JPS626576Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power switching circuit that supplies bias power to an audio circuit such as a tape recorder.

Recording bias power supply for tape recorders etc.
Since the noise generated during ON-OFF is largely influenced by the rise and fall characteristics of the bias voltage waveform, conventionally it changes gradually within a permissible time (e.g. 100msec or 200msec). That's what I do. An example of such a conventional circuit is shown in FIG. This circuit consists of a changeover switch SW provided between the +B power supply and ground, an NPN switching transistor Q _{0 whose collector is connected to the +B power supply via a resistor R 0 ,} and a capacitor C ₁ connected between its base and ground. and an oscillation circuit (or buffer circuit) that takes the emitter side output of this transistor Q ₀ as input.
It consists of an OSC and a recording head HD inserted and connected between the output side of this oscillation circuit OSC and the ground.By turning the changeover switch SW ON and OFF, the switch SW and the base of the transistor _Q0 are connected. The voltage waveforms V A and V _B as shown in FIG. 2, which have rise and fall characteristics based on the time constants of the resistor R ₁ and the capacitor _{C 1} inserted between them, are applied to the output point A of the transistor Q ₀ and They are generated at output point B of the oscillation circuit OSC.

The rising characteristic T _ON of the voltage waveform _V A at point A in Fig. 1 (shown in Fig. 2) is expressed by the following equation (1), and the falling characteristic T _OFF is expressed by the following equation (2). Become. Note that t is time.

If we consider the rise here, the first 1 time constant (x = t/C ₁ R ₁ ) shows a fast rise of about 70%, the 2nd time constant shows a fast rise of about 70%, the 3rd time constant shows a fast rise of 95%, and so on. As the level increases, the rise becomes more gradual, and the rise speed becomes slower at high levels where noise is likely to occur, thus exhibiting approximately ideal rise characteristics.

On the other hand, if we consider the falling edge, the first 1
It exhibits a fast fall with a time constant of 70% and then a slow fall, which is undesirable because it falls quickly at a high level where noise is likely to occur. Here, in order to slow down the falling speed, it is necessary to set the falling time constant to about three times the rising time constant, but in general, for professional tape recorders, the rising and falling times are shortened. Simply increasing the falling time constant will not satisfy the above requirement.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a power supply switching circuit that has a fall time equivalent to the rise time and is capable of reducing noise generation when switching a bias power supply. The purpose is to

The present invention will be specifically explained below with reference to Examples.

FIG. 3 is a circuit diagram of one embodiment of the circuit of the present invention.
This circuit consists of a changeover switch SW with an OFF contact (black circle) connected to the +B power supply side, an ON contact (white circle) connected to the ground side, and a contactor connected to the +B power supply via resistor _R5 . A PNP switching transistor Q ₁ has its emitter connected and its base connected to the contact of the switch SW via a resistor ₆ , and a field effect transistor Q 2 and a resistor R ₇ are connected between the collector of this transistor Q ₁ and _ground . A resistor _R4 is connected in series between the collector of the transistor _Q1 and the base of the buffer NPN transistor _Q3 ,
Capacitor between the base of transistor Q ₃ and ground
C ₃ is inserted and connected, and a forward-connected diode D ₂ is connected to the discharge path, the contactor of the changeover switch SW and the source S of the transistor Q ₂ of the constant current means CIC. A resistor R ₂ and a capacitor C ₂ are connected in series between the resistor R ₂
forward connected diode D ₁ in the discharge path in parallel with
and a resistor R ₃ (this resistor R ₃ is a low resistor for preventing excessive current to the diode D ₁ ) connected in series, and the buffer transistor Q ₃ . Oscillation circuit (or buffer circuit) connected to the emitter and ground side of
It consists of an OSC and a recording head HD connected to the output side of this oscillation circuit OSC.
The transistor _Q2 in the constant current means CIC is, for example, an N-channel junction field effect transistor, and its gate G is grounded. Therefore, regardless of the voltage at the drain D, this transistor
The current flowing through Q ₂ is constant, and the value of the constant current changes depending on the voltage between SG (source, gate). For example, if the voltage between SG and When the voltage is large, it changes so that it decreases.

Next, the operation of the circuit will be explained with reference to the waveform diagram of FIG. 4.

Now, when the switch SW is changed to the RecON contact side (ground side), the PNP transistor Q ₁ becomes conductive, and the current from the +B power supply passes through this transistor Q ₁ to the resistor R ₄ and capacitor C that constitute the first time constant circuit. ₃ to the ground side and charges capacitor _C3 . At this time, the charges of the resistor R ₂ and capacitor C ₂ that constitute the second time constant circuit are transferred to the diode D ₁
is discharged through the resistor R ₃ and the changeover switch SW, but the transistor Q ₁ conducts without being affected by this, so the voltage E across the capacitor C ₃ of the first time constant circuit is calculated by the following equation (3 ).

Here, V _B is the voltage of the +B power supply, and t is the time. Therefore, the rise characteristic T _ON exhibits an ideal characteristic in that it rises within the allowable time t as in the conventional circuit, and also rises slowly especially in the large level portion. Here, if the input impedance of the transistor _Q3 is sufficiently larger than the resistor _R4 , a bias voltage substantially equivalent to the voltage E can be obtained from the emitter of the transistor _Q3 .

Next, when the switch SW is switched to the _Rec OFF contact side (+B power supply side), the PNP transistor Q ₁ becomes non-conductive, and the capacitor C ₃ of the first time constant circuit
The charge accumulated in is discharged through the diode D ₂ through the transistor Q ₂ and the resistor R ₇ of the constant current means CIC. At the same time, a current I flows from the +B power supply through the switch SW to the ground side through the resistor R ₂ and capacitor C ₂ forming the second time constant circuit, and through the resistor R ₇ to charge the capacitor C ₂ . At this time, the current I is connected to the resistor R ₂ of the second time constant circuit and the capacitor C ₂ as shown in FIG.
and the time constant determined by the resistor _R7 . Therefore, the voltage V _A at the source S (point A) of the transistor Q ₂ of the constant current means CIC has a waveform that rises at the moment the switch is turned off and decreases in response to the change in the current I. Therefore, the source-gate voltage of the transistor _Q2 in the constant current means CIC changes from a high state to a sudden low value, so that the constant current value changes from a small value to a large value. As a result, the discharge of the capacitor _C3 constituting the first time constant circuit changes slowly at first and then becomes faster in the latter half, and has an ideal falling characteristic _TOFF as shown in FIG. A voltage E will be obtained. That is, if the time constant circuits R ₂ and C ₂ were not provided, the falling waveform would show a straight line like the chain line X of the E waveform in FIG. 4, and would not be an ideal falling waveform. Therefore, the voltage V _C of the oscillation circuit OSC exhibits a waveform as shown in FIG. In the above embodiment circuit, when configuring each time constant circuit and constant current means, the rise and fall times t
It goes without saying that these are set to be included within an equivalent short period of time. Also, the charge accumulated in the capacitor _C2 of the second time constant circuit is R _ec ON
When , the voltage is discharged through the resistor R ₃ , diode D ₁ , and switch SW.

The present invention is not limited to the above-mentioned embodiments; for example, the constant current means may be configured in any combination as long as the constant current value can be changed by a time constant circuit. Alternatively, the polarity of the transistor and the polarity of the power source may be completely reversed.

According to the present invention described in detail above, it is possible to provide a power supply switching circuit which has a fall time equivalent to a rise time and is capable of reducing noise generation when switching a bias power supply.

In addition, in the present invention, the first
The electric charge stored in the capacitor 3 of the time constant circuit is discharged through the constant current means CIC, and the discharge current is corrected by the charging current of the second time constant circuit R2, C2. Therefore, the voltage E of the capacitor C3 at the time of falling has a characteristic that combines the characteristics of the constant current means CIC and the second time constant circuit R2, C2, and has the characteristic of a single time constant circuit or the characteristic of a single constant current circuit. A power switching circuit in a tape recorder is obtained which has a shorter fall time than in the case of the characteristics of the means and which does not generate noise.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an example of a conventional circuit, Figure 2 is a waveform diagram for explaining its operation, Figure 3 is a circuit diagram of an embodiment of the circuit of the present invention, and Figure 4 is a diagram for explaining its operation. FIG. SW...Switch, _Q1 , _Q2 ...Transistor, _Q2 ...Field effect transistor, _R1 to _R7 ...
Resistor, C ₂ , C ₃ ... Capacitor, D ₁ , D ₂ ... Diode, OSC ... Oscillator circuit, CIC ... Constant current means, HD ... Recording head.

Claims (1)

[Claims for Utility Model Registration] In a power switching circuit in a tape recorder for connecting the circuit power supply of the tape recorder, a changeover switch SW having one end connected to a power supply and the other end connected to ground; a transistor Q1 connected to said changeover switch so as to be conductive when switched to ground and non-conductive when switched to power; and a transistor Q1 connected to the output side of said transistor Q1 so that said transistor Q1 becomes conductive. a first time constant circuit formed by a resistor R4 and a capacitor C3 that start charging when the transistor Q1 becomes non-conducting; and a diode D2 that forms a discharge path for the capacitor C3 when the transistor Q1 becomes non-conductive. and a field effect transistor Q2 connected to the discharge path of the capacitor C3 and a resistor R7 so that the discharge current of the capacitor C3 becomes constant when the transistor Q1 becomes non-conductive. a constant current means CIC, one end of which is connected to the changeover switch SW so that charging is started when the changeover switch SW is switched to the power source, and a charging current flowing through the constant current means CIC; A second time constant circuit formed by a resistor R2 and a capacitor C2, the other end of which is connected to the resistor R7, and a capacitor C3 of the first time constant circuit are electrically connected or connected by the voltage of the capacitor C3. A power switching circuit in a tape recorder, characterized in that the transistor Q3 is connected to a capacitor C3 so as to be non-conductive, and is connected between a power supply and a circuit section of the tape recorder. .