JPH0213850B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that prevents the generation of noise, called shock noise, generated by an amplifier circuit when a power switch is closed and opened.

Generally, an amplifier circuit generates a shock noise during the transition from a transient state to a steady state when power is supplied and cut off. In particular, tape recorders change rapidly and frequently from playback to fast-forward, rewind to playback, etc., which frequently produces a shock sound, and tape recorders that use a headphone can cause discomfort to the user. will give. There are various reasons why such a shock noise may occur, but one reason is that the difference in charging and discharging times of the decoupling capacitors and bypass capacitors that make up the amplifier circuit causes an unstable state in the transistors that make up the amplifier circuit. This is the biggest cause.

The circuit shown in Figure 1 is a general circuit configuration diagram of a tape recorder. In the figure, 1 is a power switch, and 2 is an electric motor that is supplied with power and starts rotating when the power switch 1 is closed. ,3
is an amplifier circuit that is supplied with power and becomes operational when the power switch 1 is closed, and is connected to a bypass capacitor and the like. Reference numeral 4 denotes a decoupling capacitor connected between the power supply line 5 to which power is supplied through the power switch 1 and the ground. In such a configuration, when the power switch 1 is closed, the decoupling capacitor 4 is charged, and the motor 2 and the amplifier circuit 3 are charged.
Power is supplied to the unit and it becomes operational. When the power switch 1 is opened in such a state, the electric charge stored in the decoupling capacitor 4 is rapidly discharged through the motor 2, but since the motor 2 has inertia, it cannot generate electricity after the power is cut off. It will operate as a machine. FIG. 2 shows the potential change of the power supply line 5 during such an operation, and To is when the power switch 1 is open. As is clear from this figure, when the power is cut off, the potential of the power supply line 5 drops rapidly until it reaches the rotational voltage V _M of the motor 2, but after that it drops slowly. Such back electromotive force due to the inertia of the electric motor 2 usually lasts several hundred milliseconds, and in some cases it may exceed 500 milliseconds. Therefore, during that time, the amplifier circuit 3 is in a state where a voltage is applied and is in an operating state.
On the other hand, in a tape recorder, when switching from rewind to playback, the time from power off to power on is 10
The time required for playback → stop → regeneration is approximately several milliseconds, and it is difficult to prevent the charging voltages of each capacitor that constitutes the amplifier circuit 3 from becoming unbalanced over such a wide time range. .

The present invention aims to provide a shock noise prevention circuit that improves the above-mentioned points, and will be described below with reference to the embodiment shown in FIG. In the figure, 6 is a power switch, and 7 and 8 are a motor and an amplifier circuit to which power is supplied through the power switch 6. 9 and 10 are capacitors constituting the amplifier circuit 8, and 11 is a decoupling capacitor connected between the power supply line 12 and the ground. 13, the emitter is connected to the power supply line 1
A first control transistor 14 connected to the power supply line 12 has a base connected to the power supply line 12 via a resistor 15.
a second control transistor whose emitter is connected to ground and whose collector is connected to the base of the first control transistor 13 via a resistor 16; 17 is the first
A control capacitor 18 connected between the collector of the control transistor 13 and ground compares the emitter side potential of the first control transistor 13, that is, the charged potential of the decoupling capacitor 11, and the collector side potential, that is, the charged potential of the control capacitor 17. The comparator circuit is equipped with a first input terminal 19, which is one side terminal connected to the emitter of the first control transistor 13, and a second input terminal 20, which is the other side terminal connected to the collector. 2
1 has a base connected to the comparison circuit 18 via a resistor 22.
This is a latch transistor whose emitter is connected to the output terminal 23 of the comparator circuit 18 and whose emitter is grounded, and whose collector is connected to the first input terminal 19 of the comparator circuit 18. 24 is a third control transistor whose collector is connected to the base of the second control transistor 14 and whose emitter is grounded, and whose base is connected to the resistor 25.
It is connected to the output terminal 23 of the comparator circuit 18 via. 26 is a discharging transistor for discharging the charge stored in the control capacitor 17, the collector is connected to the collector of the first control transistor 13 via the resistor 27, the emitter is grounded, and the base is connected to the resistor 2.
8 to the output terminal 23 of the comparison circuit 18. 29 and 30 are switching transistors whose collectors and emitters are respectively connected to both ends of capacitors 9 and 10 constituting the amplifier circuit 8, and whose bases are connected to the output of the comparator circuit 18 via resistors 31 and 32. It is connected to terminal 23. In such a circuit configuration, the value of the resistor 27 is set to a value that allows the electric charge stored in the control capacitor 17 to be discharged in a predetermined period of time.

The present invention is constructed as described above, and its operation will be explained next. When the power switch 6 is closed, the decoupling capacitor 11 is charged, and power is supplied to the motor 7 and the amplifier circuit 8, so that they become operational. Also, the second control transistor 1
A bias current flows through the resistor 15 to the base of the second transistor 14, which inverts the second transistor 14 to a conductive state, so that the first control transistor 13 becomes conductive. When the first control transistor 13 becomes conductive, a control capacitor 17 connected between the collector of the transistor 13 and ground is charged by the current supplied between the emitter and the collector of the transistor 13. Since the first control transistor 13 is turned into a conductive state immediately after the power switch 6 is closed,
The charging operation of the decoupling capacitor 11 and the charging operation of the control capacitor 17 are performed substantially simultaneously. Such a big spring capacitor 11
Since there is no potential difference of more than a predetermined value between the two voltages, a comparison circuit 18 which receives the charging voltage of the control capacitor 17 as an input outputs an L (low) level signal to its output terminal 23. Therefore, the latch transistor 21, the third control transistor 24, the discharge transistor 26, and the switching transistors 29 and 30 whose bases are connected to the output terminal 23 of the comparison circuit 18 are all non-conductive. When the power switch 6 is closed, the above-described operations are carried out, and the motor 7 and the amplifier circuit 8 are operated, for example, for reproduction in a tape recorder.

Next, the operation when the power switch 6 is opened will be explained. When the power switch 6 is opened, the charging potential of the decoupling capacitor 11 rapidly drops to the potential V _M shown in FIG. 2, as described above, and then gradually drops. On the other hand, the charging potential of the control capacitor 17 connected to the collector of the first control transistor 13 gradually drops after the power switch 6 is opened. As a result, the first
A potential difference of a predetermined value or more is generated between the input terminal 19 and the second input terminal 20, and the signal output to the output terminal 23 is inverted from the L level to the H (higher) level. When the output of the comparison circuit 18 becomes H level, the latch transistor 21 whose base is connected to the output terminal 23 and the third control transistor 2
4. The discharge transistor 26 and the switching transistors 29 and 30 are all turned on. When the latch transistor 21 becomes conductive, the first input terminal 19 of the comparison circuit 18 is grounded, so even if the power switch 6 is closed again and the charged potential of the coupling capacitor 11 increases, the first The potential of the 1 input terminal 19 is at ground potential. Further, the third transistor 24
becomes conductive, the second control transistor 14
Since the base of the second control transistor 14 is grounded, the second control transistor 14 is reverse biased and becomes non-conductive. When the second control transistor 14 is inverted to a non-conducting state, the first control transistor 13 whose base is connected to the collector of the transistor 14 is inverted to a non-conducting state. Since the third control transistor 24 is in a conductive state while the H level signal is output to the output terminal 23 of the comparator circuit 18, even if the power switch 6 is closed again during that time, the second control transistor 14 and the third control transistor 24 remain conductive. 1 control transistor 13 is never inverted to a conductive state. Furthermore, when the discharging transistor 26 becomes conductive, the charge stored in the control capacitor 17 is discharged through the collector-emitter path of the discharging transistor 26, but since the resistor 27 is connected to the discharge path, the electric charge stored in the control capacitor 17 is not discharged. will take a predetermined amount of time. Furthermore, as the switching transistors 29 and 30 become conductive, the charges stored in the capacitors 9 and 10 constituting the amplifier circuit 8 are immediately discharged. When a predetermined period of time has elapsed after such an operation has been performed, that is, when the charge stored in the control capacitor 17 is discharged, the comparator circuit 18
The output signal of becomes L level. When the output of the comparison circuit 18 becomes L level, the latch transistor 21, the third control transistor 24, the discharge transistor 26, and the switching transistors 29 and 30 all become non-conductive. The output of the comparison circuit 18 is inverted from L level to H level,
If the time that the output is at the H level is set to be longer than the time required for the charging potential of the decoupling capacitor 11 to drop, that is, for the motor 7 to stop rotating, the third control transistor 24 can be turned off. Even if the first control transistor 13 is reversed to the conductive state, the first control transistor 13 is not reversed to the conductive state. As described above, the operation is performed when the power switch 6 is opened, but when the power switch 6 is opened, the switching transistors 29 and 30
Since the electrical charges in the capacitors 9 and 10 are instantly discharged due to the conduction, the amplifier circuit 8 will not be in an unstable state and no shock noise will be generated from the amplifier circuit 8.

The operation is performed when the power switch 6 is opened as described above, but when the power switch 6 is closed immediately after being opened, that is, when the output of the comparator circuit 18 is at H level, the power switch 6 is opened again. The case of closing will be explained. The comparison circuit 1
When the power switch 6 is closed while an H level signal is being output to the output terminal 23 of the decoupling capacitor 11, the decoupling capacitor 11 is charged and power is supplied to the motor 7 and the amplifier circuit 8. Since the first input terminal 19 of the comparison circuit 18 is grounded by the latch transistor 21, the output signal of the comparison circuit 18 is not inverted to the L level but remains at the H level. When the power switch 6 is closed again, the amplifier circuit 8 is closed because both ends of the capacitors 9 and 10 are short-circuited by the switching transistors 29 and 30, respectively.
The amplifier circuit 8 will not be in an unstable state and no shock noise will be generated from the amplifier circuit 8. After a predetermined period of time has elapsed, the output of the comparison circuit 18 becomes L level, and the latch transistor 21, the third control transistor 24, the discharge transistor 26, and the switching transistors 29 and 30 become non-conductive. When the third control transistor 24 is inverted to a non-conducting state, the second control transistor 14 and the first control transistor 13 are both inverted to a conducting state, and the control capacitor 17 is charged. When the first control transistor 13 is turned on, the second input terminal 2 of the comparison circuit 18
A high voltage is applied to the first input terminal 19 of the comparator circuit 18 as the latch transistor 21 is inverted to the non-conducting state. The output never inverts to H level.

In this embodiment, the switching transistors 29 and 30 discharge the charges in the capacitors 9 and 10 that constitute the amplifier circuit 8, thereby preventing the amplifier circuit 8 from entering an unstable state. Although the shock noise is prevented from occurring, it is also possible to configure the output signal path of the amplifier circuit 8 to be cut off for a predetermined period. Furthermore, although a transistor is used as a control element inserted and connected within the power supply line, a diode or the like may also be used.

As explained above, the present invention provides a charging potential of a capacitor provided on the power supply side and the power supply side of a control element connected to supply a voltage obtained from a power supply line to an amplifier circuit to a comparison circuit. When a difference of more than a predetermined value occurs between the potentials, the switching element is turned on by the inverted output of the comparison circuit, thereby preventing the generation of shock noise from the amplifier circuit and opening the power switch. Since the switching element is maintained in a conductive state for a predetermined period of time to prevent the generation of shock noise during that time, it is ideal as a shock noise prevention circuit for audio equipment such as tape recorders where switching operations are frequently performed. be.

[Brief explanation of drawings]

The circuit shown in FIG. 1 is a circuit configuration diagram of a tape recorder, FIG. 2 is a voltage change diagram of a power supply line, and FIG. 3 is an embodiment of the present invention. Explanation of main figure numbers, 6...Power switch, 7...
Electric motor, 8...Amplification circuit, 11...Decoupling capacitor, 12...Power supply line, 13...
...First control transistor, 14...Second control transistor, 17...Control capacitor, 18
... Comparison circuit, 21 ... Latch transistor, 24 ... Third control transistor, 26 ...
Discharge transistor, 29, 30... switching transistor.

Claims (1)

[Claims] 1 Comparison that has a power switch that controls power supply to an amplifier circuit, etc., and has first and second input terminals, and that inverts when the voltage difference between the input terminals is equal to or higher than a predetermined value and outputs an inverted output to the output terminal. a control element connected to supply a voltage obtained from a power supply line to the amplifier circuit to the comparator circuit and rendered non-conductive by an inverted output of the comparator circuit; and a power supply for the control element. A first capacitor connected between the power supply line on the supply side and the ground, a second capacitor connected between the power supply line on the power supply side of the control element and the ground, and the inverted output of the comparison circuit establish continuity. a switching element which is made conductive by the inverted output of the comparator circuit and which prevents the generation of shock noise in the amplifier circuit;
A first input terminal and a second input terminal provided in the comparator circuit respectively include a discharging element that discharges the charge of the capacitor at a predetermined time constant, and the charge potential of the first capacitor and the second capacitor are respectively connected to the first input terminal and the second input terminal. is inputted into the power supply switch, and when the power switch is opened, the reversal operation of the comparator circuit caused by the decrease in the charging potential of the first capacitor is maintained for a predetermined time by the discharging time constant of the second capacitor, during which the A shock noise prevention circuit characterized in that the generation of shock noise from an amplifier circuit is prevented by conduction of a switching element.