JP2525911B2 - Magnetic recording / reproducing device protection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording / reproducing apparatus having a fan in order to prevent an internal temperature rise, and particularly when a DC fan motor fails. The present invention relates to a protection circuit for a magnetic recording / reproducing device.

[Prior Art] In a magnetic recording / reproducing apparatus, the internal temperature rises significantly due to the heat generated by electronic circuits such as amplifiers and various motors such as cylinder motors and capstan motors. Adversely affect. In order to prevent this, it is conceivable to provide a fan and cool the inside by air cooling. As the fan motor in this case, a DC (direct current) motor using a direct current power source of the magnetic recording / reproducing apparatus as a power source is used.

By the way, if the DC fan motor fails and does not rotate, air cooling cannot be performed and the internal temperature of the magnetic recording / reproducing apparatus rises. Therefore, a means for protecting the magnetic recording / reproducing apparatus main body against the failure of the DC fan motor is required.

As a protection means for such a device failure, which relates to protection of a power amplifier, a means for detecting an overcurrent of a transistor is provided as described in, for example, Japanese Utility Model Publication No. 1-15222. A means for cutting off the power supply by operating a fuse or the like provided in series with the power supply when the current is detected is known.

Therefore, also in the magnetic recording / reproducing apparatus, a fuse or the like is provided in series with the power supply to detect the presence or absence of overcurrent of the DC fan motor. When the overcurrent is detected, the fuse or the like is activated to shut off the power. It is possible to do so. According to this, when the DC fan motor fails and an overcurrent flows, the power supply is cut off, the power supply voltage is not supplied to the electronic circuit in the magnetic recording / reproducing apparatus, and the apparatus body is protected.

[Problems to be Solved by the Invention] However, the above protection means is effective only when a failure such as an overcurrent flows in the DC fan motor occurs. In addition to the above-mentioned short circuit faults in which overcurrent flows due to wiring short-circuits, DC motor failures include discharge faults that prevent rotation due to wire breakages, and foreign matter between the stator and rotor. There is a motor lock mode in which the rotor cannot rotate due to such reasons.

When this open failure or motor lock mode occurs, the DC fan motor does not rotate, but in the case of open failure, the DC fan motor current becomes zero or very small. In case of DC
A current flows through the fan motor, but this current is smaller than in the case of a short circuit failure.

For this reason, in the protection means that operates by the above-mentioned overcurrent, when an open failure or a motor lock mode occurs in the DC fan motor, this is not detected and the fan is stopped, The magnetic recording / reproducing apparatus continues to operate and its internal temperature rises significantly.

An object of the present invention is to provide a protection circuit for a magnetic recording / reproducing apparatus which solves the above problems and can protect the magnetic recording / reproducing apparatus main body in response to any failure of the fan motor. It is in.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a means for detecting the magnitude of the current of a fan motor, and the magnitude of the current detected by the means is preset. Means for outputting a failure detection signal when it is out of the predetermined range, and the power supply is shut off by the failure detection signal.

[Operation] The upper limit of the above-mentioned predetermined range is set to a value smaller than the magnitude of the current when the fan motor is in the short-circuit fault or the motor lock mode, and the lower limit of the above-mentioned predetermined range is when the fan motor is in the open fault. Is set to a value greater than the magnitude of its current.

When the fan motor rotates normally, the magnitude of the current is in the above-mentioned predetermined range. However, when the fan motor cannot rotate due to a short-circuit failure or motor lock mode, or when the fan motor is abnormally rotated, the magnitude of the current of the fan motor exceeds the upper limit of the predetermined range, and a failure detection signal is generated. Further, when the fan motor cannot be rotated due to an open failure or when it is abnormally rotated, the magnitude of the current is smaller than the lower limit of the above-mentioned predetermined range, and in this case, the failure detection signal is generated.

In this way, whichever failure the fan motor has, it is detected, a failure detection signal is generated, and the power is cut off.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a protection circuit for a magnetic recording / reproducing apparatus according to the present invention, in which 1 is a DC fan motor,
2 is an input terminal, 3 and 4 are transistors, 5 to 10 are resistors, and 11
Is a capacitor, 12 is a detector, 13, 14 are comparators, 15,
16 is a diode and 17 is an output terminal.

In the figure, when a voltage is applied to the input terminal 2, the transistor 3 turns on. When the DC fan motor 1 is normal, the drive current i flows through the DC fan motor 1 to which the DC power supply voltage of 20 (V) is applied, and the DC fan motor 1 rotates. The drive current i flows through the resistor 5 and the transistor 3, and the resistor 5 and the transistor 3 generate a voltage V ₁ having a magnitude corresponding to the value of the drive current i. This voltage V ₁ is held in the capacitor 11, and the comparator 13, ₁ of the detector 12
Supplied to 4.

On the other hand, 5 (V) is applied to the emitter of the PNP type transistor 4.
When the transistor 3 is turned on by applying the DC power supply voltage of, the transistor 4 turns on because its base is grounded via the resistor 6 and the transistor 3.
As a result, the detection circuit 12 passes through the transistor 4 to 5
A DC power supply voltage of (V) is applied and the operation state is set.

When the transistor 4 is turned on, a DC power supply voltage of 5 (V) is also applied to the resistors 8, 9 and 10 connected in series.
The DC power supply voltage is divided by the resistors 8 and 9, 10 to generate the first reference voltage V ₂ , and the detection circuit 12
Of the DC power supply voltage is divided by the resistors 8 and 9 to generate the second reference signal V _{3, which} is supplied to the comparator 14 of the detection circuit 12. To be done. Here, V ₂ > V ₃ .

In the comparator 12, the magnitude of the voltage V ₁ held in the capacitor 11 and the first reference voltage V ₂ are compared, and V ₁ ≦ V ₂
“L” (0 (V) at low level) when, and “H” when V ₁ > V ₂
A signal of (5 (V) at high level) is output. Further, the comparator 13 compares the magnitude of the voltage V ₁ and the second reference voltage V ₃ and outputs a signal which becomes “L” when V ₁ ≧ V ₃ and “H” when V ₁ <V ₃ To be done. The output signals of the comparators 13 and 14 are supplied to the diodes 15 and 16, respectively, and these diodes 15 and 16 form an OR circuit that receives the output signals of the comparators 13 and 14 as input. When one is "H", the signal output from this OR circuit and obtained at the output terminal 17 is "H".

Here, the first reference voltage V ₂ is applied to the capacitor 11 when the DC fan motor 1 is in a short circuit fault or in the motor lock mode.
Is set to be lower than the voltage V ₁ held by the DC fan motor 1 and is set to be higher than the voltage V ₁ held by the capacitor 11 when the DC fan motor 1 normally rotates. The second reference voltage V ₃ is set to be higher than the voltage V ₁ when the DC fan motor 1 has an open circuit failure and lower than the voltage V ₁ when the DC fan motor 1 normally rotates. That is, the detection circuit 12 constitutes a window-type comparator in which a predetermined voltage range in which the upper limit voltage is V ₂ and the lower limit voltage is V ₃ is set, and the voltage V ₁ held in the capacitor 11 is It is detected whether or not it is within a predetermined voltage range.

Therefore, when the DC fan motor 1 normally rotates, V ₂ ≧ V ₁ ≧ V ₃ , and therefore the output signals of the comparators 13 and 14 are both “L”, and accordingly, the output signal is obtained at the output terminal 17. The signal is also "L". On the other hand, when the DC fan motor 1 has a short circuit failure or is in the motor lock mode, the voltage
V ₁ is a DC power supply voltage of 20 (V), which is higher than when DC fan motor 1 rotates normally, and V ₁ > V ₂ , and the output signal of comparator 13 is “H”. After all, the signal obtained at the output terminal 17 also becomes "H". When the DC fan motor 1 has an open circuit failure, the voltage V ₁ is 0
Even if it is a very low value such as (V), V ₁ <V ₃ , and the output signal of the comparator 14 becomes “H” and the signal obtained at the output terminal 17 also becomes “H”.

In this way, the DC fan motor 1 with excessive drive current
The short-circuit failure, the motor lock mode, and the open failure of the DC fan motor 1 in which the drive current becomes abnormally small are detected, and the detection result is obtained as an "H" signal at the output terminal 17, that is, as a failure detection signal.

The signal obtained at the output terminal 17 is supplied to the reset terminal of a system microcomputer (not shown) which controls the operation of the magnetic recording / reproducing apparatus. Then, when a failure detection signal of "H" is supplied from the output terminal 17 to the reset terminal of the system microcomputer, the system microcomputer shuts off the power supply and resets the magnetic recording / reproducing apparatus to the initial state in which the power supply voltage is not applied.

As described above, even if the DC fan motor 1 is in a short-circuit fault, a motor lock mode, or an open fault, these are detected and the power is cut off. The power supply to the electronic circuits is stopped to prevent the internal temperature from rising. For this reason, the reliability of each electronic circuit is not impaired.

Further, as described above, even if the power supply is cut off by the system microcomputer, the power supply switch is turned on again to turn on the power supply of the system microcomputer again. When a fuse is provided in series with the power source as in the conventional example described above, this fuse is provided inside the magnetic recording / reproducing apparatus, and when this is cut off,
It is needless to say that the general user cannot replace it, but at least the replacement work is necessary, which is troublesome, but in the above-described embodiment, such work is unnecessary.

Note that in FIG. 1, the transistor 4 and the resistor 6 may be omitted, and a DC power supply voltage of 5 (V) may be directly applied to the detection circuit 12 and the series circuit of the resistors 8, 9 and 10.

Further, the numerical values shown in the above embodiments are merely examples shown for convenience of explanation.

[Effects of the Invention] As described above, according to the present invention, even if any failure occurs in the fan motor, the failure can be reliably detected and the power supply can be cut off. It is possible to prevent the internal temperature of the device from rising. Therefore, it is possible to prevent the performance deterioration of the electronic circuit and the like in the apparatus and improve the reliability.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a protection circuit for a magnetic recording / reproducing apparatus according to the present invention. 1 ... DC fan motor, 3 ... Transistor, 5,8,9,
10 …… Resistance, 11 …… Capacitor, 12 …… Detection circuit, 13,1
4 …… Comparator, 17 …… Output terminal.

Claims (1)

(57) [Claims] 1. A magnetic recording / reproducing apparatus, wherein a DC voltage is supplied from an internal power supply to drive a DC motor for rotating a fan, and the fan prevents the internal temperature from rising. Means for detecting the magnitude of the current, and a value smaller than the value of the current of the direct current motor in the short circuit fault or the motor lock mode of the direct current motor is set as the upper limit value, and the direct current when the open fault of the direct current motor occurs. A means for generating a failure detection signal when a predetermined range having a lower limit value larger than the value of the motor current is set, and the magnitude of the current detected by the means is outside the predetermined range; And a protection circuit for the magnetic recording and reproducing apparatus, characterized in that the power supply is shut off in response to the failure detection signal.