Overvoltage detection device and overvoltage protection circuit

Abstract

The present invention provides an overvoltage detection device capable of detecting overvoltage with high reliability.　An overvoltage detection device (10) detects overvoltage of a power supply voltage (VDC), comprises a voltage detection circuit (11) that generates a voltage obtained by reducing the power supply voltage at a predetermined ratio, and outputs the voltage generated by the voltage detection circuit (11). The overvoltage detection device (10) further comprises a clamp circuit (12) that clamps an output voltage (VO) of the overvoltage detection device (10) to zero when the power supply voltage (VDC) is lower than a predetermined threshold.

Description

Overvoltage detection device and overvoltage protection circuit

[0001] The present invention relates to an overvoltage detection device that detects an overvoltage of a power supply that supplies power to a main circuit, and an overvoltage protection circuit that includes an overvoltage detection device.

[0002] 2. Description of the Related Art When the voltage of a power supply that supplies power to a main circuit such as a power conversion circuit becomes overvoltage due to noise or surges, an overvoltage protection circuit is provided to protect circuit devices from the overvoltage.

[0003] A known prior art overvoltage protection circuit uses a voltage dividing resistor as an overvoltage detection device and a comparator that determines whether an overvoltage has been detected (see, for example, Patent Document 1). The divided voltage of the power supply voltage output by the voltage dividing resistor is input to the comparator. The comparator compares the input divided voltage with a reference voltage generated by a reference voltage generation circuit. If the comparator determines that the divided voltage is greater than the reference voltage, it outputs a control signal to stop a main circuit device such as an inverter.

[0004] Japanese Patent Application Laid-Open No. 2004-70666

[0005] In the above-described conventional technology, if noise is superimposed on the output of the voltage dividing resistor, the overvoltage protection circuit may malfunction at a voltage lower than the overvoltage setting value, which may cause the overvoltage detection device to erroneously detect an overvoltage.

[0006] Therefore, the present invention provides an overvoltage detection device that can detect overvoltage with high reliability, and an overvoltage protection circuit that includes such an overvoltage detection device.

[0007] To solve the above problems, an overvoltage detection device according to the present invention detects an overvoltage of a power supply voltage, includes a voltage detection circuit that generates a voltage that is the power supply voltage reduced by a predetermined ratio, and outputs the voltage generated by the voltage detection circuit. The overvoltage detection device according to the present invention further includes a clamp circuit that clamps the output voltage of the overvoltage detection device to zero when the power supply voltage is lower than a predetermined threshold.

[0008] In order to solve the above problems, the overvoltage protection circuit according to the present invention protects a main circuit from an overvoltage of a power supply voltage, and includes an overvoltage detection device that detects an overvoltage of the power supply voltage, and a comparator that compares the output voltage of the overvoltage detection device with a reference voltage and outputs a command signal to stop operation of the main circuit if the output voltage exceeds the reference voltage, and this overvoltage detection device is the overvoltage detection device according to the present invention.

[0009] According to the present invention, erroneous detection of an overvoltage is prevented, thereby improving the reliability of the overvoltage detection device and the overvoltage protection circuit.

[0010] Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments.

[0011] Fig. 1 is a block diagram showing a circuit configuration of an overvoltage detection device according to an embodiment; Fig. 2 is a block diagram showing a circuit configuration of an overvoltage detection device according to Example 1; Fig. 3 is a circuit diagram showing a first configuration example of an overvoltage detection device according to Example 1; Fig. 4 is a circuit diagram showing a second configuration example of an overvoltage detection device according to Example 1; Fig. 5 is a block diagram showing a circuit configuration of an overvoltage detection device according to Example 2; Fig. 6 is a circuit diagram showing a configuration example of an overvoltage detection device according to Example 2;

[0012] FIG. 1 is a block diagram showing the circuit configuration of an overvoltage detection device according to one embodiment of the present invention.

[0013] The overvoltage detector 10 and the comparator 20 detect the DC power supply voltage V ＤＣ An overvoltage protection circuit is configured to protect against overvoltage.

[0014] A DC / AC converter circuit (inverter circuit) or a DC / DC converter circuit including a parallel circuit of a semiconductor switching element (an IGBT in FIG. 1 ) and a free wheeling diode is applied as the power conversion circuit 100. The power conversion circuit 100 converts input DC power into desired power by the control device 200 controlling the switching of the semiconductor switching element.

[0015] The overvoltage detection device 10 detects the input DC power supply voltage V ＤＣis reduced by the voltage detection circuit 11. The overvoltage detection device 10 detects the reduced voltage (V Ｏ The comparator 20 outputs the output voltage V Ｏ and a reference voltage V generated by a reference voltage generating circuit (not shown). ｒｅｆ The comparator 20 compares V Ｏ V ｒｅｆ exceeded (V Ｏ >V ｒｅｆ ) is determined, that is, V ＤＣ becomes equal to or greater than a preset overvoltage setting value, and the overvoltage detection device 10 determines that an overvoltage has been detected, the control device 200 sends a command signal to stop the operation of the power conversion circuit 100. When the control device 200 receives the command signal from the comparator 20, it stops the switching of the semiconductor switching elements.

[0016] The voltage detection circuit 11 detects the input DC power supply voltage V ＤＣ is reduced by a predetermined ratio so that the voltage value is within the range of the allowable input voltage of the subsequent comparator 20 (V Ｏ ) and output it.

[0017] The overvoltage detection device 10 further detects the output voltage V Ｏ The output voltage (V Ｏ ) clamp circuit 12. The output voltage clamp circuit 12 clamps the DC power supply voltage V ＤＣ is lower than the overvoltage setting value, the output potential of the overvoltage detection device 10 is clamped to the reference potential (GND). Ｏ is clamped to zero volts. ＤＣ is lower than the overvoltage setting value, the overvoltage detection device 10 is prevented from erroneously detecting an overvoltage.

[0018] In this embodiment, the output voltage clamp circuit 12 is ＤＣ is a preset threshold V ＤＣ＿ｔｈ If it is lower (V ＤＣ <V ＤＣ＿ｔｈ ) and the output voltage V Ｏ is clamped to zero volts. ＤＣ＿ｔｈis a voltage value that is lower than the overvoltage setting value, and V Ｏ is set to a voltage value equal to or greater than that at the time of overvoltage detection.

[0019] According to this embodiment, the overvoltage detection device 10 includes the output voltage clamp circuit 12, so that V ＤＣ is lower than the overvoltage setting value, erroneous detection by the overvoltage detection device 10 is prevented, thereby improving the reliability of the overvoltage detection device 10. Therefore, the reliability of the overvoltage protection circuit is improved.

[0020] Hereinafter, embodiments of the present invention will be described with reference to the drawings, based on the following Examples 1 and 2. In each drawing (including the aforementioned FIG. 1), the same reference numerals indicate the same components or components with similar functions.

[0021] FIG. 2 is a block diagram showing a circuit configuration of an overvoltage detection device according to a first embodiment of the present invention.

[0022] The voltage detection circuit 11 detects the DC power supply voltage V ＤＣ Enter the V you entered. ＤＣ The voltage detection circuit 11 detects the reduced voltage (V Ｏ ) is output.

[0023] In the first embodiment, the output voltage clamp circuit 12 includes a short circuit 13 connected between the output of the voltage detection circuit 11 and the reference potential GND, and a DC power supply voltage V ＤＣ is the above-mentioned threshold V ＤＣ＿ｔｈ and a threshold detection circuit 14 that activates the short circuit 13 when it detects that the voltage is lower than the threshold.

[0024] According to the first embodiment, the DC power supply voltage V ＤＣ is the above-mentioned threshold V ＤＣ＿ｔｈ If the voltage V is lower than the reference potential GND, the short circuit 13 operates to short-circuit the output of the voltage detection circuit 11 and the reference potential GND. Ｏ is clamped to zero volts.

[0025] Furthermore, according to this embodiment, by using the short circuit 13, the output voltage clamp circuit 12 can have a relatively simple circuit configuration.

[0026] FIG. 3 is a circuit diagram showing a first configuration example of the overvoltage detection device according to the first embodiment.

[0027] 3, the voltage detection circuit 11 is configured by a resistive voltage divider circuit. In a first configuration example, the resistive voltage divider circuit has a series circuit of resistors R1 to R4, one end of which is connected to the high potential VDC of the DC power supply and the other end of which is connected to the reference potential GND, respectively.

[0028] 3, resistors R1, R2, R3, and R4 are connected in series in this order from VDC to GND. The symbols R1, R2, R3, and R4 indicate the resistors and also represent their resistance values.

[0029] The resistor voltage divider circuit divides the DC power supply voltage V ＤＣ The voltage divided from Ｏ ) is output from a series connection point A between a resistor R4 connected to GND and a resistor R3 connected in series with the resistor R4. ０ is the resistance value R of the series connection circuit of resistors R1 to R4 (in FIG. 3, R = R1 + R2 + R3 + R4) and the resistance value R between the output of the resistive voltage divider circuit and GND Ｏ (In Figure 3, R ０ =R4) Ｏ / R) in V ＤＣ The voltage is divided from (V Ｏ = (R Ｏ / R) x V ＤＣ The voltage division ratio is V Ｏ The voltage value of V Ｏ In this embodiment (FIG. 1), the output voltage is set to a voltage value within the range of the allowable input voltage of the comparator 20.

[0030] The short circuit 13 is composed of a MOSFET M1, which is a semiconductor switching element. The MOSFET M1 is connected in parallel with the resistor R4. That is, the MOSFET M1 is connected between GND and a series connection point A between the resistors R3 and R4, which is the output of the resistive voltage divider circuit. In the configuration example of FIG. 3, an N-channel MOSFET is used as the MOSFET M1. The drain and source of the MOSFET M1 are connected to the series connection point A and GND, respectively.

[0031] MOSFET M1 is V ＤＣ V ＤＣ＿ｔｈ If it is lower, it is turned on by the threshold detection circuit 14, shorting both ends of the resistor R4, i.e., between the output of the resistor divider circuit and GND.

[0032] The threshold detection circuit 14 is composed of a resistive voltage dividing circuit and a NOT circuit L1 which serves as a drive circuit for the MOSFET M1.

[0033] The resistive voltage divider circuit has a series circuit of resistors R5 to R8, one end and the other end of the series circuit being connected to the high potential VDC of the DC power supply and the reference potential GND, respectively.

[0034] 3, resistors R5, R6, R7, and R8 are connected in series in this order from VDC to GND. The symbols R5, R6, R7, and R8 indicate the resistors and also represent their resistance values.

[0035] The resistor voltage divider circuit divides the DC power supply voltage V ＤＣ The voltage input from the resistor voltage divider circuit to the NOT circuit L1 is V ｉｎ Then, the voltage division ratio is V ＤＣ >V ＤＣ＿ｔｈ and V ＤＣ <V ＤＣ＿ｔｈ In the case of V ｉｎ are set so that they correspond to 1 (HIGH) and 0 (LOW) of the inputs of the NOT circuit, respectively. As a result, the output of the NOT circuit L1 is V ＤＣ >V ＤＣ＿ｔｈand V ＤＣ <V ＤＣ＿ｔｈ , they become 0 (LOW) and 1 (HIGH), respectively.

[0036] That is, V ＤＣ V ＤＣ＿ｔｈ If (V ＤＣ =V ＤＣ＿ｔｈ ) in V ｉｎ is the input threshold V ｉｎ＿ｔｈ Then, the NOT circuit L1 is V ｉｎ >V ｉｎ＿ｔｈ In addition, the NOT circuit L1 outputs a control signal to turn off the MOSFET M1 when V ｉｎ <V ｉｎ＿ｔｈ When the voltage Vcc is 0, the control signal for turning on the MOSFET M1 is output.

[0037] The output of the NOT circuit L1 is connected to the gate of the MOSFET_M1. ＤＣ >V ＤＣ＿ｔｈ and V ＤＣ <V ＤＣ＿ｔｈ are in the off state and the on state, respectively. ＤＣ <V ＤＣ＿ｔｈ In this case, a short circuit is made between the output of the voltage detection circuit 11, which is made up of a resistive voltage divider circuit made up of resistors R1 to R4, and the reference potential GND.

[0038] According to the first configuration example, the voltage detection circuit 11, the short circuit 13, and the threshold detection circuit 14 can be configured from relatively simple circuits, so that the circuit scale of the overvoltage detection device 10 can be reduced.

[0039] FIG. 4 is a circuit diagram showing a second configuration example of the overvoltage detection device according to the first embodiment.

[0040] The differences from the first configuration example (FIG. 3) will be described below.

[0041] As shown in FIG. 4, in the second configuration example, the input of the NOT circuit L1 is connected to the high potential VDC of the DC power supply.

[0042] The voltage input to the NOT circuit L1 is V ｉｎ Then, V ｉｎ =VＤＣ and V ＤＣ >V ＤＣ＿ｔｈ and V ＤＣ <V ＤＣ＿ｔｈ In the case of V ｉｎ The threshold of the NOT circuit L1 is set so that V corresponds to 1 (HIGH) and V corresponds to 0 (LOW) of the input of the NOT circuit. ＤＣ >V ＤＣ＿ｔｈ and V ＤＣ <V ＤＣ＿ｔｈ , they become 0 (LOW) and 1 (HIGH), respectively.

[0043] Therefore, V ＤＣ＿ｔｈ is the input threshold V ｉｎ＿ｔｈ Then, the NOT circuit L1 is V ｉｎ >V ｉｎ＿ｔｈ When V ｉｎ <V ｉｎ＿ｔｈ When the voltage Vcc is 0, the control signal for turning on the MOSFET M1 is output.

[0044] Therefore, similarly to the first configuration example, MOSFET_M1 has a V ＤＣ <V ＤＣ＿ｔｈ In this case, the output of the voltage detection circuit 11 is short-circuited to the reference potential GND.

[0045] According to the second configuration example, the total number of circuit components constituting the overvoltage detection device 10 can be reduced.

[0046] FIG. 5 is a block diagram showing a circuit configuration of an overvoltage detection device according to a second embodiment of the present invention.

[0047] The differences from the first embodiment (FIG. 2) will be described below.

[0048] The voltage detection circuit 11 detects the DC power supply voltage V ＤＣ Enter the V you entered. ＤＣ The voltage detection circuit 11 detects the reduced voltage (V Ｏ As will be described later, the operation of the voltage detection circuit 11 is controlled by the threshold detection circuit 14.

[0049] In the second embodiment, the output voltage clamp circuit 12 includes a short circuit 13 formed of a passive circuit connected between the output of the voltage detection circuit 11 and the reference potential GND, and a DC power supply voltage V ＤＣ is the above-mentioned threshold V ＤＣ＿ｔｈ and a threshold detection circuit 14 that stops the operation of the voltage detection circuit 11 when it detects that the voltage is lower than the threshold value.

[0050] According to the second embodiment, the DC power supply voltage V ＤＣ is the above-mentioned threshold V ＤＣ＿ｔｈ If it is lower, the voltage detection circuit 11 detects V ＤＣ From V ＤＣ When the operation of generating and outputting the reduced voltage is stopped, the potential of the output of the voltage detection circuit 11 is clamped to the reference potential GND by the short circuit 13. Therefore, the output voltage V Ｏ is clamped to zero volts.

[0051] Furthermore, according to the second embodiment, the output voltage clamp circuit 12 can have a relatively simple circuit configuration by using the short circuit 13 that is configured as a passive circuit.

[0052] FIG. 6 is a circuit diagram showing an example of the configuration of an overvoltage detection device according to the second embodiment.

[0053] 6, the voltage detection circuit 11 is configured by a resistive voltage divider circuit. In this configuration example, the resistive voltage divider circuit has a series circuit of resistors R1 to R4 and a MOSFET M1, and one end and the other end of the series circuit are connected to the high potential VDC of the DC power supply and the reference potential GND, respectively.

[0054] 6, resistors R1, R2, R3, MOSFET M1, and resistor R4 are connected in series in this order from VDC to GND. The symbols R1, R2, R3, and R4 indicate the resistors and also represent their resistance values.

[0055] When the MOSFET M1 is in the on state, the resistive voltage divider circuit divides the DC power supply voltage V ＤＣ The voltage divided from Ｏ) is output from a series connection point A of a resistor R4 connected to GND and a MOSFET M1 connected in series with the resistor R4.

[0056] The on-resistance of MOSFET M1 is much smaller than that of R1 to R4, so V ０ is the resistance value R of the series connection circuit of resistors R1 to R4 (in FIG. 6, R=R1+R2+R3+R4) and the resistance value R between the output of the resistive voltage divider circuit and GND. Ｏ (In Figure 6, R Ｏ =R4) Ｏ / R) in V ＤＣ The voltage is divided from (V Ｏ = (R Ｏ / R) x V ＤＣ The voltage division ratio is V Ｏ The voltage value of V Ｏ In this embodiment (FIG. 1), the output voltage is set to a voltage value within the range of the allowable input voltage of the comparator 20.

[0057] The short circuit 13 is composed of a resistor R4, which is a passive element.

[0058] The threshold detection circuit 14 is configured with a MOSFET M1. In the configuration example of Fig. 6, an N-channel MOSFET is used as the MOSFET M1. The drain and source of the MOSFET M1 are connected to one end of the resistor R3 on the GND side and one end of the resistor R4 on the VDC side, respectively.

[0059] The gate of MOSFET M1 is connected to VDC. Therefore, MOSFET M1 is connected to V ＤＣ is input as a control signal. The input voltage threshold of the control signal in MOSFET M1, i.e., the gate threshold voltage, is V ＤＣ >V ＤＣ＿ｔｈ MOSFET M1 is turned on when V ＤＣ <V ＤＣ＿ｔｈ V so that MOSFET M1 is in an off state when ＤＣ＿ｔｈ is set to

[0060] When MOSFET M1 is in the off state, the electrical connection between R3 and the output in the resistive voltage divider circuit is released, and the operation of the resistive voltage divider circuit stops. At this time, the connection between the output of the resistive voltage divider circuit and resistor R4 is maintained, and the output of the resistive voltage divider circuit and GND are connected by resistor R4. As a result, the output potential is clamped to the reference potential GND, and the output voltage V Ｏ is clamped to zero volts. ＤＣ <V ＤＣ＿ｔｈ When Ｏ is clamped to zero volts.

[0061] According to the example configuration of the overvoltage detection device 10 shown in FIG. 6, the voltage detection circuit 11, short circuit 13, and threshold detection circuit 14 can be configured from relatively simple circuits, so the circuit scale of the overvoltage detection device 10 can be reduced.

[0062] The present invention is not limited to the above-described embodiments and examples, and includes various modifications. For example, the above-described examples have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, some of the configurations of each example can be deleted, other configurations can be added, or other configurations can be replaced.

[0063] For example, the resistive voltage divider circuit constituting the voltage detection circuit may include a parallel circuit of a plurality of resistors, or the voltage detection circuit may include a capacitive voltage divider circuit using a capacitor.

[0064] Moreover, instead of the MOSFET M1, other semiconductor switching elements such as a junction type FET may be used.

[0065] REFERENCE SIGNS LIST 10 Overvoltage detection device 11 Voltage detection circuit 12 Output voltage clamp circuit 13 Short circuit 14 Threshold detection circuit 20 Comparator 100 Power conversion circuit 200 Control device

Claims

1. An overvoltage detection device that detects an overvoltage of a power supply voltage, comprising: a voltage detection circuit that generates a voltage that is the power supply voltage reduced by a predetermined ratio; and a clamp circuit that outputs the voltage generated by the voltage detection circuit; and that clamps the output voltage of the overvoltage detection device to zero when the power supply voltage is lower than a predetermined threshold.

2. An overvoltage detection device according to claim 1, wherein the clamp circuit comprises: a short circuit connected between the output of the overvoltage detection device and a reference potential; and a threshold detection circuit that activates the short circuit when it detects that the power supply voltage is lower than the threshold.

3. An overvoltage detection device according to claim 2, wherein the voltage detection circuit has a first resistive voltage divider circuit, the short circuit has a semiconductor switching element, and the threshold detection circuit turns on the semiconductor switching element when it detects that the power supply voltage is lower than the threshold.

4. An overvoltage detection device according to claim 3, wherein the threshold detection circuit comprises: a second resistive voltage divider circuit; and a drive circuit which receives the divided voltage by the second resistive voltage divider circuit, sets the divided voltage when the power supply voltage is at the threshold as an input threshold, and outputs a control signal to turn on the semiconductor switching element when the divided voltage is lower than the input threshold.

5. An overvoltage detection device according to claim 3, wherein the threshold detection circuit comprises a drive circuit which inputs the power supply voltage, sets the threshold as an input threshold, and outputs a control signal to turn on the semiconductor switching element when the power supply voltage is lower than the input threshold.

6. An overvoltage detection device according to claim 1, wherein the clamp circuit comprises: a short circuit formed of a passive element connected between the output of the overvoltage detection device and a reference potential; and a threshold detection circuit which stops operation of the voltage detection circuit when it detects that the power supply voltage is lower than the threshold.

7. An overvoltage detection device according to claim 6, wherein the voltage detection circuit has a resistor voltage divider circuit in which a plurality of resistors and a semiconductor switching element are connected in series and which operates when the semiconductor switching element is in an on state, and the threshold detection circuit turns off the semiconductor switching element when it detects that the power supply voltage is lower than the threshold.

8. An overvoltage detection device according to claim 7, wherein the short circuit is constituted by some of the plurality of resistors, the threshold detection circuit is constituted by the semiconductor switching element, and the semiconductor switching element receives the power supply voltage as a control signal, uses the threshold as an input voltage threshold, and turns off when the voltage of the control signal is lower than the input voltage threshold.

9. An overvoltage protection circuit for protecting a main circuit from an overvoltage of a power supply voltage, comprising: an overvoltage detection device for detecting the overvoltage of the power supply voltage; and a comparator for comparing the output voltage of the overvoltage detection device with a reference voltage, and for outputting a command signal for stopping operation of the main circuit if the output voltage exceeds the reference voltage, wherein the overvoltage detection device is the overvoltage detection device described in claim 1.

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