JP4040013B2 - Switching circuit, audio signal reproducing apparatus using the same, and switching element protection method - Google Patents

Description

  The present invention relates to a circuit for reproducing a signal by controlling a switching element such as a power MOS FET (metal-oxide semiconductor field effect transistor).

  2. Description of the Related Art Conventionally, a switching circuit that constitutes a switching amplification unit of an audio signal reproduction device or the like, and a bridge circuit constituted by a switching element such as a power MOSFET performs power amplification by switching a constant voltage using a digital signal as a control signal As the switching circuit, a half bridge circuit and a full bridge circuit are used.

  FIG. 3 includes a half-bridge circuit 102 to which + Vd and −Vd are applied as constant voltages, a low-pass filter (LPF) 103 that removes a high-frequency component from the switching signal, and a speaker 104. It is a circuit block diagram which shows a part of audio signal reproducing | regenerating apparatus. FIG. 4 shows control signals for controlling the switching elements Q1 and Q2 constituting the half bridge circuit 102 to perform a switching operation. In FIG. 4, S1 is a control signal for turning on / off the switching element Q1 on the high side, and S2 is a control signal for turning on / off the switching element Q2 on the low side.

  The switching elements Q1 and Q2 are turned on when each control signal is an H (High) signal and turned off when the control signal is an L (Low) signal. Accordingly, in the half-bridge circuit 102, when the switching element Q1 is on, the switching element Q2 is off, and when the switching element Q1 is off, the switching element Q2 is on. As described above, during normal operation, the switching elements Q1 and Q2 are alternately turned on and off, and are controlled so that neither of them is turned on.

  FIG. 5 shows a part of an audio signal reproducing apparatus configured to include a full bridge circuit 112 to which + Vd and −Vd are applied as constant voltages, a low-pass filter 103 that removes a high frequency component from a switching signal, and a speaker 104. FIG. FIG. 6 shows control signals for controlling the switching elements Q11 to Q14 constituting the full bridge circuit 112 to perform the switching operation. In FIG. 6, S11 is a control signal for turning on / off switching elements Q11, Q14, and S12 is a control signal for turning on / off switching elements Q12, Q13.

  The switching elements Q11 to Q14 are turned on when each control signal is an H (High) signal and turned off when the control signal is an L (Low) signal. Accordingly, in the full bridge circuit 112, when the switching elements Q11 and Q14 are on, the switching elements Q12 and Q13 are off, and when the switching elements Q11 and Q14 are off, the switching elements Q12 and Q13 are on. Therefore, during normal operation, the signal current is from + Vd to the high-side switching element Q11, LPT 103, speaker 104, low-side switching element Q14, -Vd, or from + Vd to high-side switching element Q13, The speaker 104 is driven by flowing through any of the LPT 103, the speaker 104, the low-side switching element Q12, and the -Vd path.

  As described above, during normal operation, the switching elements Q11 and Q14 and the switching elements Q12 and Q13 are alternately turned on and off, and the switching elements Q11 and Q12 or the switching elements Q13 and Q14 are simultaneously turned on. There is no control.

  However, in the half-bridge circuit 102 shown in FIG. 3, a driver (not shown) that supplies the control signal S1 to the switching element Q1, a driver (not shown) that supplies the control signal S2 to the switching element Q2, or a further upstream thereof. When an abnormality that always turns on the switching element Q1 or Q2 occurs in a control device or the like (not shown), the switching elements Q1 and Q2 are turned on simultaneously, and the switching elements Q1 and Q2 are turned on. There is a possibility that a large through current flowing through the switching element flows and the switching elements Q1 and Q2 are destroyed. In addition, even when either of the switching elements Q1 or Q2 fails so that it is always turned on, a large through current that flows through the switching elements Q1 and Q2 flows, and the switching element that has not failed is destroyed. There is a possibility.

  Also in the full bridge circuit 112 shown in FIG. 5, a driver (not shown) for supplying the control signal S11 to the switching elements Q11 and Q14, a driver (not shown) for supplying the control signal S12 to the switching elements Q12 and Q13, Alternatively, when an abnormality that always turns on any of the switching elements Q11 to Q14 occurs in a control device or the like (not shown) further upstream thereof, the switching elements Q11 and Q12, or the switching element Q13 Q14 is turned on at the same time, and a large through current that flows through switching elements Q11 and Q12 or switching elements Q13 and Q14 flows, so that any of switching elements Q11 to Q14 or a plurality of switching elements may be destroyed. There is sex. Even when one of the switching elements Q11 to Q14 is always turned on, a large through current that passes through the switching elements Q11 and Q12 or the switching elements Q13 and Q14 flows and is not broken. There is a possibility that even the switching element is destroyed.

  Conventionally, in order to prevent the switching element from being destroyed by an overcurrent, a resistor is connected to the power supply line to which the switching element is connected, and the current flowing through the switching element is detected from the voltage generated at both ends of the resistor. There is a switching circuit that protects the switching element by turning off the switching element when an overcurrent flows.

In addition, in the signal detection circuit including a plurality of MOSFET gate delay circuits constituting the H-bridge circuit, by providing a temperature rise detection circuit, the switching interval at the time of rising or falling of each MOSFET can be controlled by temperature. There are some (see, for example, Patent Document 1).
JP-A-7-177010

  However, the switching circuit that protects the switching element by connecting the overcurrent detection resistor to the power supply line to which the switching element is connected has a signal current that flows through the current detection resistor even during normal operation. This current detection resistor generates heat and wasteful power consumption occurs.

  Further, in the prior art described in Patent Document 1, it is a MOSFET that constitutes an H-bridge circuit, and a through current based on the difference between the turn-on time and the turn-off time of the upper and lower MOSFETs connected in series to the power supply flows. Even if a temperature change occurs, it can be stably prevented. However, in the case of an abnormal situation where one of the upper and lower MOSFETs remains on, a through current that passes through the upper and lower MOSFETs flows. There is a problem that the destruction of the MOSFET cannot be prevented.

  In view of the above-mentioned points, the present invention switches between two switching elements when an abnormality occurs in which one of two switching elements that are connected in series to a constant voltage power source and constitute a bridge circuit remains on. An object of the present invention is to provide a switching circuit capable of preventing a switching element from being destroyed by a through current passing through the element, an audio signal reproducing apparatus using the switching circuit, and a switching element protection method.

  To achieve the above object, the present invention includes first and second switching elements connected in series between a high-level power supply terminal and a low-level power supply terminal, and the first switching element is turned on and second switching is performed in accordance with an input signal. A switching circuit for taking out an output from a connection point of the first and second switching elements by switching between a first period in which the element is turned off and a second period in which the first switching element is turned off and the second switching element is turned on The first current detecting means for detecting the current flowing through the first switching element, the second current detecting means for detecting the current flowing through the second switching element, and the first and second current detecting means both have predetermined current values. And a protection means for protecting the first and second switching elements by turning off the first and second switching elements and cutting off the through current when a current exceeding the current is detected. It is.

  In this way, when a malfunction or the like occurs in which one of the first and second switching elements remains on, and a large through current that passes through the first and second switching elements flows, Since the flow of the through current can be detected and interrupted, it is possible to prevent the first and second switching elements from being destroyed by the continuous flow of the through current.

  Further, for example, if the first current detection means is a first voltage detection circuit that detects the voltage across the first switching element, and the second current detection means is a second voltage detection circuit that detects the voltage across the second switching element. good. In this way, it can be detected from the voltage across the switching element that a large current flows in each switching, and there is no need to attach a current detector that generates wasteful power consumption such as a current detection resistor.

  In addition, for example, the protection unit detects that the voltage detected by the first voltage detection circuit is smaller than the first predetermined voltage and the voltage detected by the second voltage detection circuit is smaller than the second predetermined voltage. A detection circuit that outputs a detection signal, a delay circuit that delays the detection signal by a predetermined time, and holds the detection signal from the delay circuit and turns off the first and second switching elements while holding the detection signal. It is preferable to provide a holding circuit that outputs a protect signal for interrupting the through current.

  In this way, the detection circuit can detect that a current exceeding a predetermined current value is flowing in both the first and second switching elements, and the delay circuit can perform a switching operation for both the first and second switching elements. It is possible to prevent erroneous detection caused by the voltage at both ends of the first and second switching elements becoming unstable over time, and to output a protect signal for interrupting the through current flowing through the first and second switching elements by the holding circuit. Therefore, the through current that penetrates the first and second switching elements can be stably interrupted.

  Further, for example, first and second switching elements sequentially connected in series between a high-level power supply terminal and a low-level power supply terminal, and third and fourth switching elements sequentially connected in series between the high-level power supply terminal and low-level power supply terminal. A first period in which the first and fourth switching elements are turned on, and the second and third switching elements are turned off according to the input signal, and the first and fourth switching elements are turned off, and the second, second In the switching circuit that switches the second period during which the three switching elements are turned on and extracts the output from between the connection point of the first and second switching elements and the connection point of the third and fourth switching elements, A first current detecting means for detecting a current flowing through the switching element; a second current detecting means for detecting a current flowing through the second switching element; and a current flowing through the third switching element. The third current detecting means, the fourth current detecting means for detecting the current flowing through the fourth switching element, and the first and second current detecting means both detect the current exceeding the first predetermined current value. The second switching element is turned off, the through currents of the first and second switching elements are cut off to protect the first and second switching elements, and the third and fourth current detection means are both set to the second predetermined current value. It is preferable to provide protection means for protecting the third and fourth switching elements by turning off the third and fourth switching elements when a current exceeding the first current is detected and cutting off the through currents of the third and fourth switching elements.

  In this way, when a malfunction or the like occurs in which one of the first and second switching elements remains on, and the through current of the first and second switching elements flows, the through current Therefore, it is possible to prevent the first and second switching elements from being destroyed by the flow of the through current, and to prevent the third and fourth switching. When a malfunction or the like that causes one of the elements to remain on occurs and a through current flows through the third and fourth switching elements, the fact that the through current has flown is detected and shut off. Therefore, it is possible to prevent the third and fourth switching elements from being destroyed by continuing the flow of the through current.

  Also, for example, the first current detection means is a first voltage detection circuit that detects the voltage across the first switching element, and the second current detection means is a second voltage detection circuit that detects the voltage across the second switching element, The third current detection means may be a third voltage detection circuit that detects the voltage across the third switching element, and the fourth current detection means may be a fourth voltage detection circuit that detects the voltage across the fourth switching element. In this way, it is possible to detect that a large current flows through each switching element from the voltage across the switching element, and there is no need to attach a current detector that generates wasteful power consumption such as a current detection resistor. .

  In addition, for example, the protection unit detects that the voltage detected by the first voltage detection circuit is smaller than the first predetermined voltage and the voltage detected by the second voltage detection circuit is smaller than the second predetermined voltage. A first detection circuit for outputting the first detection signal, a first delay circuit for delaying the first detection signal by a first predetermined time, and holding and holding the first detection signal from the first delay circuit. The first holding circuit that outputs the first protect signal for turning off the first and second switching elements and shutting off the through current of the first and second switching elements and the third voltage detecting circuit detect A second detection circuit that outputs a second detection signal upon detecting that the detected voltage is lower than the third predetermined voltage and the voltage detected by the fourth voltage detection circuit is lower than the fourth predetermined voltage; Delay signal for second predetermined time The second delay circuit to be turned off, and while holding the second detection signal from the second delay circuit, the third and fourth switching elements are turned off to cut off the through current of the third and fourth switching elements And a second holding circuit for outputting a second protect signal for the purpose.

  In this way, it can be detected by the first detection circuit that a current exceeding a predetermined current value flows in both the first and second switching elements, and both the first and second switching elements are switched by the first delay circuit. First detection for blocking the through current of the first and second switching elements by the first holding circuit can be prevented because the voltage across the first and second switching elements becomes unstable during a very short time. Since the protect signal can be continuously output, the through current of the first and second switching elements can be stably cut off. Further, the second detection circuit can detect that a current exceeding a predetermined current value flows in both the third and fourth switching elements, and the second delay circuit can detect the third and fourth switching elements in a minute time for switching operation. It is possible to prevent erroneous detection caused by the voltage across the third and fourth switching elements becoming unstable, and the second holding circuit outputs a second protect signal for interrupting the through current of the third and fourth switching elements. Therefore, the through current of the first and second switching elements can be stably interrupted.

  Further, for example, when the switching element is a MOSFET, the power consumption can be reduced and switching can be performed at a high speed, so that a highly efficient audio signal reproducing apparatus can be obtained.

  For example, when the voltage detection circuit is a differential amplifier circuit that detects and amplifies the voltage between the drain and source of the MOSFET, the voltage between the drain and source of the MOSFET can be detected accurately.

  Further, for example, a 1-bit signal conversion means for converting an audio signal composed of an analog signal or a digital signal assigned and expressed in multiple bits into a 1-bit signal assigned in 1 bit, and between a high-level power supply terminal and a low-level power supply terminal A switching circuit composed of first and second switching elements connected in series, a first period in which the first switching element is turned on and the second switching element is turned off according to the 1-bit signal, and a first switching element In an audio signal reproducing apparatus for reproducing the audio signal from a speaker connected to a connection point of the first and second switching elements, comprising a driver for switching off and a second period in which the second switching element is turned on. In the switching circuit, a first current detection for detecting a current flowing in the first switching element. And the second current detecting means for detecting the current flowing through the second switching element, and the first and second switching elements are turned off when both the first and second current detecting means detect a current exceeding a predetermined current value. And a protective means for interrupting the through current and protecting the first and second switching elements.

  In this case, malfunctions of the first and second switching elements occur, and even when a large through current that passes through the first and second switching elements flows, the through current flows. Since the first and second switching elements can be turned off by detection, an audio signal reproducing apparatus capable of preventing the first and second switching elements from being destroyed by the flow of the through current continues. realizable.

  Further, for example, a 1-bit signal conversion means for converting an audio signal composed of an analog signal or a digital signal assigned and expressed in multiple bits into a 1-bit signal assigned in 1 bit, and between a high-level power supply terminal and a low-level power supply terminal A switching circuit comprising first and second switching elements sequentially connected in series, and third and fourth switching elements sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal; Accordingly, the first period in which the first and fourth switching elements are turned on, the second and third switching elements are turned off, and the first and fourth switching elements are turned off, and the second and third switching elements are turned on. And a driver for switching between the two periods, and is connected between the connection point of the first and second switching elements and the connection point of the third and fourth switching elements. In the audio signal reproducing apparatus for reproducing the audio signal from the speaker, the first current detecting means for detecting the current flowing in the first switching element and the second current for detecting the current flowing in the second switching element in the switching circuit. The current detection means, the third current detection means for detecting the current flowing through the third switching element, the fourth current detection means for detecting the current flowing through the fourth switching element, and the first and second current detection means are both the first and second current detection means. When a current exceeding a predetermined current value of 1 is detected, the first and second switching elements are turned off to cut off the through currents of the first and second switching elements to protect the first and second switching elements, and 3. When the fourth current detection means detects a current exceeding the second predetermined current value, the third and fourth switching elements are turned off. The third block the through current of the fourth switching element, may fourth providing a protection means for protecting the switching element.

  In this case, malfunctions of the first and second switching elements occur, and even when a large through current that passes through the first and second switching elements flows, the through current flows. Since the first and second switching elements can be turned off by detection, it is possible to prevent the first and second switching elements from being destroyed due to the flow of the through current, and to prevent the third and fourth switching elements from being destroyed. Even when a malfunction of the element occurs and a large through current that flows through the third and fourth switching elements flows, the third and fourth switching elements are detected by detecting that the through current has flowed. Since it can be turned off, it is possible to realize an audio signal reproduction device that can prevent the third and fourth switching elements from being destroyed by the flow of the through current. .

For example, the first and second switching elements connected in series between the high-level power supply terminal and the low-level power supply terminal are provided, and the first switching element is turned on and the second switching element is turned off according to the input signal. In the switching element protection method in the switching circuit for taking out the output from the connection point of the first and second switching elements by switching between the period of 1 and the second period in which the first switching element is turned off and the second switching element is turned on, The current flowing through the first switching element and the current flowing through the second switching element are detected, and both the detected current value of the current flowing through the first switching element and the detected current value of the current flowing through the second switching element are both When the predetermined current value is exceeded, the first and second switching elements may be turned off.

  In this way, when a malfunction or the like occurs in which one of the first and second switching elements remains on, and a large through current that passes through the first and second switching elements flows, Since the first and second switching elements are turned off by detecting that the through current has flown, it is possible to prevent the first and second switching elements from being destroyed due to the flow of the through current. .

  According to the present invention, the first and second switching elements connected in series between the high-level power supply terminal and the low-level power supply terminal are provided, and the first switching element is turned on and the second switching element is turned off according to the input signal. In the switching circuit for taking out the output from the connection point of the first and second switching elements by switching between the period 1 and the second period in which the first switching element is turned off and the second switching element is turned on, the first switching element When the first current detecting means for detecting the current flowing through the second current detecting means, the second current detecting means for detecting the current flowing through the second switching element, and the first and second current detecting means both detect a current exceeding a predetermined current value. And a protection means for protecting the first and second switching elements by turning off the first and second switching elements and blocking the through current. When an abnormal state occurs in which either one of the chucking elements remains on, and a large through current flows through the first and second switching elements, both the first and second switching elements are turned off and the The flow of the through current can be blocked, and the first and second switching elements can be prevented from being destroyed.

  Further, according to the present invention, the first and second switching elements sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal, and the third, sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal. A first switching period in which the first and fourth switching elements are turned on, the second and third switching elements are turned off according to the input signal, and the first and fourth switching elements are turned off, 2. In a switching circuit that switches between a second period during which the third switching element is turned on and extracts an output between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements. The first current detecting means for detecting the current flowing through the first switching element, the second current detecting means for detecting the current flowing through the second switching element, and the current flowing through the third switching element When the third current detecting means for detecting, the fourth current detecting means for detecting the current flowing through the fourth switching element, and the first and second current detecting means both detect a current exceeding the first predetermined current value. The first and second switching elements are turned off to cut off the through currents of the first and second switching elements to protect the first and second switching elements, and the third and fourth current detection means are both second predetermined Protecting means for protecting the third and fourth switching elements by turning off the third and fourth switching elements when the current exceeding the current value is detected and cutting off the through current of the third and fourth switching elements is provided. Therefore, when an abnormal state occurs in which one of the first and second switching elements remains on, and a large through current that flows through the first and second switching elements flows, the first and second switching elements flow. Both the switching elements can be turned off to interrupt the flow of the through current, and the first and second switching elements can be prevented from being destroyed, and any of the third and fourth switching elements can be prevented. When an abnormal state occurs in which one of them remains on and a large through current flows through the third and fourth switching elements, the through current flows with both the third and fourth switching elements turned off. Can be blocked, and the third and fourth switching elements can be prevented from being destroyed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing an electrical configuration of an audio signal reproduction device according to an embodiment of the present invention. The audio signal reproducing device shown in FIG. 1 is composed of a digital amplifier (switching circuit) 1, low-pass filters 2 and 3, a speaker 4, a ΔΣ modulation unit (1-bit signal converting means) 5, and a driver 6. Yes.

  The ΔΣ modulation unit 5 represents an analog signal or multi-bit that is an input audio signal by a ΔΣ modulation method well known as a method for encoding an analog signal or a digital signal represented by multiple bits into a 1-bit signal. The converted digital signal is converted into a 1-bit signal. Based on the 1-bit signal, the driver 6 generates a control signal for driving the switching element of the digital amplifier 1 at the subsequent stage and supplies the control signal to the switching element. The 1-bit signal supplied to the driver 6 may be a PWM (Pulse Width Modulation) signal generated by comparing an analog signal, which is an input audio signal, with a reference sawtooth wave.

  The digital amplifier 1 includes an N-channel MOSFET (switching element) M1 connected in series between a constant voltage power supply (high power supply terminal) VBB that supplies a voltage + VBB [V] and a ground (low power supply terminal) GND. M2 and N-channel MOSFETs (switching elements) M3 and M4 connected in series between the constant voltage power supply VBB and the ground GND, and the connection midpoint of the MOSFETs M1 and M2 and the connection of the MOSFETs M3 and M4 A full bridge circuit is configured by connecting the speaker 4 via the low-pass filters 2 and 3 between the center point and the center point. Here, the MOSFETs M1 and M3 are high-side FETs connected to the constant voltage power supply VBB side, and the MOSFETs M2 and M4 are low-side FETs connected to the ground GND side.

  The low-pass filter 2 includes a coil L1 and a capacitor C1, and one end of the coil L1 is connected to a connection midpoint between the MOSFETs M1 and M2, and the other end is connected to one end of the speaker 4 and is grounded via the capacitor C1. Connected to GND. The low-pass filter 3 includes a coil L2 and a capacitor C2. One end of the coil L2 is connected to the connection midpoint of the MOSFETs M3 and M4, the other end is connected to the other end of the speaker 4, and the capacitor C2 is connected. To the ground GND.

  The gates of the MOSFETs M1 to M4 are connected to the driver 6. The driver 6 turns on the MOSFETs M1 and M4, turns off the MOSFETs M2 and M3, and turns off the MOSFETs M1 and M4, based on the 1-bit signal from the ΔΣ modulator 5. , A control signal is applied to the gates of MOSFETs M1 to M4 so that the periods during which M3 is turned on are alternately switched. In this way, power amplification is performed by switching the constant voltage power supply VBB, and the speaker 4 is driven by the output to reproduce the audio signal.

  In addition, when MOSFET M1 remains on due to some abnormality, for example, failure of driver 6 driving MOSFET M1 or failure of MOSFET M1 itself, the period during which MOSFET M1, M4 is on and MOSFET M2, M3 is off Although there is no problem, during the period when the MOSFETs M1 and M4 are turned off and the MOSFETs M2 and M3 are turned on, the MOSFET M1 that should be turned off remains on, so both the MOSFETs M1 and M2 are turned on, and the MOSFET M1 from the constant voltage power supply VBB. , A large through current flows through the ground GND through M2. The through current causes the MOSFET M1 and / or the MOSFET M2 to be easily destroyed, and the wiring on the path through which the through current flows may be destroyed. It should be noted that the same destruction phenomenon occurs in any of the MOSFETs M1 to M4 that are in an abnormal state while being turned on.

  Therefore, the digital amplifier 1 is provided with protection means for preventing destruction of the MOSFET and the like in such an abnormal state. Hereinafter, the configuration and operation of this protection means will be described. First, in order to detect the voltage between the drain and source of the MOSFET M1, a differential amplifier circuit (current detection means, voltage detection circuit) including diodes D1 and D2, resistors R1 to R4, and an operational amplifier X1 is provided. The inverting input terminal (−) of the operational amplifier X1 is connected to the cathode of the diode D1 for backflow prevention via the resistor R1, and the anode of the diode D1 is connected between the drain of the MOSFET M1 and the constant voltage power supply VBB. The non-inverting input terminal (+) of the operational amplifier X1 is connected to the cathode of the diode D2 for backflow prevention via the resistor R3, and the anode of the diode D2 is connected between the source of the MOSFET M1 and the drain of the MOSFET M2. A power supply 5V having an output voltage of 5 [V] is connected between the non-inverting input terminal (+) of the operational amplifier X1 and the resistor R3 via the resistor R4, and the output of the operational amplifier X1 is connected to the inverting input terminal ( -) Negative feedback.

  The operational amplifier X1 connected in this way operates by obtaining a DC power supply of ± 12 [V] from a DC power supply (+, −) (not shown), and the drain voltage of the MOSFET M1 applied to the inverting input terminal (−). The voltage difference from the source voltage of the MOSFET M1 applied to the non-inverting input terminal (+) is inverted and amplified with a gain determined by the resistance values of the resistors R1 to R4 as a reference. The drain voltage of the MOSFET M1 is always + VBB [V], and the source voltage is + VBB [V] when the MOSFET M1 is on, and 0 [V] when the MOSFET M1 is off. Therefore, when the MOSFET M1 is on, the voltage difference is The output voltage of the operational amplifier X1 is 5 [V]. On the other hand, when the MOSFET M1 is off, the voltage difference is + VBB [V], so the output voltage of the operational amplifier X1 is smaller than 5 [V]. When the voltage at this time is set to 0 [V] from + VBB [V] and the resistance values of the resistors R1 to R4, the output voltage of the operational amplifier X1 is 5 [V] / 0 in accordance with the on / off of the MOSFET M1. Change to [V].

  In order to detect the voltage between the drain and source of the MOSFET M2, a differential amplifier circuit (current detection means, voltage detection circuit) including diodes D3 and D4, resistors R5 to R8, and an operational amplifier X2 is provided. The inverting input terminal (−) of the operational amplifier X2 is connected to the cathode of the backflow preventing diode D3 via the resistor R5, and the anode of the diode D3 is connected to the drain of the MOSFET M2. The non-inverting input terminal (+) of the operational amplifier X2 is connected to the cathode of the backflow prevention diode D4 via the resistor R7, and the anode of the diode D4 is connected between the source of the MOSFET M2 and the ground GND. The power supply 5V is connected between the non-inverting input terminal (+) of the operational amplifier X2 and the resistor R7 via the resistor R8, and the output of the operational amplifier X2 is negatively fed back to the inverting input terminal (−) via the resistor R6. .

  The operational amplifier X2 connected in this manner operates by obtaining a DC power supply of ± 12 [V] from a DC power supply (+, −) (not shown), and the voltage of the drain of the MOSFET M2 applied to the inverting input terminal (−). The voltage difference from the source voltage of the MOSFET M2 applied to the non-inverting input terminal (+) is inverted and amplified with a gain determined by the resistance values of the resistors R5 to R8 as a reference. The source voltage of the MOSFET M2 is always 0 [V], and the drain voltage is + VBB [V] when the MOSFET M2 is off, and 0 [V] when the MOSFET M2 is on. Therefore, when the MOSFET M2 is on, the voltage difference is As a result, the output voltage of the operational amplifier X2 becomes 5 [V]. On the other hand, when the MOSFET M2 is off, the voltage difference is + VBB [V], so that the output voltage of the operational amplifier X2 is smaller than 5 [V]. For example, if the voltage at this time is set to 0 [V] from + VBB [V] and the resistance values of the resistors R5 to R8, the output voltage of the operational amplifier X2 is 5 [V] according to the on / off of the MOSFET M2. / 0 [V].

  The output terminal of the operational amplifier X1 is connected to one of the two input terminals of the AND circuit (detection circuit) U1 via the diode D5, and the output terminal of the operational amplifier X2 is connected to the two input terminals of the AND circuit U1 via the diode D6. Is connected to the other of the two. The AND circuit U1 has a predetermined threshold level between 0 [V] and 5 [V] set at the input, and when a voltage exceeding this threshold level is applied to the input terminal, It is determined that an H (High) level signal has been input. The AND circuit U1 sets the output to the H level when both H level signals are input to the two input terminals. The output of the AND circuit U1 at other times is L (Low) level. Therefore, when the output voltages of the operational amplifiers X1 and X2 are both 5 [V], that is, when both the MOSFETs M1 and M2 are on, the AND circuit U1 sets the output to the H level because both of the input terminals are at the H level. In other cases, that is, when at least one of the MOSFETs M1 and M2 is OFF, the AND circuit U1 sets the output to the L level because both of the two input terminals do not become the H level.

  In this case, the output of the AND circuit U1 becomes the H level only when a large through current that passes through the MOSFETs M1 and M2 flows in the abnormal state as described above with both the MOSFETs M1 and M2 turned on. . That is, it can be detected that a large through current that passes through the MOSFETs M1 and M2 flows while both the MOSFETs M1 and M2 are turned on. This is because, during normal operation, a large current flows through either the high-side FET or the low-side FET. At that time, only a small current flows through the other FET, and both FETs when both FETs are turned on. Both focus on the point that a large through current flows.

  The output of the AND circuit U1 is connected to a delay circuit composed of a resistor R13 and a capacitor C7. The output terminal of the AND circuit U1 is connected to one end of the resistor R13, and the other end of the resistor R13 is connected to the ground terminal GND via the capacitor C7. The connection point between the resistor R13 from which the output of the delay circuit is output and the capacitor C7 is connected to the input terminal of the inverter X5 having hysteresis, and the output terminal of the inverter X5 is connected to the holding circuit X6.

  With such a configuration, while the output of the AND circuit U1 is at the H level, the voltage at the connection point between the resistor R13 and the capacitor C7 increases in a time corresponding to the time constant between the resistor R13 and the capacitor C7, When the voltage exceeds the voltage v1 for inverting the output of the inverter X5, the output of the inverter X5 is inverted and becomes L level. On the other hand, when the output of the AND circuit U1 becomes L level, the voltage at the connection point between the resistor R13 and the capacitor C7 drops and becomes lower than the voltage v2, which is a voltage lower than the voltage v1, the inverter X5 The output is inverted and becomes H level. The reason why the inverter X5 has such hysteresis is to prevent chattering of the output of the inverter X5.

  When the output of the inverter X5 becomes L level even for a moment, a holding relay (not shown) inside the holding circuit X6 is turned on, and the on state is held. While the holding relay is on, a protect signal for forcibly turning off the MOSFETs M1 and M2 is output to the driver 6, and both the MOSFETs M1 and M2 are forcibly turned off. In this way, a large through current flowing through the MOSFETs M1 and M2 can be cut off, and the destruction of the MOSFETs M1, M2 and the like by the large through current can be protected. This protect signal is not necessarily output to the driver 6 and used to forcibly turn off the MOSFETs M1 and M2. That is, the present invention is not limited to this as long as it operates a circuit for the purpose of interrupting a large through current passing through the MOSFETs M1 and M2. For example, a circuit that cuts off the power supply line of the constant voltage power supply VBB supplied to the MOSFETs M1 and M2 may be operated.

  Next, the reason why a delay circuit composed of the resistor R13 and the capacitor C7 is provided and a method for setting the resistance value of the resistor R13 and the capacitance value of the capacitor C7 will be described. This delay circuit protects from the holding circuit X6 if the AND circuit U1 does not continue to output the H level for a predetermined time or more, that is, if the time during which both the MOSFETs M1 and M2 are on does not continue for the predetermined time or more. This is provided to prevent signals from being output.

  FIG. 2 is a waveform diagram showing a voltage waveform at a connection point of MOSFETs M1 and M2 for extracting the output voltage of the digital amplifier 1. The vertical axis indicates voltage and the horizontal axis indicates time. A period t1 shown in FIG. 2 is a period in which the MOSFET M1 is switched from OFF to ON and the MOSFET M2 is switched from ON to OFF. The MOSFET M1 is gradually turning on and the MOSFET M2 is gradually turning off. Accordingly, the voltage at the connection point of the MOSFETs M1 and M2 gradually increases from the voltage level of the ground GND (0 [V]) to the voltage level of the constant voltage power supply terminal VBB (+ VBB [V]).

  Next, the period t2 is a period in which the MOSFET M1 is completely turned on and the MOSFET M2 is completely turned off, and the voltage at the connection point of the MOSFETs M1 and M2 is + VBB [V]. The period t3 is a period in which the MOSFET M1 is switched from on to off and the MOSFET M2 is switched from off to on. The MOSFET M1 is gradually turned off and the MOSFET M2 is being turned on little by little. Therefore, the voltage at the connection point of the MOSFETs M1 and M2 gradually decreases from + VBB [V] to 0 [V]. The period t4 is a period in which the MOSFET M1 is completely turned off and the MOSFET M2 is completely turned on. The voltage at the connection point of the MOSFETs M1 and M2 is 0 [V]. Thereafter, the states in the periods t1 to t4 are repeated.

  Here, the periods t1 and t3 are periods of an unstable situation in which the voltage between the drain and source of the MOSFET M1 and the voltage between the drain and source of the MOSFET M2 cannot be defined, and thus occurred during this period. The detection result of the drain-source voltage of the MOSFETs M1 and M2 may not be a result of detecting a large through current passing through the MOSFETs M1 and M2. That is, even if the output of the AND circuit U1 becomes H level during this period, there is a possibility of erroneous detection that is not a detection of a large through current passing through the MOSFETs M1 and M2.

  Therefore, in order to eliminate erroneous detection during this period, a delay circuit for delaying the output of the AND circuit U1 is provided, and the time constant of the resistor R13 and the capacitor C7 constituting the delay circuit is set to the period t1 (t3) <detection. It is set so that the relationship of time> period t2 (t4) is established. Here, the detection time is a time required for the voltage at the connection point of the resistor R13 and the capacitor C7 to rise from the level of the ground GND to the voltage v1 that is the input sense voltage of the inverter X5. Then, the resistance value of the resistor R13 and the capacitance value of the capacitor C7 are determined so as to have the set time constant.

  With this setting, even if an erroneous detection occurs during the period t1 (t3) and the output of the AND circuit U1 becomes H level, the time when the output is H level must continue longer than the period t1 (t3). For example, the output of the inverter X5 is not inverted. In this way, it is possible to prevent malfunction of the protection circuit due to erroneous detection during the switching period in which the drain-source voltages of the MOSFETs M1 and M2 are unstable.

  In FIG. 1, the protection means for the MOSFETs M3 and M4 are not shown, but the same protection means as those described above for the MOSFETs M1 and M2 are provided. At this time, the holding circuit for the MOSFETs M3 and M4 that outputs a protection signal for protecting the MOSFETs M3 and M4 may be shared with the holding circuit X6 that is a holding circuit for the MOSFETs M1 and M2. In such a case, when a large through current passing through the MOSFETs M1 and M2 or a large through current passing through the MOSFETs M3 and M4 is detected, all of the MOSFETs M1 to M4 may be forcibly turned off, or the MOSFET M1. All of the power lines supplied to M4 may be cut off.

  In this embodiment, the audio signal reproducing device is described as an example. However, the signal switched by the switching circuit is not limited to the audio signal, and the switching circuit according to the present invention is applied to other devices having the switching circuit. It is possible to use. In addition, the switching circuit of this embodiment uses a switching circuit in which a full bridge circuit is configured by four N-channel MOSFETs as an example, but the present invention can also be applied to a switching circuit that configures a half bridge circuit. Needless to say, there are. The switching elements constituting the bridge circuit are not limited to N-channel MOSFETs, but may be other switching elements such as P-channel MOSFETs and bipolar transistors.

  As described above, according to the present invention, the first and second switching elements connected in series between the high-level power supply terminal and the low-level power supply terminal are provided, and the first switching element is turned on according to the input signal. In a switching circuit that switches between a first period in which the first switching element is turned off and a second period in which the first switching element is turned off and the second switching element is turned on to extract the output from the connection point of the first and second switching elements. The first current detecting means for detecting the current flowing through the first switching element, the second current detecting means for detecting the current flowing through the second switching element, and the first and second current detecting means both exceed a predetermined current value. Since the first and second switching elements are turned off when the current is detected and the through current is cut off to provide protection means for protecting the first and second switching elements, When an abnormal state occurs in which one of the first and second switching elements remains on, and a large through current that flows through the first and second switching elements flows, both the first and second switching elements are connected. It can be turned off to block the through current from flowing, and the first and second switching elements can be prevented from being destroyed.

  Further, according to the present invention, the first and second switching elements sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal, and the third, sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal. A fourth period, a first period in which the first and fourth switching elements are turned on, a second and third switching elements are turned off according to an input signal, and the first and fourth switching elements are turned off, 2. In a switching circuit that switches between a second period during which the third switching element is turned on and extracts an output between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements. The first current detecting means for detecting the current flowing through the first switching element, the second current detecting means for detecting the current flowing through the second switching element, and the current flowing through the third switching element When the third current detecting means for detecting, the fourth current detecting means for detecting the current flowing through the fourth switching element, and the first and second current detecting means both detect a current exceeding the first predetermined current value. The first and second switching elements are turned off to cut off the through currents of the first and second switching elements to protect the first and second switching elements, and the third and fourth current detection means are both second predetermined Protecting means for protecting the third and fourth switching elements by turning off the third and fourth switching elements when the current exceeding the current value is detected and cutting off the through current of the third and fourth switching elements is provided. Therefore, when an abnormal state occurs in which one of the first and second switching elements remains on, and a large through current that flows through the first and second switching elements flows, the first and second switching elements flow. Both the switching elements can be turned off to interrupt the flow of the through current, and the first and second switching elements can be prevented from being destroyed, and any of the third and fourth switching elements can be prevented. When an abnormal state occurs in which one of them remains on and a large through current flows through the third and fourth switching elements, the through current flows with both the third and fourth switching elements turned off. Can be blocked, and the third and fourth switching elements can be prevented from being destroyed.

These are the circuit block diagrams which show the electric constitution of the audio signal reproducing | regenerating apparatus of embodiment of this invention. FIG. 2 is a waveform diagram of an output voltage of the digital amplifier shown in FIG. 1. These are circuit block diagrams which show a part of audio signal reproducing apparatus having a conventional half-bridge circuit. FIG. 4 is a waveform diagram of a control signal of the half bridge circuit shown in FIG. 3. These are circuit block diagrams which show a part of audio signal reproducing | regenerating apparatus which has the conventional full bridge circuit. FIG. 6 is a waveform diagram of a control signal of the full bridge circuit shown in FIG. 5.

Explanation of symbols

1 Digital amplifier (switching circuit)
2, 3 Low-pass filter 4 Speaker 5 ΔΣ modulator (1-bit signal conversion means)
6 Driver C1, C2, C7 Capacitor D1-D6 Diode L1, L2 Coil M1-M4 MOSFET (switching element)
Q1, Q2, Q11 to Q14 Switching elements R1 to R8, R13 Resistance U1 AND circuit (detection circuit)
X1, X2 Operational amplifier X5 Inverter X6 Holding circuit VBB Constant voltage power supply (high power supply terminal)
GND ground (low power supply terminal)

Claims (11)

First and second switching elements connected in series between a high-level power supply terminal and a low-level power supply terminal, and a first period during which the first switching element is turned on and the second switching element is turned off according to an input signal In a switching circuit that switches between a second period in which one switching element is turned off and a second switching element is turned on to extract an output from a connection point of the first and second switching elements,
First current detecting means for detecting a current flowing through the first switching element;
Second current detection means for detecting a current flowing through the second switching element;
Protection means for protecting the first and second switching elements by turning off the first and second switching elements to interrupt the through current when both the first and second current detection means detect a current exceeding a predetermined current value; ,
A switching circuit comprising:   The first current detection means is a first voltage detection circuit that detects the voltage across the first switching element, and the second current detection means is a second voltage detection circuit that detects the voltage across the second switching element. The switching circuit according to claim 1. The protective means is
A detection circuit that detects that the voltage detected by the first voltage detection circuit is lower than the first predetermined voltage and that the voltage detected by the second voltage detection circuit is lower than the second predetermined voltage, and outputs a detection signal; ,
A delay circuit for delaying the detection signal by a predetermined time;
A holding circuit that holds the detection signal from the delay circuit and outputs a protect signal for turning off the first and second switching elements and cutting off the through current while holding the detection signal;
The switching circuit according to claim 2, further comprising: First and second switching elements sequentially connected in series between a high-level power supply terminal and a low-level power supply terminal, and third and fourth switching elements sequentially connected in series between the high-level power supply terminal and the low-level power supply terminal. The first and fourth switching elements are turned on, the second and third switching elements are turned off according to the input signal, and the first and fourth switching elements are turned off, and the second and third switching elements are turned off. In the switching circuit that switches the second period to be turned on and extracts the output between the connection point of the first and second switching elements and the connection point of the third and fourth switching elements,
First current detecting means for detecting a current flowing through the first switching element;
Second current detection means for detecting a current flowing through the second switching element;
Third current detection means for detecting a current flowing through the third switching element;
Fourth current detection means for detecting a current flowing through the fourth switching element;
When both the first and second current detecting means detect a current exceeding the first predetermined current value, the first and second switching elements are turned off to cut off the through currents of the first and second switching elements. Protecting the second switching element, and turning off the third and fourth switching elements when the third and fourth current detection means both detect a current exceeding the second predetermined current value. Protection means for blocking the through current of the switching element and protecting the third and fourth switching elements;
A switching circuit comprising:   The first current detection means is a first voltage detection circuit that detects the voltage across the first switching element, and the second current detection means is a second voltage detection circuit that detects the voltage across the second switching element, The third current detection means is a third voltage detection circuit that detects the voltage across the third switching element, and the fourth current detection means is a fourth voltage detection circuit that detects the voltage across the fourth switching element. The switching circuit according to claim 4. The protective means is
A first detection signal is output by detecting that the voltage detected by the first voltage detection circuit is lower than the first predetermined voltage and the voltage detected by the second voltage detection circuit is lower than the second predetermined voltage. 1 detection circuit;
A first delay circuit for delaying the first detection signal by a first predetermined time;
The first protection signal for holding the first detection signal from the first delay circuit and for turning off the first and second switching elements and blocking the through current of the first and second switching elements while holding the first detection signal. A first holding circuit that outputs
A second detection signal is output by detecting that the voltage detected by the third voltage detection circuit is lower than the third predetermined voltage and the voltage detected by the fourth voltage detection circuit is lower than the fourth predetermined voltage. Two detection circuits;
A second delay circuit for delaying the second detection signal by a second predetermined time;
The second protection signal for holding the second detection signal from the second delay circuit and for turning off the third and fourth switching elements and blocking the through current of the third and fourth switching elements while holding the second detection signal. A second holding circuit that outputs
The switching circuit according to claim 5, further comprising:   The switching circuit according to claim 1, wherein the switching element is a MOSFET.   The switching circuit according to claim 7, wherein the voltage detection circuit is a differential amplifier circuit that detects and amplifies a voltage between a drain and a source of a MOSFET. 1-bit signal conversion means for converting an audio signal composed of an analog signal or a digital signal expressed by being assigned with multiple bits into a 1-bit signal assigned with 1 bit;
A switching circuit comprising first and second switching elements connected in series between a high level power supply terminal and a low level power supply terminal;
A driver that switches between a first period in which the first switching element is turned on and the second switching element is turned off and a second period in which the first switching element is turned off and the second switching element is turned on in accordance with the 1-bit signal. When,
An audio signal reproducing apparatus for reproducing the audio signal from a speaker connected to a connection point of the first and second switching elements,
In the switching circuit,
First current detecting means for detecting a current flowing through the first switching element;
Second current detection means for detecting a current flowing through the second switching element;
Protection means for protecting the first and second switching elements by turning off the first and second switching elements to interrupt the through current when both the first and second current detection means detect a current exceeding a predetermined current value; ,
An audio signal reproducing apparatus comprising: 1-bit signal conversion means for converting an audio signal composed of an analog signal or a digital signal expressed by being assigned with multiple bits into a 1-bit signal assigned with 1 bit;
First and second switching elements sequentially connected in series between a high power supply terminal and a low power supply terminal, and third and fourth switching elements sequentially connected in series between the high power supply terminal and the low power supply terminal. A switching circuit;
A first period in which the first and fourth switching elements are turned on and the second and third switching elements are turned off according to the 1-bit signal, and the first and fourth switching elements are turned off, and the second and third switching elements A driver that switches between a second period of turning on
An audio signal reproducing apparatus for reproducing the audio signal from a speaker connected between a connection point of the first and second switching elements and a connection point of the third and fourth switching elements,
In the switching circuit,
First current detecting means for detecting a current flowing through the first switching element;
Second current detection means for detecting a current flowing through the second switching element;
Third current detection means for detecting a current flowing through the third switching element;
Fourth current detection means for detecting a current flowing through the fourth switching element;
When both of the first and second current detecting means detect a current exceeding the first predetermined current value, the first and second switching elements are turned off to cut off the through currents of the first and second switching elements. Protecting the second switching element and turning off the third and fourth switching elements when the third and fourth current detection means both detect a current exceeding the second predetermined current value. Protection means for blocking the through current of the switching element and protecting the third and fourth switching elements;
An audio signal reproducing apparatus comprising: First and second switching elements connected in series between a high-level power supply terminal and a low-level power supply terminal, and a first period during which the first switching element is turned on and the second switching element is turned off according to an input signal In a switching circuit that switches between a second period in which one switching element is turned off and a second switching element is turned on to extract an output from a connection point of the first and second switching elements,
The current flowing through the first switching element and the current flowing through the second switching element are detected, and both the detected current value of the current flowing through the first switching element and the detected current value of the current flowing through the second switching element are both A switching element protection method, wherein the first and second switching elements are turned off when a predetermined current value is exceeded.

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