JPH048486Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an improvement in an autoback space device incorporated into a transcriber or the like.

Traditionally, in order to improve work efficiency, the manuscript of a letter or document was recorded on a tape in advance, and then a secretary or the like played back the tape and operated the type while listening to it to create the letter or document. It is being done.

In order to reproduce such tape contents, a so-called transcriber is used which allows the reproduction speed to be arbitrarily adjusted and which allows playback and stop operations to be performed using a foot switch.

By the way, when using such a transcriber to type while listening to the tape contents, the typing may not be able to keep up with the tape playback speed, so it is often necessary to stop the tape playback at each sentence break, for example. It can be done.

However, when performing a stop operation to stop tape playback, the next sentence and other parts may pass through the playback head due to a delay in the operation. For this reason, when the next time the playback operation is performed again, the beginning of the sentence may be cut off, making it impossible to understand the playback content, and the tape has to be rewound by a predetermined length each time, which is a tedious and time-consuming process.

Therefore, when there is a conventional operation to stop tape running,
A so-called autobackspace device has been proposed which automatically rewinds the tape by a predetermined amount of time so that the user can reliably understand the next playback content.

Conventionally, this type of autobackspace device uses a time constant circuit, and when a stop operation is performed, the tape is rewound for a predetermined amount of time corresponding to the time constant of the time constant circuit.

However, since such devices are easily affected by fluctuations in power supply voltage, the tape rewind time becomes shorter as the battery voltage decreases, especially in the case of recently used battery-powered devices. There was a risk that it would not be carried out at all.

Therefore, instead of such a time constant circuit, there is a method using a one-shot multivibrator, but such multivibrators are expensive, especially those for low voltage such as battery power sources, so it is difficult to use them economically. There were flaws.

This idea was made in view of the above circumstances,
It is an object of the present invention to provide an economically advantageous autoback space device which can always obtain a predetermined tape rewinding time regardless of fluctuations in power supply voltage, can perform accurate reproduction, and is economically advantageous.

An embodiment of this invention will be described below with reference to the drawings.

In the drawing, P is the positive bus bar, N is the negative bus bar,
The positive bus P is connected to the power supply Vcc, and the negative bus N is connected to the ground terminal GND.

A series circuit of a resistor R ₁ and a regeneration (PLY) operation switch PS is connected between the bus lines P and N, and a regeneration input terminal PLY is connected to the connection point between the resistor R ₁ and the switch PS of this series circuit. And switch
When the PS is turned on, a reproduction means (not shown) is activated via the reproduction input terminal PLY.

Furthermore, the connection point between the resistor R ₁ and the switch PS is connected to the transistor TR ₁ via the capacitor C ₁ and the resistor R ₂ .
A diode D with the polarity shown is connected between the connection point of the capacitor C ₁ and the resistor R ₂ and the bus line N.

Further, the emitter of the transistor _TR1 is connected to the bus line N, and the collector is connected to the base of the transistor _TR2 via a resistor _R3 . This transistor TR ₂ has its emitter connected to the bus line N and is also connected via a resistor R ₄ to the base of the first TR ₃ associated with the discharge of the capacitor C ₂ .

In addition, in the above circuit, resistor R ₁ , capacitor C ₁ ,
A conduction time regulating circuit is constituted by the resistor R ₂ and the transistors TR ₁ and TR ₂ .

A rewind (REW) operation switch REWS is connected between the emitter and collector of the transistor _TR3 , and the emitter is connected to the bus N, and the collector is connected to the tape rewind input terminal REW. Then, when the switch REWS is turned on, a tape rewinding means (not shown) is activated via the tape rewinding terminal REW.

Further, the connection point between the transistor TR ₂ and the capacitor C ₂ for defining the tape rewinding time during which power is supplied during the first time when the conduction time regulating circuit continues to be conductive is connected to the discharge of the capacitor C ₂ . It is connected to the collector of the associated second transistor _TR4 . This transistor TR ₄ has its emitter connected to the bus line N and its base connected to the base of the transistor TR ₅ associated with the discharge of the capacitor C ₂ . And the above transistors TR ₄ and TR ₅
This constitutes a current mirror circuit.

Note that the emitter of the transistor TR ₅ is connected to the bus line N, and the collector is connected to the bus line P via a resistor R ₅ and a variable resistor VR.

Next, its effect will be explained.

It is now assumed that the playback operation switch PS is turned on and a tape is being played back by a playback means (not shown) via the playback input terminal PLY.

In this state, when the playback operation switch PS is released to stop the tape playback, the playback means activated via the playback input terminal PLY is stopped and the tape playback is stopped. In addition, when the regeneration operation switch PS is opened, the time constant circuit of the resistor R ₁ , capacitor C ₁ , and resistor R ₂ in the conduction time regulation circuit passes the capacitor through the base and emitter of the transistor TR ₁ .
The charging current of _C1 flows and transistor _TR1 is turned on. This also turns on transistor _TR2 .
In this case, transistors TR ₁ and TR ₂ are connected to capacitor C ₁
conducts for a time corresponding to the time constant of resistors R ₁ and R ₂ .

A charging current flows through the capacitor _C2 during the conduction time of the transistor _TR2 . After the conduction time has elapsed, the transistors TR ₁ and TR ₂ are turned off, so the capacitor C ₂ starts discharging. The discharge current of the above capacitor C ₂ is the transistor TR ₄
On the other hand, a part of this discharge current flows through the resistor _R4 as the base current of the transistor _TR3 , and the transistor _TR3 is turned on. In this case, turning on the transistor _TR3 is the same as turning on the tape rewinding switch REWS, so a tape rewinding means (not shown) is activated via the tape rewinding input terminal REW and rewinding of the tape is started.

When the discharge of capacitor C ₂ causes the voltage across it to drop below the voltage V _TH required to keep transistor TR ₃ on, transistor TR ₃ turns off, thus stopping tape rewinding. Ru.

In the above, when the transistor TR ₂ is initially conductive and the capacitor C ₂ is charged, the amount of charge is substantially proportional to the power supply voltage Vcc. However, the current flowing through transistor TR4, which is the main discharge path of capacitor _C2 , also flows through transistor _TR4 .
Since TR ₄ and TR ₅ form a current mirror circuit, the current is substantially equal to the collector current of transistor TR ₅ , and therefore has a value substantially proportional to power supply voltage Vcc. As a result, even if the power supply voltage Vcc fluctuates, the time it takes for the voltage of the capacitor C ₂ to reach a predetermined value (V _TH in the above) also remains approximately constant.

The reason for this will be explained in detail below.

The discharge current of capacitor C ₂ above is
When the current flows to TR ₄ , it passes through variable resistor VR and resistor _R5 to transistor TR ₅ (Vcc - V _F )/
A predetermined current of (VR+R ₅ ) is flowing. here
Vcc is the power supply voltage, and _VF is the forward voltage of the transistor _TR5 .

Here, since transistors TR ₄ and TR ₅ constitute a current mirror circuit, transistor TR ₄
A current of (Vcc−V _F )/(VR + R ₅ ) also flows. This makes capacitor _C2 a transistor
A constant current will be discharged through TR ₄ . Thereafter, when the terminal voltage of the capacitor _C2 reaches a predetermined voltage _VTH , that is, the off-voltage of the transistor _TR3 , the transistor _TR3 is turned off and tape rewinding is stopped.

In this case, the terminal voltage of capacitor _C2 is from Vcc to
The discharge charge up to V _TH is expressed as Q=C×(Vcc−V _TH )=T·i (1). Here, C is the capacitance value of the capacitor _C2 , Vcc is the power supply voltage, and T is the tape rewinding time.

Further, as described above, the discharge current of the capacitor C ₂ is i=(Vcc−V _F )/(VR+R ₅ ) (2). However, when formula (2) is substituted into formula (1), C×(Vcc−V _TH )=T·(Vcc−V _F )/(VR+R ₅ ) ……(3).

Generally, the forward voltage of a transistor is between V _F and V _TH because there is not much difference between each transistor.

Therefore, from equation (3), T=C×(VR+R ₅ )...(4) is obtained.

As is clear from equation (4), the discharge conditions of capacitor C ₂ can be determined by variable resistor VR and resistor R ₅ regardless of power supply voltage Vcc. As a result, the tape rewinding time T can be set almost constant even if there are fluctuations in the power supply voltage Vcc.

As described above, according to the device according to one embodiment of the present invention, both the charge charged in the capacitor for defining the tape rewinding time immediately after the playback stop operation and the discharge current of this charge are Since the voltage of the capacitor changes substantially in proportion to the power supply voltage, the voltage of the capacitor is
The time it takes to reach V _TH ) remains almost constant. As a result, the tape rewind time can be set substantially constant even if the power supply voltage Vcc fluctuates, and a stable autoback space can be obtained.

Note that this invention is not limited to the above-mentioned embodiments, and can be implemented with appropriate modifications within the scope of the invention without changing the gist. For example, although the transcriber has been consistently described above, it goes without saying that the present invention can also be applied to general tape recorders.

As mentioned above, according to the autobackspace device of this invention, a substantially constant tape rewinding time can be obtained regardless of fluctuations in the power supply voltage. Even if the speed decreases, it is possible to reliably eliminate the inconvenience that tape rewinding time is shortened and tape rewinding is not performed at all, and a stable autoback space can be obtained. Furthermore, it is cheaper and more economically advantageous than a method using an expensive constant voltage multivibrator.

[Brief explanation of the drawing]

The drawing is a circuit diagram showing an embodiment of this invention. P, N...Bus bar, _R1 to _R5 ...Resistance, _C1 , _C2 ...
...Capacitor, TR ₁ to _{TR 5} ...Transistor,
PS...Playback switch, REWS...Tape rewind switch.

Claims (1)

[Scope of Claim for Utility Model Registration] A switch for controlling tape playback and stopping of the playback, a conduction time regulating circuit that is conductive for a predetermined time starting from the point in time when the switch is activated, and conduction of the conduction time regulating circuit. A capacitor is charged by being supplied with power during the first period during which the current continues, and a base current is supplied from the capacitor and conducts only when the voltage across the capacitor is above a predetermined level, and the second period during which this conduction continues. A first transistor for rewinding the tape during time 2, a second transistor connected to form a discharge path for the capacitor, and a collector current corresponding to the voltage level of the power supply. a third transistor connected to the same power source so that the current flows therein, and connected to form a current mirror circuit together with the second transistor,
As a result, by making both the amount of charge charged to the capacitor and the current value that is the discharge of the same charge through the second transistor substantially proportional to the power supply voltage, it is possible to control the power supply voltage. An automatic backspace device characterized in that the amount of backspace remains substantially constant regardless of the situation.