JPS6213212Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a bias switching circuit for a tape recorder, and particularly to providing a bias switching circuit that can supply a stable bias current to a recording head.

Currently, there are several types of cassette tapes available on the market, including normal tape, chrome tape, metal tape, etc. These tapes have different magnetic properties, so unless a bias is applied to each tape, linearity and other problems will occur.
This is undesirable as it leads to deterioration of distortion characteristics, high frequency characteristics, MOL (maximum recording level), etc. For this reason, various circuits have been proposed to supply bias according to the tape.

The present invention has been developed in view of the above points, and will be described below based on embodiments of the present invention with reference to the drawings. The figure shows one embodiment of the present invention.
2 is an input terminal connected to a power supply; 2 is a constant current circuit 3; a reference voltage generating circuit 4 that generates a reference voltage of a predetermined value according to the constant current flowing through the constant current circuit 3; a control transistor 5; Voltage generation circuit 4
and a first terminal that divides the emitter voltage of the control transistor 5, which becomes the output voltage.
9 is a constant voltage circuit consisting of an error voltage detection circuit 8 having an input terminal connected to the connection midpoint of the second voltage dividing resistors 6 and 7, and an output terminal connected to the base of the control transistor 5; An oscillation circuit that generates an AC bias with an amplitude corresponding to the constant voltage generated from the constant voltage circuit 2 , 10 is the left channel (Lch)
11 is a recording head for the right channel (Rch), 12 is an erase head for both channels, and 13 and 14 are first and second Zener diodes inserted in the constant current path of the constant voltage circuit 4. ,
15 is a first switching transistor in which a collector-emitter path is inserted between the cathode of the first Zener diode 13 and ground, and 16 is a second switching transistor in which a collector-emitter path is inserted between the anode of the first Zener diode 13 and ground. A switching transistor, 17 is a second Zener diode 14
a third switching transistor with a collector-emitter path inserted between the anode and ground of the transistor, 18;
is a changeover switch whose fixed contacts are connected to the bases of the first, second, and third switching transistors 15, 16, and 17, respectively, and whose movable contacts are connected to the input terminal 1.

Now, if the movable contact of the changeover switch 18 is connected to the first fixed contact 18a as shown in FIG.
is in a conductive state, and the lower end of the reference voltage generating circuit 4 is grounded via the collector-emitter path of the first switching transistor 15. A reference voltage generated from the generation circuit 4 itself (for example,
5V) is applied, and a first level output voltage (approximately 5V) corresponding to the reference voltage from the reference voltage generation circuit 4 is generated at the emitter of the control transistor 5. Then, by applying the output voltage to the oscillation circuit 9, an oscillation output of a predetermined level is generated from the oscillation circuit 9, and a first predetermined output is applied to the recording head and erasing head 10, 11, and 12 for Lch and Rch, respectively. bias current and erase current are supplied.

Next, if the movable contact of the changeover switch 18 is connected to the second fixed contact 18b, the second switching transistor 16 becomes conductive, and the lower end of the reference voltage generation circuit 4 connects to the first Zener diode 13.
and is grounded via the collector-emitter path of the second switching transistor 16. Therefore, the first input terminal of the error voltage detection circuit 8 is connected to the voltage generated from the reference voltage generation circuit 4 itself (for example,
5V) plus the voltage drop (for example, 2V) of the first Zener diode 13 (7V) is applied as a reference voltage, and a second level output voltage (about 7V) is generated at the emitter of the control transistor 5. . Therefore, an oscillation output is generated from the oscillation circuit 9 at a level corresponding to the second level output voltage,
Recording head and erasing head 10 for Lch and Rch,
A second predetermined bias current and an erase current are supplied to 11 and 12, respectively.

The movable contact of the changeover switch 18 is the third fixed contact 1
The same can be said for the case where it is connected to 8c. In this state, the third switching transistor 17 is conductive, and the voltage generated by the reference voltage generating circuit 4 itself plus the voltage drop of the first and second Zener diodes 13 and 14 (9V ) is applied as a reference voltage to the first input terminal of the error voltage detection circuit 8, and a third level output voltage (approximately 9V) is applied to the emitter of the control transistor 5.
occurs. Therefore, an oscillation output is generated from the oscillation circuit 9 at a level corresponding to the output voltage at the third level, and the recording head and erasing head 1 for Lch and Rch are generated.
0, 11 and 12 are supplied with predetermined bias current and erase current.

The changeover switch 18 may be switched depending on the type of recording tape such as normal tape, chrome tape, metal tape, etc., and by doing so,
Appropriate bias is supplied to the head, making it possible to make the most of the characteristics of the recording tape.

As described above, according to the present invention, a plurality of constant voltages are generated from the constant voltage circuit by selectively using Zener diodes to switch the reference voltage of the constant voltage circuit. Since the constant voltage characteristics of the voltage circuit itself are not impaired, a constant voltage of a predetermined level can be supplied to the oscillation circuit, and a stable bias current can be supplied to the recording head depending on the type of recording tape.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of a bias switching circuit for a tape recorder according to the present invention. Explanation of main drawing numbers 2 ... Constant voltage circuit, 9... Oscillator circuit, 13, 14... Zener diode, 15, 1
6, 17... Switching transistor, 18... Changeover switch.

Claims (1)

[Scope of utility model registration request] In a tape recorder configured to switch the head bias depending on the material of the tape used,
The recording head, an oscillation circuit that supplies the recording head with a bias current according to the supplied voltage, compares the reference voltage and the output voltage, detects the difference, obtains a constant voltage, and sends a constant voltage to the oscillation circuit. a voltage switching circuit comprising a constant voltage circuit that supplies voltage, and a plurality of Zener diodes and switching elements connected to switch a reference voltage of the constant voltage circuit;
and a power source that supplies an operating voltage to the voltage switching circuit, and by controlling the voltage switching circuit, selectively switches the reference voltage of the constant voltage circuit using a Zener diode, and outputs a plurality of voltages from the constant voltage circuit. A tape recorder bias switching circuit characterized in that it is configured to generate a constant voltage.