JP2007060849A - Inverter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a through current from flowing under transient state immediately after turn on power. <P>SOLUTION: A class D output stage 2 comprises MOSFETs 4 and 6 connected in half-bridge. A buffer 14 supplies a drive voltage to the gate of the MOSFET 4 and 6. The voltage increases transiently in response to closing of a power switch 20, and a DC power supply circuit 8 supplies that voltage as an operation voltage to the buffer 14. When the voltage increases, a transistor 22 blocks drive voltage supply to the gate of the MOSFET 6 until that voltage reaches a threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a DC-AC converter that converts a direct current into an alternating current.

  An example of the DC-AC converter is a digital amplifier. An example of this digital amplifier is disclosed in Patent Document 1. In the technique of this Patent Document 1, in a digital amplifier having a bridge circuit composed of a plurality of power MOSFETs, when the volume control unit controls the volume level to be small, the dead time of the power MOSFET is reduced and the volume level is controlled to be large. Doing so increases the dead time.

  In general, in a digital amplifier, the high-side power MOSFET and the low-side power MOSFET of the bridge circuit are simultaneously turned on, and a through current flows from the high potential side to the low potential side, possibly destroying the power MOSFET. In order to prevent this, a dead time is provided in order to provide a time difference between rising and falling of the high-side and low-side power MOSFETs. If this dead time is set large, the degree of distortion of the reproduction signal becomes large. Further, when reproducing with high power output, the power MOSFET generates heat and the switching speed of the power MOSFET is slowed down. When the dead time is short, a through current flows. Therefore, in the technique of Patent Document 1, the dead time is shortened in the case of a small volume to prevent the reproduction signal from being distorted, and the dead time is reduced in the case of a large volume (in the case of high power output). This is intended to prevent the power MOSFET from being damaged by the through current.

JP 2004-179945 A

  With the technique of Patent Document 1, it is possible to prevent a through current from flowing by increasing the dead time when the volume is high. In addition to the above cases, for example, in the transient state immediately after the power supply device is turned on, the state of the high-side and low-side power MOSFETs is on, off or indefinite, and the high-side and low-side When both of the power MOSFETs are turned on, a through current flows and the power MOSFET is damaged.

  An object of the present invention is to provide a DC-AC converter that can reliably prevent a through current from flowing even in a transient state immediately after a power supply device is turned on.

  The DC / AC converter according to the invention comprises an output stage. The output stage has at least two power semiconductor elements. The power semiconductor element has a conductive path that is changed to a conductive state when a drive signal is supplied to the control electrode. For example, a power MOSFET, an IGBT (insulated gate bipolar transistor), a power bipolar transistor, or the like can be used. In these power semiconductor elements, the conductive paths are connected to the load so as to form two current supply paths that flow in opposite directions to the load when conducting, and drive signals are alternately supplied to the control electrodes. The drive means supplies the drive signal to the control electrode of each power semiconductor element. The DC voltage supply means changes the voltage transiently from zero to a predetermined value in response to closing of the power switch, and this voltage is supplied as an operating voltage to the output stage and the driving means. The power semiconductor element in which the conductive path exists in at least one of the two current supply paths until the voltage reaches a predetermined threshold value whose absolute value is smaller than the predetermined value from zero when the voltage changes The blocking means blocks the supply of the drive signal to the control electrode.

  With this configuration, since the power semiconductor element existing in the current supply path is surely turned off, it is ensured that the through current flows when the voltage of the DC voltage supply means is transiently changing. Can be prevented.

  The blocking means may include a normally closed switching element connected between a control electrode of the power semiconductor element and a reference potential point. In this case, there is provided control means for opening the normally closed switching element when the value of the voltage reaches a threshold value.

  With this configuration, the normally closed switching element is closed while the voltage of the voltage supply means is in a transient state, and the control electrode of the power semiconductor element is connected to the reference potential point. The state can be maintained and the through current can be reliably prevented from flowing.

  As the normally closed switching element, a first semiconductor element having a first conductive path and a first control electrode can be used. In this case, the first semiconductor element increases the conductivity of the first conductive path according to an increase in the value of the control signal supplied to the first control electrode, and the first conductive path is used as the power semiconductor element. Between the control electrode and the reference potential point. A voltage related to the voltage from the power supply means is supplied to the first control electrode. The control means includes a second conductive path and a second control electrode, and a second semiconductor that increases the conductivity of the conductive path in accordance with an increase in the value of a control signal supplied to the second control electrode. Use the element. A second conductive path is connected between the first control electrode of the first semiconductor element and the reference potential point, and a control signal whose value increases as the voltage value increases is supplied to the second control electrode. Supplied.

  With this configuration, immediately after the voltage of the voltage supply means starts to change from zero, the first and second semiconductor elements are both non-conductive, but eventually the first semiconductor element becomes conductive, Prevents through current from flowing. Then, when the voltage of the DC voltage supply means reaches a threshold value, the second semiconductor element is turned on, the first semiconductor element is turned off, and thereafter the power semiconductor element is turned on and off according to the drive signal. repeat.

  Alternatively, the blocking means may include a normally open switching element interposed between the control electrode of the power semiconductor element and the driving means. In this case, when the voltage value of the DC voltage supply means reaches the second value, the control means closes the normally open switching element.

  With this configuration, since the normally open switching element is open while the voltage of the voltage supply means is in a transient state, the power semiconductor element maintains a non-conductive state and reliably prevents a through current from flowing. be able to.

  In addition, for example, a power MOSFET or IGBT in which the power semiconductor element has an insulated gate insulated from the conductive path as a control electrode, and a drive voltage is supplied as the drive signal can be used.

  The output stage may be a half bridge type having two power semiconductor elements or a full bridge type having four power semiconductor elements.

  As described above, according to the present invention, when the voltage of the DC voltage supply means changes in a transient state, the drive signal to the power semiconductor element is cut off, so that the through current can be reliably prevented from flowing. And damage to the power semiconductor element can be prevented.

  The DC-AC converter according to the first embodiment of the present invention is implemented in a class D digital amplifier, and has an output stage 2 as shown in FIG.

  The output stage 2 is configured, for example, in a half-bridge type, and includes power semiconductor elements, for example, N-channel power MOSFETs (hereinafter referred to as MOSFETs) 4 and 6. These MOSFETs 4 and 6 have a conductive path, for example, a drain-source conductive path, and a control electrode, for example, a gate. This gate is insulated from the drain-source conductive path. The drain-source conductive paths of the MOSFETs 4 and 6 are connected in series. For example, the source of the MOSFET 4 and the drain of the MOSFET 6 are connected, and the drain of the MOSFET 4 is connected to DC voltage supply means, for example, the first positive power supply terminal 8P1 of the DC power supply circuit 8. The source of the MOSFET 6 is connected to the negative power supply terminal 8N of the DC power supply circuit 8. The DC power supply circuit 8 includes two DC power supplies 8a and 8b connected in series, the positive electrode of the DC power supply 8a is connected to the first positive power supply terminal 8P1, and the negative electrode of the DC power supply 8b is connected to the DC power supply circuit 8. It is connected to the negative power supply terminal 8N. The negative electrode of the DC power supply 8 a and the positive electrode of the DC power supply 8 b are connected, and the connection point is connected to the midpoint terminal 8 M of the power supply circuit 8. A connection point between the source of the MOSFET 4 and the drain of the MOSFET 6 is connected to one end of the load 10, and the other end of the load 10 is connected to a midpoint terminal 8M of the DC power supply circuit 8. The load 10 includes, for example, a speaker and an output filter.

  When the MOSFET 4 is conductive and the MOSFET 6 is non-conductive, current flows from the positive power supply terminal 8P through the MOSFET 4 and the load 10 to the midpoint terminal 8M. Conversely, when the MOSFET 4 is non-conductive and the MOSFET 6 is conductive, a current flows from the midpoint terminal 8M to the negative power supply terminal 8N via the load 10 and the MOSFET 6. Thus, the MOSFETs 4 and 6 form a current path through which current flows in different directions with respect to the load 8.

  In order to drive these MOSFETs 4 and 6 to be conductive and non-conductive, the MOSFET 4 is provided with a drive means, for example, a drive unit 11, and the MOSFET 6 is provided with a drive means, for example, a drive unit 11 a. Since the structure of the drive parts 11 and 11a is substantially the same, only the drive part 11 is demonstrated in detail.

  In the drive unit 11, a control signal, for example, a drive voltage is supplied to the gate of the MOSFET 4 through the buffer 14. This drive voltage is, for example, a positive positive voltage with respect to the source of the MOSFET 4. The drive unit 11 includes, for example, an inverter 16 in addition to the buffer 14. The inverter 16 is supplied with a pulse signal that serves as a basis for the buffer 14 to generate a drive voltage from an input stage (not shown). A voltage having a positive predetermined value with respect to its source is also supplied to the MOSFET 6 as a drive voltage by the drive unit 11a. For example, when the MOSFET 4 is conducting, the MOSFET 6 is non-conducting, and when the MOSFET 4 is non-conducting, the driving units 11 and 11a generate two driving voltages so that the MOSFET 6 is conducting, that is, the phases are opposite to each other. As described above, the pulse signal is supplied from the input stage to the drive units 11 and 11a.

  The drive unit 11 has a positive power supply terminal 17P and a negative power supply terminal 17N. The positive power supply terminal 17P is connected to the positive power supply terminal of the buffer 14 and the inverter 16, and the negative power supply terminal 17N is a negative power supply terminal of the buffer 14 and the inverter 16. The negative power supply terminal 17N is also connected to the source of the MOSFET 4. In order to supply a voltage higher than that of the negative power supply terminal 17N to the positive power supply terminal 17P, a power supply electrolytic capacitor 18 is connected between the positive and negative power supply terminals 17P and 17N, and a backflow prevention diode 19 is connected to the positive power supply terminal 17P. The anode of the diode 19 is connected to the positive power supply terminal 8P of the DC power supply circuit 8.

  The positive power supply terminal 8P of the DC power supply circuit 8 is connected to the positive electrode of a DC power supply 8c built in the DC power supply circuit 8. The negative electrode of the DC power supply 8c is connected to the negative power supply terminal 8N of the DC power supply circuit 8. The positive power supply terminal 8P is connected to the positive power supply terminal 20P of the drive unit 11a, and the negative power supply terminal 8N is connected to the drive unit 11a.

  When the MOSFET 6 is conductive and the MOSFET 4 is non-conductive, current flows from the positive power supply terminal 8P to the diode 19, the electrolytic capacitor 18, and the MOSFET 6, and the electrolytic capacitor 18 is charged. When the MOSFET 6 becomes non-conductive, the inverter 16 and the buffer 14 are operated by the current flowing from the positive electrode of the electrolytic capacitor 18 through the inverter 16 and the buffer 14 and returning to the negative electrode of the electrolytic capacitor 18.

  The DC power supply circuit 8 also has a power switch 21. When the power switch 21 is opened, the voltages of the positive power supply terminals 8P and 8P1 with respect to the negative power supply terminal 8N are zero, and the power switch 21 is closed. For example, the voltage of the positive power supply terminal 8P increases transiently to a predetermined value, for example, + Vcc, for example, exponentially as shown by a solid line in FIG.

  Therefore, it is uncertain whether the MOSFETs 4 and 6 are in a conductive state or a non-conductive state until the voltage of the positive power supply terminal 8P is stabilized at + Vcc. If the MOSFETs 4 and 6 become conductive at the same time, a large through current flows through the MOSFETs 4 and 6, and the MOSFETs 4 and 6 may be damaged.

  Therefore, in this embodiment, the drive unit 11 is provided with a blocking means. The blocking means includes normally closed switching means, for example, a first semiconductor element, specifically, an NPN bipolar transistor 22 (hereinafter referred to as transistor 22). An output electrode, for example, a collector of the transistor 22 is connected to the input side of the buffer 14 connected to the gate of the MOSFET 4. The common electrode, for example, the emitter of the transistor 22 is connected to a reference potential point, for example, a negative power supply terminal 17N. The control electrode, for example, the base of the transistor 22 is connected to the positive power supply terminal 17P via the current limiting resistor 24.

  This blocking means also has control means, for example a control circuit 25. The control circuit 25 includes a second semiconductor element, for example, an NPN bipolar transistor 26 (hereinafter referred to as a transistor 26), and an output electrode, for example, a collector, is connected to the base of the transistor 22. A common electrode, for example, an emitter of the transistor 26 is connected to a reference potential point, for example, a negative power supply terminal 17N. The base of the transistor 26 is connected to the energizing circuit 30 via the current limiting resistor 28. The energizing circuit 30 is connected between the positive power supply terminal 17P and the negative power supply terminal 17N. In the energizing circuit 30, a constant voltage element, for example, the cathode of a Zener diode 32 is connected to the positive power supply terminal 17P, the anode is connected to one end of the resistor 34, and the other end of the resistor 34 is connected to the negative power supply terminal 17N. It is connected. A connection point between the anode of the Zener diode 32 and one end of the resistor 34 is connected to the base of the transistor 26 via the current limiting resistor 28.

  In the class D digital amplifier configured as described above, when the power switch 21 is closed, the voltage of the positive power supply terminal 8P with respect to the negative power supply terminal 8N starts to rise as shown in FIG. At this time, if the MOSFET 6 is conductive, the voltage of the positive power supply terminal 17P with respect to the power supply terminal 17N also rises. Along with this, the base-emitter voltage of the transistor 22 also rises. However, during the period t1 in FIG. 2, the base-emitter voltage of the transistor 22 is set to the set voltage V1 necessary for making the transistor 22 conductive. The transistor 22 is not conducting. During the period t1, the base-emitter voltage of the transistor 26 does not increase to a threshold value necessary for making the transistor 26 conductive, and the transistor 26 is also nonconductive.

  When the period t1 is exceeded and the period t2 is entered, the voltage of the positive power supply terminal 8P with respect to the negative power supply terminal 8N increases, and the voltage of the positive power supply terminal 17P with respect to the negative power supply terminal 17N also increases. As a result, the base-emitter voltage of the transistor 22 exceeds the set voltage V1, and the transistor 22 becomes conductive. As a result, the input side of the buffer 14 is connected to the reference potential, the gate voltage of the MOSFET 4 is also close to the reference potential, and the MOSFET 4 maintains a non-conductive state. Therefore, even if the MOSFET 6 is conductive for some reason, no through current flows through the MOSFETs 4 and 6.

  Note that in the period t2, the voltage between the base and the emitter of the transistor 26 does not reach the threshold value Vbe, which is a voltage necessary for making the transistor 26 conductive, and the transistor 26 maintains a non-conductive state.

  In the period t3, due to an increase in the voltage of the positive power supply terminal 8P with respect to the negative power supply terminal 8N, the value becomes close to + Vcc, which is a predetermined value. Etc. to perform stable operation. At this time, as shown in FIG. 2, the voltage of the positive power supply terminal 8P with respect to the negative power supply terminal 17N is equal to the threshold value Vbe which is a base-emitter voltage necessary for conducting the Zener voltage Vzd of the Zener diode 32 and the transistor 26. And the base of the transistor 26. The emitter-to-emitter voltage reaches Vbe and the transistor 26 becomes conductive. As a result, the base-emitter voltage of the transistor 22 decreases, and the transistor 22 becomes non-conductive. Thereafter, the MOSFET 4 repeats conduction and non-conduction in accordance with the drive voltage supplied from the buffer 14. At this time, a voltage close to + Vcc is also supplied to the drive unit 11a, the buffer 14 and the inverter corresponding to the buffer 14 and the inverter 16 operate normally, and the MOSFET 6 normally repeats conduction and non-conduction.

  A class D digital amplifier according to the second embodiment is shown in FIG. In this digital amplifier, the driving stage 2a is of a full bridge type, and has N-channel MOSFETs (hereinafter referred to as MOSFETs) 4a, 4b, 6a and 6b similar to those of the digital amplifier of the first embodiment. . The drain-source conductive paths of the high-side MOSFET 4a and the low-side MOSFET 6a are connected in series. Similarly, the drain-source conductive paths of the high-side MOSFET 4b and the low-side MOSFET 6b are connected in series, and these series circuits are connected in parallel. The DC power supply circuit 8 is connected between a positive power supply terminal 8P1 and a negative power supply terminal 8N. A load 10 is connected between the connection point of the conductive paths of the MOSFETs 4a and 6a and the connection point of the MOSFETs 4b and 6b. The configuration of the load 10 is the same as that of the first embodiment.

  A driving voltage is supplied to the gates of the MOSFETs 4a, 4b, 6a and 6b from the corresponding driving units 110a, 110b, 110c and 110d. These drive voltages are applied when the MOSFETs 4a and 6b located on one diagonal are turned on, and the MOSFETs 4b and 6b located on the other diagonal are turned off. The MOSFETs 4b and 6a are supplied so as to be conductive.

  Similarly to the first embodiment, the driving units 110a and 110b are supplied with operating voltages from the positive power supply terminal 8P and the negative power supply terminal 8N of the power supply circuit 8 via the electrolytic capacitors 18a and 18b and the backflow prevention diodes 19a and 19b. Is supplied. Operating voltages are directly supplied to the driving units 110c and 100d from the positive power supply terminal 8P and the negative power supply terminal 8N of the power supply circuit 8.

  Of these MOSFETs 4a, 4b, 6a, 6b, blocking means are provided in the drive units 110a, 110b of the high-side MOSFETs 4a, 6b. These blocking means have normally closed switching elements 22a and 22b. These normally closed switching elements 22a and 22b are configured in the same manner as the transistor 22 and its attached circuit of the first embodiment, and the input side of the buffer corresponding to the buffer 14 included in the drive units 110a and 110b is used as a reference potential point. Connect or release. The power terminals of the normally closed switching elements 22a and 22b are connected to both ends of the electrolytic capacitors 18a and 18b, and an operating voltage is supplied to these from the electrolytic capacitors 18a and 18b. Control circuits 25a and 25b are provided to control the switching elements 22a and 22b. These control circuits 25a and 25b correspond to the control circuit 25 of the first embodiment. These control circuits 25a and 25b are also supplied with operating voltage from both ends of the electrolytic capacitors 18a and 18b.

  Also in this class D digital amplifier, the normally closed switching elements 22a and 22b are in a non-conductive state for a certain period t1 after the power switch of the DC power supply circuit 8 is closed, but during the period t2, The conduction state is maintained, and the through current is prevented from flowing between the MOSFETs 4a and 6a, 4b and 6b. Then, when entering the period t3, the normally closed switching elements 22a and 22b are opened, and the MOSFETs 4a, 4b, The conduction and non-conduction of 6a and 6b are controlled.

  In the first and second embodiments, the normally closed switching elements 22, 22a, and 22b are used. For example, in the first embodiment, between the gate of the MOSFET 6 and the buffer 14, a normally open switching element, For example, an SSR or a relay contact may be installed so that the normally closed switching element is opened and then closed until the voltage of the positive power supply terminal 8P with respect to the negative power supply terminal 8N exceeds a preset value. it can. Similarly in the second embodiment, a normally open switching element can be used.

  Although the transistor 22 is provided on the input side of the buffer 14 in the first embodiment, it can be provided on the gate side of the MOSFET 4. The same applies to the second embodiment.

  In the above two embodiments, the blocking means is provided in the high-side drive unit. However, the MOSFETs 4 and 6 are driven by the drive unit 210 such as the class D digital amplifier of the third embodiment shown in FIG. When the is driven, the blocking means can be provided on the low side. That is, the driving unit 210 includes buffers 212 and 214 that generate driving voltages for driving the MOSFETs 4 and 6, and these include pulses having phases opposite to each other from the two secondary windings 218 and 220 included in the pulse transformer 216. A signal is supplied. A pulse signal is supplied from the pulse amplifier 224 to the primary winding 222. A normally closed switching element 226 similar to the normally closed switching elements 22a and 22b is provided on the input side of the pulse amplifier 224, and a control circuit 228 corresponding to the control circuits 25a and 25b for controlling the normally closed switching element 226 is provided. It is done. The normally closed switching element 226, the control circuit 228, and the pulse amplifier 224 are supplied with operating voltages from the positive power supply terminal 8P and the negative power supply terminal 8N of the DC power supply circuit 8.

  In each of the above embodiments, the present invention is implemented in the class D digital amplifier. However, the present invention is not limited to this. For example, the present invention can also be implemented in a device that converts direct current into alternating current, such as an inverter.

1 is a block diagram of a class D digital amplifier according to a first embodiment of the present invention. It is operation | movement explanatory drawing of the class D digital amplifier of FIG. It is a block diagram of the class D digital amplifier of the 2nd Embodiment of this invention. It is a block diagram of the class D digital amplifier of the 3rd Embodiment of this invention.

Explanation of symbols

2 2a Output stage 4 4a 4b 6 6a 6b MOSFET (power semiconductor device)
8 DC power supply circuit (DC voltage supply means)
10 Load 22 Transistor (Normally closed switching element)
25 Control circuit (control means)

Claims (7)

The power semiconductor element has at least two power semiconductor elements that are changed to a conductive state when a drive signal is supplied to the control electrode, and these power semiconductor elements have two current supply paths that flow in opposite directions to the load when conductive. An output stage in which each of the conductive paths is connected to the load to form and a drive signal is alternately supplied to the control electrode;
Drive means for supplying the drive signal to a control electrode of each power semiconductor element;
In response to closing of the power switch, the voltage changes transiently to a predetermined value, and a DC voltage supply means for supplying this voltage as an operating voltage to the driving means;
When the voltage changes, the control of the power semiconductor element in which the conductive path exists in at least one of the two current supply paths until the voltage reaches a predetermined threshold value that is smaller than the predetermined value and reaches a predetermined threshold value. Blocking means for blocking the supply of the drive signal to the electrode;
DC-AC converter provided.   2. The DC-AC converter according to claim 1, wherein the blocking means includes a normally closed switching element connected between a control electrode of the power semiconductor element and a reference potential point for the control electrode, and a value of the voltage. And a control means for opening the normally closed switching element when the threshold value reaches a threshold value.   3. The DC-AC converter according to claim 2, wherein the normally closed switching element includes a first conductive path and a first control electrode, and the first conductive path is connected to the control electrode of the power semiconductor element and the reference potential. A first semiconductor element connected to a point and increasing the conductivity of the first conductive path according to an increase in the value of a control signal supplied to the first control electrode, A voltage related to the voltage from the DC voltage supply means is supplied, the control means has a second conductive path and a second control electrode, and the second conductive path is a first control of the first semiconductor element. A second semiconductor element connected between an electrode and the reference potential point and increasing the conductivity of the second conductive path in accordance with an increase in a value of a control signal supplied to the second control electrode, A control signal whose value increases in response to an increase in the voltage value is supplied to the second control electrode. DC - AC converter.   2. The DC-AC converter according to claim 1, wherein the blocking means includes a normally open switching element interposed between a control electrode of the power semiconductor element and the driving means, and a value of the voltage reaches a threshold value. A DC-AC converter comprising control means for closing the normally open switching element.   2. The DC-AC converter according to claim 1, wherein the power semiconductor element has an insulated gate insulated from the conductive path as a control electrode, and a driving voltage is supplied as the driving signal.   The DC-AC converter according to claim 1, wherein the output stage is a half-bridge type having two power semiconductor elements. 2. The DC-AC converter according to claim 1, wherein the output stage is a full-bridge type having the four power semiconductor elements.

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