JP2007028888A - Rectifying circuit and voltage conversion circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-loss rectifying circuit having a control function for dispensing with dead time control for preventing the backflow of current to a voltage conversion circuit from a capacitor connected to a load in parallel when it is used for a switching supply, and preventing a through-current in a flywheel FET and a diode. <P>SOLUTION: The rectifying circuit comprises a first current path in which a transistor Q1 is driven by a constant-current element CS1, a second current path in which a transistor Q2 is driven where an emitter and a base are short-circuited by a constant-current element CS2, a rectifying current path intermittently controlled by the FET1, and a transistor Q5 bypassing the transistor Q1. When the FET1 is energized, the base of the transistor Q5 is driven, and the transistor Q5 is turned on, thus turning on the first current path, driving the gate of the FET1, turning off the FET1, and interrupting the rectifying current path when positive potential is applied to the drain of the FET1 and the collector of the transistor Q2, and negative potential is applied to the source of the FET1. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention is suitable for use in a power supply apparatus including a voltage conversion circuit (DC-DC converter) that converts a DC voltage, and has a control function that facilitates control, and voltage conversion including the rectification circuit Regarding the circuit.

  A voltage conversion circuit (DC-DC converter) that converts a DC voltage is widely used in a switching power supply circuit and the like. A conventional voltage conversion circuit of this type includes a rectifier circuit using a solid semiconductor diode element. However, there is a problem that power loss occurs due to a relatively large forward voltage drop (VF) due to the diode. Therefore, in the voltage conversion circuit, switching elements with a low forward voltage drop such as MOS-FET (Metal-Oxide-Semiconductor Field Effect Transistor) are used instead of the conventional diodes, and these switching elements are used as input-side switching elements. A configuration including a synchronous rectifier circuit that performs on / off control in synchronization with a signal is proposed and put into practical use.

  A voltage conversion circuit 200 shown in FIG. 5 is a circuit diagram showing a typical example of a forward type voltage conversion circuit using a synchronous rectification circuit. In the conversion circuit 200, the supply of DC voltage from the DC power supply 1 to the primary coil P of the transformer T is turned on / off by the FET 21. A flywheel FET 22, a smoothing capacitor C21, and a load L are connected in parallel to the secondary coil S of the transformer T. One end of the secondary coil S is connected to the anode of the diode D21. The cathode of the diode D21 is connected to the drain of the flywheel FET 22, and the other end of the secondary coil S is connected to the source of the flywheel FET 22. The cathode of the diode D21 and the drain of the flywheel FET 22 are connected to one end of the choke coil L21, and the other end of the choke coil L21 is connected to the smoothing capacitor C21.

  A gate G1 of the FET 21 and a gate G2 of the flywheel FET 22 are control terminals for driving the FET 21 and the FET 22, respectively. The FET 22 is turned off when the FET 21 is turned on, and the FET 22 is turned on when the FET 21 is turned off. Thus, a predetermined voltage is applied.

  Next, the schematic operation of the voltage conversion circuit 200 will be described with reference to the voltage / current waveforms of the respective parts shown in FIG. 6A and 6B are schematic diagrams showing voltage / current waveforms of respective parts of the voltage conversion circuit 200. FIG. 6A shows a voltage waveform applied to the gate G1 of the FET 21, and FIG. 6B shows a voltage applied to the gate G2 of the FET 22 for flywheel. The applied voltage waveform, (c) shows the current waveform that flows through the diode D21 when the load L is heavy, and (d) shows the current waveform that flows through the flywheel FET 22 when the load L is heavy. Yes. In FIG. 6, (e) shows the current waveform flowing through the diode D21 when the load L is light load, and (f) shows the current waveform flowing through the flywheel FET 22 when the load L is light load. Yes.

When the FET 21 is turned on at time t0 and a DC voltage is supplied to the coil P, an electromotive force generated in the coil S causes a current to flow in the current path from the coil S via the diode D21 and the choke coil L21. , 6 outputs a DC voltage to the load L. At this time, the flywheel FET 22 is turned off (period T1).
At time t1, the flywheel FET 22 is turned on in synchronization with the FET 21 being turned off. The on state of the FET 22 is maintained until the time (t3) when the FET 21 is turned on again (period T2).
When the FET 21 is turned off and voltage supply to the choke coil L21 is stopped, a counter electromotive force is generated in the choke coil L21. At this time, since the flywheel FET 22 is turned on, a current flows from the choke coil L21 through the load L and the flywheel FET 22 due to the back electromotive force of the choke coil L21. A DC voltage is output (period T31 or T32).

  That is, the voltage conversion circuit 200 shown in FIG. 5 outputs a DC voltage by the electromotive force generated in the secondary coil S of the transformer T when the FET 21 is on, and when the FET 21 is switched off, DC voltage is output by the stored energy.

  In the voltage conversion circuit 200 shown in FIG. 5, a diode is used for the rectifying element connected to the secondary coil S and an FET 22 is used for the flywheel section. An example in which an FET is used instead of the diode connected to the coil S on the next side has been proposed (for example, Patent Document 1).

Japanese Patent Laid-Open No. 11-69804

  Referring again to FIG. 5, the current flowing through the choke coil L <b> 21 of the voltage conversion circuit 200 changes according to the load L connected between the output terminals 5 and 6. For example, when the load L is a heavy load, as shown in the current waveform of FIG. 6 (c), the diode 21 is connected to the diode from the secondary coil S during the period T1 when the FET 21 is on (the flywheel FET 22 is off). Since the current flowing through D21 and the choke coil L21 is large, the magnetic energy accumulated in the choke coil L21 is also large. For this reason, as shown in the current waveform of FIG. 6D, even after the FET 21 is switched off (flywheel FET 22 is turned on), the choke coil L21 passes through the load L and the flywheel FET 22. Current flows for a long time.

  On the other hand, when the load L is a light load, as shown in the current waveform of FIG. 6E, the current flowing from the secondary coil S via the diode D21 and the choke coil L21 in the period T1. Is small, the magnetic energy accumulated in the choke coil L21 is also small. Then, as shown in the current waveform in FIG. 6 (f), the energy supply from the choke coil L21 stops at a certain time t2 within the period T2 until the FET 21 is turned off and then turned on again. Thereafter, no current flows from the choke coil L21 via the load L and the flywheel FET 22.

  That is, in the period T2 during which the flywheel FET 22 is on (hereinafter also simply referred to as “on time T2”), a period in which current flows through the flywheel FET 22 based on the energy accumulated in the choke coil L21 (FIG. 6). The periods T31 and T32 shown in (d) and (f) (hereinafter also referred to as “flywheel time”) vary depending on the load L. For this reason, there were the following problems.

  When the load is light, the flywheel time T32 is shorter than the ontime T2 of the flywheel FET 22, and therefore, after the flywheel time T32, when the flywheel FET22 is on, the drain potential becomes the ground potential. Therefore, a current flows from the smoothing capacitor C21 through the choke coil L21 and the on-state FET 22. That is, the load current flows backward, resulting in a large power loss and poor efficiency.

  Here, at the time of light load, the voltage applied to the gate G2 of the flywheel FET 22 is switched from High to Low at an early stage, the flywheel FET 22 is turned off early, and the on time T2 is changed to the flywheel time T32. Is assumed to be equal to or slightly shorter than. In this way, it is considered that the above backflow can be prevented. However, this time control is difficult.

  Furthermore, another problem that must be considered in a voltage conversion circuit using a conventional synchronous rectification circuit is the operation delay time of the flywheel FET.

  Referring to FIGS. 5 and 6 again, in the voltage conversion circuit 200, the flywheel FET 22 is quickly turned off (exactly in the cut-off state) after time t3 when the applied voltage of the gate G2 becomes zero volts (Low). It is desirable that the drain current does not flow. However, even if the voltage applied to the gate G2 of the flywheel FET 22 is set to zero volts and the FET 22 is turned off, a current flows through the parasitic diode of the FET 22 from the source of the FET 22 to the drain due to the back electromotive force of the choke coil L21. In addition, even when this current stops flowing, the minority carrier annihilation time is required, so that the FET 22 cannot be completely cut off at this point. Therefore, if a positive potential is applied to the drain of the FET 22 at the time when a current due to the parasitic diode flows or minority carriers do not disappear, the FET 22 can be in a conductive state. Therefore, when the FET 21 is turned on, a through current flowing from the secondary coil S via the diode D21 and the FET 22 flows, resulting in a large power loss and a reduction in efficiency. Further, the FET 22 is destroyed by a large current. This is also one factor that makes it difficult to determine the on-time T2 of the flywheel FET 22.

  As described above, in the voltage conversion circuit using the conventional synchronous rectification circuit, it is extremely difficult to determine the ON time of the switching means so that the efficiency is the best. Therefore, it is desired to solve such problems and to introduce a new active rectifier that replaces the conventional FET or the like.

  Therefore, one object of the present invention is to prevent current backflow from a capacitor connected in parallel to a load to a voltage conversion circuit, and to prevent fly-through current of a flywheel FET and a diode when used in a switching power supply with low loss. An object of the present invention is to provide a rectifier circuit with a control function that does not require the dead time control. Another object of the present invention is to provide a low-loss, high-efficiency voltage conversion circuit using such a rectifier circuit as a switching means.

  In order to achieve the above object, the present invention generally includes an off-control terminal in a rectifier circuit in which a rectifier current path is intermittently controlled according to the polarity of an applied potential. More specifically, the present invention has the following features.

According to the first aspect of the present invention, the first current path in which the first semiconductor element having the first control terminal is driven by the first constant current source and the PN junction element is driven by the second constant current source. A second current path that is controlled, a rectification current path that is intermittently controlled by a second semiconductor element having a second control terminal, and a third that bypasses the first semiconductor element that the first current path has. A third semiconductor element having a control end of
When a positive potential is applied to one end of the second semiconductor element and one end of the PN junction element, and a negative potential is applied to the other end of the second semiconductor element, the second current path is interrupted. Thus, the first current path is conducted, drives the second control end of the second semiconductor element, shuts off the second semiconductor element, and shuts off the rectified current path,
When a negative potential is applied to one end of the second semiconductor element and one end of the PN junction element, and a positive potential is applied to the other end of the second semiconductor element, the second current path is conducted. Thus, the first current path is interrupted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is made conductive, and the rectified current path is made conductive,
When the second current path is turned on, the third control element of the third semiconductor element is driven to turn on the third semiconductor element, whereby the first current path is turned on. Driving the second control end of the second semiconductor element to turn off the second semiconductor element, and applying a positive potential to one end of the second semiconductor element and one end of the PN junction element. The rectifier circuit is characterized in that the rectifier current path is interrupted when a negative potential is applied to the other end of the semiconductor element.

According to a second aspect of the present invention, there is provided a first current path in which a first semiconductor element having a first control end is driven by a first constant current source, and a fourth control end by a second constant current source. A second current path driven by a fourth semiconductor element having a second control element, a rectifying current path controlled intermittently by a second semiconductor element having a second control end, and the first current path having the first current path. A third semiconductor element having a third control end for bypassing one semiconductor element,
When a positive potential is applied to one end of the second semiconductor element and one end of the fourth semiconductor element and a negative potential is applied to the other end of the second semiconductor element, the second current path is interrupted. By doing so, the first current path is conducted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is shut off, the rectified current path is shut off,
When a negative potential is applied to one end of the second semiconductor element and one end of the fourth semiconductor element, and a positive potential is applied to the other end of the second semiconductor element, the second current path becomes conductive. By doing so, the first current path is interrupted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is made conductive, and the rectified current path is made conductive,
When the second current path is turned on, the third control element of the third semiconductor element is driven to turn on the third semiconductor element, whereby the first current path is turned on. , Driving the second control end of the second semiconductor element to turn off the second semiconductor element, and applying a positive potential to one end of the second semiconductor element and one end of the fourth semiconductor element. The rectifier circuit is characterized in that the rectifier current path is interrupted when a negative potential is applied to the other end of the second semiconductor element.

  In any of the above-described rectifier circuits, the potential of one end of the first semiconductor element included in the first current path is detected to detect the first current path. When the current flows through the second semiconductor element, the second control terminal of the second semiconductor element is driven, the second semiconductor element is shut off, and when the current does not flow through the first current path, the second semiconductor element The emitter follower circuit which drives the 2nd control end which has and controls the voltage applied to the 2nd control end for conducting the 2nd semiconductor element can be provided.

According to a fourth aspect of the present invention, there is provided a transformer in which a first coil is disposed on the primary side, and a second coil magnetically coupled to the first coil is disposed on the secondary side; A third coil connected in series to the current path of the coil, first switching means for switching on / off of DC voltage supply to the primary side of the transformer, and voltage supply to the transformer by the first switching means. A first load current path that outputs a DC voltage based on an electromotive force generated in the second coil in a turned-on state, and a second switching means, and the first switching means After the voltage supply is switched from on to off, the second load current that outputs the DC voltage based on the back electromotive force generated in the third coil by turning on the second switching means. In the voltage conversion circuit which includes a road, a
The second switching means includes the rectifier circuit according to any one of claims 1 to 3,
Before the first switching means is switched from OFF to ON, the third control element of the third semiconductor element included in the rectifier circuit is driven to make the third semiconductor element conductive, thereby making the first semiconductor element conductive. The current path of the second semiconductor element included in the rectifier circuit is driven to turn off the second semiconductor element, and the one end of the second semiconductor element is connected to the PN junction. When a positive potential is applied to one end of the element or one end of the second semiconductor element and one end of the fourth semiconductor element, and a negative potential is applied to the other end of the second semiconductor element, the rectifying current path It is a voltage conversion circuit characterized by shutting off.

  The rectifier circuit according to claim 1 includes a first semiconductor element (for example, a base of the transistor Q1 in FIG. 1) having a first control terminal (for example, a base of the transistor Q1 in FIG. 1) by a first constant current source (for example, the constant current element CS1 in FIG. 1). Transistor in which a PN junction element (for example, emitter-base in FIG. 1 is short-circuited by a first current path in which transistor Q1 in FIG. 1) is driven and a second constant current source (for example, constant current element CS2 in FIG. 1) A second current path in which Q2) is driven, and a rectification current path that is intermittently controlled by a second semiconductor element (eg, FET1 in FIG. 1) having a second control terminal (eg, the gate of FET1 in FIG. 1). A third semiconductor element (for example, FIG. 1) having a third control terminal (for example, the base of the transistor Q5 in FIG. 1) that bypasses the first semiconductor element (for example, the transistor Q1 in FIG. 1) included in the first current path. And it includes a transistor Q5) and.

  A positive potential is applied to one end of the second semiconductor element (for example, the drain of the FET 1 in FIG. 1) and one end of the PN junction element (for example, the collector of the transistor Q2 in FIG. 1), and the other end of the second semiconductor element (for example, FIG. When a negative potential is applied to the source of the first FET 1, the second current path is cut off, whereby the first current path is conducted and the second control end (for example, FIG. 1), the second semiconductor element is cut off and the rectification current path is cut off. On the other hand, a negative potential is applied to one end of the second semiconductor element (for example, the drain of the FET 1 in FIG. 1) and one end of the PN junction element (for example, the collector of the transistor Q2 in FIG. 1). For example, when a positive potential is applied to the source of the FET 1 in FIG. 1, the second current path is turned on, whereby the first current path is interrupted and the second control terminal ( For example, the gate of the FET 1 in FIG. 1 is driven, the second semiconductor element is made conductive, and the rectification current path is made conductive.

  In this way, a rectifier circuit in which the rectification current path is intermittently controlled according to the positive / negative of the potential applied to one end and the other end of the second semiconductor element is realized. In addition, no current flows through the body diode in a state where no voltage is applied to the control terminal such as the gate, and the power loss can be greatly reduced.

  In the rectifier circuit according to claim 1, particularly, when the second current path is conducted, the first current path is cut off, but the third control terminal ( For example, by driving the base of the transistor Q5 in FIG. 1 and turning on the third semiconductor element, the first current path is turned on, and the second control terminal (for example, FET1 in FIG. 1) of the second semiconductor element. The second semiconductor element is turned off. Therefore, even when the rectifying current path is in the conductive state, when a voltage is applied to the third control terminal, the reverse current (current flowing from the drain of the FET 1 to the source) is cut off and maintained (first) 3 while the voltage continues to be applied to the control end. This is because, when the rectifier circuit of the present invention is used for the switching means D10 of the circuit as shown in FIG. 3 to be described later, a diode having a small forward voltage drop such as a Schottky diode is connected in parallel to the switching means D10. When the FET 1 existing inside the switching means D10 is OFF, there is no current flowing through the parasitic diode of the FET 1 (current flowing from the source to the drain of the FET 1), and therefore no current flows through the FET 1. Here, by applying a control voltage to the Voff application terminal of the switching means D10 and turning off the FET 1, the FET 1 can be switched to a cut-off state (the current flowing from the drain of the FET 1 to the source is cut off). The reverse voltage of the switching means D10 can be blocked with a sufficient margin before the positive potential is applied. This has the effect that it is not necessary to consider the minority carrier disappearance time due to the parasitic diode current of the FET. Since the switching speed of the FET 21 in FIG. 3 is very fast, normally, dead time control of the FET 21 and the FET 1 is necessarily required, but this need not be taken into account in this rectifier circuit.

  The rectifier circuit according to claim 2 includes a first semiconductor element (for example, a base of the transistor Q1 in FIG. 1) having a first control terminal (for example, a base of the transistor Q1 in FIG. 1) by a first constant current source (for example, the constant current element CS1 in FIG. 1). The fourth control terminal (for example, the base of the transistor Q2 in FIG. 1) is connected to the first current path in which the transistor Q1 in FIG. 1 is driven and the second constant current source (for example, the constant current element CS2 in FIG. 1). A second semiconductor element (for example, FIG. 1) having a second current path for driving a fourth semiconductor element (for example, the transistor Q2 in FIG. 1) and a second control terminal (for example, the gate of the FET 1 in FIG. 1). And a third control terminal (for example, the base of the transistor Q5 in FIG. 1) that bypasses the first semiconductor element (for example, the transistor Q1 in FIG. 1) included in the first current path. ) And a third semiconductor element (e.g., transistor Q5 of FIG. 1) having.

  A positive potential is applied to one end of the second semiconductor element (for example, the drain of the FET 1 in FIG. 1) and one end of the fourth semiconductor element (for example, the collector of the transistor Q2 in FIG. 1), and the other end ( For example, when a negative potential is applied to the source of the FET 1 in FIG. 1, the second current path is interrupted, whereby the first current path is made conductive and the second control terminal ( For example, the gate of the FET 1 in FIG. 1 is driven to cut off the second semiconductor element and cut off the rectified current path.

  On the other hand, a negative potential is applied to one end of the second semiconductor element (for example, the drain of the FET 1 in FIG. 1) and one end of the fourth semiconductor element (for example, the collector of the transistor Q2 in FIG. 1). When a positive potential is applied to the end (for example, the source of the FET 1 in FIG. 1), the second current path is turned on, whereby the first current path is cut off and the second control of the second semiconductor element is performed. The end (for example, the gate of the FET 1 in FIG. 1) is driven, the second semiconductor element is made conductive, and the rectification current path is made conductive. Further, when the second current path is conducted, the third control terminal of the third semiconductor element (for example, the base of the transistor Q5 in FIG. 1) is driven, and the third semiconductor element is conducted. The first current path is conducted, drives the second control terminal of the second semiconductor element (for example, the gate of the FET 1 in FIG. 1), and turns off the second semiconductor element. At this time, since a negative potential is applied to one end of the second semiconductor element and one end of the fourth semiconductor element and a positive potential is applied to the other end of the second semiconductor element, the second semiconductor element is Even if it is off, the current from the source to the drain due to the parasitic diode of this element cannot be cut off, but it is possible to control to turn off the second semiconductor element in advance (the same applies to the rectifier circuit of claim 1).

  Therefore, a rectifier circuit is realized in which the rectification current path is intermittently controlled according to the polarity of the potential applied to one end and the other end of the second semiconductor element, and even when the rectification current path is in the conductive state, When a voltage is applied to the control terminal, the reverse current cut-off state can be maintained and the same effect as that of the first aspect of the invention can be obtained.

  Any of the above rectifier circuits detects the potential of one end (for example, the emitter of the transistor Q1 in FIG. 1) of the first semiconductor element included in the first current path, and current flows through the first current path. When a second control terminal (for example, the gate of the FET 1 in FIG. 1) of the second semiconductor element is driven, the second semiconductor element is shut off, and no current flows in the first current path, the second semiconductor element A configuration including an emitter follower circuit (for example, transistors Q3 and Q4 in FIG. 1) that controls a voltage applied to the second control terminal for driving the second control terminal of the first semiconductor element and conducting the second semiconductor element. It can be. This operates as a buffer amplifier, can increase the output current with low impedance, and ensures the gate drive (ON / OFF) of the FET 1.

  As described above, according to the present invention, the rectification current path is intermittently controlled according to the polarity of the applied potential, and a voltage is applied to the third control terminal even when the rectification current path is in a conductive state. In this case, a rectifier circuit having a control terminal that can be switched to and maintained in the reverse current cutoff state can be simply realized using a semiconductor element or using a semiconductor element and a PN junction element. .

  The rectifier circuit is particularly advantageous when used as a flywheel switching means in the voltage conversion circuit shown in FIG. That is, the first coil (for example, the coil P in FIG. 3) is disposed on the primary side, and the second coil (for example, the coil S in FIG. 3) magnetically coupled to the first coil is disposed on the secondary side. And a first switching means (for example, FIG. 3) for switching on / off of DC voltage supply to the primary side of the transformer, a transformer (for example, the transformer T in FIG. 3), a third coil (for example, the coil L21 in FIG. 3), and the primary side of the transformer. FET 21), a first load current path for outputting a DC voltage based on an electromotive force generated in the second coil in a state where the voltage supply to the transformer is turned on by the first switching means, and a second load current path And the reverse of the voltage generated in the third coil by turning on the second switching means after the voltage supply to the transformer is switched from on to off by the first switching means. In a voltage conversion circuit including a second load current path that outputs a DC voltage based on electric power, the second switching means includes the rectifier circuit described above (for example, the switching means D10 in FIG. 3). In the example of FIG. 3, a Schottky barrier diode DS is connected in parallel to the switching means D10. Then, when the second switching means is turned on, the third control terminal of the third semiconductor element included in the rectifier circuit (for example, the switching shown in FIG. 3) before the first switching means is switched from OFF to ON. Even when the voltage VOFF is applied to the third control terminal even when the voltage VOFF application end of the means D10 is driven and the rectification current path included in the second switching means is in a conductive state, the FET 1 provided in the rectifier circuit is It is turned off and maintained in the reverse current cut-off state, and it can wait until the first switching means is turned on with a margin.

  According to the voltage conversion circuit configured in this way, the on-time of the switching means can be easily controlled based on the voltage applied to the third control end so that the efficiency becomes the best, so that the load current It is possible to easily realize a voltage conversion circuit that eliminates the problems of reverse current and through current.

  The above objects and advantages of the present invention and other objects and advantages will be more clearly understood through the following description of embodiments. However, the embodiments described below are merely examples, and the present invention is not limited to these.

  FIG. 1 is a circuit diagram showing a basic configuration of a rectifier circuit 10 according to an embodiment to which the present invention is applied.

  In the rectifier circuit 10 shown in FIG. 1, an FET 1 having a large collector withstand voltage and a large current capacity, such as an N channel power MOS-FET, is provided in a current path having an anode end 1 and a cathode end 2. The source of the FET 1 is connected to the anode end 1, the drain of the FET 1 is connected to the cathode end 2, and when High is input to the gate of the FET 1, the FET 1 is turned on to make the current path conductive, and the FET 1 gate input Is lowered from High to Low, the FET 1 is turned off and the current path from the cathode terminal 2 to the anode terminal 1 is interrupted. That is, the FET 1 intermittently controls the rectified current path between the anode end 1 and the cathode end 2 by the switching operation (only current flowing from the anode end 1 to the cathode end 2 flows). The transistors Q1 and Q2 are NPN bipolar transistors having substantially the same characteristics, and the bases of the transistors Q1 and Q2 are connected in common, and the collector of the transistor Q1 is connected to the source of the FET1, that is, the anode terminal 1, and the other The transistor Q2 has a collector connected to the cathode terminal 2, an emitter connected to the base, and a short circuit between the emitter and base.

  A constant voltage diode D1, a diode D2, a junction transistor J-FET (Junction Field Effect Transistor), a resistor R1, and a capacitor C1 drive the gates of the transistors Q1 and Q2, transistors Q3, Q4 and Q5, and FET1, which will be described later. A drive voltage source is configured. Such a drive voltage source charges a capacitor C1 through a diode D2 whose junction is connected to the cathode end 2 and a junction transistor J-FET in a half cycle in which a positive potential is applied to the cathode end 2 as will be described later. Then, a voltage is generated in which one side of the capacitor C1 connected to the anode end 1 is negative and the other side is positive. The collector of the transistor Q1, the source of the FET1, the collector of the transistor Q4 described later, and the emitter of the transistor Q5 are connected to one side (negative side as a drive source) of the capacitor C1 connected to the anode terminal 1. On the other hand, a collector of a transistor Q3, which will be described later, is connected to the other side (positive side as a drive source) of the capacitor C1 connected to the cathode terminal 1 via the diode D2 and the junction transistor J-FET, and the transistor Q1. And the emitter of the transistor Q2 are connected via a constant current element CS1 and a constant current element CS2, respectively.

  Therefore, in the rectifier circuit 10, when the connection relationship between the capacitor C1 as a drive voltage source and the transistor Q1 is seen, one side of the capacitor C1 (as a drive source) passes from the constant current element CS1 through the emitter and collector of the transistor Q1. Connected to the negative side). The transistor Q2 is connected from the constant current element CS2 to one side of the capacitor C1 through the emitter and collector of the transistor Q2 (in a direct current through an external load and a commercial system). Accordingly, the transistor Q2 is also supplied with power from the capacitor C1 and can operate (see the quasi-short state between the anode 1 and the cathode in FIG. 2). Further, the transistor Q5 is connected from the constant current element CS1 to the one side of the capacitor C1 through the collector and emitter of the transistor Q5.

  FIG. 2 is a circuit diagram showing an equivalent circuit of a circuit portion (broken line portion in FIG. 1) including transistors Q1, Q2, Q5, constant current elements CS1 and CS2 in rectifier circuit 10 shown in FIG. As already described with reference to FIG. 1, the emitter of the transistor Q2 is connected to the base, and the base and emitter are short-circuited. For this reason, the transistor Q2, which is an NPN bipolar transistor, provides a PN junction diode between the base and the collector. Here, considering a current path (FIG. 1) from the constant current element CS2 through the emitter and collector of the transistor Q2 to the drain of the FET 1, that is, the cathode end 2, this current path is constant as shown in FIG. This is equivalent to a current path in which a PN junction diode is inserted so that the anode of the PN junction diode is connected from the current element CS2 to the drain of the FET 1, that is, the cathode terminal 2. Therefore, in the current path including the constant current element CS2 and the transistor Q2, the potential of the cathode terminal 2 is applied to the collector of the transistor Q2, that is, the cathode of a PN junction diode equivalent to the transistor Q2.

  When the transistor Q2 is off, the base-emitter potential (about 0.6 volts) of the transistor Q2 is applied to the base of the transistor Q1, so that the transistor Q1 is on and the cathode terminal 2 (at the collector of the transistor Q2) Similarly, unless the cathode of the PN junction diode becomes a negative potential, the conduction between the anode end 1 and the cathode end 2 is cut off.

  In the current path including the constant current element CS2 and the transistor Q2, as described above, the potential of the cathode terminal 2 is applied to the collector of the transistor Q2. Here, when a positive potential is applied to the cathode terminal 2, it is equivalent to applying a reverse voltage to a PN junction diode equivalent to the transistor Q2. At this time, since the base current is supplied to the base of the transistor Q1 through the constant current element CS2, the transistor Q1 is in the on state, and the current flowing toward the emitter of the transistor Q1 through the constant current element CS1 using the capacitor C1 as a driving voltage source. Current flows through the road. At this time, the emitter and collector currents of the transistor Q1 flow, the transistor Q3 is off, and the Q4 is on.

  On the other hand, when a negative potential is applied to the cathode terminal 2, it is equivalent to applying a forward voltage to a PN junction diode equivalent to the transistor Q2. For this reason, when a negative potential is applied to the cathode terminal 2, the collector potential of the transistor Q2 decreases, and at the same time, the base potential of the transistor Q2 tries to maintain the collector-base potential (approximately 0.6 V generated in the PN junction diode). Also decreases. When the base potential of the transistor Q2 is lowered, the base potential of the transistor Q1 is also lowered, the transistor Q1 is turned off, and the current path toward the emitter of the transistor Q1 through the constant current element CS1 is interrupted. At this time, the transistor Q3 is on and Q4 is off.

  Basically, an equivalent circuit using the PN junction element shown in FIG. 2 shows the operating principle of the rectifier circuit 10 of the present invention. The reason why the transistor Q2 is used in this embodiment is that the transistor Q1 needs to be a bipolar transistor, and a transistor having substantially the same characteristics (temperature characteristics, base-emitter voltage, etc.) of the transistor Q1 is used as a PN junction element. It is because it is more preferable to use it. Although bipolar transistors are used as the transistors Q1 and Q2, it goes without saying that FETs may be used instead.

  Referring again to FIG. 1, the transistor Q3 and the transistor Q4 constitute an emitter follower type buffer amplifier. For example, bipolar transistors can be used as the transistors Q3 and Q4. In this embodiment, an NPN bipolar transistor is used as the transistor Q3, and a PNP bipolar transistor is used as the transistor Q4. The emitters of both the transistors Q3 and Q4 are connected in common, and the common emitter is connected to the gate of the FET1. Has been. The bases of both transistors Q3 and Q4 are also connected in common, and the emitter of the transistor Q1 is connected to the base.

  A predetermined constant current is supplied to the emitter of the transistor Q1 and the emitter of the transistor Q2 through the constant current elements CS1 and CS2, respectively, using the capacitor C1 as a drive voltage source.

  A resistor R2 is connected between the common base of the transistors Q3 and Q4 and the collector of the transistor Q4. The resistor R2 is a bleeder resistor and stabilizes the circuit operation by preventing the bases of the transistors Q3 and Q4 from being opened.

  The transistors Q3 and Q4 constitute an emitter-follower type buffer amplifier, and the common emitter of the transistors Q3 and Q4 is connected to the gate of the FET1, and the collector of the transistor Q4 is connected to the source of the FET1. The emitter potential of the transistor Q1, that is, the same voltage as the emitter-collector voltage of the transistor Q1, is directly input to the gate of the FET1. Therefore, for example, when the transistor Q1 is turned on and a current flows from the emitter to the collector of the transistor Q1 through the constant current element CS1, the potential of the common base of the transistors Q3 and Q4 is substantially zero volts (at this time, the NPN bipolar transistor The transistor Q3 is off and the transistor Q4, which is a PNP bipolar transistor, is on.) As will be described later, the gate input of the FET 1 is also zero volts (Low). On the contrary, when the transistor Q1 is turned off, the voltage charged in the capacitor C1 is applied to the bases of the transistors Q3 and Q4 through the constant current element CS1, the transistor Q3 is forward biased, and the transistor Q4 is reverse biased. At this time, the transistor Q3 is on and the transistor Q4 is off, and the gate input of the FET 1 is also high as described later.

  The rectifier circuit 10 further includes a transistor Q5 as shown in FIG. The collector of the transistor Q5 is connected to the common base of the transistors Q3 and Q4, and the emitter is connected to the source of the FET 1 (hence the collector of the transistor Q1 and the anode terminal 1). The base of the transistor Q5 is connected to one input terminal 3 of the voltage input terminals 3 and 4 via the resistor R3, and the emitter of the transistor Q5 is connected to the other input terminal 4. A resistor R4 is connected between the base and emitter of the transistor Q5. A desired pulse voltage generated by voltage generation means (not shown) is applied between the voltage input terminals 3 and 4.

Next, the operation of the rectifier circuit 10 will be described.
First, consider the basic rectification operation of the rectifier circuit 10 when a positive potential is applied to the cathode terminal 2 of the rectifier circuit 10. As described above, applying a positive potential to the cathode terminal 2 is equivalent to applying a reverse voltage to a PN junction diode equivalent to the transistor Q2, so that no current flows through the transistor Q2, and the transistor Q1 Since the base current is supplied to the base of the transistor Q1 through the constant current element CS2, the transistor Q1 is in the ON state, and the current flows through the constant current element CS1 toward the emitter of the transistor Q1 using the capacitor C1 as a driving voltage source. .

  When the transistor Q1 is turned on, the emitter potential (collector-emitter voltage) of the transistor Q1 is substantially zero volts (Low), so that the PNP bipolar transistor Q4 is switched from OFF to ON, and the NPN bipolar transistor The transistor Q3 is switched from on to off. When the transistor Q3 is off and the transistor Q4 is on, the potential of the common emitter of the transistors Q3 and Q4 is zero volts (Low). Therefore, the gate input of the FET1 is zero volts (Low), and the FET1 is turned off. As a result, when a positive potential is applied to the cathode end 2, the current path connecting the anode end 1 and the cathode end 2 is interrupted by the FET 1, and in the direction from the cathode end 2 toward the drain, source, and anode end 1 of the FET 1. No current flows.

  When a positive potential is applied to the cathode terminal 2, the capacitor C1 is charged through the diode D2 and the junction transistor J-FET, and the charging voltage is controlled by controlling the gate of the junction transistor J-FET by the constant voltage diode D1. Limited to a constant value (eg, about 10 volts).

  Next, in a state where no voltage is applied to the voltage input terminals 3 and 4, the potential at the cathode terminal 2 decreases to zero after a positive potential is applied to the cathode terminal 2 of the rectifier circuit 10, and then the anode terminal Consider the basic rectification operation of the rectifier circuit 10 when the polarity between the cathode end 2 and the cathode end 2 changes to a state where a negative potential is applied to the cathode end 2.

  When the potential at the cathode terminal 2 becomes zero and a negative potential is applied thereafter, a current flows through the transistor Q2 because it is equivalent to applying a forward voltage to a PN junction diode equivalent to the transistor Q2. For this reason, when a negative potential is applied to the cathode terminal 2, the collector potential of the transistor Q2 decreases, and at the same time, the base potential of the transistor Q2 tries to maintain the collector-base potential (approximately 0.6 V generated in the PN junction diode). Also decreases. When the base potential of the transistor Q2 is lowered, the base potential of the transistor Q1 is also lowered, the transistor Q1 is turned off, and the current path toward the emitter of the transistor Q1 through the constant current element CS1 is interrupted. When the transistor Q1 is turned off, the current passing through the constant current element CS1 does not flow as the emitter-collector current of the transistor Q1, flows as the base current of the transistor Q3, forward biases the transistor Q3, and reverse biases the transistor Q4. Thus, when the emitter potential of the transistor Q1 rises (inverts to High), the PNP bipolar transistor Q4 switches from on to off, and the NPN bipolar transistor transistor Q3 switches from off to on. When the transistor Q3 is on and the transistor Q4 is off, the potential of the common emitter of the transistors Q3 and Q4 rises (inverts to High). Therefore, the gate input of FET1 is inverted to High, and FET1 is turned on. As a result, when the potential at the cathode end 2 drops to zero, and then the polarity between the anode end 1 and the cathode end 2 is reversed and a negative potential is applied to the cathode end 2, the anode end 1 and the cathode end 2 are connected. The current path is made conductive by the FET 1, and a current flows in a direction from the anode end 1 toward the source, drain, and cathode end 2 of the FET 1.

  For example, when the rectifier circuit 10 of the present embodiment is used as switching means for flywheels in a synchronous rectifier circuit of a power supply device, the efficiency of the power supply device can be improved. In this case, preferably, when a positive potential is applied to the anode terminal 1 of the rectifier circuit 10, that is, when the rectified current path of the rectifier circuit 10 is in a conductive state, a voltage is applied between the voltage input terminals 3 and 4. By applying, FET1 is turned off. The basic operation of the rectifier circuit 10 will be described below.

  Referring to FIG. 1, in the rectifier circuit 10, when no voltage is applied between the voltage input terminals 3 and 4, no voltage is applied to the base of the transistor Q5, so that the base current is between the base and emitter of the transistor Q5. It does not flow and transistor Q5 is off. That is, the current path passing through the constant-current element CS1 and further between the collector and emitter of the transistor Q5 is blocked. Therefore, when no voltage is applied between the voltage input terminals 3 and 4, the collector of the transistor Q5 is connected to the emitter of the transistor Q1 (the transistor Q1 is in an off state at this time) and the common base of the transistors Q3 and Q4. However, the potential of the emitter of the transistor Q1 and the common base of the transistors Q3 and Q4 are not affected at all.

  Next, in the rectifier circuit 10, when a voltage (for example, a control pulse signal) having the voltage input terminal 3 side positive between the voltage input terminals 3 and 4 is applied to the base of the transistor Q5 through the resistor R3, the transistor Q5 A base current flows between the base and the emitter, turning on the transistor Q5. Then, since the collector-emitter voltage of the transistor Q5 is substantially zero volts, the inversion of the transistor Q5 from off to on lowers the emitter potential of the transistor Q1 in the off state to substantially zero volts. As a result, the emitter potential of the transistor Q1 is lowered (inverted to Low), and the common base of the transistors Q3 and Q4 is also lowered (inverted to Low). Then, since the emitter potentials of the transistors Q3 and Q4 constituting the emitter follower type buffer amplifier are lowered (inverted to Low), the gate input of the FET1 is inverted to Low, and the FET1 is turned off. As a result, when a positive potential is applied to the anode terminal 1, a voltage with the input terminal 3 side being positive is applied to the voltage input terminals 3 and 4, so that the FET 1 is turned on when a voltage (VOFF) is applied. Turn off.

  As described above, the rectifier circuit 10 responds to the positive / negative of the voltage applied to the anode terminal 1 and the cathode terminal 2 in a state where the voltage input terminals 3 and 4 are not applied with a positive voltage on the input terminal 3 side. Since the rectification current path is intermittently controlled, the same rectification function as that of the conventional semiconductor diode element is realized. When a voltage with the input terminal 3 side being positive is applied to the voltage input terminals 3 and 4, the FET 1 is reversed. The rectification circuit 10 can be converted to a reverse direction interruption by switching to a direction current interruption.

  FIG. 3 is a basic circuit diagram when the voltage conversion circuit 100 is configured by applying the rectifier circuit 10 of the present embodiment. In the conversion circuit 100 shown in FIG. 3, the rectifier circuit 10 of this embodiment is used as the flywheel switching means D10. The same parts as those of the conventional voltage conversion circuit 200 shown in FIG.

  In the voltage conversion circuit 100, when the FET 21 is turned from on to off, a current path from the coil L21 via the load L and the flywheel switching means D10 (rectifier circuit 10) is generated by the back electromotive force generated in the coil L21. In the off-period of the FET 21, a voltage is applied to the voltage input terminal of the flywheel switching means D10 (corresponding to the voltage input terminal 3 in the rectifier circuit 10 in FIG. 1, and so on). By applying, the second semiconductor element included in the switching means D10 can be switched off.

  FIG. 4 is a schematic diagram showing voltage and current waveforms of each part of the voltage conversion circuit 100. 4, (a) is the voltage waveform applied to the gate G1 of the FET 21, (b) is the voltage waveform of the voltage (VOFF) applied to the voltage application terminal of the switching means D10 for flywheel, and (c) is the voltage waveform. A current waveform flowing through the diode D21 when the load L is light load, (d) is a current waveform flowing through the flywheel switching means D10 when the load L is light load, and (e) is when the load L is heavy load. (F) shows the current waveform flowing through the flywheel switching means D10 when the load L is heavy.

If a counter electromotive force is generated in the choke coil L21 after the FET 21 is switched off at time t1, the direction of the electromotive force corresponds to the forward voltage of the flywheel switching means D10. For this reason, a current flows in the current path from the choke coil L21 through the load L and the flywheel switching means D10 due to the back electromotive force of the choke coil L21 (see (d) and (f) of FIG. 4, see T31). Or the period of T32). Therefore, in the voltage conversion circuit 100, it is not necessary to apply a voltage for switching the flywheel switching means D10 from OFF to ON to the control end.
Consider the case where the connected load L is light. As already described in connection with the background art, the energy supply from the choke coil L21 is performed at a certain time t2 within the period T2 after the FET 21 is switched off at the time t1 until it is switched on again at the time t3. After that, the current from the choke coil L21 via the load L and the flywheel switching means D10 does not flow ((d) of FIG. 4).

  At this time, the load current tends to flow backward from the smoothing capacitor C21 connected in parallel to the load L toward the switching means D10 through the choke coil L21. However, in the voltage conversion circuit 100, the switching means D10 functions as a diode having the choke coil L21 side as the cathode end. Therefore, when a voltage having the choke coil L21 side as positive is applied, this voltage is a reverse voltage. The switching means D10 is cut off. For this reason, the current in the direction from the coil L21 toward the switching means D10 does not flow until time t3 when the FET 21 is switched from OFF to ON again after time t2. In a conventional voltage conversion circuit using an FET as a switching means for a flywheel, the timing for switching the flywheel FET from on to off can be controlled in accordance with load fluctuations to prevent backflow of the load current. Although indispensable, according to the voltage conversion circuit 100, there is an advantage that the backflow prevention effect of the load current can be obtained by the rectifying function of the switching means D10 without such timing control.

  Next, consider the case where the load L to be connected is a heavy load. At a time t2 within a period T2 in which the FET 21 is switched off at time t1 and then switched on again at time t3, a relatively short voltage (VOFF) is applied to the voltage application terminal of the flywheel switching means D10. ) Is applied to turn off the switching means D10 (see (e) and (f) of FIG. 4). Here, the application time (t4-t2) of the voltage (VOFF) is longer than the OFF operation delay time toff of the switching means D10 (FET1 of the rectifier circuit 10), and the following is applied to the gate G1 of the FET21. It is preferable to select so as to overlap with the time t3 when the period voltage (VG1) is applied.

  When such a voltage (VOFF) is applied to the voltage application terminal of the flywheel switching means D10 under heavy load, the flywheel switching means D10 is already in the cut-off state when the FET 21 is turned on at time t3. It is said that. Therefore, the through current passing through the diode D21 and the flywheel switching means D10 does not flow from the secondary coil S while the flywheel switching means D10 remains conductive.

  In the conventional voltage conversion circuit, in order to prevent the FET on the primary side and the FET for the secondary flywheel from turning on at the same time, a through current flows and a large power loss occurs, and the FET 22 is prevented from being destroyed. It was necessary to adjust the application time of the voltage applied to the gate of the next flywheel FET. That is, it is indispensable to forcibly create a period in which the primary side FET and the secondary side flywheel FET are simultaneously turned off by so-called dead time control. According to the voltage conversion circuit 100 of this embodiment shown in FIG. 3, the dead time is obtained by applying a voltage (VOFF) as shown in FIG. 5B to the voltage application terminal of the flywheel switching means D10. There is a further advantage that the same effect as the control can be achieved. Moreover, there is no reduction in efficiency due to dead time loss.

  Note that the voltage conversion circuit may be separately provided with a PWM (Pulse Width Modulation) control circuit that detects the voltage applied to the load L and feedback-controls the ON width of the primary FET. Even in such a case, if the switching means D10 is cut off by applying a voltage (VOFF) to the voltage application terminal of the switching means D10 for the flywheel, it is effective for preventing the backflow of the load current and the through current. Obviously.

  According to the voltage conversion circuit of the present invention, the practical problems of the conventional synchronous rectification voltage conversion circuit can be solved as follows.

  In the conventional synchronous rectification type voltage conversion circuit, in order to prevent the backflow of the load current when the load fluctuates, the timing for turning off the flywheel FET is controlled, in other words, the adjustment of the off control cycle. Is required. In other words, apart from the PWM control of the primary side FET, it is also necessary to control to make the off timing earlier at the time of light load and to delay it at the time of heavy load. This is because, when the off-timing is not controlled and maintained at a constant period, the load current flows backward at a light load, and energy loss occurs at the choke coil at a heavy load. However, since it is not known at what time the FET should be turned off when the load actually fluctuates, it is extremely difficult to control the off-timing of the flywheel FET in the conventional synchronous rectification type voltage conversion circuit. It was difficult. Further, the conventional synchronous rectification type voltage conversion circuit also requires on-timing control to turn on the flywheel FET at an appropriate timing when the supply of the DC voltage to the primary coil is turned off. It was.

  On the other hand, the voltage conversion circuit of the present invention is based on the above-described OFF control that applies a voltage to the voltage application terminal of the flywheel switching means D10 before the DC voltage supply to the primary coil is turned on. Can solve the problem. That is, the rectifier circuit 10 used as the flywheel switching means D10 has the same rectification function as that of the conventional semiconductor diode element, so that the load to be connected is light or heavy. When the energy supply from the choke coil L21 is stopped and the load current tries to flow backward from the smoothing capacitor C21 connected in parallel to the load L to the switching means D10 through the choke coil L21, the rectifier circuit 10 itself is turned off. This is because the reverse flow is prevented, and when the back electromotive force is generated in the choke coil L21 after the supply of the DC voltage to the primary side coil is turned off, the rectifier circuit 10 itself is turned on ( This is because it is possible to supply energy from the choke coil to the load. As described above, when the rectifier circuit 10 of this embodiment is used for the switching means D10 of the circuit as shown in FIG. 3, a diode having a small forward voltage drop such as a Schottky diode is connected in parallel to the switching means D10. Then, when the FET 1 existing inside the switching means D10 is off, there is no current flowing through the parasitic diode of the FET 1, so that a control voltage is applied to the Voff application terminal of the switching means D10, and the FET 1 is turned off. Before the positive potential is applied to the switching means D10, the reverse voltage of the switching means D10 can be blocked with a sufficient margin. This has the effect that it is not necessary to consider the minority carrier disappearance time due to the parasitic diode current of the FET. Since the switching speed of the FET 21 in FIG. 3 is very fast, normally, dead time control of the FET 21 and the FET 1 is necessarily required, but this need not be taken into account in this rectifier circuit.

  In the above embodiment, bipolar transistors are used as the transistors Q1 to Q5 of the rectifier circuit 10. However, it is of course possible to use FETs (MOS-FETs). The same effect as that of the embodiment can be obtained. Further, in the rectifier circuit 10, the NPN type bipolar transistor is changed to a PNP type bipolar transistor, the PNP type bipolar transistor is changed to an NPN type bipolar transistor, and the N channel power MOS-FET is similarly changed to a P channel power MOS-FET. It may be changed. In this case, the polarity of the voltage is reversed.

  In the above embodiment, any element such as a resistor or an active semiconductor element can be used as the constant current elements CS1 and CS2.

  The specific configuration of the rectifier circuit 10 is not particularly limited, and it is of course possible to replace part or all of the rectifier circuit 10 with an equivalent circuit. For example, it is possible to replace the constant current element included in the rectifier circuit 10 with a current mirror circuit, and it is needless to say that other detailed configurations can be changed as appropriate without departing from the scope of the claims.

  The rectifier circuit of the present invention is widely applicable to devices that convert alternating current (high-frequency voltage) into direct current, for example, a synchronous rectifier circuit of a voltage conversion circuit (DC-DC converter) that performs energy conversion by a transformer or a coil, or The rectifier circuit of the present invention can be used as an alternative to the switching means included in the synchronous rectification switching power supply circuit that outputs a desired DC voltage from the AC voltage. In addition, it goes without saying that the rectification operation of the rectifier circuit of the present invention can be applied to various circuits that require rectification operation and devices equipped with the circuit as long as the rectification operation of the present invention matches the operation purpose of these circuits and devices. is there.

It is a circuit diagram which shows the structure of the rectifier circuit in embodiment to which this invention is applied. FIG. 2 is a circuit diagram showing an equivalent circuit of a circuit portion including transistors Q1, Q2, Q5 and constant current elements CS1 and CS2 in the rectifier circuit shown in FIG. It is a circuit diagram of the voltage converter circuit which applied the rectifier circuit shown in FIG. 1 as a switching means for flywheels. FIG. 4 is a schematic diagram showing current and voltage waveforms at various parts in a light load and a heavy load in the voltage conversion circuit shown in FIG. 3. It is a circuit diagram which shows the example of the forward type voltage converter circuit using the conventional synchronous rectifier circuit. FIG. 6 is a schematic diagram showing voltage and current waveforms at various parts in a heavy load and a light load in the conventional voltage conversion circuit shown in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode end 2 Cathode end 3,4 Voltage input end 10 Rectifier circuit 100 Voltage conversion circuit C1, C21 Capacitor CS1, CS2 Constant current element D1 Constant voltage diode D2, D21, DS diode D10 Switching means for flywheel (rectifier circuit 10 )
FET1, FET21 FET
J-FET Junction transistor L Load L21 Coil Q1-Q5 Transistor R1-R4 Resistance T Transformer

Claims (4)

A first current path in which a first semiconductor element having a first control terminal is driven by a first constant current source; a second current path in which a PN junction element is driven by a second constant current source; A rectifying current path that is intermittently controlled by a second semiconductor element having a second control end, and a third control end that bypasses the first semiconductor element that the first current path has. A semiconductor element,
When a positive potential is applied to one end of the second semiconductor element and one end of the PN junction element, and a negative potential is applied to the other end of the second semiconductor element, the second current path is interrupted. Thus, the first current path is conducted, drives the second control end of the second semiconductor element, shuts off the second semiconductor element, and shuts off the rectified current path,
When a negative potential is applied to one end of the second semiconductor element and one end of the PN junction element, and a positive potential is applied to the other end of the second semiconductor element, the second current path is conducted. Thus, the first current path is interrupted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is made conductive, and the rectified current path is made conductive,
When the second current path is turned on, the third control element of the third semiconductor element is driven to turn on the third semiconductor element, whereby the first current path is turned on. Driving the second control end of the second semiconductor element to turn off the second semiconductor element, and applying a positive potential to one end of the second semiconductor element and one end of the PN junction element. A rectifier circuit that cuts off the rectified current path when a negative potential is applied to the other end of the semiconductor element. A first current path in which a first semiconductor element having a first control end is driven by a first constant current source; and a fourth semiconductor element having a fourth control end by a second constant current source. A second current path to be driven; a rectification current path that is intermittently controlled by a second semiconductor element having a second control end; and a first current path that bypasses the first semiconductor element that the first current path has. A third semiconductor element having three control ends,
When a positive potential is applied to one end of the second semiconductor element and one end of the fourth semiconductor element and a negative potential is applied to the other end of the second semiconductor element, the second current path is interrupted. By doing so, the first current path is conducted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is shut off, the rectified current path is shut off,
When a negative potential is applied to one end of the second semiconductor element and one end of the fourth semiconductor element, and a positive potential is applied to the other end of the second semiconductor element, the second current path becomes conductive. By doing so, the first current path is interrupted, the second control terminal of the second semiconductor element is driven, the second semiconductor element is made conductive, and the rectified current path is made conductive,
When the second current path is turned on, the third control element of the third semiconductor element is driven to turn on the third semiconductor element, whereby the first current path is turned on. , Driving the second control end of the second semiconductor element to turn off the second semiconductor element, and applying a positive potential to one end of the second semiconductor element and one end of the fourth semiconductor element. A rectifier circuit that cuts off the rectified current path when a negative potential is applied to the other end of the second semiconductor element.   Detecting a potential of one end of the first semiconductor element included in the first current path, and driving a second control terminal included in the second semiconductor element when a current flows in the first current path; Cutting off the second semiconductor element, driving a second control terminal of the second semiconductor element when no current flows in the first current path, and conducting the second semiconductor element; The rectifier circuit according to claim 1, further comprising an emitter follower circuit that controls a voltage applied to the second control terminal. A first coil is disposed on the primary side, a transformer having a second coil magnetically coupled to the first coil on the secondary side, and a current path of the second coil are connected in series. A third coil, first switching means for switching on / off of DC voltage supply to the primary side of the transformer, and voltage supply to the transformer being turned on by the first switching means, A first load current path for outputting a DC voltage based on an electromotive force generated in the second coil; and a second switching means, wherein the voltage supply to the transformer is switched from on to off by the first switching means. And a second load current path that outputs a DC voltage based on a back electromotive force generated in the third coil by turning on the second switching means. In the circuit,
The second switching means includes the rectifier circuit according to any one of claims 1 to 3,
Before the first switching means is switched from OFF to ON, the third control element of the third semiconductor element included in the rectifier circuit is driven to make the third semiconductor element conductive, thereby making the first semiconductor element conductive. The current path of the second semiconductor element included in the rectifier circuit is driven to turn off the second semiconductor element, and the one end of the second semiconductor element is connected to the PN junction. When a positive potential is applied to one end of the element or one end of the second semiconductor element and one end of the fourth semiconductor element, and a negative potential is applied to the other end of the second semiconductor element, the rectifying current path A voltage conversion circuit characterized by shutting off.

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