JP2008118825A - Power supply control unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent an output transistor from causing thermal breakage due to temperature rise, and to prevent a power supply voltage that is supplied to an amplifier circuit from switched to a low voltage, resulting in distortion of audio signal. <P>SOLUTION: When the voltage from a second power supply circuit 3 is a first threshold value or higher and the level of an output signal of an amplifier circuit 6 is a second threshold value or higher, a voltage switching part 4 is controlled so that a normal voltage is outputted from a secondary winding 1B of a transformer 1. When the voltage from the second power supply circuit 3 is less than the first threshold value, or the output signal of the amplification circuit 6 is less than the second threshold value, the voltage switching part 4 is controlled so that a low voltage is outputted from the secondary winding 1B of the transformer 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply control device that switches a power supply voltage supplied to an amplifier circuit between a normal voltage and a low voltage by switching the number of turns of a secondary winding of a transformer.

  Conventionally, an audio amplifier circuit including an npn transistor and a pnp transistor, which are output transistors, has been adopted. In this amplifier circuit, collectors of both transistors are connected to a positive power supply line and a negative power supply line, respectively, and emitters are connected to an output terminal (a load such as a speaker). The output transistor consumes power in proportion to the power output from the amplifier circuit. As a result, the output transistor generates heat and rises in temperature. Furthermore, the power consumption of the output transistor is substantially proportional to the power supply voltage connected to the collector, and heat is generated according to the power supply voltage, and the temperature rises. The power supply voltage supplied to the collector of the output transistor is a DC voltage that is generally rectified and smoothed by converting a commercial AC power supply voltage (hereinafter referred to as a primary AC voltage) into a secondary AC voltage via a transformer. The primary AC voltage has a fluctuation range of about ± 10%. For example, in Japan, the rated voltage is 100V, but actually varies in the range of 90V to 110V. Since the power supply voltage connected to the collector is a voltage obtained by rectifying and smoothing the primary AC voltage after passing through the transformer as described above, it is supplied to the output transistor corresponding to the fluctuation range of the primary AC voltage. The power supply voltage fluctuates. As a result, even if the amplifier circuit is used at the same input signal level / output signal level, the amount of heat generated by the output transistor changes due to fluctuations in the primary AC voltage. In other words, even if the amplifier circuit is operating at the same volume value, if the primary AC voltage is close to the maximum voltage (110 V) in the fluctuation range compared to the rated voltage, the amount of heat generated by the output transistor becomes very large, resulting in thermal destruction. Sometimes.

  In order to solve this problem, the level of the output signal of the amplifier circuit is monitored by a microcomputer, and when the output signal exceeds a predetermined level, the secondary AC voltage from the transformer becomes a low voltage so that the secondary voltage of the transformer becomes low. It has been proposed to switch the number of turns of the winding. Further, Patent Document 1 below monitors the value of the primary AC voltage with a microcomputer, and when the predetermined threshold value is exceeded, the number of turns of the secondary winding of the transformer so that the secondary AC voltage from the transformer becomes a low voltage. Is described. However, in these methods, since the output signal from the amplifier exceeds the predetermined threshold value or the primary AC voltage exceeds the predetermined threshold value, the output transistor is switched to a low voltage, so that the output transistor is thermally destroyed. The power supply voltage supplied to the amplifier circuit is frequently switched to a low voltage despite the fact that the temperature does not rise up to. As a result, there is a problem that the output signal of the amplifier circuit is clipped and distortion occurs in the output signal.

Japanese Patent Laid-Open No. 11-110054

  The present invention has been made in order to solve the above-described conventional problems, and an object of the present invention is to prevent the output transistor from being thermally destroyed due to a temperature rise, and the power supply voltage supplied to the amplifier circuit is frequently reduced. It is an object of the present invention to provide a power supply control device that can be switched to a low voltage to prevent distortion in an audio signal.

  A power supply control device according to a preferred embodiment of the present invention includes a primary winding to which a primary AC voltage is supplied, and a secondary winding that outputs a secondary AC voltage converted from the voltage supplied to the primary winding. And a voltage switching unit that switches the number of turns of the secondary winding to one of a first number of turns that outputs a secondary AC voltage of a normal voltage and a second number of turns that outputs a secondary AC voltage of a low voltage. And when the voltage corresponding to the primary AC voltage is equal to or higher than the first threshold and the output signal of the amplifier circuit is equal to or higher than the second threshold, the voltage is switched to switch the secondary winding to the second number of turns. The secondary winding is controlled when the voltage corresponding to the primary AC voltage is less than the first threshold or the output signal of the amplifier circuit is less than the second threshold. Control means for controlling the voltage switching unit so as to switch to one winding number. .

  Preferably, when the voltage corresponding to the primary AC voltage is greater than or equal to the first threshold and the period during which the output signal of the amplifier circuit is greater than or equal to the second threshold continues for a predetermined period or longer, the control means The voltage switching unit is controlled to switch the secondary winding to the second number of turns.

  Preferably, after the secondary winding is switched to the second number of turns, a voltage corresponding to the primary AC voltage is less than the first threshold value, or an output signal of the amplifier circuit is less than the second threshold value. When the period of time continues for a predetermined period or longer, the control means controls the voltage switching unit to switch the secondary winding to the first number of turns.

  Preferably, the transformer further includes a second secondary winding that outputs a voltage converted from a voltage supplied to the primary winding, and a voltage corresponding to the primary AC voltage is the second secondary winding. This is the voltage supplied from the secondary winding.

  When it is detected that the voltage corresponding to the primary AC voltage is equal to or higher than the first threshold value and the output signal of the amplifier circuit is equal to or higher than the second threshold value, the control means outputs a low-voltage secondary AC voltage. To control the voltage switching unit. Therefore, the temperature rise of the output transistor can be suppressed and damage can be prevented. The reason why the voltage value corresponding to the primary AC voltage is set as the voltage switching condition is that the power supply voltage supplied to the amplifier circuit is substantially proportional to the primary AC voltage. The voltage corresponding to the primary AC voltage is typically a secondary AC voltage output from the second secondary winding. The condition that the voltage corresponding to the primary AC voltage is equal to or higher than the first threshold and the output signal of the amplifier circuit is equal to or higher than the second threshold is that the temperature of the output transistor of the amplifier circuit is particularly increased, and this state continues. It is a condition that sometimes causes the transistor to be thermally destroyed. By switching the power supply voltage supplied to the amplifier circuit to a low voltage for the first time after satisfying this condition, it prevents thermal damage to the output transistor, and the power supply voltage supplied to the amplifier circuit cannot be frequently switched to a low voltage. It is possible to prevent the output signal from being distorted.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings. However, the present invention is not limited to these embodiments. FIG. 1 is a schematic circuit diagram illustrating a power supply control device 100 according to a preferred embodiment of the present invention. The power supply control device 100 includes a power supply circuit and a control unit that controls the power supply circuit. Specifically, the power supply control device 100 includes a transformer 1, a first power supply circuit 2, a second power supply circuit 3, a voltage switching unit 4, and a control unit (for example, a microcomputer, hereinafter referred to as a microcomputer) 5. Prepare. These are connected to the amplifier circuit 6 and supply the power supply voltage to the amplifier circuit 6.

  The transformer 1 is a secondary that converts a primary AC voltage into a secondary AC voltage and outputs it based on a turn ratio between the primary winding 1A that is connected to a commercial AC power source and receives a primary AC voltage and the primary winding 1A. Winding 1B. The secondary AC voltage output from the secondary winding 1 </ b> B is used as a power supply voltage for the amplifier circuit 6. As shown in the figure, the secondary winding 1B has two types of wires drawn out, and outputs a normal secondary AC voltage and a low secondary AC voltage. For example, when the primary AC voltage is 100V, which is the rated voltage, for example, the secondary AC voltage of the normal voltage is 57V and the secondary AC voltage of the low voltage is 28V.

  Further, the transformer 1 has a secondary winding 1C (second secondary winding) that outputs a secondary AC voltage based on a turns ratio with the primary winding 1A. For the secondary AC voltage output from the secondary winding 1C, the microcomputer 5 determines whether or not the primary AC voltage is higher than the rated voltage, and controls the voltage switching unit 4 based on the result. Used for.

  The first power supply circuit 2 is supplied with a secondary AC voltage from the secondary winding 1B of the transformer 1, rectifies and smoothes the secondary AC voltage, and supplies it to the amplifier circuit 6 (hereinafter referred to as a DC power supply voltage). Simply called power supply voltage). The first power supply circuit 2 is supplied with a secondary AC voltage of a normal voltage and is supplied with a full-wave rectifier circuit D1 that rectifies the power supply voltage to a normal voltage, and a secondary AC voltage that is lower than the normal voltage. A full-wave rectifier circuit D2 that rectifies the power supply voltage, and capacitors C1 and C2 that smooth the voltages from the full-wave rectifier circuits D1 and D2. That is, the full-wave rectifier circuit D1 is connected to the secondary winding 1B so that the number of turns of the secondary winding 1B of the transformer 1 is larger than the connection destination of the full-wave rectifier circuit D2, and the full-wave rectifier circuit D2 The secondary winding 1B is connected to the secondary winding 1B so that the number of turns is smaller than the connection destination of the full-wave rectifier circuit D1.

  The second power supply circuit 3 is supplied with a secondary AC voltage from the secondary winding 1 </ b> C, rectifies and smoothes the secondary AC voltage, and supplies it to the microcomputer 5. The second power supply circuit 3 includes a full-wave rectifier circuit D3 and a capacitor C3. The output terminal of the second power supply circuit 3 is connected to a power supply voltage detection terminal 5 </ b> A (described later) of the microcomputer 5.

  The voltage switching unit 4 switches (selects) the power supply voltage supplied to the amplifier circuit 6 to either a normal power supply voltage or a low power supply voltage. That is, the voltage switching unit 4 switches the number of turns of the secondary winding 1B between the first number of turns for outputting the secondary AC voltage of the normal voltage and the second number of turns for outputting the secondary AC voltage of the low voltage. More specifically, the voltage switching unit 4 is provided between the full-wave rectifier circuits D1 and D2 of the first power supply circuit 2 and the capacitors C1 and C2, and supplies voltages (amplifiers) to the capacitors C1 and C2. The voltage supplied to the power supply lines V + and V− of the circuit 6 is selected and output from either the normal voltage from the full-wave rectifier circuit D1 or the low voltage from the full-wave rectifier circuit D2.

  The voltage switching unit 4 can typically employ a relay circuit having a winding (solenoid, coil, etc.). The voltage switching unit 4 includes switches 4A and 4B and a winding 4C, which are relay circuits, and a relay drive transistor Q1 for controlling the relay circuit. The switch 4A has one end connected to the positive power supply line V + of the amplifier circuit 6 and one end of the capacitor C1, and the other end connected to one end of the output of the full-wave rectifier circuit D1 and the output of the full-wave rectifier circuit D2. One end is switchably connected. The switch 4B has one end connected to the negative power supply line V− of the amplifier circuit 6 and one end of the capacitor C2, and the other end connected to the other end of the output of the full-wave rectifier circuit D1 and the full-wave rectifier circuit D2. The other end of the output is switchably connected. The switches 4A and 4B are switched to the full-wave rectifier circuit D1 side or D2 side in conjunction with each other. One end of the winding 4C is connected to the DC power source DC, and the other end is connected to the collector of the transistor Q1. The base of the transistor Q1 is connected to a control signal output terminal 5C described later of the microcomputer 5, and the emitter is grounded.

  In the normal state, since the transistor Q1 is in the off state, no current flows through the winding 4C, and the switches 4A and 4C select the full-wave rectifier circuit D1 side. Therefore, the normal power supply voltage is supplied to the power supply lines V + and V− of the amplifier circuit 6 from the full-wave rectifier circuit D1. On the other hand, when the voltage corresponding to the primary AC voltage is equal to or higher than the first threshold and the output signal of the amplifier circuit 6 is equal to or higher than the second threshold (preferably, when the state continues for a predetermined time or longer), the transistor Q1 is turned on, a current flows through the winding 4C, and the switches 4A and 4B select the full-wave rectifier circuit D2 side. Therefore, a low power supply voltage is supplied from the full-wave rectifier circuit D2 to the power supply lines V + and V− of the amplifier circuit 6.

  The microcomputer 5 has a power supply voltage detection terminal 5A, an output signal detection terminal 5B, and a control signal output terminal 5C. The power supply voltage detection terminal 5A is a terminal for detecting the power supply voltage supplied to the positive power supply line V + and the negative power supply line V− of the amplifier circuit 6, and the positive power supply line V + and the negative power supply line V−. A voltage corresponding to the primary AC voltage is supplied in place of the power supply voltage supplied to, and the value is detected. The voltage corresponding to the primary AC voltage is a primary AC voltage or a secondary AC voltage obtained by converting the primary AC voltage with the transformer 1. Preferably, as shown in FIG. 1, the secondary AC voltage generated by the second power supply circuit 3 is supplied to the power supply voltage detection terminal 5A as a voltage corresponding to the primary AC voltage. That is, in this example, the power supplied to the positive power supply line V + and the negative power supply line V− of the amplifier circuit 6 by comparing the secondary AC voltage generated by the second power supply circuit 3 with the first threshold value. It is determined whether or not the voltage is large.

  The output signal detection terminal 5B is a terminal for detecting the level of the output signal of the amplifier circuit 6, and the output terminal 6A of the amplifier circuit 6 is connected thereto. Although only one amplifier circuit 6 is shown in FIG. 1 for simplification, for example, in the case of an LR 2-channel amplifier, two LR amplifier circuits 6 are provided in detail. As shown in FIG. 2, the output terminal 6AL of the L channel amplifier circuit and the output terminal 6AR of the R channel amplifier circuit are connected to the output signal detection terminal 5B via diodes D4 and D5, respectively. A capacitor C4, a resistor R1, and a Zener diode D6 are connected between the cathodes of the diodes D4 and D5 and the output signal detection terminal 5B. The capacitor C4 is charged / discharged by the signal having the higher level among the output signals of the L channel amplifier or the R channel amplifier, and the voltage of the capacitor C4 is supplied to the output signal detection terminal 5B.

  Returning to FIG. 1, the control signal output terminal 5 </ b> C is a terminal that outputs a control signal for controlling the relay circuit of the voltage switching unit 4. That is, the control signal output terminal 5C is a terminal that outputs a signal for controlling the transistor Q1 for relay driving.

  The microcomputer 5 determines whether or not the power supply voltage supplied to the positive power supply line V + of the amplifier circuit 6 is equal to or higher than a predetermined voltage (similarly, the power supply voltage supplied to the negative power supply line V− is equal to the predetermined voltage). To determine if: The power supply voltage supplied to the power supply lines V + and V− is a voltage that becomes the maximum value of the output signal of the amplifier circuit 6. In this example, the microcomputer 5 determines whether the voltage supplied from the second power supply circuit 3 to the power supply voltage detection terminal 5A is equal to or higher than the first threshold value instead of the power supply voltage supplied to the power supply lines V + and V−. Judging. For example, the rated voltage of the primary AC voltage is 100 V, and the primary AC voltage varies between 90 V and 110 V. As a result, when the voltage generated by the second power supply circuit 3 is the rated voltage, the rated voltage is 10 V and 9 V to If it varies between 11V, the first threshold value is set to 10.5V, for example.

  Further, the microcomputer 5 determines whether or not the level of the output signal input to the output signal detection terminal 5B is equal to or higher than a predetermined level. Specifically, as described above, the capacitor C4 is charged based on the larger one of the output signal of the L channel amplifier and the output signal of the R channel amplifier, and the charging voltage of the capacitor C4 is input to the output signal detection terminal 5B. The microcomputer 5 compares the charging voltage of the capacitor C4 with the second threshold value.

  As a result of the determination, if the voltage input to the power supply voltage detection terminal 5A is equal to or higher than the first threshold value and the voltage input to the output signal detection terminal 5B is equal to or higher than the second threshold value, the microcomputer 5 A high level signal for turning on the transistor Q1 is output from the output terminal 5C. On the other hand, when the voltage input to the power supply voltage detection terminal 5A is less than the first threshold value or the voltage input to the output signal detection terminal 5B is less than the second threshold value, the microcomputer 5 controls the control signal output terminal 5C. Outputs a low level signal for turning off the transistor Q1.

  Preferably, the microcomputer 5 continues for a predetermined period during which the voltage input to the power supply voltage detection terminal 5A is equal to or higher than the first threshold and the voltage input to the output signal detection terminal 5B is equal to or higher than the second threshold. For the first time, a high level signal for turning on the transistor Q1 is output from the control signal output terminal 5C. The predetermined period can be set to an arbitrary value depending on the temperature resistance characteristics of the output transistor of the amplifier circuit 6, and is, for example, 5 seconds. Specifically, a timer processing unit 5D is provided in the microcomputer 5, the voltage input to the power supply voltage detection terminal 5A is equal to or higher than the first threshold value, and the voltage input to the output signal detection terminal 5B is the first. When it is detected that the threshold value is 2 or more, the timer starts counting. And while the said state continues, the count of a timer is continued. If the transistor Q1 is turned on before the predetermined period of time elapses, the power supplied to the power supply lines V + and V− is supplied even though the temperature of the output transistor of the amplifier circuit 6 has not risen to near the temperature at which it is damaged. There is a problem that the voltage is switched to a low voltage, and as a result, distortion occurs in the output signal of the amplifier circuit 6. In this example, this problem can be solved.

  Any appropriate amplifier circuit can be adopted as the amplifier circuit 6. In this example, the amplifier circuit 6 includes an npn output transistor Q2, a pnp output transistor Q3, driver transistors Q4 and Q5 for driving the output transistors Q2 and Q3, resistors R2 to R6, capacitors C5. The output transistor Q2 has a collector connected to the positive power supply line V +, an emitter connected to the output terminal 6A via the resistor R4, and a base connected to the emitter of the driver transistor Q4 via the resistor R2. The output transistor Q3 has a collector connected to the negative power supply line V-, an emitter connected to the output terminal 6A via the resistor R5, and a base connected to the emitter of the driver transistor Q5 via the resistor R3. Since the operation of the amplifier circuit 6 is well known, the description thereof is omitted.

  The operation of the power supply control apparatus 100 having the above configuration will be described. First, the operation in the normal state will be described. The normal state is a state in which it is determined that the temperature of the transistors Q2 and Q3 is not a temperature at which the transistors Q2 and Q3 are damaged, and the voltage input to the power supply voltage detection terminal 5A is less than the first threshold or the output signal detection terminal In this state, the voltage input to 5B is less than the second threshold. In this case, since the microcomputer 5 outputs a low level signal from the control signal output terminal 5C, the transistor Q1 is off because the base-emitter voltage is less than the conduction start voltage. Therefore, since no current flows through the winding 4C of the relay circuit, the switches 4A and 4B select the full-wave rectifier circuit D1 side. As a result, the amplifier circuit 6 is supplied with the normal power supply voltage from the full-wave rectifier circuit D1.

  Next, an operation is performed when a period in which the voltage supplied to the power supply voltage detection terminal 5A is equal to or higher than the first threshold and the voltage supplied to the output signal detection terminal 5B is equal to or higher than the second threshold continues for a predetermined time. explain. In this case, if the normal power supply voltage is continuously supplied to the amplifier circuit 6, it is estimated that the output transistors Q2 and Q3 will be damaged. Therefore, the power supply voltage supplied to the amplifier circuit 6 is set to a low voltage. Switch. That is, since the microcomputer 5 outputs a high level signal from the control signal output terminal 5C, the transistor Q1 is turned on when the base-emitter voltage becomes equal to or higher than the conduction start voltage. Therefore, a current flows through the winding 4C of the relay circuit in the direction from the DC power supply DC to the transistor Q1, and the switches 4A and 4B are switched so as to select the full-wave rectifier circuit D2. As a result, the amplifier circuit 6 is supplied with a power supply voltage which is a low voltage from the full-wave rectifier circuit D2. Therefore, when the power supply voltage supplied to the amplifier circuit 6 is switched to a low voltage, the temperature rise of the output transistors Q2 and Q3 can be suppressed, and damage can be prevented.

  Next, in a state where a low power supply voltage is supplied to the amplifier circuit 6 (that is, a state where the switches 4A and 4B select the full-wave rectifier circuit D2), the voltage input to the power supply voltage detection terminal 5A is the first voltage. When the state in which the voltage input to the output signal detection terminal 5B is less than the second threshold or the state in which the voltage input to the output signal detection terminal 5B is less than the second threshold continues for a predetermined period (for example, 1 minute), the temperature of the output transistors Q2, Q3 It is presumed that the transistor voltage was sufficiently lowered so as not to be damaged even if the power supply voltage is continuously applied. Accordingly, the microcomputer 5 outputs a low level signal from the control signal output terminal 5C, and the transistor Q1 is turned off because the base-emitter voltage becomes less than the conduction start voltage. Therefore, no current flows through the winding 4C of the relay circuit, and the switches 4A and 4B are switched again to the full-wave rectifier circuit D1 side. As a result, the amplifier circuit 6 is supplied with the normal power supply voltage from the full-wave rectifier circuit D1.

  As described above, in this embodiment, when the voltage input to the power supply voltage detection terminal 5A is equal to or higher than the first threshold and the voltage input to the output signal detection terminal 5B is equal to or higher than the second threshold, the amplifier The power supply voltage supplied to the circuit 6 is switched to a low voltage. By switching the power supply voltage supplied to the amplifier circuit 6 to a low voltage, the temperature of the transistors Q2 and Q3 can be lowered. Further, it is possible to prevent the output signal from being distorted because the voltage supplied to the amplifier circuit 6 is frequently switched to a low voltage even though the transistors Q2 and Q3 are not at a temperature leading to damage.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment. As a practical example, when the withstand voltage of the microcomputer 5 is 5V, if the secondary AC voltage from the secondary winding 1C is 25V when the primary AC voltage is rated 100V, the voltage of 25V is 1 by the resistance element. The voltage may be divided into a voltage of / 10 to a voltage of 2.5 V and input to the microcomputer. At this time, the first threshold is set to 2.625 V, for example. Similarly, the Zener diode of FIG. 2 with a Zener voltage of 5V may be used so that the output signal of the amplifier circuit 6 does not exceed 5V. As a voltage corresponding to the primary AC voltage, the primary AC voltage may be directly supplied to the power supply voltage detection terminal 5C via a photocoupler or the like instead of the secondary AC voltage as in the above embodiment.

  The present invention can be suitably employed in power supply circuits of various electronic devices such as AV amplifiers and DVD players.

1 is a schematic circuit diagram showing a power supply control device 100 according to a preferred embodiment of the present invention. 2 is a circuit diagram showing a detailed connection configuration between an amplifier circuit 6 and a microcomputer 5. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Power supply control apparatus 1 Transformer 2 1st power supply circuit 3 2nd power supply circuit 4 Voltage switching part 5 Control part 6 Amplifier circuit

Claims (4)

A transformer having a primary winding to which a primary AC voltage is supplied, and a secondary winding for outputting a secondary AC voltage converted from the voltage supplied to the primary winding;
A voltage switching unit that switches the number of turns of the secondary winding to either the first number of turns that outputs a secondary AC voltage of a normal voltage or the second number of turns that outputs a secondary AC voltage of a low voltage;
The voltage switching unit switches the secondary winding to the second number of turns when the voltage corresponding to the primary AC voltage is equal to or higher than the first threshold and the output signal of the amplifier circuit is equal to or higher than the second threshold. When the voltage corresponding to the primary AC voltage is less than the first threshold value or the output signal of the amplifier circuit is less than the second threshold value, the secondary winding is connected to the first number of turns. And a control means for controlling the voltage switching unit so as to switch to the power supply control device.   When the voltage corresponding to the primary AC voltage is greater than or equal to the first threshold and the period during which the output signal of the amplifier circuit is greater than or equal to the second threshold continues for a predetermined period or longer, the control means The power supply control device according to claim 1, wherein the voltage switching unit is controlled to switch a next winding to the second number of turns.   After the secondary winding is switched to the second number, the voltage corresponding to the primary AC voltage is less than the first threshold, or the output signal of the amplifier circuit is less than the second threshold The power supply control device according to claim 2, wherein the control means controls the voltage switching unit to switch the secondary winding to the first number of turns when the voltage continues for a predetermined period or longer. The transformer further comprises a second secondary winding for outputting a voltage converted from a voltage supplied to the primary winding;
The power supply control device according to any one of claims 1 to 3, wherein a voltage corresponding to the primary AC voltage is a voltage supplied from the second secondary winding.

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