between the drain and source of the semiconductor switching element is increased, while the inductance component of the current transformer 3 The rise and fall speeds (≈di / dt) of the current flowing through the transformer 4 are alleviated.

  For this reason, there has been a concern about the increase in surge voltage due to higher frequency and higher speed of the semiconductor switching element in the past, but in each of the above embodiments, the semiconductor switching element can reduce switching loss by high speed switching, while the transformer side Is suppressed by the inductance component of the current transformer 3, so that the surge voltage does not increase. Further, it is possible to prevent the surge voltage due to the inductance component of the current transformer 3 from being applied to the transformer 4 by the first surge suppression diode 1 and the second surge suppression diode 2.

  As described above, the first and second embodiments of the present invention have been described. However, within the scope of the present invention, the embodiments can be freely combined, or each embodiment can be appropriately modified or omitted. it can.

1 first surge suppression diode, 2 second surge suppression diode, 3 current transformer, 4 transformer, 5 first rectifier diode, 6 second rectifier diode, 7 smoothing reactor, 8 smoothing capacitor, 9 control circuit unit, 10a, 10b signal line, 11 input voltage detection circuit, 12 output voltage detection circuit, 13 control unit, 14a14b communication line, 15a, 15b, 15c, 15d gate drive signal line, 40 reactor, 90 first capacitor, 91 second capacitor 120 capacitor, Q1, Q2, Q3, Q4 semiconductor switching elements, _{V i} input voltage, _{V o} output voltage

Claims (6)

Connected to an input power source, a transformer having a primary winding and a secondary winding, a current transformer connected in series to the primary winding to detect current, and a series circuit of the primary winding and the current transformer In a DC-DC converter having a full-bridge semiconductor switching circuit and a rectifier circuit connected to the secondary winding,
The DC-DC converter includes a first surge suppression diode and a second surge suppression diode connected to the primary winding,
An anode terminal of the first surge suppression diode and a cathode terminal of the second surge suppression diode are connected to a connection point between the current transformer and the primary winding,
The cathode terminal of the first surge suppression diode is connected to the positive side of the input power supply, and the anode terminal of the second surge suppression diode is connected to the negative side of the input power supply. DC-DC converter.   The DC-DC converter according to claim 1, wherein the DC-DC converter is driven by phase shift control. Connected to an input power source, a transformer having a primary winding and a secondary winding, a current transformer connected in series to the primary winding to detect current, and a series circuit of the primary winding and the current transformer In a DC-DC converter having a half-bridge semiconductor switching circuit including the two semiconductor switching elements, and a rectifier circuit connected to the secondary winding,
The DC-DC converter, Rutotomoni comprises a first surge suppression diode and the second surge suppression diode connected to the primary winding, one end of the current transformer is connected between the two semiconductor switching elements The other end is connected to the primary winding,
An anode terminal of the first surge suppression diode and a cathode terminal of the second surge suppression diode are connected to a connection point between the current transformer and the primary winding,
The cathode terminal of the first surge suppression diode is connected to the positive side of the input power supply, and the anode terminal of the second surge suppression diode is connected to the negative side of the input power supply. DC-DC converter. The DC-DC converter according to any one of claims 1 to 3 , wherein the rectifier circuit is a rectifier circuit made of a diode. The rectifier circuit is a center tap type rectifier circuit in which a center tap of the secondary winding is one end of an output and a rectifier is connected to both ends of the secondary winding. The DC-DC converter as described in any one of 1-4 . Semiconductor switching elements constituting the semiconductor switching circuit, silicon carbide, DC-DC converter according to claims 1, characterized in that the wide band gap semiconductor with a gallium nitride-based material in any one of 5 .

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