JP5440034B2 - Audio equipment - Google Patents

Description

  The present invention relates to an audio apparatus equipped with a DC / DC converter that generates a power supply voltage for an audio signal amplification power amplifier.

  The in-vehicle audio device is equipped with a DC / DC converter that generates a power amplifier power supply voltage from a battery voltage. The rated power of the DC / DC converter is conveniently set corresponding to the standard power supply voltage of the battery, 14.4V. However, since the battery voltage may be 16.0V, the audio device is connected to the battery. The operation needs to be guaranteed even for a voltage of 16.0 V, and the power capacity of the power amplifier is designed to be large.

  Patent Document 1 discloses an audio device equipped with a power amplifier and a DC / DC converter for its supply voltage (Patent Document 1 FIG. 2). In the audio apparatus, when the volume operation amount M is (a) Mmin ≦ M <Mthd with respect to the minimum operation amount Mmin, the threshold value Mthd, and the maximum operation amount Mmax (Mmin <Mthd <Mmax), the battery voltage 14. 4V is used as the secondary output voltage as it is (paragraph 0032 of Patent Document 1), and when (b) Mthd ≦ M <Mmax, the secondary output voltage is switched to the output voltage of the DC / DC converter 16.0V (patent) Literature 1 paragraph 0034), (c) After the above (b), when the primary current of the DC / DC converter becomes larger than the maximum value, the secondary voltage of the DC / DC converter is changed to 14.4V and 16.0V. The value is lowered to an intermediate value (Patent Document 1, paragraph 0042).

  In Patent Document 1, as a method of detecting the primary current of the DC / DC converter in the case of (c), the magnetic flux of the primary current is detected, or a part of the primary current is shunted to a fixed resistor, and the fixed current is detected. The voltage of the resistance is measured (Patent Document 1, paragraph 0025).

  Patent Document 2 is equipped with an amplifier power source that generates amplifier power from an AC power source, a DSP that converts an audio signal into a PWM modulation signal, and a power amplifier that is supplied with power from the amplifier power source and amplifies the audio signal from the DSP An audio device is disclosed (Patent Document 2 FIG. 1). In the audio device, the supply current to the power amplifier is detected, and when an overcurrent state is detected for the supply current, (a) in order of the input audio signal of the power amplifier until the overcurrent state is eliminated. Steps are proceeded with peak compression, (b) attenuation of the input audio signal, (c) load speaker cutoff, and (d) power supply stop to the power amplifier (Patent Document 2, paragraphs 0019 to 0021).

  Patent Document 3 discloses an audio device equipped with a power amplifier that amplifies an audio signal when power is supplied from a battery (Patent Document 3 FIG. 1). In the audio device, the power amplifier current and voltage supplied in the two power consumption states of the power amplifier are measured, and the no-load voltage and power source resistance of the battery are calculated ((1) to (3) of Patent Document 3). Next, the maximum guaranteed power consumption is calculated based on the no-load voltage and the power supply resistance (equation (4) to (8) in Patent Document 3), and then the maximum power consumption of the power amplifier is calculated from the maximum guaranteed power consumption. The level limit value of the input signal is calculated (Equation (9) in Patent Document 3). Then, the signal level control circuit on the input side of the power amplifier is controlled so that the input signal of the power amplifier does not exceed the level limit value (Patent Document 3, paragraph 0075).

JP 2004-104922 A JP 2003-37452 A JP 2009-21840 A

  Japanese Patent Application No. 2008-97635 (hereinafter referred to as “Prior Application 1”) by the present applicant discloses a power amplifier unit interposed between an in-vehicle battery and a speaker (Prior Application 1 FIG. 1). The power amplifier unit includes a DC / DC converter that converts a battery voltage into a plurality of positive and negative DC voltages using a transformer, an FET (Field Effect) that alternately turns on and off to generate a primary current of opposite direction. Transistor) pair, a controller for controlling the gate voltage of the FET pair, a power amplifier unit using the output voltage of the DC / DC converter as a power source, and a mute circuit for controlling mute of the audio signal input to the power amplifier unit . The primary current flowing between the FET and the grant during the mute period immediately after the power is turned on is monitored. When an excessive primary current is detected, a power stop control signal is sent to the controller to stop the operation of the DC / DC converter. Thus, the DC / DC converter and the power amplifier are prevented from being damaged by a large current (paragraph 0019 in the prior application).

  Japanese Patent Application No. 2008-316931 (hereinafter referred to as “prior application 2”) by the present applicant is a power amplifier, a temperature detection circuit (eg, a thermistor) for detecting the temperature of the power amplifier, and an audio signal input to the power amplifier. An audio device equipped with a soft clipper circuit that limits the amplitude of the signal based on the output of the temperature detection circuit is disclosed (prior application 2 FIG. 1). Specifically, the soft clipper circuit includes a generation circuit that generates a positive limit voltage and a negative limit voltage that decrease and increase as the temperature of the power amplifier increases, and a positive side from the passing point of the audio signal to the power amplifier. And two diodes connected in a forward direction toward the limit voltage point and from the negative limit voltage point toward the audio signal input point.

  When the primary current of the DC / DC converter becomes larger than the maximum value during the period when the output voltage of the DC / DC converter is set to 16.0V, the audio device disclosed in Patent Document 1 increases the output voltage of the DC / DC converter. Reduce to a value lower than 16.0V. The audio device of Patent Document 1 uses a fuse of 10A to avoid the primary current from exceeding 10A (Patent Document 1, paragraphs 0072 to 0074), and to the high power amplifier in which the primary current reaches about 50A. Application is not intended. Further, depending on the power amplifier, when the supply voltage (the output voltage of the DC / DC converter) decreases, the operation may be hindered. Furthermore, a magnetometer and a shunt circuit are necessary to detect the primary current of the DC / DC converter.

  The battery voltage may rise from the usual 14.4V to 16.0V, and the power amplifier needs to guarantee the operation even for the battery voltage of 16.0V. On the other hand, in the audio device of Patent Document 2, the peak of the input audio signal of the power amplifier is sequentially detected until the overcurrent state of the supply current to the power amplifier is detected and the overcurrent state is resolved. Compression, (b) input audio signal attenuation, (c) load loudspeaker shutoff, and (d) power supply to power amplifier stop, but steps (c) and (d) stop power amplifier operation This is not a measure to guarantee the operation of the power amplifier. Patent Document 2 refers to peak compression of the input audio signal of the power amplifier and attenuation of the input audio signal, but does not disclose a configuration that specifically realizes them. Further, in order to measure the current supplied to the power amplifier (secondary current of the DC / DC converter), as in the detection of the primary current of the DC / DC converter of Patent Document 1, a magnetometer, a shunt circuit, etc. It is necessary to add a circuit dedicated to current detection.

  Although the audio device of Patent Document 3 discloses limiting the input signal level of the power amplifier, it does not disclose a specific limiting circuit, and in order to calculate the no-load voltage and power supply resistance of the battery, It is necessary to measure the power supply current and power supply voltage of the power amplifier in the two power consumption states of the power amplifier, which complicates the processing.

  Prior application 1 discloses an FET pair for controlling the primary current of a power amplifier. However, the apparatus of prior application 1 copes with an abnormal current in a mute period immediately after power-on, and performs DC / DC conversion when detecting an abnormal current. The operation of the vessel is stopped. When the battery voltage is high within the normal range, the operation is not guaranteed by placing the power amplifier within the power capacity.

  The device of the prior application 2 copes with the temperature rise of the power amplifier and limits the amplitude of the audio signal to the power amplifier. When the battery voltage is high within the normal range, the operation is not guaranteed by placing the power amplifier within the power capacity.

  The object of the present invention is to provide a power amplifier designed based on the rated power set for the lower input voltage of the DC / DC converter, when the input voltage of the DC / DC converter becomes higher in the normal range. It is also to provide an audio device that can guarantee the operation.

  According to the present invention, an integrator for charging / discharging corresponding to the increase / decrease of the primary current of the transformer of the DC / DC converter and an amplitude control unit for limiting the amplitude of the audio signal input to the power amplifier are prepared. To do. The amplitude limit value in the amplitude control unit is controlled based on the output of the integrator.

The audio apparatus of the present invention is a DC / DC converter that converts a single input DC voltage into positive and negative output DC voltages using a transformer, and whether the primary current of the transformer is equal to or greater than a predetermined threshold. An integrator having a capacitor that is charged or discharged depending on whether or not, an amplitude control unit that controls the amplitude of the audio signal based on the output of the integrator, and an input audio signal from the amplitude control unit using the output DC voltage as a power source A first FET that passes and blocks a primary current in the first direction in the transformer by turning on and off, and a primary current in a direction opposite to the first direction in the transformer by turning on and off FET control section for supplying the first and second FET with a gate signal for alternately turning on the first FET and the second FET, and the first FET in the on period. And a corresponding voltage applying unit to which a corresponding voltage of the terminal voltage of the second FET is applied, and a switching element that is turned on and off according to the corresponding voltage to control charging and discharging of the capacitor, The second FET is an element of the DC / DC converter.

  According to the present invention, the amplitude of the audio signal input to the power amplifier is controlled based on the primary current of the transformer of the DC / DC converter, that is, it is not necessary to lower the supply voltage of the power amplifier. The operation of the amplifier can be maintained, and even if the primary voltage of the DC / DC converter becomes high, it is possible to suppress the power amplifier from being applied with power exceeding the rated power.

It is a principal part block diagram of a vehicle-mounted audio system. It is a figure which shows schematic structure of the principal part of a vehicle-mounted audio system centering on the DC / DC converter power supply of a power amplifier unit. It is a detailed circuit diagram of a soft clipper circuit and a clipper control circuit. It is a figure which shows the input / output characteristic of a soft clipper circuit. It is a detailed circuit diagram of a range including a part of a DC / DC converter power supply, a large current detection circuit, and an integration circuit. FIG. 6 is a voltage waveform diagram at a plurality of predetermined points of the DC / DC converter power supply and the large current detection circuit of FIG. 5. FIG. 6 is a voltage waveform diagram at a plurality of predetermined points of the primary current of the transformer and the large current detection circuit and the integration circuit of FIG. 5. It is a block diagram of another vehicle-mounted audio system. FIG. 2 is a block diagram of an audio device that abstracts the audio device of FIG. 1. FIG. 9 is a block diagram of an audio device that abstracts the audio device of FIG. 8.

  FIG. 1 is a configuration diagram of a main part of an in-vehicle audio system 10. The in-vehicle audio system 10 includes a power amplifier unit 11, a center unit 12, an in-vehicle battery 13 and a speaker 14. The center unit 12 sends audio signals such as CD and radio to the power amplifier unit 11. The power amplifier unit 11 receives power supply from the in-vehicle battery 13. The in-vehicle battery 13 is charged by an automobile generator and supplies power not only to the in-vehicle audio system 10 but also to electrical components such as an air conditioner and a headlight of the automobile. The rated voltage of the in-vehicle battery 13 is 14.4V and increases to 16.0V depending on the situation. When the power is turned on, the center unit 12 sends a P-Con (power control signal) to the power amplifier unit 11.

  In the power amplifier unit 11, the audio signal from the center unit 12 is input to the gain circuit 19, and the gain circuit 19 amplifies the audio signal with a gain corresponding to the volume indicated by the user, and then sends it to the soft clipper circuit 20. . Details of the soft clipper circuit 20 will be described later with reference to FIG. The power amplifier unit 21 amplifies the audio signal from the soft clipper circuit 20 and outputs it to the speaker 14, and the speaker 14 outputs sound corresponding to the input audio signal. The power amplifier unit 21 may be a high power amplifier of about 50A, for example.

  The DC / DC converter power supply 25 is supplied with a single voltage from the in-vehicle battery 13 and is controlled to turn on and off FETs (Field Effect Transistors) 44 and 45 (FIGS. 2 and 5) by a gate signal from the control circuit 26. The single input voltage is converted into positive and negative voltages (± B, see FIG. 2). ± B is used as a power source for the power amplifier unit 21.

  The power control circuit 27 receives a P-Con signal from the center unit 12 when the power switch of the in-vehicle audio system 10 is turned on, and accordingly, sends a control start signal to the control circuit 26 to supply a DC / DC converter power supply. 25 starts its operation. When the power switch of the in-vehicle audio system 10 is turned off and the P-Con signal disappears from the center unit 12, the power control circuit 27 stops the operation of the DC / DC converter power supply 25 via the control circuit 26.

  The large current detection circuit 31 monitors the primary current of the DC / DC converter power supply 25 and distinguishes between the period of large current (current larger than Lb in FIG. 7 described later) and the period of small current to charge the integration circuit 32. Control the discharge. The output of the integrating circuit 32 is sent to the clipper control circuit 33. The temperature element 34 detects the temperature of the DC / DC converter power supply 25 and sends a detection signal to the clipper control circuit 33. The clipper control circuit 33 controls the soft clipper circuit 20 and the control circuit 26 based on input signals from the integration circuit 32 and the temperature element 34. The large current detection circuit 31, the integration circuit 32, and the clipper control circuit 33 will be described in detail with reference to FIGS.

  Various abnormality protection circuits 37 such as overcurrent monitor the overcurrent, temperature, etc. of the power amplifier unit 21, and if an abnormal state is detected for these, a control signal is sent to the control circuit 26, and DC / The operation of the DC converter power supply 25 is stopped.

  FIG. 2 is a diagram showing a schematic configuration of a main part of the in-vehicle audio system 10 with the DC / DC converter power supply 25 of the power amplifier unit 11 as a center. The transformer 42 includes three terminals on the primary side and the secondary side, respectively. The three terminals are both end terminals and an intermediate terminal. The capacitor 43 has a positive terminal connected to the positive terminal of the in-vehicle battery 13 and an intermediate terminal on the primary side of the transformer 42, and a negative terminal connected to the ground. The negative terminal of the in-vehicle battery 13 is connected to the ground. The FET 44 is interposed between one end of the primary coil of the transformer 42 and the ground, and the FET 45 is interposed between the other end of the primary coil of the transformer 42 and the ground.

  Both terminals of the secondary coil of the transformer 42 are connected to a pair of input terminals of the diode bridge 49, and the intermediate terminal is connected to the ground. The capacitors 50 and 51 are connected in series, and both ends of the series connection are connected to a pair of output terminals of the secondary side coil of the transformer 42. The connection point of the capacitors 51 and 52 is connected to the ground. The diode bridge 49 generates two rectified currents from the AC secondary current of the transformer 42, and charges the capacitors 50 and 51 with the two rectified currents, respectively. As a result, ± B voltages are generated at both ends of the series connection of the capacitors 50 and 51, respectively. ± B is supplied to AVR (DC stabilized power supply circuit) 54 and 55, and AVR 54 and 55 generate a voltage of ± 15V, respectively. The output voltages of ± B and AVR 54 and AVR 55 are supplied to the power amplifier unit 21 for power.

  FIG. 3 is a detailed circuit diagram of the soft clipper circuit 20 and the clipper control circuit 33. In the reference numerals of FIG. 3 and FIG. 5 described later, R is a resistor, TH is a thermistor, Tr is a transistor, O is an operational amplifier, C is a capacitor, K is a coil, F is an FET (Field Effect Transistor), and D is Each means a diode. Description will be made using only symbols, omitting element names such as resistors and thermistors. In addition, since the connection between each element is as the description of FIG.3 and FIG.5, description of a structure is abbreviate | omitted. Further, Va1 to Va4 (FIG. 3), Vb1 to Vb9 (FIG. 5: Vb6 is not provided), and Vc1 and Vc2 (FIG. 5) indicate voltages at respective points on the circuit. I1 indicates the primary current of the transformer 42 (FIG. 2).

  Prior to the description of FIG. 3, FIG. 4 will be described. FIG. 4 shows the input / output characteristics of the soft clipper circuit 20. The horizontal axis represents the level Vi of the input signal Vin input to the soft clipper circuit 20, and the vertical axis represents the level Vo of the output signal Vout output from the soft clipper circuit 20. Vo is also an input of the power amplifier unit 21. Vin and Vout mean voltages at the gain circuit 19 side terminal and the R105 side terminal of R104 in FIG.

  In FIG. 4, Vt is a peak value (amplitude limit value) of the output signal level Vo when soft clip processing is performed by the soft clipper circuit 20. That is, the output signal Vout is clipped at a portion exceeding the peak value Vt. Vp and Vmin are the maximum value and the minimum value of the peak value Vt. That is, the peak value Vt changes between the maximum peak value Vp and the minimum peak value Vmin by the operation of the soft clipper circuit 20 (Vmin ≦ Vt ≦ Vp). Here, the difference ΔV (= Vp−Vt) between the maximum peak value Vp and the peak value Vt is referred to as a clip amount when the peak value is Vt. The maximum peak value Vp is a maximum input voltage that the power amplifier unit 21 can amplify while maintaining the set amplification factor. The minimum peak value Vmin corresponds to the lowest level within a range in which the change in volume feeling due to the clip is not felt.

  In FIG. 3, the detection amount input unit 60 and the clip amount instruction unit 61 constitute a clipper control circuit 33 (FIG. 1). The output voltage of the integrating circuit 32 (FIG. 1) is supplied to a connection point (measurement point of Va1) between R67 and R68 of the detection amount input unit 60. The detection amount input unit 60 includes TH75, which constitutes the temperature element 34 and detects the temperature of the DC / DC converter power supply 25. TH75 decreases the resistance value as the temperature increases. The clipper control circuit 33 controls the amplitude limit of the audio signal in the soft clipper circuit 20 according to the output of TH75 in addition to the output from the integration circuit 32. TH75 may detect the temperature of the power amplifier unit 21 instead of the temperature of the DC / DC converter power supply 25. In that case, as in the above-described prior application 2, the circuit of FIG. 3 controls the amplitude of the audio signal to the power amplifier unit 21 in accordance with the temperature of the power amplifier unit 21. Prior to the description of the operation of the clipper control circuit 33 by the output of the integration circuit 32, the amplitude control of the audio signal to the power amplifier unit 21 by the output of TH75 will be described.

  The resistance value of TH75 is the temperature U of the DC / DC converter power supply 25 (in order to distinguish from the period of FIG. 6 described later, “U” is used for temperature and “T” is used for the period). While it is below the limit value Uc, it exceeds the predetermined value, so Tr80 is in the on state. Therefore, the emitter voltage Va1 of Tr80 does not decrease until Tr79 is turned on, and Tr79 maintains the off state. At this time, Tr97, Tr110, and Tr111 are in an OFF state, the collector voltage Va3 of Tr97 is 6 [V], the emitter voltage Va4 of Tr110 is 5 [V], and the base voltage Va5 and emitter voltage Va6 of Tr111 are −6 [ V] and -5 [V].

  Thereafter, when the temperature U of the DC / DC converter power supply 25 reaches the temperature limit value Uc, the resistance value of TH75 becomes a predetermined value or less, so Tr80 is turned off, the voltage Va1 is lowered, and Tr79 is turned on. Become. Further, when the temperature U of the DC / DC converter power supply 25 exceeds Uc, the resistance value of TH75 decreases, the collector current of Tr79 increases, and the voltage Va2 increases. That is, the increase amount ΔU of the temperature U from Uc appears as the increase amount ΔVa2 of the voltage Va2. In this way, TH75 outputs voltage Va2 corresponding to temperature U as a temperature detection signal when temperature U of DC / DC converter power supply 25 is equal to or higher than temperature limit value Uc.

  When the temperature U of the DC / DC converter power supply 25 reaches Uc, Tr97 is turned on by the voltage Va2. When the voltage Va2 further rises in this state, the collector current of the Tr97 increases and the collector-emitter voltage decreases, the collector voltage Va3 of the Tr97 becomes smaller than +6 [V], and the base voltage Va5 of the Tr111 becomes − It becomes larger than 6 [V]. This voltage Va3 is applied as a positive control voltage to the base of Tr110 via R91. The voltage Va5 is applied as a negative control voltage to the base of Tr111. Thus, when the temperature U of the DC / DC converter power supply 25 is equal to or higher than the temperature limit value Uc, the clipper control circuit 33 generates a control voltage having a level corresponding to the level of the temperature detection signal Va2 from TH75. 20 is output.

  When the voltage Va3 becomes smaller than +6 [V], the Tr 110 is turned on. Then, according to the characteristics of Tr110, the voltage Va4 becomes smaller than 5 [V] by the decrease of the voltage Va3. Similarly, when the voltage Va5 becomes larger than −6 [V], the Tr 111 is turned on. Then, according to the characteristics of Tr111, the voltage Va6 becomes larger than −5 [V] by the increase of the voltage Va5. That is, when the temperature U of the DC / DC converter power supply 25 is equal to or higher than the temperature limit value Uc, the cathode voltage of D115 and the anode voltage of D116 (FIG. 3) correspond to the increase in the temperature U of the DC / DC converter power supply 25. Decrease and increase. Along with this, the anode and cathode voltages of D115 and D116 that conduct D115 and D116 also decrease and increase. Accordingly, the clip amount ΔV increases. In this manner, the soft clipper circuit 20 determines that the temperature U of the DC / DC converter power supply 25 is based on the control voltage from the clipper control circuit 33 when the temperature U of the DC / DC converter power supply 25 is equal to or higher than the temperature limit value Uc. As it increases, the clip amount ΔV is increased and the peak value Vt is decreased.

  According to this, for example, as shown in FIG. 4, when the waveform 118 of the input signal whose peak level is the maximum peak value Vp is input, the temperature U of the DC / DC converter power supply 25 may be equal to or lower than the temperature limit value Uc. If the temperature U of the DC / DC converter power supply 25 exceeds the temperature limit value Uc, the clip corresponding to the temperature U as shown in the waveform 120 is not clipped. Clipped by an amount ΔV. The form of the clip is the above-described soft clip due to the characteristics of D115 and D116. The maximum amplitude value Vt decreases as the temperature U increases, and can decrease to the minimum value Vmin as shown by the waveform 121. The minimum value Vmin can be determined by R102 and R103.

  That is, the TH 75, the clipper control circuit 33, and the soft clipper circuit 20 are configured such that the temperature of the DC / DC converter power supply 25 is the temperature limit so that the temperature of the DC / DC converter power supply 25 does not exceed the temperature limit value Uc. When the value Uc is reached, the clip amount ΔV is adjusted based on the temperature of the DC / DC converter power supply 25, and feedback control is performed to maintain the temperature of the DC / DC converter power supply 25 at the temperature limit value Uc. The same applies when the TH 75 detects the temperature of the power amplifier unit 21 instead of the DC / DC converter power supply 25.

  According to the soft clipper circuit 20, since the minimum peak value Vmin is set within a level range in which the change in volume feeling due to the clip is not felt, the amplitude of the audio signal is not changed much without changing the volume feeling or the power feeling. Limits can be achieved.

  In addition, as a form of clip that restricts the peak value, soft clipping is performed, so that while maintaining the original volume of the input signal with a large volume, a change in volume feeling and a punching power at low frequencies can be achieved for users who enjoy a large volume. There is no much deterioration.

  Further, according to the soft clipper circuit 20, a conventional limiter circuit for limiting the signal level (such as a soft clipper, in which the waveform in the vicinity of the limit level is not curved but is cut linearly at the limit level. )), The load on the tweeter, which is a high-frequency speaker, can be increased, and unnecessary high-frequency components that may cause damage to the tweeter can be reduced.

  5 is a detailed circuit diagram of a range including a part of the DC / DC converter power supply 25, the large current detection circuit 31 and the integration circuit 32. FIG. 6 is a circuit diagram of the DC / DC converter power supply 25 and the large current detection circuit 31 in FIG. It is a voltage waveform figure in a plurality of predetermined points. Since the connection between each element is as shown in FIG. 5, the description thereof is omitted. The operation of the circuit of FIG. 5 will be described with reference to FIG.

  The control circuit 26 outputs the gate voltages Vb1 and Vb2 of the FETs 44 and 45. As shown in FIG. 6, Vb1 and Vb2 are low and high binary signals. In the high period Ton of Vb1 and Vb2, the FETs 44 and 45 are turned on, and in the low period Toff of Vb1 and Vb2, The FETs 44 and 45 are turned off. If Ton <Toff and Td = Toff−Ton, the FETs 44 and 45 are alternately turned on, and there is a Td (dead time) that turns off both before and after each Ton. The cathode side voltage Vb5 of D134 and D135 is maintained at the higher one of Vb1 and Vb2 (Vb5 in FIG. 6).

  As the FETs 44 and 45 are turned on and off, the primary current of the transformer 42 (FIG. 2) is passed and cut off. In the ON period of the FETs 44 and 45, the source voltages Vb3 and Vb4 of the FETs 44 and 45 decrease, and in the OFF period of the FETs 44 and 45, the source voltages Vb3 and Vb4 of the FETs 44 and 45 increase (Vb3 and Vb4 in FIG. 6). On / off of the FET 44 passes and blocks the primary current in the first direction in the transformer 42. On / off of the FET 45 passes and blocks the primary current in the direction opposite to the first direction in the transformer 42. In other words, the primary current in the reverse direction is a primary current that creates a magnetic flux in a direction opposite to the direction of the magnetic flux produced in the transformer 42 by the primary current in the first direction. Since the on-resistance value between the source and drain of the FETs 44 and 45 is constant, the source-side voltages Vb3 and Vb4 of the FETs 44 and 45 increase and decrease according to the increase and decrease of the primary current during the ON period of the FETs 44 and 45 ( Vb3, Vb4 upward arrows and broken lines in FIG. 6). As FETs 44 and 45 are switched from on to off, in the dead time Td immediately after the switching, induced voltages in the reverse direction are generated in K124 and K123, and Vb4 and Vb3 are Vb4 and Vb3 when FET45 and FET44 are on. (The bottoms of Vb4 and Vb3 in FIG. 6).

  The voltage Vb7 on the anode side of D136 and D137 is the lower one of Vb3 and Vb4, and becomes a value that increases and decreases with the increase and decrease of the primary current except for the dead time Td (the arrow and broken line of Vb7 in FIG. 6). The waveform of Vb7 in FIG. 6 is a waveform for convenience of explanation (a waveform when it is assumed that there is no C146), and is actually the terminal voltage Vb8 of C146.

  FIG. 7 is a voltage waveform diagram at a plurality of predetermined points of the primary current of the transformer 42 and the large current detection circuit 31 and the integration circuit 32 of FIG. In the time axis of FIG. 6 described above, the gate signals Vb1 and Vb2 of the FETs 44 and 45 are 30 kHz and Ton is shown in a magnitude of several tens of μsec, whereas in the time axis of FIG. This corresponds to the case where the user is actually listening to music, and the time interval between P0 and P4 is several milliseconds to several tens of milliseconds. The operation of the circuit of FIG. 5 will be described with reference to FIG.

  In FIG. 7, La is the rated current of the primary current I1, and Lb is the allowable maximum current of the primary current I1 (La <Lb). I1 may have rising currents P0 to P4 that rise in units of several milliseconds to several tens of milliseconds during music playback. Assume that P0, P4 ≦ Lb, and P1, P2, P3> Lb. Regarding I1, the period before t1 and the period after t3 are small current periods, and the period from t1 to t3 is a large current period.

  At time t1, as the terminal voltage Vb8 of C146 becomes equal to or higher than a predetermined value, Tr149 is switched from OFF to ON, and the collector voltage Vc1 of Tr149 falls stepwise from high to low.

  By switching Vc1 from high to low, Tr158 is switched from off to on, and the output terminal 164 side voltage Vc2 of C161 starts to decrease with a predetermined time constant due to the discharge through Tr158.

  At time t2, Vc2 reaches the minimum value, and thereafter holds that value during the ON period of Tr158.

  At time t3, as the terminal voltage Vb8 of C146 returns to less than a predetermined value, Tr149 is switched from ON to OFF, and the collector voltage Vc1 of Tr149 rises in a step shape from low to high.

  By switching Vc1 from low to high, Tr158 is switched from on to off, and the output terminal 164 side voltage Vc2 of C161 starts to rise with a predetermined time constant by the charging current via R153. At time t4, Vc2 returns to the value before time t1, and thereafter holds that value during the off period of Tr158.

In Vc2 of FIG. 7, the meanings of the periods T1 to T4 are as follows.
T1: A delay period from when the primary current I1> Lb is reached until the audio signal amplitude limit in the soft clipper circuit 20 is started. T1 is a time for suspending the start of audio signal amplitude limitation with respect to I1 of a single large current.
T2: An audio signal amplitude restriction release period in the soft clipper circuit 20. Since the restriction on the amplitude of the audio signal to the power amplifier unit 21 is gradually released over the release period T2, the volume of the sound from the speaker 14 gradually returns to that before clipping.
T3: An implementation period of audio signal amplitude limitation in the soft clipper circuit 20.
T4: The audio signal amplitude limit non-execution period in the soft clipper circuit 20.

  Vc2, that is, the voltage at the output terminal 164 of the integrating circuit 32 is supplied to the location of Vb2 in FIG. When the primary current exceeds the allowable maximum current Lb, Tr158 is turned on, and accordingly, Tr79 in FIG. 3 is turned on. As described above with respect to TH75, when the temperature of the DC / DC converter power supply 25 reaches the temperature limit value Uc so that the temperature of the DC / DC converter power supply 25 does not exceed the temperature limit value Uc. The soft clipper circuit 20 adjusts the clip amount ΔV based on the temperature of the DC / DC converter power supply 25 and performs feedback control for maintaining the temperature of the DC / DC converter power supply 25 at the temperature limit value Uc. Similarly, when the voltage of the output terminal 164 of the integrating circuit 32 is supplied to the position of Vb2 in FIG. 3, the primary current of the transformer 42 is the allowable maximum current Lb when the voltage is supplied to the location of Vb2 in FIG. When the primary current of the transformer 42 reaches the allowable maximum current Lb, the soft clipper circuit 20 adjusts the clip amount ΔV based on the primary current of the transformer 42 so that the primary current of the transformer 42 does not increase. The feedback control for maintaining the primary current of the transformer 42 at the allowable maximum current Lb is performed.

  By such feedback control, the primary current I1 ′ after the feedback control is maintained at Lb or less in P1 to P3 as shown at the bottom of FIG.

  FIG. 8 is a configuration diagram of another in-vehicle audio system 200. In the in-vehicle audio system 200, the same elements as those in the in-vehicle audio system 10 (FIG. 1) are designated by the same reference numerals as those assigned to the corresponding elements in the in-vehicle audio system 10, and their descriptions are omitted.

  The in-vehicle audio system 200 includes a power amplifier unit 201. In the power amplifier unit 201, the same elements as those in the power amplifier unit 11 of the in-vehicle audio system 10 (FIG. 1) are designated by the same reference numerals as the corresponding elements in the power amplifier unit 11, and their description is omitted. The difference of the power amplifier unit 201 with respect to the power amplifier unit 11 of the vehicle-mounted audio system 10 will be described.

  In the power amplifier unit 201, the output of the integrating circuit 32 is sent not to the clipper control circuit 33 but to various abnormality protection circuits 37 such as overcurrent. Various abnormality protection circuits 37 such as overcurrents inherently detect the overcurrent in the power amplifier unit 21, and send this detection signal to the control circuit 26 to stop the generation of the gate signal in the control circuit 26. Thus, the operation of the DC / DC converter power supply 25 is stopped.

  Various abnormality protection circuits 37 such as an overcurrent of the power amplifier unit 201 further send a detection signal based on an input from the integration circuit 32 to the control circuit 26. In response to the detection signals from various abnormality protection circuits 37 such as overcurrent, the control circuit 26 normally supplies the gate signals Vb1 and Vb2 to the gates of the FETs 44 and 45 in the T4 and T1 periods (see the stage of Vc2 in FIG. 7). As a result, the DC / DC converter power supply 25 normally performs voltage conversion.

  With the start of the T3 period, the control circuit 26 stops supplying the gate signals Vb1 and Vb2 to the gates of the FETs 44 and 45. As a result, the output voltage of the DC / DC converter power supply 25 becomes 0, and the operation of the power amplifier unit 21 is stopped. Further, with the stop of the supply of Vb1 and Vb2, the input of the large current detection circuit 31 disappears, the large current detection circuit 31 and the integration circuit 32 become substantially inoperable, making it difficult to resume the operation. . Therefore, the clipper control circuit 33 measures the elapse of the predetermined time Tx from the start of the T3 period (Tx <standard T3 or Tx≈standard T3) and holds the detection signal immediately after the start of the T3 period in the latch. And hold for Tx.

  Then, after the predetermined time Tx has elapsed, the detection signal is temporarily returned to the one immediately before the start of the T3 period. If Vc2 does not rise, the detection signal is returned again immediately after the start of the T3 period, and the output voltage of the DC / DC converter power supply 25 is set to zero. On the other hand, if Vc2 rises, the detection signal is maintained just before the start of the T3 period, the control circuit 26 restarts the supply of the gate signals Vb1 and Vb2 to the gates of the FETs 44 and 45, and the DC The operation of the DC converter power supply 25 and the power amplifier unit 21 is resumed. The detection signals from various abnormality protection circuits 37 such as overcurrent after restarting to the control circuit 26 are based on the output of the integrating circuit 32 after restarting operation.

  FIG. 9 is a block diagram of the audio device 220. A specific example of the audio device 220 is the power amplifier unit 11. The audio device 220 includes a DC / DC conversion circuit 221, an integrator 222, an amplitude control unit 223, and a power amplifier 224.

  The DC / DC conversion circuit 221 uses the transformer 226 to convert a single input DC voltage into positive and negative output DC voltages. The integrator 222 has a capacitor 227 that is charged and discharged according to whether or not the primary current of the transformer 226 is equal to or greater than a predetermined threshold value. The amplitude control unit 223 controls the amplitude of the audio signal based on the output of the integrator 222. The power amplifier 224 amplifies the input audio signal from the amplitude control unit 223 using the output DC voltage as a power source.

  Specific examples of the DC / DC conversion circuit 221, the integrator 222, the amplitude control unit 223, and the power amplifier 224 are the DC / DC converter power source 25, the integration circuit 32, the clipper control circuit 33, and the power amplifier unit 21 of the power amplifier unit 11, respectively. is there. A specific example of the predetermined threshold is Lb in FIG.

  In the audio apparatus 220, when the input DC voltage of the DC / DC conversion circuit 221 increases from the rated value, the supply voltage from the DC / DC conversion circuit 221 to the power amplifier 224 is not dealt with, and the supply voltage is rated. Can be dealt with by reducing the amplitude level of the audio signal. Therefore, it is possible to prevent the power amplifier 224 from being damaged by keeping the power of each element of the power amplifier 224 within the rated value while ensuring the operation (maximum volume) of the power amplifier 224.

  Typically, the DC / DC conversion circuit 221 includes first and second FETs 230 and 231, and the audio device 220 further includes an FET control unit 232, a corresponding voltage application unit 233, and a switching element 234. The first FET 230 passes and blocks the primary current in the first direction in the transformer 226 by turning on and off. The second FET 231 passes and blocks the primary current in the direction opposite to the first direction in the transformer 226 by turning on and off. The FET control unit 232 supplies a gate signal for alternately turning on the first and second FETs 230 and 231 to the first and second FETs 230 and 231. The corresponding voltage application unit 233 is applied with the corresponding voltage of the terminal voltages of the first and second FETs 230 and 231 in the on period. The switching element 234 is turned on / off according to the corresponding voltage to control charging / discharging of the capacitor 227.

  Specific examples of the first and second FETs 230 and 231 and the FET control unit 232 are the FETs 44 and 45 and the control circuit 26 (FIG. 5), respectively. Specific examples of the corresponding voltage application unit 233 are D136, D137, R141, and C146. A specific example of the switching element 234 is Tr158.

  The first and second FETs 230 and 231 have a constant on-resistance. Therefore, the terminal voltage increase / decrease of the first and second FETs 230 and 231 during the ON period corresponds to the increase / decrease of the primary current. By generating the voltage of the integrator 222 using the terminal voltages of the first and second FETs 230 and 231 in the on period, it is possible to suppress elements added for primary current detection.

  Preferably, the amplitude controller 223 includes a limiting voltage generator 240, a positive diode 241 and a negative diode 242. The limit voltage generator 240 generates positive and negative limit voltages according to the output of the integrator 222. The positive side diode 241 is interposed between the passing point and the positive side limiting voltage point so as to be forward from the passing point of the audio signal to the positive side limiting voltage point. The negative side diode 242 is interposed between the passing point and the negative side limiting voltage point so as to be forward from the negative side limiting voltage point to the passing point.

  Specific examples of the limiting voltage generator 240, the positive side diode 241, and the negative side diode 242 are the clip amount indicating units 61, D115, and D116 (FIG. 3), respectively. A specific example of the audio signal passing point is the connecting point of R104 and R105 in FIG. The positive-side diode 241 and the negative-side diode 242 perform soft clip processing in limiting the amplitude of the audio signal, as described above for D115 and D116. Therefore, the audio signal immediately before clipping, that is, immediately before reaching the limit level, is converted to a smoothly changed waveform (a waveform from which high-frequency components have been removed), not steep, and the output of the power amplifier 224 has good responsiveness and unnecessary high-frequency noise. Will be reduced.

  Typically, the corresponding voltage application unit 233 and the first and second FETs 230, 231 are forwarded from the corresponding voltage application unit 233 toward the first and second FETs 230, 231. Respectively.

  Specific examples of the two diodes are D136 and D137 (FIG. 5). The corresponding voltage application unit 233 is applied with the lower terminal voltage of the first and second FETs 230 and 231, that is, the terminal voltage of the FET that is turned on. A primary current is caused to flow through the resistor, whereby a voltage related to the primary current can be generated in the corresponding voltage application unit 233.

  FIG. 10 is a block diagram of another audio device 250. A specific example of the audio device 250 is the in-vehicle audio system 200 (FIG. 8). The audio device 250 includes a DC / DC converter 251, a power amplifier 252, an integrator 253, and an FET control unit 254. The DC / DC converter 251 includes the transformer 260, the first FET 261 that passes and blocks the primary current in the first direction in the transformer 260 by turning on and off, and the DC / DC converter circuit 221 by turning on and off. A second FET 262 that passes and blocks primary current in a direction opposite to the first direction, and uses a transformer 260 to convert a single input DC voltage to a positive and negative output DC voltage.

  The power amplifier 252 operates using the output DC voltage of the DC / DC converter 251 as a power source, and amplifies the input audio signal. The integrator 253 includes a capacitor 265 that is charged / discharged depending on whether or not the primary current when the first and second FETs 261 and 262 are on is greater than or equal to a predetermined threshold value. The FET control unit 254 generates a gate signal for alternately turning on the first and second FETs 261 and 262 based on the output of the integrator 253, and supplies the gate signal to the first and second FETs 261 and 262.

  The audio device 250 can simplify the configuration for detecting the primary current when controlling the operation of the DC / DC converter 251 based on the primary current of the DC / DC converter 251. That is, in order to detect the primary current, the on-resistances of the first and second FETs 261 and 262 are used, so that addition of a shunt circuit and the like can be omitted.

  It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications (including addition and deletion) are possible without departing from the scope of the present invention.

  This specification discloses various ranges and levels of the invention. In addition to various devices and methods of various technical scopes and specific levels described in the present specification, the present invention has operations and effects independent of each device and each method within the scope of expansion or generalization. Extracting one or more elements, changing one or more elements within the scope of expansion or generalization, and combining one or more elements between devices and methods Includes replacements.

220: Audio device, 221: DC / DC conversion circuit, 222: Integrator, 223: Amplitude control unit, 224: Power amplifier, 226: Transformer, 227: Capacitor, 230: First FET, 231: Second FET, 232: FET control unit, 233: corresponding voltage application unit, 234: switching element, 240: limiting voltage generator, 241: positive side diode, 242: negative side diode, 250: audio device, 251: DC / DC conversion 252: power amplifier, 253: integrator, 254: FET controller, 260: transformer, 261: first FET, 262: second FET, 265: capacitor.

Claims (3)

DC / DC converter that converts a single input DC voltage to positive and negative output DC voltage using a transformer,
An integrator having a capacitor that is charged and discharged according to whether or not a primary current of the transformer is equal to or greater than a predetermined threshold;
An amplitude controller for controlling the amplitude of the audio signal based on the output of the integrator ;
A power amplifier that amplifies an input audio signal from the amplitude control unit using the output DC voltage as a power source;
A first FET that passes and blocks primary current in a first direction in the transformer by turning on and off;
A second FET that passes and blocks primary current in a direction opposite to the first direction in the transformer by turning on and off;
An FET control unit for supplying a gate signal for alternately turning on the first and second FETs to the first and second FETs;
A corresponding voltage applying unit to which a corresponding voltage of the terminal voltage of the first and second FETs in the on period is applied; and
A switching element that controls charging and discharging of the capacitor by turning on and off according to the corresponding voltage,
With
The audio apparatus according to claim 1, wherein the first and second FETs are elements of the DC / DC converter . The amplitude controller is
A limiting voltage generator for generating positive and negative limiting voltages according to the output of the integrator;
A positive diode interposed between the passing point and the positive side limiting voltage point so as to be forward from the passing point of the audio signal to the positive side limiting voltage point, and a forward direction from the negative side limiting voltage point to the passing point A negative diode interposed between the passing point and the negative limit voltage point so that
The audio apparatus according to claim 1, further comprising: Two intervening between the corresponding voltage application unit and the first FET and the second FET so as to be forward from the corresponding voltage application unit to the first and second FETs, respectively. diode,
The audio apparatus according to claim 1 or 2, further comprising:

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