JPH0646449B2 - Magnetic head degaussing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a degaussing device for a magnetic head such as a tape recorder. The degaussing effect is achieved by sharpening the oscillation rise of an oscillation circuit portion for generating a degaussing magnetic field. It is an object of the present invention to provide a device capable of increasing the power consumption.

[Conventional technology]

Recording / playback magnetic heads such as tape recorders are magnetized by long-term use and cause deterioration of recording / playback characteristics.
Since it is necessary to periodically degauss the magnetic head, a cassette degaussing device in which the degaussing head is built in a cassette case has been widely implemented as a device that can easily perform degaussing. FIG. 1 shows an electric circuit of a conventional degaussing device of this type. A DC-DC converter circuit 22, a drive display circuit 23, a switching circuit 24 and a constant voltage circuit 25 are connected to a power supply battery 21 to provide a large capacity. Capacitor 2
The magnetic heads such as tape recorders are demagnetized by the gradually decreasing alternating magnetic field generated in the degaussing head 28 by driving the oscillating circuit 27 due to the discharge of the electric charges accumulated in 6.

The oscillator circuit 27 of this device operates as follows.

The constant voltage circuit 25 such as the zener diode 29 detects that the charge amount of the large-capacity capacitor 26 reaches a predetermined value, and the switching circuit 24 is driven by this output signal to connect to the switching circuit 24. The oscillation circuit 27 starts oscillating.

At this time, the switching circuit 24 uses the large-capacity capacitor 2
The oscillating state of the DC-DC converter circuit 22 for charging 6 is controlled by controlling the transistor 30 so that the switching transistor 31 between the converter circuit 22 and the large-capacity capacitor 26 is cut off at the same time. It is designed to drive in the direction.

[Problems to be solved by the invention]

Therefore, the rising characteristics of each part such as the switching circuit 24, the converter circuit 22, the oscillation circuit 27, etc. are affected by the detection accuracy of the constant voltage circuit 25, specifically, the degree of detection steepness. Explaining the constant voltage circuit 25 here, a zener diode 29 is usually used as a constant voltage detecting element. Generally, when a voltage is applied in the opposite direction, the zener diode generally causes a current to flow from a saturated region where current does not easily flow. The characteristic shifts to the yield region where the flow begins, but at this time, there is a Zener knee near the boundary of both regions, so the operation in this region is unstable.

Moreover, the large-capacity capacitor 26 detected is the power supply battery 2
Since the DC-DC converter circuit 22 charges the low voltage of 1 while charging it, the rate of increase in the terminal voltage of the capacitor 26 is gentle, and the terminal voltage gradually increases to a Zener knee. When approaching, the current flowing through the Zener diode 29 becomes slow, and the switching circuit 24 which receives this output signal starts the switching operation slowly, and the output thereof causes DC.
The -DC converter circuit 22 is controlled so as to gradually reduce the output, and the switching transistor 31 is also gradually controlled in the shutoff direction. This means that the voltage applied to the Zener diode 29 only gradually increases, the time for which the terminal voltage of the large-capacitance capacitor 26 passes through the Zener knee becomes long, and therefore the gradual increase of the detection voltage is further promoted. The sharp rotation drive of the switching circuit 24 is not performed.

On the other hand, regarding the oscillation circuit connected to the switching circuit 24, the switching circuit 24 performs slow inversion driving, so that oscillation is gradually started, whereby the charging capacity of the large capacity capacitor 26 is discharged, and the constant voltage is maintained. Circuit 2
The voltage applied to 5 is changed more gradually, so that the reversal drive is further deteriorated and the degaussing head 2
The rising of the alternating magnetic field generated in No. 8 is also aggravated.

As described above, in the conventional device, the trigger for oscillation changes in the direction in which each circuit portion mutually deteriorates the rising characteristics, and as a result, the first rising of the demagnetizing alternating magnetic field is as shown in FIG. In the rising area A, there is a drawback that a magnetic head such as a tape recorder may be magnetized in the opposite direction.

[Means for solving problems]

The present invention has been made in view of the above circumstances, and includes a power supply battery 1, a booster circuit connected to the power supply battery to increase a voltage, a capacitor charged by the booster circuit through a switching circuit, and A timer circuit comprising an oscillating circuit and a degaussing head connected to the capacitor is provided between the boosting circuit and the switching circuit, the timer circuit being supplied with power by the boosting circuit to start integration, and the switching signal is output by the timer circuit. It is designed to control the circuit.

〔Example〕

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is an electric circuit diagram of a degaussing device incorporated in a cassette case. Is a converter circuit,
The switch circuit 2 includes a variable contact 2a on the converter circuit 3 side,
It is composed of a fixed contact 2b on the negative side of the power supply battery 1 and a fixed contact 2c on the side of a capacitor C3, which will be described later. When the cassette case is set on the tape recorder, the variable contact 2 is formed.
a is thrown into the contact 2b side, and is thrown into the contact 2c side when it is removed from the tape recorder. The converter circuit 3 includes a resistor R1, coils L1 and L2, capacitors C1 and C2,
It consists of diode D1, transistors Q1, Q2, etc.,
The terminal voltage of the power supply battery 1 is boosted.

A timer circuit 4 including a resistor R2 and a capacitor C3 is connected to the output stage of the converter circuit 3, and a switching section 5 is connected to the timer circuit 4. Switching-unit 5 driving display circuit 5 ₁ consists driving display circuit 5 ₁ and switching-circuit 5 ₂ which is a light emitting diode D2 as a light emitting element made of transistors Q3, resistors R3, R4, etc., the light emitting diode D2 is the capacitor The low antibodies R3 and R4 are connected in parallel with C3 and to the base side of the transistor Q1. Low antibody R of capacitor C3
The 2 side is connected to the fixed contact 2c of the switch circuit 2 and is also connected to the base side of a transistor Q5 described later via a diode D3.

Switching-circuit _{5 2} one of the transistors Q4, Q5, and Narutsu low antibody R5, R6, R7, R8 Prefecture, the base of the transistor Q4 is connected through a resistor R6, R7 to the base side of the transistors Q3, Low antibody R6, R
7 is connected to the collector side of the transistor Q5.
The base side of the transistor Q5 is connected to the collector side of the transistor Q3 via the resistor R8, and is also connected to the capacitor C3 via the diode D3 as described above.

Reference numeral 6 denotes a constant voltage circuit connected to the switching section 5, which is composed of a zener diode D4, and a large capacity capacitor C4 is connected to the constant voltage circuit 6.

Reference numeral 7 denotes an oscillator circuit driven by the discharge current of the capacitor C4, which includes capacitors C5, C6, low antibodies R9, R10,
A degaussing head 8 including degaussing coils L3 and L4 and a capacitor C7 is connected to the oscillation circuit 7 and is composed of transistors Q6 and Q7. The transistor L6, the emitter side of the Q7 is switching-circuit _{5 and second} transistors Q
5 is connected to the collector side.

The present apparatus has the above-mentioned configuration, and the operation will be described next.

When the cassette case is set on the tape recorder, the variable contact 2a of the switch circuit 2 is turned on to the fixed contact 2b side, the terminal voltage of the power supply battery 1, for example, 1.5V, is gradually boosted by the converter circuit 3, and the transistor Q4 is turned on. It conducts and the capacitor C4 is charged.

Since the constant voltage circuit 6 is connected in parallel to the capacitor C4, when the constant voltage value, for example, 16 V is reached,
The charging current of the capacitor C4 is bypassed to the constant voltage circuit 6, and the capacitor C4 continues to maintain the constant voltage value.

In parallel with this charging, the capacitor C3 of the timer circuit 4 is also charged via the resistor R2 to start integration, and when its terminal voltage reaches a predetermined value, that is, when a predetermined time elapses, its discharge current Switching circuit 5
_{The second} transistor Q5 is triggered to be biased in the conduction direction, and the transistor Q3 is simultaneously biased in accordance with the conduction, and both the transistors Q5 and Q3 are biased to each other to perform the inversion operation and become the full conduction state.

Here, from the time until the large-capacity capacitor C4 reaches 16V (about 300 mS), the time of the timer circuit 4 (about 1
(Seconds) is set long enough, during the reversing operation,
The converter circuit 3 supplies the capacitor C4 so that the output voltage is weakened so that the capacitor C4 is kept at a constant voltage. Moreover, since the converter circuit 3 is supplied directly from the converter circuit 3, the circuit after the transistor Q4 is supplied. It is not affected by the rising characteristics of the latter stage, and therefore the inversion operation period is the time required for the inversion operation of the transistors Q3 and Q5. Moreover, since both transistors Q3 and Q5 are biased mutually, it takes a short time. As a result, the oscillation circuit 7 rises steeply.

In this way, the oscillator circuit 7 which is supplied with power from the capacitor C4
When the operation starts, the demagnetizing head 8 produces a gradually decreasing alternating magnetic field based on the discharge time constant, and the recording / reproducing magnetic head of the tape recorder is demagnetized. Also transistor Q
When 3 becomes conductive, a base current flows through the transistor Q1 and the transistor Q1 becomes conductive, the output of the converter circuit 3 is suppressed to an output of about 3V, and the light emitting diode D2
Is supplied to supply electric power for maintaining the operation of the switching unit 5.

When the capacitor C4 is completely discharged and the degaussing operation is completed, the cassette case is removed from the tape recorder. Then, the variable contact 2a is switched to the fixed contact 2c side, the capacitors C2 and C3 are immediately discharged, and are ready for the next use.

〔effect〕

As described above, the degaussing device according to the present invention includes the power supply battery 1,
Booster circuit 3 connected to the power supply battery 1 to raise the voltage
When the capacitor C4 and the capacitor C4 is charged via a switching-circuit 5 ₂ The booster circuit 3
Oscillating circuit 7 connected to consist degaussing head 8 Prefecture, the timer circuit 4 starts the power supply integrated by the booster circuit 3 is provided between the booster circuit 3 and the switching-circuit 5 _2, of the timer circuit 4 since it is configured to control the switching-circuit 5 ₂ output signal, the oscillation start rising characteristic of the oscillation circuit 7 can be made good, and a steep reversal operation of switching-circuit 5 _2, demagnetizing head 8
It is possible to make the rising response of the gradually decreasing alternating magnetic field generated in the above-mentioned manner good, and to surely perform the demagnetization action.

In recent years, with a feather touch type switch,
A tape deck that automatically advances the recording head of the tape deck into the cassette by using the power of a motor or the like to start operation is becoming mainstream, but boosts pressure by moving the recording / reproducing head of the tape deck as in the past. In the case where the operation of the circuit is started and the capacitor C4 is charged to a predetermined voltage to start demagnetization, the recording / reproducing head is in the middle of automatic advancement, that is, the contact between the recording / reproducing head and the demagnetizing head is insufficient (tilt contact). ), Demagnetization starts, and an undesirable phenomenon such as reverse magnetization occurs.

However, according to the present invention, in consideration of the time (usually within 1 second) until the contact between the recording / reproducing head and the degaussing head is stabilized,
The time until the output signal of the timer circuit 4 is output can be made sufficiently long and stable demagnetization can be performed.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a conventional example of the present invention, FIG. 2 is an alternating magnetic field characteristic diagram obtained by the conventional example, and FIG. 3 is a circuit diagram of an embodiment of the present invention. 1 ... Power supply battery 3 ... Booster circuit 4 ... Timer circuit 7 ... Oscillation circuit 8 ... Degaussing head 5 ₂ ... Switching circuit C4 ... Capacitor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Bibliography Sho 55-108547 (JP, U) Rikai 54-143616 (JP, U) Rikai 57-184519 (JP, U)

Claims (1)

[Claims] And 1. A power source battery 1, a booster circuit 3 to increase the voltage connected to the power source battery 1, a capacitor C which is charged through the switching-circuit 5 ₂ The booster circuit 3
4 and the oscillator circuit 7 connected to this capacitor C4,
Consists demagnetizing head 8 Prefecture, between the booster circuit 3 and the switching-circuit 5 _2, the timer circuit 4 starts the power supply integrated by the booster circuit 3 is provided, the switching-circuit 5 by the output signal of the timer circuit 4 _{2. A} magnetic head degaussing device that controls ₂ .