JP2008219547A - Excess current protection device of amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the excess current protection device of an amplifier capable of controlling currents flowing in the respective D-class amplifiers constituting a bridge connection type amplifier with the same design value as the one when a single end type amplifier is constituted when the state of a load short-circuit, etc. is continued for a long period of time when the bridge connection type amplifier is constituted. <P>SOLUTION: The excess current protection device of the amplifier is provided with a plurality of D-class amplifiers 6, 7 operably constituted as the single end type amplifier or the bridge connection type amplifier each of which has an input and an output and in which a duty ratio of a PWM modulation signal is controlled by a DSP 5 and an output level is controlled. The excess current protection device is constituted so as to create OR signals of outputs of the excess current detection circuits 8, 9 provided at the D-class amplifiers 6, 7 constituting the bridge connection type amplifier and to supply the OR signals to the DSP 5 when the D-class amplifiers 6, 7 constitute the bridge connection type amplifier. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an overcurrent protection device for an amplifier, and more particularly to an overcurrent protection device optimal for a digital amplifier configured to be operable as a single-ended amplifier or a bridge-connected amplifier.

  In digital amplifiers that output with the power stage operating in digital mode (switching mode), the power that constitutes the power stage when the load connected to the output terminal is short-circuited or the impedance becomes very small and the output current becomes excessive It is necessary to protect components such as MOSFETs from destruction.

  As a conventional digital amplifier overcurrent protection device for protecting the power stage from such an overcurrent state, for example, a voltage applied to a reactor coil constituting a low-pass filter is detected, and this detection signal is input to a microcomputer. The input detection signal is compared with a preset reference value (operation level), and when the detection signal exceeds the reference value, the output relay circuit and the like are shut off and the power MOSFET that constitutes the power stage There have been proposed components configured to protect against overcurrent. (For example, refer to Patent Document 1).

  Further, the conventional amplifier includes a plurality of D class amplifiers each having an input and an output, and the output level is controlled by controlling the duty ratio of a PWM (Pulse Width Modulation) modulation signal by a DSP (Digital Signal Processor). Some are configured to operate as single-ended amplifiers or bridge-connected amplifiers.

  As described above, the overcurrent protection device in the configured amplifier has, for example, each D-class amplifier when the load connected to the output terminal is short-circuited or the impedance becomes very small and the overcurrent state occurs. The overcurrent detection circuit detects the overcurrent, and based on this detection signal, the DSP controls the duty ratio of the PWM modulation signal to attenuate the output of the D class amplifier where the overcurrent has occurred and limit the amount of current, Some are configured to protect components such as power MOSFETs constituting the stage from overcurrent.

A specific example of such an overcurrent protection device for an amplifier is, for example, one having a circuit configuration as shown in FIG. The circuit configuration of FIG. 2 shows a state where a bridge connection type amplifier is configured.
The overcurrent protection device for an amplifier shown in FIG. 2 includes the following parts.
First, for example, a left channel signal of a stereo signal or an input signal at the time of bridge connection is applied to the input terminal 1. On the other hand, the right channel signal of the stereo signal is applied to the input terminal 2. Reference numerals 3 and 4 denote AD converters that convert the analog signals applied to the input terminals 1 and 2 into digital signals and supply them to the DSP 5.

  The DSP 5 includes level control units 51 and 52 formed corresponding to the D class amplifiers 6 and 7, respectively. By this DSP 5, the D class amplifiers 6 and 7 are configured such that the output level is controlled by controlling the duty ratio of the PWM modulation signal. The D class amplifiers 6 and 7 are provided with overcurrent detection circuits 8 and 9 on their output sides. Reference numerals 10 and 11 denote low-pass filters provided on the output side of the D class amplifiers 6 and 7.

  The overcurrent detection circuits 8 and 9 detect the overcurrent when the load 14 such as a speaker connected to the output terminals 12 and 13 is in a short state or when the impedance becomes very small and the overcurrent state is entered. This detection signal is configured to be supplied to the level controllers 51 and 52 of the DSP 5, respectively. The level controllers 51 and 52 to which the detection signal is supplied control the duty ratio of the PWM modulation signal based on the detection signal, thereby attenuating the outputs of the D class amplifiers 6 and 7 to limit the current amount, The current amount is limited and protected so as not to exceed the maximum rating of the power MOSFET for switching.

  Further, in the amplifier having the overcurrent protection device configured as described above, when the load 14 continues to be short-circuited or the impedance is very small, the overcurrent detection circuits 8 and 9 and the DSP 5 are The level controllers 51 and 52 are configured to operate so that the amount of current flowing through the power MOSFET can be kept below a certain value.

  In FIG. 2, when the current value of either the overcurrent detection circuit 8 on the channel CH1 side or the overcurrent detection circuit 9 on the channel CH2 side exceeds the detection sensitivity, the overcurrent detection circuit 8 or 9 detects the overcurrent. Then, the detection signal is output, and the level control unit 51 or 52 of the DSP 5 operates to instantaneously reduce the current level on the side where the overcurrent is detected.

  The time chart showing the change in current in FIG. 3 shows an example of the state of the current that is controlled and changed by the DSP 5 when the circuit in the normal operation state becomes an overcurrent state due to a short circuit of the load 14.

  As shown in FIG. 3, when a large current flows through a circuit operating at a normal current value, the overcurrent detection circuit 8 (or the overcurrent detection circuit 9) works, and immediately after that, the DSP 5 causes the circuit shown in FIG. As shown by A, the output level is narrowed down. Thereafter, if the overcurrent detection signal is not input to the DSP 5, the DSP 5 gradually increases the output. The DSP 5 gradually returns the current amount to the output level before the occurrence of the short circuit.

  Therefore, in the overcurrent protection device of this amplifier, if the load 14 has been in a short state or low impedance state for a long time, “overcurrent detection circuit 8 (or overcurrent detection circuit 9) detects overcurrent → FIG. As shown by A, the DSP 5 throttles the output → no overcurrent detection signal → the DSP 5 gradually increases the output level and reaches B in FIG. 3 → the overcurrent is detected again, and the DSP 5 throttles the output → ... ”, And the same operation is repeated until the short state or low impedance state of the load 14 is resolved.

JP 2005-203968 A

  In the overcurrent protection device for the conventional amplifier shown in FIG. 2 described above, when overcurrent protection is activated with the load connected to form a single-ended amplifier, the amount of current is controlled by the PWM control of the DSP 5. Control can be performed by attenuating the voltage applied to the load output by the driven D class amplifiers 6 and 7, and the current value does not increase due to other factors.

  On the other hand, the accuracy of detecting the overcurrent of the overcurrent detection circuits 8 and 9 always has errors and temperature characteristics. In particular, when a bridge connection type amplifier is configured as shown in FIG. 2, even if the same amount of current flows in the channel CH1 side and the channel CH2 side constituting the bridge connection, and this becomes an overcurrent state, There was a problem that the overcurrent detection circuits 8 and 9 of the two circuits could not be operated simultaneously for the same period.

  That is, when one of the channels CH1 and CH2 constituting the bridge connection type amplifier, for example, only the overcurrent detection circuit 8 detects the overcurrent, and the other overcurrent detection circuit 9 does not detect the overcurrent. In this case, the DSP 5 lowers the output level on the channel CH1 side where the overcurrent is detected, and does not lower the other channel CH2 side where the overcurrent is not detected.

  In this way, when the bridge connection type amplifier is configured, even if the overcurrent detection circuit 8 on one channel CH1 side works to lower the current value due to the overcurrent state, the other channel CH2 side supplies the current. The current level of the bridge-connected amplifier as a whole cannot be reduced because it keeps flowing. For this reason, there is a problem that current continues to flow halfway and the current value does not decrease to the level intended by the DSP 5 as the bridge-connected amplifier total.

  Furthermore, even if the two channels on the channel CH1 side and the channel CH2 side both detect an overcurrent, if the timing at which the DSP 5 lowers the level of the current value or increases it again shifts, the DSP5 will again achieve the intended level. Until the current value does not fall. For this reason, when the load 14 in the bridge-connected amplifier is short-circuited, the operation of “overcurrent detection → thresholding the current value level → sequentially increasing the output without channel CH1 and channel CH2 being synchronized” is repeated. Compared with the case where an end-type amplifier is configured, the amount of current flowing through the power MOSFET increases, and the power MOSFET may be destroyed due to the temperature rise caused by this current.

  The present invention seeks to solve the problems of the conventional amplifier overcurrent protection device as shown in FIG. 2, and particularly when a bridge-connected amplifier is configured. An overcurrent protection device for an amplifier that can simultaneously reduce the current of the channels on both sides of the bridge-connected amplifier to the same level by the DSP even if a situation occurs and the overcurrent detection circuit operates only on one side of the bridge-connected channel It is intended to provide.

  In order to achieve the above object, the overcurrent protection device for an amplifier according to the present invention attenuates the output of the amplifier based on the detection result when the overcurrent detection means provided in the amplifier detects the overcurrent. The current amount is reduced.

Further, the second problem solving means can operate as a single-ended amplifier or a bridge-connected amplifier, each having an input and an output, and the output level is controlled by controlling the duty ratio of the PWM modulation signal by the DSP. When an overcurrent is detected by a plurality of configured D class amplifiers and an overcurrent detection circuit provided in each of the D class amplifiers, the DSP controls the duty ratio of the PWM modulation signal based on the detection result, and the overcurrent is detected. In an overcurrent protection device for an amplifier comprising an overcurrent protection circuit configured to attenuate the output of the generated D class amplifier and reduce the amount of current,
When the D class amplifier constitutes a bridge connection type amplifier, the OR signal of the output of the overcurrent detection circuit provided in each D class amplifier constituting the bridge connection type amplifier is generated, and this OR signal is supplied to the DSP. When the D class amplifier that constitutes the bridge connection generates an overcurrent, the output of the D class amplifier that constitutes the bridge connection amplifier is simultaneously attenuated by the same operation to reduce the current amount. It is a thing.

  According to a third problem solving means, in the overcurrent protection device for an amplifier in the second problem solving means, the overcurrent detection circuit is provided on the output side of each of the plurality of D class amplifiers. Form a bridge connection type amplifier, an OR signal of the output of the overcurrent detection circuit provided in each D class amplifier constituting the bridge connection type amplifier is generated, and this OR signal constitutes the bridge connection type amplifier. Each D-class amplifier is configured to be supplied to each input terminal of the DSP that controls the D-class amplifier.

  According to the amplifier overcurrent protection device of the present invention, when the overcurrent detection means provided in the amplifier detects an overcurrent, based on this detection result, the output of the amplifier is attenuated to reduce the amount of current. It is possible to prevent the power transistor of the amplifier from being destroyed due to a temperature rise due to an unintended current.

  The overcurrent protection device for an amplifier according to the present invention generates an OR signal of an output of an overcurrent detection circuit included in each D class amplifier constituting the bridge connection type amplifier, and supplies the OR signal to the DSP. When an overcurrent occurs in the D class amplifier constituting the bridge connection, the current is reduced by attenuating the output of the D class amplifier constituting the bridge connection type amplifier by the same operation at the same time. Even when the load is short-circuited when the amplifier is configured or when the impedance state close to the short-circuit continues for a long time, the current flowing through each D-class amplifier constituting the bridge-connected amplifier is configured as a single-ended connected amplifier. It can be controlled with the same design value as the case. For this reason, it is possible to prevent the power MOSFET of the D-class amplifier from being destroyed due to a temperature rise due to an unintended current.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
In the present embodiment, the present invention is applied to the conventional overcurrent protection device for an amplifier already described with reference to FIG. 2, and the same reference numerals are given to the parts performing the same configuration operation as in FIG. The description of the configuration operation is omitted or simplified, and the main part of the present invention will be described in detail.

  In FIG. 1, reference numeral 1 denotes an input terminal to which, for example, a left channel signal of a stereo signal or an input signal at the time of bridge connection is applied. Reference numeral 2 denotes an input terminal to which a right channel signal of a stereo signal is applied. Reference numerals 3 and 4 denote AD converters that convert the analog signals applied to the input terminals 1 and 2 into digital signals and supply them to the DSP 5.

  The DSP 5 includes level control units 51 and 52 formed corresponding to the D class amplifiers 6 and 7, respectively. By this DSP 5, the D class amplifiers 6 and 7 are configured such that the output level is controlled by controlling the duty ratio of the PWM modulation signal. The D class amplifiers 6 and 7 are provided with overcurrent detection circuits 8 and 9 on their output sides. Reference numerals 10 and 11 denote low-pass filters provided on the output side of the D class amplifiers 6 and 7.

  The overcurrent detection circuits 8 and 9 detect the overcurrent when the load 14 such as a speaker connected to the output terminals 12 and 13 is in a short state or when the impedance becomes very small and the overcurrent state is entered. This detection signal is configured to be supplied to the level control unit input terminals 511 and 521 of the DSP 5, respectively. The level control units 51 and 52 to which the detection signal is supplied control the duty ratio of the PWM modulation signal based on the detection signal, thereby attenuating the outputs of the D class amplifiers 6 and 7 to reduce the current amount and switching. Therefore, the current MOSFET is configured to be protected by limiting the amount of current so as not to exceed the maximum rating of the power MOSFET.

  An OR signal transmission line 15 is arranged between both outputs of the overcurrent detection circuits 8 and 9, and when the D class amplifiers 6 and 7 constitute a bridge connection type amplifier as shown in FIG. An OR signal of the output of the circuits 8 and 9 is generated and this OR signal is supplied to the level control unit input terminals 511 and 521 of the DSP 5, respectively, and overcurrent protection when a bridge connection type amplifier is configured is simultaneously provided. , So that the same operation can be performed.

  As described above, in the present embodiment, the OR signals of the outputs of the overcurrent detection circuits 8 and 9 provided in the respective D class amplifiers 6 and 7 constituting the bridge connection type amplifier are generated via the OR signal transmission line 15. The OR signal is supplied to the level control unit input terminals 511 and 521 of the DSP 5, respectively. When an overcurrent occurs in the D class amplifiers 6 and 7 constituting the bridge connection, the current amount can be reduced by attenuating the output of the D class amplifier constituting the bridge connection amplifier by the same operation at the same time. It is possible to prevent the MOSFET from being destroyed.

  Further, when the bridge connection type amplifier is configured, even if the load is short-circuited or the impedance state close to the short-circuit continues for a long time, the amount of current flowing through each of the D class amplifiers 6 and 7 constituting the bridge connection type amplifier Can be controlled with the same design value as when a single-ended connection type amplifier is configured. As a result, the power MOSFETs of the D class amplifiers 6 and 7 can be destroyed due to a temperature rise caused by an unintended current. An amplifier overcurrent protection device that can be prevented can be realized.

It is a figure which shows schematic circuit structure of the overcurrent protection apparatus of the amplifier which concerns on embodiment of this invention. It is a figure which shows schematic circuit structure of the overcurrent protection apparatus of the conventional amplifier. 6 is a time chart illustrating an example of a state of a current that is controlled and changed by a DSP when a circuit in a normal operation state becomes an overcurrent state due to a short circuit of a load.

Explanation of symbols

1 Input Terminal 2 Input Terminal 3 AD Converter 4 AD Converter 5 DSP
51 Level Control Unit 52 Level Control Unit 511 Level Control Unit Input Terminal 521 Level Control Unit Input Terminal 6 D Class Amplifier 7 D Class Amplifier 8 Overcurrent Detection Circuit 9 Overcurrent Detection Circuit 10 Low Pass Filter 11 Low Pass Filter 12 Output Terminal 13 Output Terminal 14 Load 15 OR signal transmission line

Claims (3)

  An overcurrent protection device for an amplifier, characterized in that when the overcurrent detection means provided in the amplifier detects an overcurrent, the output of the amplifier is attenuated based on the detection result to reduce the amount of current. A plurality of D-class amplifiers each configured to be operable as a single-ended amplifier or a bridge-connected amplifier, each having an input and an output, the output level of which is controlled by controlling the duty ratio of the PWM modulation signal by the DSP;
When an overcurrent detection circuit provided in each of the D class amplifiers detects an overcurrent, the DSP controls the duty ratio of the PWM modulation signal based on the detection result to attenuate the output of the D class amplifier in which the overcurrent has occurred. In an overcurrent protection device for an amplifier having an overcurrent protection circuit configured to reduce the amount of current,
When the D class amplifier constitutes a bridge connection type amplifier, the OR signal of the output of the overcurrent detection circuit provided in each D class amplifier constituting the bridge connection type amplifier is generated, and this OR signal is supplied to the DSP. When the D class amplifier that constitutes the bridge connection generates an overcurrent, the output of the D class amplifier that constitutes the bridge connection amplifier is simultaneously attenuated by the same operation to reduce the current amount. An overcurrent protection device for an amplifier.   The overcurrent detection circuit is provided on the output side of each of the plurality of D class amplifiers, and when the D class amplifier constitutes a bridge connection type amplifier, each of the D class amplifiers constituting the bridge connection type amplifier is provided. An OR signal of the output of the overcurrent detection circuit is generated, and this OR signal is supplied to each input terminal of the DSP that controls each D class amplifier constituting the bridge connection type amplifier. The overcurrent protection device for an amplifier according to claim 2.

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