JP2010246179A - Semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an overload current detection circuit capable of suppressing erroneous detection of overload currents of switching elements, and to provide a semiconductor device including the overcurrent detection circuit. <P>SOLUTION: The semiconductor device includes a main switching element 1, namely a MOSFET for controlling the drive current supplied to a load, based on a control signal Vg applied to a gate terminal; and the overload current detection circuit for detecting an overload current of the main switching element 1. The overload current detection circuit is constituted of a series circuit. The series circuit includes a current sense element 2, namely a MOSFET, including a gate terminal to which a control signal Vg is applied; a MOSFET 3 for current detection, where a threshold voltage is not less than a voltage drop of the main switching element 1 in normal operation and the gate terminal is connected to a drain terminal; and a resistive element 7. A voltage drop Vs1 of the resistive element 7 is used as a detection signal, indicating the occurrence of an overload current. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor device including a switching element that supplies a current to a load such as an electric motor, and more particularly to an overcurrent detection circuit for the switching element.

  In power electronics equipment, IGBTs (Insulated Gate Bipolar Transistors) and MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) are used as switching elements for switching between supply / cutoff of currents (drive currents) that drive loads such as electric motors. . In recent years, the use of a silicon carbide MOSFET for the switching element has also been studied. These are all insulated gate semiconductor devices.

  In such a switching element, when an overcurrent flows due to, for example, a load being short-circuited, problems such as element destruction occur. Therefore, various semiconductor devices including an overcurrent detection circuit that detects an overcurrent of the main switching element and a protection circuit that limits a current flowing through the main switching element when an overcurrent is detected have been proposed (for example, Patent Document 1). -2).

  The overcurrent detection circuit disclosed in Patent Document 1 includes a sense element for passing a minute current (sense current) proportional to a drive current flowing through a main switching element, and a current detection resistor connected in series thereto. A voltage drop proportional to the drive current occurs in the current detection resistor, and the voltage drop is used as an overcurrent detection signal.

  Patent Document 2 discloses a configuration in which a current detection MOSFET having a gate electrode connected to a drain electrode is connected in series to a sense element instead of a current detection resistor. In the overcurrent detection circuit having this configuration, the voltage applied between the source and gate (drain) of the current detection MOSFET is used as an overcurrent detection signal. Therefore, the voltage value of the detection signal when an overcurrent occurs is expressed as the current value. The threshold voltage of the detection MOSFET can be made higher. Since a detection signal with a higher voltage can be output than when a current detection resistor is used, overcurrent detection with high accuracy becomes possible.

Japanese Patent No. 3649154 JP-A-9-191103

  In the overcurrent detection circuit of Patent Document 1, a current proportional to the drive current flowing through the main switching element flows through the current detection resistor not only when an overcurrent occurs but also during a normal operation where no overcurrent occurs. Therefore, the voltage of the overcurrent detection signal always has a certain level. Similarly, in the overcurrent detection circuit of Patent Document 2, a voltage corresponding to the drive current flowing through the main switching element is applied to the current detection MOSFET not only when an overcurrent occurs but also during a normal operation. The voltage of the signal will always have a certain magnitude.

  Thus, if the voltage of the overcurrent detection signal has a voltage different from 0V, erroneous detection of overcurrent is likely to occur due to the influence of noise and the like, and there is a concern that the protection circuit malfunctions.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an overcurrent detection circuit capable of suppressing erroneous detection of an overcurrent of a switching element and a semiconductor device including the same.

  A semiconductor device according to the present invention includes a driving switching element that controls a driving current supplied to a load based on a control signal applied to a gate terminal, and an overcurrent detection circuit that detects an overcurrent of the driving switching element. The overcurrent detection circuit includes a current sensing switching element having a gate terminal to which the control signal is applied, and a threshold voltage equal to or higher than a voltage drop of the driving switching element during normal operation. A first detection MOSFET having a gate terminal connected to the drain terminal, and a first resistance element, wherein in the overcurrent detection circuit, the current sensing switching element, the first detection MOSFET, and the first resistance A series circuit of elements is connected in parallel with the switching element for driving, and the voltage drop of the first resistance element. But is used as a first detection signal indicating the occurrence of said overcurrent.

  According to the present invention, during the normal operation of the driving switching element, since the detection MOSFET is kept off, no current flows through the current sensing switching element. In the meantime, since no current flows through the resistance element, the voltage drop, that is, the voltage of the first detection signal is 0V. On the other hand, when an overcurrent occurs, the detection MOSFET is turned on, a current flows through the sensing switching element and the resistance element, and the voltage of the first detection signal increases. Thus, when the voltage of the first detection signal during normal operation becomes 0 V, the distinction from the occurrence of overcurrent becomes clear, and erroneous detection of overcurrent is suppressed. Therefore, the detection accuracy of overcurrent is improved.

1 is a circuit diagram of a semiconductor device including an overcurrent detection circuit according to a first embodiment. FIG. 6 is a signal waveform diagram illustrating an operation of the semiconductor device according to the first embodiment. FIG. 6 is a diagram showing a modification of the semiconductor device according to the first embodiment. FIG. 6 is a circuit diagram of a semiconductor device including an overcurrent detection circuit according to a second embodiment. FIG. 10 is a diagram showing a relationship between first and second sense voltages Vs1, Vs2 and drive current Ic in the second embodiment. FIG. 10 is a signal waveform diagram showing an operation when an overcurrent is detected in the semiconductor device according to the second embodiment. FIG. 10 is a circuit diagram showing a modification of the semiconductor device according to the second embodiment.

<Embodiment 1>
FIG. 1 is a circuit diagram of a semiconductor device according to Embodiment 1 of the present invention. The semiconductor device is formed by using a semiconductor substrate of silicon or silicon carbide, and includes a driving switching element (hereinafter referred to as “main switching element”) 1 for switching between supply / cutoff of a driving current flowing to a load, and the main switching element 1. An overcurrent detection circuit for detecting an overcurrent is provided. The main switching element 1 is a MOSFET that receives a control signal Vg generated by the control signal generator 6 at its gate terminal. The main switching element 1 is turned on when the control signal Vg is high (H) level and turned off when the control signal Vg is low (L) level.

  The power source 5 is a power source for causing a load current to flow through the load 4, and the low voltage side terminal is grounded. The load 4 and the main switching element 1 are connected in series between the high voltage side terminal and the low voltage side terminal of the power supply 5. Here, the main switching element 1 is connected to the low voltage side, and its source terminal is grounded.

  The overcurrent detection circuit is configured by connecting a series circuit including a current sensing switching element 2 (hereinafter “current sensing element”), a detection MOSFET 3 and a resistance element 7 in parallel to the main switching element 1. The current sensing element 2 is a MOSFET that receives a control signal Vg at its gate terminal, similarly to the main switching element 1, and its drain terminal is connected to the drain terminal of the main switching element 1. The current sense element 2 is also turned on when the control signal Vg is at the H level and turned off when the control signal Vg is at the L level.

  The current detection MOSFET 3 has a gate terminal connected to the drain terminal, and the drain terminal is connected to the source terminal of the current sensing element 2. The threshold voltage of the current detection MOSFET 3 is set to be equal to or higher than the voltage drop of the main switching element 1 that occurs during normal operation (operation in which the main switching element 1 supplies / cuts off the load current without overcurrent). .

  The resistance element 7 is connected between the source terminal of the current detection MOSFET 3 and the source terminal (ground potential) of the main switching element 1. In the overcurrent detection circuit, the voltage drop Vs1 generated in the resistance element 7 is used as a detection signal indicating the occurrence of overcurrent. Hereinafter, this voltage drop Vs1 is referred to as a “sense voltage”.

  The operation of the semiconductor device of FIG. 1 will be described with reference to FIG. First, the operation during normal operation, that is, when no overcurrent has occurred in the main switching element 1 will be described.

  When the control signal Vg output from the control signal generator 6 becomes H level, the main switching element 1 and the current sensing element 2 are turned on. Therefore, the drive current Ic supplied from the power supply 5 flows through the load 22. A voltage drop VL occurs in the load 4 due to the drive current Ic. Therefore, the drain-source voltage Vds of the main switching element 1, that is, the voltage drop generated in the main switching element 1 is a value obtained by subtracting the voltage drop VL of the load 4 from the generated voltage (power supply voltage) VB of the power supply 5 (Vds = VB). -VL).

  At this time, since the current sense element 2 is on, a voltage substantially equal to the source-drain voltage Vds of the main switching element 1 is applied between the source and drain (gate) of the current detection MOSFET 3. However, since the threshold voltage of the current detection MOSFET 3 is set to be equal to or higher than the voltage drop of the main switching element 1 generated during normal operation, the current detection MOSFET 3 is kept off. Therefore, the current (sense current) Is does not flow through the current sense element 2 (Is = 0), and no current flows through the resistance element 7, so the sense voltage Vs1 is zero. Since the sense current Is is 0 V, the main current Ic2 flowing through the main switching element 1 at this time is equal to the drive current Ic flowing through the load 4.

  Subsequently, when the control signal Vg becomes the L level, the main switching element 1 and the current sense element 2 are turned off, so that the drive current Ic does not flow through the load 4 (Ic = 0). Naturally, neither the main current Ic2 nor the sense current Is flows (Ic = 0, Is = 0). Therefore, even at this time, no current flows through the resistance element 7, and the sense voltage Vs1 is 0V.

  Next, an operation when an overcurrent flows through the main switching element 1 due to a short circuit of the load 4 or the like will be described. Assume that a short circuit of the load 4 occurs at time t1 in FIG. Then, since the drive current Ic becomes excessive, the main current Ic2 flowing through the main switching element 1 also increases. As a result, the voltage drop (source-drain voltage Vds) of the main switching element 1 increases, and the drain (gate) voltage of the current detection MOSFET 3 also increases. As a result, the voltage between the source and drain (gate) of the current detection MOSFET 3 becomes larger than the threshold voltage, and the current detection MOSFET 3 is turned on. Accordingly, the sense current Is flows through the current sense element 2 and a voltage drop occurs in the resistance element 7, so that the sense voltage Vs increases from 0V. A protection circuit (not shown) or the like can detect the occurrence of an overcurrent by detecting the increase in the sense voltage Vs.

  In the overcurrent detection circuit of the present embodiment, when no overcurrent is generated, the sense voltage Vs1 that is an overcurrent detection signal is always 0 V regardless of whether the main switching element 1 is on or off. When an overcurrent occurs, the sense voltage Vs1 changes from 0V. As described above, when the overcurrent is not generated, the overcurrent detection signal is fixed at 0 V, so that the distinction between the overcurrent occurrence and the normal state becomes clear, and the overcurrent is not likely to be erroneously detected. Become. Therefore, the detection accuracy of overcurrent is improved.

  In FIG. 1, the main switching element 1 and the current sensing element 2 are MOSFETs, but IGBTs may be used. A circuit diagram in that case is shown in FIG. The drain terminal and source terminal of the MOSFET correspond to the collector terminal and emitter terminal of the IGBT, respectively.

<Embodiment 2>
FIG. 4 is a circuit diagram of a semiconductor device including the overcurrent detection circuit according to the second embodiment. The semiconductor device is obtained by connecting another series circuit consisting of a current detection MOSFET 8 and a resistance element 9 in parallel to the series circuit consisting of a current detection MOSFET 3 and a resistance element 7 to the circuit of FIG. . Hereinafter, the current detection MOSFET 3 is the “first current detection MOSFET”, the resistance element 7 is the “first resistance element”, the current detection MOSFET 8 is the “second current detection MOSFET”, and the resistance element 9 is the “first resistance element”. 2 ".

  The second current detection MOSFET 8 has a gate terminal connected to the drain terminal, and the drain terminal connected to the source terminal of the current sensing element 2. The threshold voltage of the second current detection MOSFET 8 is set to a value that is equal to or higher than the voltage drop of the main switching element 1 generated during normal operation and smaller than that of the first current detection MOSFET 3. The second resistance element 9 is connected between the source terminal of the second current detection MOSFET 8 and the source terminal (ground potential) of the main switching element 1.

  FIG. 5 is a diagram showing the relationship between the drive current Ic flowing through the main switching element 1 and the voltage drops Vs1 and Vs2 of the first and second resistance elements 7 and 9. In FIG. Since the second current detection MOSFET 8 has a lower threshold voltage than the first current detection MOSFET 3, a current starts to flow through the second current detection MOSFET 8 when the drive current Ic is smaller. For the same drive current Ic, more current flows in the second current detection MOSFET 8 than in the first current detection MOSFET 3. Therefore, as shown in FIG. 5, the level of the voltage drop Vs2 of the second resistance element 9 starts to increase at a smaller value of the drive current Ic than the voltage drop Vs1 of the first resistance element 7, The value is larger than the voltage drop Vs1 of the first resistance element 7.

  In the present embodiment, the voltage drop Vs1 of the first resistance element 7 is used as a detection signal (first detection signal) indicating the occurrence of overcurrent, and the voltage drop Vs2 of the second resistance element 9 is Used as a detection signal (second detection signal) indicating cancellation. Hereinafter, the voltage drop Vs1 of the first resistor element 7 is referred to as a “first sense voltage”, and the voltage drop Vs2 of the second resistor element 9 is referred to as a “second sense voltage”.

  The reference voltage Vs0 shown in FIG. 5 is used as a threshold for detecting the first and second sense voltages Vs1 and Vs2 in the protection circuit or the like. In the semiconductor device of the present embodiment, it is determined that an overcurrent has occurred when the first sense voltage Vs1 exceeds the reference voltage Vs0 (point A in FIG. 5), and the second sense voltage Vs2 has the reference voltage Vs0. When it falls below (point B in FIG. 5), it is determined that the overcurrent has been eliminated.

  For example, the operation of the overcurrent detection circuit when the drive current Ic and the first and second sense voltages Vs1, Vs2 change as shown in FIG. 6 will be described. First, at time t1, the first and second sense voltages Vs1, Vs2 are both smaller than the reference voltage Vs0, so that the drive current Ic (Icc) at this time is not determined as an overcurrent. Subsequently, when the drive current Ic increases at time t2, the second sense voltage Vs2 exceeds the reference voltage Vs0, but the first sense voltage Vs1 that is a detection signal for the occurrence of overcurrent is smaller than the reference voltage Vs0. The drive current Ic (Icb) is not determined as an overcurrent. At time t3, when the drive current Ic further increases and both the first and second sense voltages Vs1, Vs2 exceed the reference voltage Vs0, the drive current Ic (Ica) at this time is determined as an overcurrent.

  Thereafter, at time t4, it is assumed that the drive current Ic returns to the same value (Icb) as at time t2. As a result, the first sense voltage Vs1 is lower than the reference voltage Vs0. However, since the second sense voltage Vs2 that is a detection signal for overcurrent cancellation remains larger than the reference voltage Vs0, it is determined that the overcurrent has not been canceled. Thus, the drive current Ic at this time is handled as an overcurrent.

  Subsequently, at time t5, it is assumed that the drive current Ic returns to the same value (Icc) as at time t1. Then, since both the first and second sense voltages Vs1, Vs2 are smaller than the reference voltage Vs0, it is determined that the overcurrent has been eliminated, and the drive current Ic (Icc) at this time is assumed not to be an overcurrent. Handled.

  As described above, in the present embodiment, the value of the drive current Ic from which the occurrence of the overcurrent is detected is different from the value of the drive current Ic from which the cancellation of the overcurrent is detected. Therefore, the overcurrent determination has a hysteresis characteristic, and an erroneous determination of overcurrent due to the influence of noise or the like can be prevented more reliably.

  In the circuit of FIG. 4, during normal operation in which no overcurrent occurs, the voltage between the source and drain (gate) of the first current detection MOSFET 3 does not exceed the threshold voltage, and the source of the second current detection MOSFET 8 Since the drain-gate voltage does not exceed the threshold voltage, the first and second current detection MOSFETs 3 and 8 are kept off. Therefore, no current flows through the first resistance elements 7 and 9, and the first and second sense voltages Vs1 and Vs2 are both zero. Therefore, the distinction between the occurrence of overcurrent and the normal state is clarified, and the effect that erroneous detection of overcurrent is less likely to occur is obtained as in the first embodiment.

  The first and second current detection MOSFETs 3 and 8 may be formed on the same substrate as the main switching element 1 and the current sensing element 2 or may be formed on different substrates. In the case of forming on the same substrate, the back gate terminal of the second current detection MOSFET 8 may be connected to the source terminal of the main switching element as shown in FIG. As a result, a potential difference is generated between the source terminal and the back gate terminal of the second current detection MOSFET 8, and the threshold voltage of the second current detection MOSFET 8 is lowered due to the back gate effect. Accordingly, the first and second current detection MOSFETs 3 and 8 can have the same configuration (the same threshold voltage without the back gate effect), which contributes to simplification of the semiconductor device design. it can.

  Although not shown, IGBTs may be used as the main switching element 1 and the current sensing element 2 in the present embodiment.

  DESCRIPTION OF SYMBOLS 1 Main switching element, 2 Current sense element, 3, 8 Current detection MOSFET, 4 Load, 5 Power supply, 6 Control signal generator, 7, 9 Resistance element.

Claims (3)

A driving switching element for controlling a driving current supplied to the load based on a control signal applied to the gate terminal;
An overcurrent detection circuit that detects an overcurrent of the driving switching element, and a semiconductor device comprising:
The overcurrent detection circuit includes:
A current sensing switching element having a gate terminal to which the control signal is applied;
A first detection MOSFET having a threshold voltage equal to or higher than a voltage drop of the driving switching element during normal operation, and a gate terminal connected to a drain terminal;
A first resistance element;
In the overcurrent detection circuit,
A series circuit including the current sensing switching element, the first detection MOSFET, and the first resistance element is connected in parallel to the driving switching element,
The semiconductor device according to claim 1, wherein a voltage drop of the first resistance element is used as a first detection signal indicating the occurrence of the overcurrent. The semiconductor device according to claim 1,
The overcurrent detection circuit includes:
A second detection MOSFET having a threshold voltage smaller than that of the first detection MOSFET and having a gate terminal connected to the drain terminal;
A second resistance element;
In the overcurrent detection circuit,
A series circuit including the second detection MOSFET and the second resistance element is connected in parallel to the series circuit including the first detection MOSFET and the first resistance element;
A semiconductor device, wherein a voltage drop of the second resistance element is used as a second detection signal indicating cancellation of the overcurrent. The semiconductor device according to claim 2,
The semiconductor device, wherein a back gate of the second detection MOSFET is connected to a source terminal of the driving switching element.

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