Inrush current prevention circuit and power conversion circuit

Abstract

To provide an inrush current prevention circuit capable of stabilizing a drive power supply voltage, preventing drive power consumption from becoming large, and miniaturizing a power conversion circuit.SOLUTION: An inrush current prevention circuit 30 for preventing an inrush current from entering into a converter 20 having a switch Q1, an inductor L1, and a diode D1 includes: an inrush current prevention resistor R1 connected between the inductor L1 and a connection point of the switch Q1 and the diode D1; a bypass switch Q2 connected in parallel with the inrush current prevention resistor R1; and a bootstrap circuit 31 connected to a drive power supply VCC and supplying power to the bypass switch Q2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inrush current prevention circuit and a power conversion circuit. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there is known an inrush current prevention circuit that suppresses an inrush current that may occur when an input voltage is applied to a predetermined current value or less (see, for example, Patent Document 1).

[0003] Such an inrush current prevention circuit can be used in a power conversion circuit 8 as shown in Fig. 3. The conventional power conversion circuit 8 includes a rectifier circuit 810, a converter 820, an inrush current prevention circuit 830, a control circuit 840, and a filter capacitor C4. The converter 820 has a switch Q1, an inductor L1, a diode D1, and an input capacitor C1, and the control circuit 840 is supplied with power from a drive power supply VCC and controls the switching operation of the switch Q1.

[0004] The inrush current prevention circuit 830 includes an inrush current prevention resistor R1, a thyristor SCR, and an auxiliary winding L2 disposed at a position opposite to the inductor L1. The inrush current prevention circuit 830 prevents an inrush current by the inrush current prevention resistor R1 when an input voltage is applied from the AC power supply AC. At this time, the thyristor SCR is turned off.

[0005] When the voltage stabilizes, the thyristor SCR is turned on by using the voltage induced in the auxiliary winding L2 by the current flowing through the inductor L1. This allows current to flow bypassing the inrush current prevention resistor R1. Therefore, while the circuit is operating, current is prevented from flowing through the inrush current prevention resistor R1, reducing conduction loss.

[0006] In the conventional inrush current prevention circuit 830 , an inrush current prevention resistor R 1 is connected between the rectifier circuit 810 and the inductor L 1 of the converter 820 . [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-142020 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the conventional power conversion circuit 8, the voltage change of the inductor L1 occurs due to the change in the alternating current power supply AC, and therefore the power induced in the auxiliary winding L2 is unstable and the driving power supply voltage supplied to the thyristor SCR is unstable. In other words, near the zero crossing of the current flowing through the inductor L1 (see the area surrounded by the dashed line A in FIG. 4(a)), the induced voltage drops, and there is a risk that the thyristor SCR cannot be turned on, resulting in an unstable driving power supply voltage.

[0009] One way to prevent this is to increase the voltage of the AC power supply, but this would result in larger conduction losses and therefore higher drive power consumption, as well as larger components, making it difficult to miniaturize the power conversion circuit.

[0010] If the polarity (winding method) of the auxiliary winding L2 is reversed, an excessive current will be induced in the auxiliary winding L2 near the zero crossing of the current flowing through inductor L1 (see the area surrounded by dashed line B in Figure 4(b)), resulting in large conduction loss. If the current flowing through inductor L1 becomes large, the induced voltage will decrease, and there is a risk that the thyristor SCR will not be able to turn on, resulting in the same issues as those of the conventional power conversion circuit 8.

[0011] It is also possible to use voltage doubler rectification or Cockcroft rectification, but in this case, although the drive power supply voltage is stable, the number of components increases, so there is a problem that it is difficult to miniaturize the power conversion circuit even in this case.

[0012] 5, an inrush current prevention circuit 930 may be connected in front of the rectifier circuit 910 (between the AC power source AC and the rectifier circuit 910). In the conventional power conversion circuit 9, it is necessary to prevent inrush current by using the current from the AC power source AC before it is rectified, so a triac TR1 capable of passing current in both directions and compatible with AC is used instead of a thyristor SCR. However, even in this case, there is a problem that it is difficult to miniaturize the power conversion circuit because the number of components increases, such as the use of an auxiliary winding.

[0013] Therefore, the present invention has been made to solve the above problems, and has an object to provide an inrush current prevention circuit that stabilizes the drive power supply voltage, prevents the drive power consumption from increasing, and enables the power conversion circuit to be miniaturized, and also to provide a power conversion circuit equipped with such an inrush current prevention circuit. [Means for solving the problem]

[0014] The inrush current prevention circuit of the present invention is an inrush current prevention circuit that prevents inrush current into a converter having a switch, an inductor, a diode, and a capacitor, and is characterized in comprising an inrush current prevention resistor connected between the inductor and a connection point of the switch and the diode, a bypass switch connected in parallel with the inrush current prevention resistor, and a bootstrap circuit connected to a drive power supply and supplying power to the bypass switch.

[0015] The power conversion circuit of the present invention comprises a rectifier circuit, a converter having an inductor, a switch, a diode and a capacitor, a control circuit connected to a driving power supply and controlling the switching operation of the switch, and the inrush current prevention circuit of the present invention, wherein the driving power supply is connected to a bootstrap circuit of the inrush current prevention circuit. Effect of the Invention

[0016] According to the inrush current prevention circuit and power conversion circuit of the present invention, since a bootstrap circuit is provided which is connected to a drive power supply and supplies power to the bypass switch, the drive power supply voltage supplied to the bypass switch does not depend on the voltage of the AC power supply. Therefore, the drive power supply voltage can be stabilized. Furthermore, since it is not necessary to increase the voltage of the AC power supply, it is possible to prevent the conduction loss from increasing and the drive power consumption from increasing. Furthermore, since components such as an auxiliary winding are not required, the power conversion circuit can be made smaller. [Brief description of the drawings]

[0017] [Figure 1] 1 is a circuit diagram showing a power conversion circuit 1 and an inrush current prevention circuit 30 according to a first embodiment. [Diagram 2] 1 is a circuit diagram showing a power conversion circuit 2 and an inrush current prevention circuit 30a according to a second embodiment. [Diagram 3] 1 is a circuit diagram showing a conventional power conversion circuit 8 and an inrush current prevention circuit 830. FIG. [Figure 4] 4A and 4B are diagrams showing the voltage induced in the auxiliary winding L2 when a current flows through the inductor L1, respectively. Fig. 4A shows the voltage induced in the auxiliary winding L2 in the case of forward polarity, and Fig. 4B shows the voltage induced in the auxiliary winding L2 in the case of reverse polarity. [Diagram 5] FIG. 1 is a circuit diagram showing a conventional power conversion circuit 9 and an inrush current prevention circuit 930. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The inrush current prevention circuit and power conversion circuit of the present invention will be described below based on the embodiments shown in the drawings. Note that the embodiments described below do not limit the invention according to the claims. Also, not all of the elements and combinations thereof described in the embodiments are necessarily essential to the solution of the present invention.

[0019] [Embodiment 1] 1. Configuration of power conversion circuit 1 according to embodiment 1 1, the power conversion circuit 1 according to the first embodiment includes a rectifier circuit 10, a converter 20, an inrush current prevention circuit 30 according to the first embodiment, and a control circuit 40. The power conversion circuit 1 is supplied with an AC input voltage from an AC power source AC.

[0020] The rectifier circuit 10 is a circuit that performs, for example, full-wave rectification on an AC input voltage from an AC power source AC. The rectifier circuit 10 is formed by, for example, connecting four diodes in a bridge configuration.

[0021] The converter 20 is disposed in the subsequent stage of the rectifier circuit 10. The converter 20 is a boost circuit having a switch Q1, an inductor L1, and a diode D1. An input capacitor C1 is disposed in the subsequent stage of the diode D1.

[0022] The inductor L1 is connected to the rear stage of the rectifier circuit 10. An inrush current prevention resistor R1, which will be described later, is disposed between the inductor L1 and the connection point of the switch Q1 and the diode D1.

[0023] The switch Q1 performs a switching operation based on a switching pulse input from the control circuit 40. A MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is used as the switch Q1, but an IGBT or other appropriate FET may also be used. Also, other appropriate switch elements may also be used.

[0024] In the diode D1, the anode electrode is connected to the inrush current prevention resistor R1, the drain electrode of the switch Q1, and the source electrode of the bypass switch Q2, and the cathode electrode is connected to the external connection terminal and the input capacitor C1. Note that appropriate inductors and diodes can be used for the inductor L1 and the diode D1.

[0025] The input capacitor C1 tolerates ripple currents caused by the switching of the switch Q1 etc. and fluctuations in the input voltage, and reduces noise caused by these. One side of the input capacitor C1 is connected to the drain electrode of the switch Q1 via the diode D1, and the other side is connected to the source electrode of the switch Q1.

[0026] The inrush current prevention circuit 30 will be described later.

[0027] The control circuit 40 controls the switching operation of the switch Q1. The control circuit 40 is connected to a drive power supply VCC and the gate electrode of the switch Q1, generates a switching pulse using power supplied from the drive power supply VCC, and outputs the pulse to the gate electrode.

[0028] 2. Configuration of the inrush current prevention circuit 30 according to the first embodiment As shown in FIG. 1, the inrush current prevention circuit 30 according to the first embodiment includes an inrush current prevention resistor R1, a bootstrap circuit 31, a bypass switch Q2, and resistors R2 and R4.

[0029] The inrush current prevention resistor R1 is connected between the inductor L1 and the connection point of the switch Q1 and the diode D1. The inrush current prevention resistor R1 makes it possible to prevent an inrush current from the AC power supply when the input voltage is turned on.

[0030] The bootstrap circuit 31 is electrically connected to the drive power supply VCC and supplies power to the bypass switch Q2. The bootstrap circuit 31 has a bootstrap diode BD and a bootstrap capacitor C2. When the switch Q1 is turned on, the bootstrap circuit 31 charges the bootstrap capacitor C2 using power supplied from the drive power supply VCC and turns on the bypass switch Q2 using the bootstrap capacitor C2 as a power supply.

[0031] The bootstrap diode BD has an anode electrode connected to the drive power supply VCC via a resistor R4, and a cathode electrode connected to the bootstrap capacitor C2 and the gate electrode of the bypass switch Q2, and also connected to the source electrode of the bypass switch Q2 via a resistor R2. The resistor R4 suppresses inrush current from the drive power supply VCC, and prevents a current greater than a predetermined value from being applied to the bootstrap diode BD.

[0032] The bootstrap capacitor C2 has one electrode connected to the cathode electrode of the bootstrap diode BD and the gate electrode of the bypass switch Q2, and the other electrode connected to the source electrode of the bypass switch Q2.

[0033] The bypass switch Q2 is connected in parallel with the inrush current prevention resistor R1. In the first embodiment, the bypass switch Q2 is a field effect transistor (FET), and in the first embodiment, a MOSFET is used. The drain electrode of the bypass switch Q2 is connected to the connection point of the inductor L1 and the inrush current prevention resistor R1, the source electrode is connected to the inrush current prevention resistor R1, the switch Q1, the diode D1, the bootstrap capacitor C2, and the resistor R2, and the gate electrode is connected to the bootstrap diode BD and the bootstrap capacitor C2.

[0034] In the first embodiment, as in the case of the conventional power conversion circuit 8 in Fig. 3, an inrush current prevention resistor R1 is provided in the subsequent stage of the rectifier circuit 10, but the filter capacitor C4 does not have to be provided. In the conventional power conversion circuit 8, the filter capacitor C4 is provided to smooth out voltage fluctuations and prevent the thyristor SCR from making an erroneous call, but in the first embodiment, an FET is used as the bypass switch Q2, making it difficult for an erroneous call to occur.

[0035] 3. Operation of the power conversion circuit 1 and the inrush current prevention circuit 30 according to the first embodiment Next, the operation of the power conversion circuit 1 and the inrush current prevention circuit 30 according to the first embodiment will be described. In the power conversion circuit 1 according to the first embodiment, when an input voltage is applied from an AC power source, an inrush current is prevented by the inrush current prevention resistor R1. At this time, the control circuit 40 is not started, and the switch Q1 of the converter 20 is not performing a switching operation.

[0036] When the control circuit 40 starts up with power supplied from the drive power supply VCC, a switching pulse is output from the control circuit 40 to the gate electrode of the switch Q1, turning on the switch Q1. At this time, power is supplied from the drive power supply VCC to the bootstrap circuit 31, the bootstrap capacitor C2 is charged, and the voltage charged in the bootstrap capacitor C2 is used as a power supply to turn on the bypass switch Q2.

[0037] Therefore, when an input voltage is applied from an AC power supply, the bypass switch Q2 is turned off and a current flows through the inrush current prevention resistor R1. After the converter 20 starts up, the bypass switch Q2 is turned on and a current flows through the bypass switch Q2 to the diode D1 and the switch Q1.

[0038] 4. Inrush current prevention circuit 30 according to embodiment 1 and Effect of power conversion circuit 1 The inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment include a bootstrap circuit 31 that is connected to the drive power supply VCC and supplies power to the bypass switch Q2, so that the drive power supply voltage supplied to the bypass switch Q2 does not depend on the voltage of the AC power supply AC. This makes it possible to stabilize the drive power supply voltage. In addition, since it is not necessary to increase the voltage of the AC power supply AC, it is possible to prevent the conduction loss from increasing, and therefore it is possible to prevent the drive power consumption from increasing. Furthermore, since components such as an auxiliary winding are not required, the power conversion circuit can be made smaller.

[0039] According to the inrush current prevention circuit 30 and the power conversion circuit 1 of the first embodiment, the driving power supply VCC is a power supply that supplies power to the control circuit 40 that controls the switching operation of the switch Q1, and therefore a power supply that supplies power to the control circuit 40 for switching the switch Q1, which is already used in the conventional power conversion circuit, can be utilized as the driving power supply. Therefore, it is not necessary to prepare a separate power supply for charging the bootstrap capacitor C2. In addition, since the driving power supply VCC that supplies power to the control circuit 40 is also used as a power supply that supplies power to the bootstrap circuit 31, power can be stably supplied to the bootstrap circuit 31. In addition, since the voltage of the driving power supply VCC is a relatively stable voltage, the resistance value of the resistor R4 provided to keep the power supplied to the bootstrap circuit 31 constant can be made small. Furthermore, the driving power supply VCC itself that drives the switch Q1 may be small, and the power supplied to the bootstrap circuit 31 may also be small, so the capacity of the bootstrap capacitor C2 of the bootstrap circuit 31 may be small.

[0040] According to the inrush current prevention circuit 30 and the power conversion circuit 1 of the first embodiment, the bootstrap circuit 31 has a bootstrap capacitor C2 and a bootstrap diode BD. The anode electrode of the bootstrap diode BD is electrically connected to the drive power supply VCC. The connection point between the cathode electrode of the bootstrap diode BD and the bootstrap capacitor C2 is connected to the gate electrode of the bypass switch Q2. Therefore, the bootstrap capacitor C2 is charged with power supplied from the drive power supply VCC, and the bypass switch Q2 can perform a switching operation using the bootstrap capacitor C2 as a power supply.

[0041] According to the inrush current prevention circuit 30 and the power conversion circuit 1 of the first embodiment, the bypass switch Q2 is a field effect transistor, so that the bypass switch Q2 is less likely to make a false call, and the inrush current prevention circuit 30 can function with high accuracy. Furthermore, the on-resistance of a field effect transistor is smaller than that of a thyristor or a triac, so that the conduction loss is further reduced. Furthermore, by connecting a plurality of bypass switches Q2 in parallel, it is possible to prevent the current capacity from becoming large.

[0042] [Embodiment 2] The inrush current prevention circuit 30a and the power conversion circuit 2 according to the second embodiment basically have the same configuration as the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment, but differ from the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment in that a thyristor SCR is used as a bypass switch instead of a field effect transistor Q2. In the second embodiment, the inrush current prevention circuit 30a includes an inrush current prevention resistor R1, a bootstrap circuit 31, resistors R2 and R3, and a capacitor C2, as shown in Fig. 2. The bootstrap circuit 31 includes a bootstrap diode BD and a bootstrap capacitor C3.

[0043] As described above, the inrush current prevention circuit 30a and the power conversion circuit 2 according to the second embodiment are different from the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment in that a thyristor SCR is used as a bypass switch instead of the field effect transistor Q2. However, as in the case of the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment, the inrush current prevention circuit 30a and the power conversion circuit 2 include a bootstrap circuit 31 that is connected to the drive power supply VCC and supplies power to the bypass switch SCR. Therefore, the drive power supply voltage supplied to the bypass switch SCR does not depend on the voltage of the AC power supply AC. Therefore, the drive power supply voltage can be stabilized. In addition, since it is not necessary to increase the voltage of the AC power supply AC, it is possible to prevent the conduction loss from increasing, and therefore it is possible to prevent the drive power consumption from increasing. Furthermore, since components such as an auxiliary winding are not required, the power conversion circuit can be made smaller.

[0044] Furthermore, in the inrush current prevention circuit 30a and the power conversion circuit 2 according to the second embodiment, the bypass switch is a thyristor SCR, and therefore switching is possible even in a situation where a large current flows.

[0045] The inrush current prevention circuit 30a and the power conversion circuit 2 according to the second embodiment have the same configuration as the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment except for using a thyristor SCR instead of the field effect transistor Q2, and therefore have the corresponding effects among the effects possessed by the inrush current prevention circuit 30 and the power conversion circuit 1 according to the first embodiment.

[0046] Although the present invention has been described based on the above embodiment, the present invention is not limited to the above embodiment. The present invention can be embodied in various forms without departing from the spirit of the present invention, and for example, the following modifications are also possible.

[0047] (1) The positions, connections, quantities, etc. described in the above embodiments (including the modified examples; the same applies below) are merely examples and may be changed without impairing the effects of the present invention.

[0048] (2) In the above-mentioned second embodiment, a thyristor is used as the bypass switch, but the present invention is not limited to this. A triac may also be used as the bypass switch. [Explanation of symbols]

[0049] 1, 2, 8, 9... power conversion circuit, 10... rectifier circuit, 20... converter, 30, 30a... inrush current prevention circuit, 31... bootstrap circuit, 40... control circuit, BD... bootstrap diode, C1... input capacitor, C2, C3... bootstrap capacitor, D1... diode, L1... inductor, Q1... switch, Q2... bypass switch (field effect transistor), R1... inrush current prevention resistor, SCR... bypass switch (thyristor), VCC... drive power supply

Claims

1. 1. An inrush current prevention circuit for preventing inrush current into a converter having a switch, an inductor, a diode, and a capacitor, comprising: an inrush current prevention resistor connected between the inductor and a connection point of the switch and the diode; a bypass switch connected in parallel with the inrush current prevention resistor; a bootstrap circuit connected to a drive power supply and supplying power to the bypass switch.

2. 2. The inrush current prevention circuit according to claim 1, wherein the drive power supply is a power supply that supplies power to a control circuit that controls a switching operation of the switch.

3. the bootstrap circuit includes a bootstrap capacitor and a bootstrap diode; an anode electrode of the bootstrap diode is electrically connected to the driving power supply; 3. The inrush current prevention circuit according to claim 1, wherein a connection point between a cathode electrode of the bootstrap diode and the bootstrap capacitor is connected to a gate electrode of the bypass switch.

4. 3. The inrush current prevention circuit according to claim 1, wherein the bypass switch is a field effect transistor.

5. 3. The inrush current prevention circuit according to claim 1, wherein the bypass switch is a thyristor or a triac.

6. A rectifier circuit; a converter having an inductor, a switch, a diode and a capacitor; A control circuit connected to a drive power supply for controlling a switching operation of the switch; The inrush current prevention circuit according to claim 1 or 2, 2. A power conversion circuit comprising: a driving power supply connected to a bootstrap circuit of the inrush current prevention circuit;

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