Rectifier circuit, and semiconductor device and power supply device using same

Abstract

Disclosed is a rectifier circuit in which the number of synchronous rectification semiconductor switching elements to be turned on can be set without using a current detection unit from among the plurality of synchronous rectification semiconductor switching elements which are to be turned on and connected in parallel. This rectifier circuit comprises: a plurality of semiconductor switching elements (Q1 to Q3) that flow currents between an anode (A) and a cathode (K) in one direction by synchronous rectification and are connected in parallel to each other between the anode and the cathode; a plurality of drive circuits (GD1 to GD3) that drive the plurality of semiconductor switching elements; and a control unit (COM) that creates a control command signal for each of the plurality of drive circuits on the basis of the inter-main-terminal voltage of each of the plurality of semiconductor switching elements. The control unit sets the number of semiconductor switching elements to be turned on from among the plurality of semiconductor switching elements on the basis of the inter-main-terminal voltage in a synchronous rectification period and generates ON control command signals for the set number of drive circuits.

Description

Rectifier circuit, and semiconductor device and power supply device using the same

[0001] The present invention relates to a rectifier circuit, and a semiconductor device and a power supply device that use the rectifier circuit.

[0002] Diode rectifier circuits and synchronous rectifier circuits using MOSFETs are used as rectifier circuits in power supply devices to convert AC to DC. Synchronous rectifier circuits have low power loss because MOSFETs do not have a built-in potential like diodes and forward current rises from 0 V. Therefore, synchronous rectifier circuits are used in power supply devices that require low loss, such as front-end power supplies.

[0003] As conventional techniques relating to synchronous rectification circuits, techniques described in Patent Documents 1 and 2 are known.

[0004] In the technology described in Patent Document 1, a control circuit and a MOSFET are mounted in a single package as a low-loss rectifier circuit for use in an alternator. This rectifier circuit operates as a two-terminal semiconductor device that has the function of passing current in one direction (rectification function), like a diode.

[0005] The rectifier circuit according to the technology described in Patent Document 1 is composed of a control circuit having a comparator and a gate driver, a capacitor that supplies power to the control circuit, and a MOSFET. The control circuit turns the MOSFET on and off using the gate driver in response to the drain-source voltage of the MOSFET detected by the comparator. When the MOSFET is off, the capacitor is charged by the drain-source voltage of the MOSFET.

[0006] In the technology described in Patent Document 2, multiple synchronous rectification MOSFETs are connected in parallel, and the number of MOSFETs that are turned on is set according to the magnitude of the load current, i.e., the rectified current, so as to reduce the total power loss.

[0007] JP 2015-116053 A JP 2010-213366 A

[0008] When the control technology described in Patent Document 2 is applied to the rectifier circuit described in Patent Document 1, it is necessary to newly add a current detection unit for detecting the rectified current, i.e., a current detection shunt resistor, a current detection transformer, etc., which hinders the miniaturization and cost reduction of the rectifier circuit. Therefore, the present invention provides a rectifier circuit, and a semiconductor device and power supply device using the same, which can set the number of semiconductor switching elements to be turned on without adding a current detection unit.

[0009] In order to solve the above problems, a rectifier circuit according to the present invention uses synchronous rectification to cause a current to flow in one direction between an anode and a cathode, and includes a plurality of semiconductor switching elements connected in parallel between the anode and the cathode, a plurality of drive circuits that drive the plurality of semiconductor switching elements, and a control unit that generates a control command signal to each of the plurality of drive circuits based on the voltage between the main terminals of the plurality of semiconductor switching elements, and the control unit sets the number of semiconductor switching elements to be turned on based on the voltage between the main terminals during the synchronous rectification period, and generates an on control command signal to the set number of drive circuits.

[0010] In order to solve the above problems, a semiconductor device according to the present invention includes a rectifier circuit and a semiconductor package incorporating the rectifier circuit, the rectifier circuit being the rectifier circuit according to the present invention.

[0011] In order to solve the above problem, a semiconductor device according to the present invention comprises a bridge rectifier circuit composed of a plurality of rectifier circuits, and a semiconductor package incorporating the bridge rectifier circuit, each of the plurality of rectifier circuits being the rectifier circuit according to the present invention.

[0012] In order to achieve the above object, a power supply device according to the present invention has a rectifier circuit section, and the rectifier circuit section is the rectifier circuit according to the present invention.

[0013] According to the present invention, the number of semiconductor switching elements to be turned on can be set without adding a current detection unit.

[0014] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0015] 1 is a circuit diagram showing the configuration of a rectifier circuit according to a first embodiment; FIG. 2 is a circuit diagram showing the configuration of a comparison unit in the first embodiment; FIG. 3 is a schematic circuit diagram showing an example of the configuration of holding circuits H1, H2 (FIG. 2); FIG. 4 is a current and voltage waveform diagram showing an example of the operation of the rectifier circuit according to the first embodiment; FIG. 5 is a circuit diagram showing the configuration of a rectifier circuit according to a second embodiment; FIG. 6 is a current and voltage waveform diagram similar to FIG. 4 showing an example of the operation of the rectifier circuit according to the second embodiment; FIG. 7 is a circuit diagram showing the configuration of a semiconductor device according to a third embodiment; and FIG. 8 is a circuit diagram showing the configuration of a power supply device according to a fourth embodiment.

[0016] Hereinafter, embodiments of the present invention will be described with reference to the following Examples 1 to 4 with reference to the drawings.

[0017] In each figure, the same reference numerals indicate the same components or components with similar functions.

[0018] FIG. 1 is a circuit diagram showing the configuration of a rectifier circuit according to a first embodiment of the present invention.

[0019] Symbols indicating current and voltage in the figure (the accompanying arrows indicate the direction), Is, Vdsi (i=1, 2, 3: the same applies below), Vgsi, and Vc respectively represent the rectified current, the voltage between the main terminals of MOSFET Qi, i.e., the drain-source voltage, the gate-source voltage of Qi, and the charging voltage of capacitor C0. These symbols will be used appropriately in the following explanation.

[0020] In the rectifier circuit of Example 1, multiple (three in FIG. 1 ) MOSFETs Q1 to Q3 are connected in parallel between an anode (A) and a cathode (K) as semiconductor switching elements for synchronous rectification. The drains and sources of Q1 to Q3 are connected to the cathode (K) and the anode (A), respectively. Q1 to Q3 are driven on and off by drive circuits GD1 to GD3, respectively. Q1 to Q3 are driven on during the rectification period (rectification current Is≧0), i.e., when the AC voltage applied between the anode (A) and the cathode (K) is in the forward direction.

[0021] In the first embodiment, enhancement type n-channel MOSFETs are used as Q1 to Q3.

[0022] Diodes D1 to D3 are connected in antiparallel to the MOSFETs Q1 to Q3, respectively. In the first embodiment, D1 to D3 are body diodes built into each MOSFET. Note that D1 to D3 may also be externally connected individual diodes.

[0023] The comparison unit COM is a control unit that generates ON / OFF control command signals to GD1 to GD3.

[0024] As will be described later, the comparison unit COM sets the number of MOSFETs Q1 to Q3 to turn on based on the anode (A)-cathode (K) voltage, i.e., the drain-source voltage Vds of the MOSFETs connected in parallel, and generates on / off control command signals to GD1 to GD3 according to the set number. GD1 to GD3 turn Q1 to Q3 on and off, respectively, according to the on / off control command signals from COM.

[0025] Capacitor C0 serves as the power source for GD1 to GD3 and COM. One end of C0 is connected to the anode (A). The other end of C0 is connected to the cathode (K) via a backflow prevention diode DR1. As a result, during the non-rectification period (rectification current Is = 0), that is, when the AC voltage applied between the anode (A) and cathode (K) is in the reverse direction, C0 is charged by the voltage applied between the anode (A) and cathode (K). The charged C0 serves as the power source for GD1 to GD3 and COM. In other words, the rectifier circuit of Example 1 provides its own power source.

[0026] Here, the operation of the comparison unit COM will be further explained.

[0027] The comparison circuit COM outputs a rectified current I from the anode (A) to the cathode (K). Ｓ During the rectification period during which V flows, an ON control command signal is generated based on Vds to turn on n (=1 to 3) number of MOSFETs so that the total power loss P of Q1, Q2, and Q3 can be reduced.

[0028] If the drain-source voltage of the MOSFETs connected in parallel is Vds, the total power loss P of n MOSFETs that are turned on can be roughly expressed by the following equation (1): P=n·P ｄ +a·(n·Vds ２ ) / R ＯＮ … (1) P ｄ is the driving loss per MOSFET, R ＯＮ is the on-resistance per MOSFET, and a is a coefficient based on the voltage waveform.

[0029] As shown in equation (1), when Vds is small, P ｄ becomes dominant, so reducing the number of MOSFETs that are turned on reduces P. When Vds becomes large, the second term of equation (1) becomes dominant, so increasing the number of MOSFETs that are turned on reduces P. Therefore, in the first embodiment, the magnitude of Vds is determined during the synchronous rectification period, and a number n (=1 to 3) of MOSFETs that can reduce P is turned on according to the determined Vds. This reduces the power loss of the rectifier circuit.

[0030] In the first embodiment, when n=1, the comparison unit COM generates an ON control command to GD1 to turn on Q1. When n=2, the comparison unit COM generates an ON control command to GD1 and GD2 to turn on Q1 and Q2. When n=3, the comparison unit COM generates an ON control command to GD1, GD2, and GD3 to turn on Q1, Q2, and Q3.

[0031] The comparison unit COM generates an OFF control command signal to the drive circuit of the MOSFET to be turned OFF in order to turn OFF the MOSFETs other than the MOSFET to be turned ON.

[0032] The comparison unit COM determines whether to set n to 2 based on Vds during the rectification period when n=1, i.e., when Q1 is on and Q2 and Q3 are off, and generates an ON control command signal to GD2 if it determines that n=2. Also, the comparison unit COM determines whether to set n to 1 based on Vds during the rectification period when n=2, i.e., when Q1 and Q2 are on and Q3 is off, and generates an OFF control command signal to GD2 if it determines that n=1.

[0033] During the rectification period when n=2, i.e., when Q1 and Q2 are on and Q3 is off, the comparison unit COM determines based on Vds whether P can be reduced more effectively with n=3 than with n=2, and if it determines that P can be reduced, it generates an ON control command signal to GD3. Also, during the rectification period when n=3, i.e., when Q1, Q2, and Q3 are on, the comparison unit COM determines based on Vds whether P can be reduced more effectively with n=2 than with n=3, and if it determines that P can be reduced, it generates an OFF control command signal to GD3.

[0034] In this way, the comparison unit COM switches the number n of MOSFETs to be turned on between 1 and 2, and between 2 and 3, based on Vds during the rectification period so as to reduce the total power loss P. The comparison unit COM determines whether to switch the number n of MOSFETs to be turned on by comparing Vds during the rectification period with a preset threshold voltage.

[0035] FIG. 2 is a circuit diagram showing the configuration of the comparison unit COM in the first embodiment (FIG. 1).

[0036] The forward direction of the MOSFETs Q1 to Q3 is defined as the positive direction of the voltage. Therefore, Vds≦0 during the rectification period.

[0037] The comparison unit COM includes comparison circuits CO1 to CO5, decision circuits JC1 and JC2, and holding circuits H1 and H2. Each circuit uses a charged capacitor C0 (FIG. 1) as a power source.

[0038] The anode (A)-cathode (K) voltage, i.e., Vds, is input to the comparator circuits CO1 to CO5. The threshold voltages (<0) compared with Vds in the comparator circuits CO1, CO2, CO3, CO4, and CO5 are set by reference voltage sources Vtha, Vthb, Vthc, Vthd, and Vthe, respectively. The comparator circuits CO1 to CO5 compare Vds with the threshold voltages, and output either a high-level (H) voltage signal (hereinafter referred to as "voltage signal H") or a low-level (L) voltage signal (hereinafter referred to as "voltage signal L") depending on the comparison result. In the first embodiment, the voltage value of the voltage signal H is the power supply voltage value of the capacitor C0 (FIG. 1), and the voltage value of the voltage signal L is zero volts.

[0039] Each reference voltage source is generated by a capacitor CO (FIG. 1) and a voltage dividing resistor or a Zener diode.

[0040] In the following description, unless otherwise specified, Vds indicates the drain-source voltage during the rectification period, and Vds ≦ 0. Therefore, the value of the threshold voltage (Vth1 described later) compared with Vds is also a negative value.

[0041] CO1 to CO3 compare the A-K voltage, i.e., Vds, with a threshold voltage Vth1, and output a voltage signal H if they determine that Vds is equal to or less than Vth1 (Vds≦Vth1, |Vds|≧|Vth1|). CO1 to CO3 also compare Vds with a threshold voltage Vth2, and output a voltage signal L (zero volts) if they determine that Vds is equal to or greater than Vth2 (Vds≧Vth2, |Vds|≦|Vth2|). That is, the reference voltage sources Vtha, Vthb, and Vthc correspond to the two threshold voltages Vth1 and Vth2, respectively.

[0042] As a result, CO1 to CO3 output a voltage signal H during the rectification period, and output a voltage signal L outside the rectification period. In other words, CO1 to CO3 determine whether the current time is within the rectification period.

[0043] In CO1 to CO3, Vth1 is the threshold voltage when each of the MOSFETs Q1 to Q3 is off, and Vth2 is the threshold voltage when each of the MOSFETs Q1 to Q3 is on. That is, the threshold voltages of CO1 to CO3 have hysteresis. For example, CO1 to CO3 are configured as hysteresis comparators.

[0044] The threshold voltages Vth1 and Vth2 may be the same value, or may be two different values ​​that satisfy Vth1<Vth2. In the latter case, chattering, which occurs when Q1 is repeatedly turned on and off in a short period of time, can be suppressed.

[0045] CO1 outputs voltage signals H and L to drive circuit GD1 as an ON control command signal and an OFF control command signal, respectively. As a result, Q1 is turned on at the start of a rectification period, maintained in the ON state during the rectification period, and turned off at the end of the rectification period. That is, Q1 is turned on during each rectification period. Therefore, in Example 1, the number n of MOSFETs turned on during a rectification period is at least one.

[0046] CO4 determines whether the number n of MOSFETs to be turned on is switched from 1 to 2 and from 2 to 1 using threshold voltages Vthd1 and Vthd2 for determining switching, respectively.

[0047] When only Q1 is on among Q1 to Q3, CO4 compares the voltage between A and K, i.e., Vds, with the threshold voltage Vthd1, and if it determines that Vds is equal to or less than Vthd1 (Vds≦Vthd1, |Vds|≧|Vthd1|), it outputs a voltage signal H. This causes CO4 to determine whether n should be switched from 1 to 2. Based on this voltage signal H, Q2 is turned on, thereby switching n from 1 to 2.

[0048] CO4 outputs a voltage signal L when it determines that Vds is greater than Vthd1 (Vds>Vthd1, |Vds|<|Vthd1|).

[0049] Furthermore, when Q1 and Q2 of Q1 to Q3 are on and Q3 is off, CO4 compares the voltage between A and K, i.e., Vds, with the threshold voltage Vthd2, and if it determines that Vds is equal to or greater than Vthd2 (Vds≧Vthd2, |Vds|≦|Vthd2|), it outputs a voltage signal L. This causes CO4 to determine whether n should be switched from 2 to 1. Based on this voltage signal L, Q2 is turned off, thereby switching n from 2 to 1.

[0050] CO4 outputs a voltage signal H when it determines that Vds is smaller than Vthd2 (Vds<Vthd2, |Vds|>|Vthd2|).

[0051] CO5 determines whether the number n of MOSFETs to be turned on is switched from 2 to 3 and from 3 to 2 using threshold voltages Vthe1 and Vthe2 for determining switching, respectively.

[0052] When Q1 and Q2 of Q1 to Q3 are on and Q3 is off, CO5 compares the voltage between A and K, i.e., Vds, with the threshold voltage Vthe1, and if it determines that Vds is equal to or less than Vthe1 (Vds≦Vthe1, |Vds|≧|Vthe1|), it outputs a voltage signal H. This causes CO5 to determine whether n should be switched from 2 to 3. Based on this voltage signal H, Q3 is turned on, thereby switching n from 2 to 3.

[0053] CO5 outputs a voltage signal L when it determines that Vds is greater than Vthe1 (Vds>Vthe1, |Vds|<|Vthe1|).

[0054] Furthermore, when Q1 to Q3 are on, CO5 compares the voltage between A and K, i.e., Vds, with the threshold voltage Vthe2, and if it determines that Vds is equal to or greater than Vthe2 (Vds≧Vthe2, |Vds|≦|Vthe2|), it outputs a voltage signal L. This causes CO5 to determine whether n should be switched from 3 to 2. Based on this voltage signal L, Q3 is turned off, thereby switching n from 3 to 2.

[0055] CO5 outputs a voltage signal H when it determines that Vds is smaller than Vthe2 (Vds<Vthe2, |Vds|>|Vthe2|).

[0056] Outside the rectification period, Vds≧0, so Vds is greater than each of the threshold voltages (Vthd1, Vthd2, Vthe1, Vthe2<0) described above, and therefore CO4 and CO5 both output a voltage signal L. As a result, Q2 and Q3 are in the OFF state. Therefore, outside the rectification period, all of the MOSFETs Q1 to Q3 are OFF.

[0057] CO4 and CO5 are configured, for example, by hysteresis comparators, similar to CO1 to CO3.

[0058] In the first embodiment, the determination results output by CO4 and CO5 as described above are reflected in the rectification period following the rectification period in which CO4 output this voltage signal. That is, when CO4 and CO5 determine that the number of MOSFETs to be turned on should be changed, the number is changed in the rectification period following the determined rectification period. For this reason, the comparison unit COM includes holding circuits H1 and H2.

[0059] The holding circuit H1 holds the determination result of CO4 as described above, i.e., the voltage signal H or voltage signal L output by CO4. The holding circuit H1 outputs the held voltage signal to the determination circuit JC1 in the rectification period following the rectification period in which CO4 output this voltage signal.

[0060] The holding circuit H2 holds the determination result of CO5 as described above, i.e., the voltage signal H or voltage signal L output by CO5. The holding circuit H2 outputs the held voltage signal to the determination circuit JC2 in the rectification period following the rectification period in which CO5 output this voltage signal.

[0061] When the determination circuit JC1 receives the voltage signal H from the holding circuit H1 and also receives the voltage signal H from CO2, which determines that the current time is within the rectification period, it outputs a voltage signal H. The output voltage signal H is input to the drive circuit GD2 as an ON control command signal. GD2 turns on Q2 in response to the input ON control command signal.

[0062] When the determination circuit JC1 receives a voltage signal L from at least one of the holding circuits H1 and CO2, it outputs a voltage signal L. The output voltage signal L is input to the drive circuit GD2 as an OFF control command signal. The drive circuit GD2 turns off Q2 in response to the input ON control command signal.

[0063] When the determination circuit JC2 receives the voltage signal H from the holding circuit H2 and also receives the voltage signal H from CO3, which determines that the current time is within the rectification period, it outputs a voltage signal H. The output voltage signal H is input to the drive circuit GD3 as an ON control command signal. GD3 turns on Q3 in response to the input ON control command signal.

[0064] When the determination circuit JC2 receives a voltage signal L from at least one of the holding circuits H2 and CO3, it outputs the voltage signal L. The output voltage signal L is input to the drive circuit GD3 as an OFF control command signal. The drive circuit GD3 turns off Q3 in response to the input ON control command signal.

[0065] The decision circuits JC1 and JC2 are configured, for example, by logical product (AND) gate circuits.

[0066] The determination circuits JC1 and JC2 can reliably generate on / off control command signals in accordance with the determination results of CO4 and CO5 during synchronous rectification in the rectification period, thereby reliably setting n based on Vds.

[0067] Instead of CO2 and CO3, it may be possible to determine whether or not it is the synchronous rectification period by detecting whether or not an on-gate current flows through the gate of Q1, and input the determination result to JC1 and JC2.

[0068] FIG. 3 is a schematic circuit diagram showing an example of the configuration of the holding circuits H1 and H2 (FIG. 2).

[0069] The holding circuit in the first embodiment holds the determination result of the comparison circuit by charging and discharging the capacitor.

[0070] The holding circuits (H1, H2) include a capacitor C1 that holds the voltage signal output by the comparison circuits (CO4, CO5), and a switch SW1 that turns on when the voltage signal held in the capacitor C1 is output to the judgment circuits (JC1, JC2).

[0071] One end of capacitor C1 is connected to the output of the comparison circuit (CO4, CO5) via a reverse current prevention diode DI. The anode and cathode of reverse current prevention diode DI are connected to the output of the comparison circuit (CO4, CO5) and one end of capacitor C1, respectively. The other end of capacitor C1 is connected to the anode (A) of the rectifier circuit (FIG. 1). One end of capacitor C1 is connected to the input of the determination circuit (JC1, JC2) via switch SW1.

[0072] In the first embodiment, the switch SW1 is configured by a semiconductor switching element, for example, a MOSFET. The switch SW1 is driven to turn on and off by a drive signal S1 from a drive circuit D. The drive circuit D generates the drive signal S1 in response to the command signal S. The drive circuit D uses a charged capacitor C0 (FIG. 1) as a power source.

[0073] When the drive circuit D receives the voltage signal H output from the comparison circuits (CO4, CO5) as the command signal S, it generates an OFF drive signal as S1 to turn off SW1. At this time, the voltage signal H is held in the capacitor C1. The voltage signal H is not input to the judgment circuits (JC1, JC2).

[0074] When the drive circuit D receives as a command signal S a voltage signal L output by any of CO1 to CO3 that is outputting a voltage signal H, it generates an ON drive signal as S1 to turn on SW1. As a result, the voltage signal H held in the capacitor C1 is input to the determination circuits (JC1, JC2) in the rectification period following the rectification period in which the voltage signal H was held in the capacitor C1.

[0075] FIG. 4 is a current and voltage waveform diagram showing an example of the operation of the rectifier circuit of the first embodiment.

[0076] In the operation example of FIG. 4, the number n of MOSFETs that are turned on is switched from three to two.

[0077] A sinusoidal AC voltage is input to a series circuit consisting of a rectifier circuit (Figure 1) and a resistive load.

[0078] 4, from the top to the bottom, the waveforms show the rectified current Is, the anode (A)-cathode (K) voltage of the rectifier circuit, i.e., the drain-source voltage Vds of the parallel-connected MOSFETs Q1 to Q3 (the forward direction of Q1 to Q2 is positive), the voltage Vc of the capacitor C0, and the gate-source voltages Vgs1 to Vgs3 of Q1 to Q3. Vgsth1 to Vgsth3 represent the gate threshold voltages of Q1 to Q3, respectively.

[0079] Vdsp indicates the peak value of the AC voltage. Because C0 is charged by a half-sine wave voltage during the non-rectification period, the maximum value of Vc is Vdsp. Note that Vc gradually decreases as it is discharged, but as shown in FIG. 4, a voltage value greater than Vgsth1 to Vgsth3 is maintained while the rectifier circuit is operating.

[0080] In the example operation shown in FIG. 4 , during the period from time t2a when the rectified current Is completes its commutation from diodes D1 to D3 to the on-resistance paths of MOSFETs Q1 to Q3 (i.e., when diode rectification transitions to synchronous rectification) to time t3 when Is becomes 0, Vds resulting from the on-resistances (Ron) of Q1 to Q3 and the rectified current Is is compared with the aforementioned threshold voltage Vthe2. As described above, Vthe2 is a voltage threshold for determining whether to switch from n=3 to n=2. As shown in FIG. 4 , because Vds≧Vthe2 during the synchronous rectification period (t2a to t3), n is switched to 2 during the next rectification period (t4 to t5).

[0081] As described above, according to the first embodiment, n is set based on Vds, so that n can be set so as to reduce the total power loss P without providing a current detection unit.

[0082] In the first embodiment, the result of the comparison is reflected in the setting of n in the rectification period following the determined rectification period, but this is not limiting and n may be switched in the determined rectification period. In this case, the holding circuits H1 and H2 (FIG. 2) can be omitted.

[0083] The second embodiment of the present invention will be described below, focusing mainly on the differences from the first embodiment.

[0084] FIG. 5 is a circuit diagram showing the configuration of a rectifier circuit according to a second embodiment of the present invention.

[0085] In the second embodiment, the anode of the reverse current prevention diode DR1 is connected to the cathode (K) of the rectifier circuit via a semiconductor switch, MOSFET QR1, whose source and drain are connected to the anode of DR1 and the cathode (K) of the rectifier circuit, respectively.

[0086] FIG. 6 is a current and voltage waveform diagram similar to FIG. 4, showing an example of the operation of the rectifier circuit of the second embodiment.

[0087] Capacitor CO is charged to the target voltage Vcref. At this time, the current flowing from the cathode K of the rectifier circuit to capacitor CO is limited by controlling the on / off of QR1 so that the voltage Vc of CO does not exceed Vcref.

[0088] According to the second embodiment, the rated voltages of the comparator COM, the drive circuits GD1 to GD3, and the capacitor C0 can be made lower than the rated voltage of the rectifier circuit, which makes it easier to increase the voltage of the rectifier circuit because the rated voltage of the rectifier circuit is no longer limited by the rated voltages of the comparator COM, the drive circuits GD1 to GD3, and the capacitor C0.

[0089] FIG. 7 is a circuit diagram showing the configuration of a semiconductor device according to a third embodiment of the present invention.

[0090] 7, in the third embodiment, four rectifier circuits 1 are built into a semiconductor package 2 as semiconductor circuits. The rectifier circuit of the second embodiment (FIG. 5) is applied as the rectifier circuits 1. The four rectifier circuits 1 form a single-phase bridge rectifier circuit.

[0091] In the semiconductor package 2, each rectifier circuit 1 is resin-sealed using molded resin or a resin case, and a pair of AC terminals T2, T3 and a pair of DC terminals T1, T4 of the single-phase bridge rectifier circuit are exposed on the outer surface of the resin that seals the four rectifier circuits 1.

[0092] According to the third embodiment, the synchronous rectifier circuit can be easily applied to a single-phase bridge rectifier circuit as a substitute for a rectifier diode, thereby reducing loss in the single-phase bridge rectifier circuit and in electric / electronic devices equipped with the single-phase bridge rectifier circuit.

[0093] The semiconductor device of Example 3 can be compatible with a packaged diode bridge by aligning the arrangement of the AC terminals T2 and T3 and the DC terminals T1 and T4 in the semiconductor package 2 with that of the packaged diode bridge. Furthermore, while using synchronous rectification, the semiconductor device of Example 3 operates as a four-terminal rectifier element similar to a single-phase diode bridge. This reduces the number of steps required for designing and mounting an electric / electronic device that includes a full-wave rectifier circuit.

[0094] The rectifier circuit of Example 1 may be applied as the rectifier circuit 1. Furthermore, a three-phase bridge rectifier circuit can be configured using six rectifier circuits of any of Examples 1 and 2. In this case, three AC terminals for three phases and a pair of DC terminals are exposed on the outer surface of the resin that seals the six rectifier circuits.

[0095] FIG. 8 is a circuit diagram showing the configuration of a power supply device according to a fourth embodiment of the present invention.

[0096] The power supply device of FIG. 8 converts AC power from a commercial AC power source into DC power of a desired voltage and outputs it.

[0097] 8, among the rectifier elements indicated by the circuit symbol of a diode, the rectifier circuit of any one of Examples 1 and 2 or the semiconductor device of Example 3 is applied to at least one of the rectifier elements CRD1 to CRD4 constituting a bridge rectifier circuit that rectifies the AC voltage of a commercial AC voltage, the rectifier element FWD for reflux in the chopper circuit unit, the rectifier elements SSD1 and SSD2 constituting a rectifier circuit unit that receives AC output power from the inverter circuit unit via a transformer and converts it into a DC voltage of a desired voltage, and the rectifier element BPD for backflow prevention. Note that the single-phase bridge rectifier circuit of Example 3 may be used for the rectifier elements CRD1 to CRD4.

[0098] In Fig. 8, the rectifying elements connected in parallel to the MOSFETs are parasitic diodes (body diodes) of the MOSFETs. If all the rectifying elements in Fig. 8 are diodes, the circuit configuration of the power supply device in Fig. 8 is a known circuit configuration.

[0099] According to the fourth embodiment, it is possible to reduce the power loss of the power supply device. The power supply device according to the fourth embodiment is suitable for a front-end power supply that requires high efficiency.

[0100] The rectifier circuits of the first and second embodiments and the semiconductor device of the third embodiment are not limited to front-end power supplies, but can be applied to various power supply devices that include a rectifier circuit section.

[0101] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments have been described in detail to facilitate understanding of the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to delete part of the configuration of each embodiment, add other configurations, or replace other configurations with other configurations.

[0102] For example, the MOSFET is not limited to an n-channel type, but may be a p-channel type. Furthermore, the MOSFET is not limited to an enhancement type, but may be a depletion type. Instead of a MOSFET, other unipolar semiconductor switching elements (such as a junction FET or a static induction transistor) may be applied. The semiconductor material constituting the semiconductor switching element is not limited to silicon (Si), but may be a wide-bandgap semiconductor such as silicon carbide (SiC).

[0103] The comparison unit COM may also be configured by software using a control device such as a microcomputer.

[0104] 1: Rectifier circuit, 2: Semiconductor package, T1, T4: DC terminals, T2, T3: AC terminals

Claims

1. A rectifier circuit which uses synchronous rectification to cause current to flow in one direction between an anode and a cathode, comprising: a plurality of semiconductor switching elements connected in parallel between the anode and the cathode; a plurality of drive circuits which drive the plurality of semiconductor switching elements; and a control unit which creates a control command signal to each of the plurality of drive circuits based on a voltage between main terminals of the plurality of semiconductor switching elements, wherein the control unit sets the number of the plurality of semiconductor switching elements to be turned on based on the voltage between the main terminals during a synchronous rectification period, and generates the control command signal to the drive circuit based on the set number.

2. A rectifier circuit as claimed in claim 1, characterized in that the control section holds the control command signal and outputs it to the drive circuit in the next synchronous rectification period.

3. A rectifier circuit according to claim 1, characterized in that the control unit compares the main terminal voltage with a predetermined threshold voltage and sets the number based on the comparison result.

4. A rectifier circuit according to claim 3, wherein the threshold voltage is preset based on the total power loss of the plurality of semiconductor switching elements.

5. A rectifier circuit according to claim 1, wherein the control unit determines whether to increase or decrease the number by one.

6. A rectifier circuit as claimed in claim 5, characterized in that the control unit compares the voltage between the main terminals with a predetermined first threshold voltage and a predetermined second threshold voltage, and determines whether to increase or decrease the number by one based on the comparison result.

7. A rectifier circuit according to claim 1, wherein the control unit determines the synchronous rectification period based on the voltage between the main terminals.

8. A rectifier circuit according to claim 1, characterized in that said control section determines said synchronous rectification period based on a drive current flowing from said drive circuit to said semiconductor switching element.

9. The rectifier circuit according to claim 1, further comprising a capacitor connected between the anode and the cathode, and the plurality of drive circuits and the control unit use the capacitor as a power source.

10. A rectifier circuit as claimed in claim 9, characterized in that one end of said capacitor is connected to said cathode via a reverse current prevention diode.

11. A rectifier circuit as claimed in claim 9, wherein one end of the capacitor is connected to the cathode via a series circuit of a reverse current prevention diode and a semiconductor switch.

12. A semiconductor device comprising: a rectifier circuit; and a semiconductor package incorporating said rectifier circuit, wherein said rectifier circuit is the rectifier circuit defined in claim 1.

13. A semiconductor device comprising: a bridge rectifier circuit composed of a plurality of rectifier circuits; and a semiconductor package incorporating the bridge rectifier circuit, wherein each of the plurality of rectifier circuits is the rectifier circuit defined in claim 1.

14. A power supply device having a rectifier circuit section, characterized in that the rectifier circuit section comprises the rectifier circuit according to claim 1.

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