JPH0441758Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a circuit for preventing false lighting of light emitting diodes used in small and portable cassette tape recorders etc. that are powered by batteries, and in particular, This improves the reliability of light emitting diode displays by preventing erroneous lighting.

[Background technology and its problems]

For example, a small and portable cassette tape recorder such as a headphone monitor type stereo cassette tape recorder is generally powered by batteries, with at least two 1.5V DC batteries.
It is designed to operate on DC3V. In order to further downsize such a cassette tape recorder, it is conceivable to reduce the number of batteries to one, but in this case the power supply voltage would drop to approximately DC 1.5V or less.

Here, a light emitting diode is used to display, for example, the rotational state of the motor of the above-mentioned cassette tape recorder, but generally the light emission starting voltage V _F of the light emitting diode is required to be about 1.5V to 2V.
When a single battery as described above is used as a power source, it is difficult to obtain enough voltage to drive the light emitting diode.

Therefore, by using the back electromotive voltage generated in the motor coil to increase the voltage applied to the light emitting diode above the power supply voltage, the light emitting diode with a light emission starting voltage of about 1.8V can be turned on even with a power supply voltage of DC1.5V or lower. The applicant had previously proposed a structure that enables driving.

However, when power is supplied to the above-mentioned cassette tape recorder using an AC adapter or the like, the power supply voltage may exceed the above-mentioned light emission start voltage, and the above-mentioned light-emitting diode is driven to turn on even when the motor rotation is stopped. This may cause misunderstanding of the operation.

[Purpose of invention]

In view of these circumstances, the present invention has been developed so that when the back electromotive force of the motor coil is used to drive the light emitting diode, the power supply voltage is lower than the standard power supply voltage that is lower than the light emission starting voltage of the light emitting diode. An object of the present invention is to provide a light emitting diode erroneous lighting prevention circuit that prevents a light emitting diode from being erroneously turned on while a motor rotation is stopped due to a light emission starting voltage or higher.

[Summary of the idea]

The circuit for preventing erroneous lighting of light emitting diodes according to the present invention is characterized by a series circuit of a motor coil and a motor drive switching element connected to a power supply voltage terminal to which power supply voltage V _DC is supplied, and a series circuit between these motor coils and a motor drive switching element. One end is connected to the connection point of the driving switching element, and the other end is connected to the above power supply voltage terminal, and the voltage is obtained by the above power supply voltage V _DC and the back electromotive voltage -V _M generated in the above motor coil. In a light emitting diode drive circuit comprising a light emitting diode that is driven to turn on, the light emitting diode is connected in parallel to the series circuit of the light emitting diode and the motor coil, and the forward voltage is lower than the light emission starting forward voltage V _F1 of the light emitting diode. It comprises a diode for preventing erroneous lighting having V _F2 (V _F2 < V _F1 ).

〔Example〕

Hereinafter, as a preferred embodiment of the present invention, an example in which the present invention is applied to a circuit for preventing erroneous lighting of a light emitting diode for displaying the motor drive status of a small portable cassette tape recorder will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention, showing the vicinity of the motor drive circuit of the cassette tape recorder. In this Figure 1,
A positive power supply voltage V _DC (for example, DC 1.5 V) is supplied to the power supply terminal 1 from, for example, one battery. The brushless motor for driving the tape running of the cassette tape recorder has, for example, six stator coils L1 to L6, of which three coils L1, L3, and L5 are connected in series to form the first phase (or A phase) is configured, and the other three coils L2,
L4 and L6 are connected in series to form the second phase (or B
phase) is composed of Then, the power terminal 1
and the ground terminal, there is also a series connection circuit of a PNP transistor 2A as an A-phase drive switching element and A-phase coils L1, L3, and L5.
A series connection circuit of a PNP type transistor 2B as a B-phase driving switching element and B-phase coils L2, L4, and L6 is connected to each other. Each of these transistors 2A, 2 for energizing drive of each phase
B is controlled to be turned on or off according to the output from the motor drive control circuit 3.

Here, as the brushless motor for driving the tape running, for example, the present applicant filed a patent application
75287 (Japanese Unexamined Patent Publication No. 57-3567) etc., for example, a pair of complementary poles is provided between a pair of main poles of a ring-shaped rotor magnet, and a two-phase A two-phase switching brushless motor may be used in which the winding spacing between the forward and backward paths of the excitation coil is set to an electrical angle other than 180°. In this case, one magnetically sensitive element, for example, a Hall element, is arranged around the rotor magnet, and the rotational angular position of the rotor magnet is detected by the Hall element and sent to the motor drive control circuit 3. A motor drive control circuit 3 drives switching transistors 2A and 2B in accordance with the rotation angle position of the rotor magnet.

Next, the cathode of a light emitting diode 4 is connected to the connection point P between the motor coil L1 of the A phase and the transistor 2A, for example, the A phase and the B phase, and the anode of the light emitting diode 4 is connected through a resistor 5. , for example, is connected to the power supply terminal 1 via the collector and emitter of a PNP transistor 6.

Here, the transistor 6 is connected to a power switch 7 of the cassette tape recorder.
When the transistor 6 is turned on, V _DC from the power supply terminal 1 is turned on.
For example, a DC 1.5V power supply voltage is supplied to the anode of the light emitting diode 4 via the transistor 6 and the resistor 5. The light emission starting forward voltage V _F1 of the light emitting diode 4 is, for example, 1.8V, and the light-emitting diode 4 is not driven to light by the DC 1.5V power supply voltage when the motor rotation is stopped.

By the way, when the above-mentioned brushless motor is rotationally driven, the motor coil connected to the off-state transistor of each transistor 2A, 2B is affected by changes in the coil flux linkage from the rotating rotor magnet. Due to the underlying electromagnetic induction, a so-called back electromotive voltage V _M is generated, and this back electromotive voltage V _M appears in the opposite direction to the direction of the applied voltage when current is applied. That is, at the connection point P, a back electromotive force of -W _M appears due to the series circuit of the A-phase coils L1, L3, and L5, one end of which is grounded when the transistor 2A is off, and the cathode terminal voltage of the light emitting diode 4 becomes approximately -. It becomes V _M. Since the anode of the light emitting diode 4 is applied with a voltage of V _DC , for example 1.5V DC, from the power supply terminal 1 via the transistor 6 and the resistor 5, the anode of the light emitting diode 4 is
Approximately V _DC −(−V _M )=V _DC +V _M
voltage will be applied. Therefore, this applied voltage V _DC +V _M is larger than the light emission starting forward voltage V _F1 of the light emitting diode 4 (V _DC +V _M > V _F1 ).
At this time, the light emitting diode 4 is turned on to indicate that the motor is rotating.

Regarding the transistor 6, the power switch 7 is turned on and the base-emitter voltage V _BE is approximately 0.7V.
When the above power supply voltage V _DC is applied, the transistor is turned on, and the voltage dividing resistors 8 and 9 on the base side of the transistor 6 are, for example, 4.7 kΩ,
If 2.4kΩ is selected respectively, V _BE ≧
The power supply voltage V _DC to establish 0.7V is approximately 1.05V
That's all. This is because when using dry batteries or rechargeable batteries as a power source, the output voltage will decrease over time, and when the power supply voltage V _DC drops to approximately 1.05V or less, the power will not be turned on. In this case, the transistor 6 is not turned on and the light emitting diode 4 is not turned on, thereby indicating that the battery life has expired. That is, the light emitting diode 4 has two functions: an indication of motor rotation drive while the power supply voltage V _DC is within the normal use range, and an indication of battery consumption.

The power switch 7 is turned on and off in conjunction with the operation of various operation buttons such as play, fast forward, and rewind on the cassette tape recorder, and when the switch 7 is turned on, the cassette tape Power is supplied to various circuit sections within the tape recorder to turn on the circuit power. In this case, the circuit power supply is performed by grounding the ground side terminal of each circuit section, for example, the motor drive control circuit 3.

By the way, when the DC voltage V _DC of the power supply terminal 1 exceeds the light emission starting forward voltage V _F1 of the light emitting diode 4, for example, by using an AC adapter or using a special battery, V _DC can be adjusted to 1.8 V or more. When
Even if the motor is not rotationally driven, the light emitting diode 4 is erroneously lit. For example, it will emit light when the tape is wound onto a reel and the motor stops rotating during fast forward or rewind mode, or when the FM reception mode is selected and the power is turned on in a cassette tape recorder with an FM receiver. Diode 4 lights up erroneously, causing the driver to mistakenly believe that the motor is rotating.

Therefore, as a main part of the present invention, the A of the above motor is
A diode 10 for preventing erroneous lighting is connected in parallel to the series circuit of the phase coils L1, L3, L5 and the light emitting diode 4. That is, the anode of the diode 10 is connected to the connection point between the anode of the light emitting diode 4 and the resistor 5, and the cathode of the diode 10 is grounded. The forward ON voltage V _F2 of this diode 10 is set lower than the light emission start voltage V _F1 (V _F2 < V _F1 ), and the power supply voltage V _DC
When exceeds V _F1 , diode 10 turns on, reducing the voltage applied to light emitting diode 4.
V _F2 is suppressed to prevent false lighting. for example,
If V _F1 is 1.8V, V _F2 should be set to about 1.5V.

As is clear from the above explanation, the standard power supply voltage is the light emission starting forward voltage V _F1 of the light emitting diode 4.
In a device that uses the back electromotive force of the motor coil to drive the light emitting diode 4, when a maximum power supply voltage equal to or higher than the above V _F1 is applied, that is, standard power supply voltage < V _F1 ≦ maximum power supply voltage. In the case of the condition, diode 1 has a forward voltage V _F2 smaller than V _F1 of light emitting diode 4 (V _F2 < V _F1 ).
By connecting 0 in parallel to the series circuit of the light emitting diode 4 and the motor coil, it is possible to prevent the light emitting diode 4 from erroneously lighting up when the motor rotation is stopped (and the power is on). Therefore, the reliability of the display of the light emitting diode 4 is increased.

Next, a second embodiment of the present invention will be described with reference to FIG.

This FIG. 2 shows the vicinity of the motor drive circuit of the cassette tape recorder as described above, and this motor drive circuit drives, for example, the motor coil L.
1, L3 and L2, L4 are alternately switched and energized by approximately 90 degrees in electrical angle, and the magnet applies rotational torque to the rotor, which is magnetized at a predetermined position, thereby driving the motor.

In the same figure, the respective collectors of NPN type transistors 12A and 12B for motor driving of a two-phase brushless motor are connected to a positive DC voltage +
It is connected to the power supply terminal 11 to which V _DC , for example, 1.5V is supplied. In addition, these transistors 12A and 1
The emitters of 2B are commonly connected, and the common connection point is grounded via an NPN transistor 21 forming a constant current circuit. Also, transistor 1
The collector of 2A is connected via a resistor 22 to the base of transistor 12B. Furthermore, noise prevention capacitors 23 and 24 are connected between the collectors of transistors 12A and 12B.

Further, in FIG. 2, 25 is a photocoupler for detecting the rotational position of the rotor 26 of the motor. The outer periphery of the rotor 26 is coated with black paint, for example, every 90 degrees, so that light from the light emitting diodes 25a is absorbed. Therefore,
Since the light from the light emitting diode 25a is reflected by the rotor 26 every 90 degrees and supplied to the phototransistor 25b, the rotational position of the rotor 26 is detected. This light emitting diode 25a is driven by a constant current circuit composed of an NPN transistor 27 and a resistor 28. A constant voltage is supplied to the base of this transistor 27 from a constant voltage circuit 29, so that the light emitting diode 25a is always driven with a constant current even if the power supply voltage +V _DC fluctuates.

The emitter of the phototransistor 25b is grounded, and its collector is connected to the power supply terminal 11 via a resistor 30.
A rotational position detection signal of the rotor 26 obtained at the connection point between the collector of the resistor 30 and the resistor 30 is supplied to the base of a PNP transistor 31. The emitter of this transistor 31 is connected to the power supply terminal 11, and its collector is connected to the transistor 12 through a resistor 32.
Connected to the base of A.

The motor drive circuit is configured as described above, and in the 90° angular range where the light from the light emitting diode 25a constituting the photocoupler 25 is reflected by the rotor 26, the transistor 31 is turned on, and therefore the transistor 12A is turned on. It turns on, and current flows through motor coils L1 and L3. On the other hand, the light from the light emitting diode 25a is transmitted to the rotor 26.
In the angular range of 90° absorbed at , the transistor 31 is off and therefore the transistor is on and current flows through the motor coils L2, L4. In this way, the transistors 12A and 12B are alternately turned on and off at 90° electrical angles. Therefore, motor coils L1, L3 and L2,
Current flows through L4 alternately at 90° electrical angle,
Rotational torque is applied to the rotor 26, and the motor is driven. In addition, in FIG. 2, a predetermined voltage is supplied to the base of the transistor 21 from the servo circuit 33, and a voltage is applied to the motor coils L2 and L4 from the connection point between the collector of the transistor 12B and the motor coil L2. A back electromotive voltage is supplied. This back electromotive voltage is
The voltage supplied from the servo circuit 33 to the base of the transistor 21 is generated when the servo circuit 33 turns off, and becomes higher as the rotational speed of the rotor 26, that is, the rotational speed of the motor, increases. The current value flowing through the motor coils L1, L3 and L2, L4 is controlled in the opposite direction depending on the height of the motor, so that the rotational speed of the motor is kept constant.

Also, in this Figure 2, the light emitting diode
The light emission starting voltage V _F1 of the LED 14 is, for example, 1.8V, which is higher than the standard power supply voltage of 1.5V DC. The cathode of this LED 14 is grounded via a resistor 15, and the anode is connected to a connection point P between the collector of the transistor 12A and the motor coil L1. As shown in FIG. 3, the connection point P has motor coils L1 and
The back electromotive voltage +V _M generated in 3 is obtained, and during this period,
The voltage value at the connection point P is +V _DC +V _M. This back electromotive force +V _M has a value that depends on the rotational speed of the motor,
It is constant when the rotational speed of the motor is constant.

In this example, when the power supply voltage +V _DC decreases and reaches the predetermined voltage V _L , the voltage +V _DC +V _M obtained at the connection point P is approximately the light emission starting voltage V _F1 of the LED 14.
The motor is set so that the back electromotive force +V _M is obtained. For example, supply voltage +V _DC is standard.
At 1.5V, the predetermined voltage V _L is 0.9V, and the light emission starting voltage V _F1 is
When the voltage is 1.8V, the motor is set so that the back electromotive force +V _M is approximately 0.9V. Therefore, when the motor is stopped, no back electromotive force +V _M is generated at the connection point P.
No current flows through the LED 14 and it does not emit light.

On the other hand, when the motor is rotating, the transistor 12A
During the off-period, a back electromotive voltage +V _M is generated in the motor coils L1 and L3, and when the power supply voltage +V _DC is higher than the predetermined voltage V _L , the voltage at the connection point P +V _DC +V _M is
The voltage becomes higher than the light emission start voltage V _F1 of the LED 14, and a current flows through the LED 14 during this period, causing it to emit light. and,
When the power supply voltage +V _DC decreases to below the predetermined voltage V _L , the voltage +V _DC +V _M obtained at the connection point P is:
The light emission starting voltage of LED14 becomes lower than V _F1 , and the LED
14, no current flows and no light is emitted. in this way,
Whether the power supply voltage +V _DC is higher or lower than the predetermined voltage V _L is displayed depending on whether the LED 14 emits light or not. That is, in order to emit light from the LED 14 whose light emission starting voltage V _F is higher than the power supply voltage +V _DC , the motor coil L
1. It utilizes the back electromotive voltage +V _M that occurs intermittently in L3, and the LED 14 emits light intermittently.
The light emission time is short and power consumption is low.
Further, since it utilizes the back electromotive voltage +V _M generated in the motor coils L1 and L3, it can be constructed at a lower cost than one that uses a DC-DC converter or the like.

Furthermore, as a main part of the present invention, the motor coil L
A diode 20 for preventing erroneous lighting is connected in parallel to the series circuit of the light emitting diode 1, L3 and the light emitting diode 14. That is, the anode of the diode 20 is connected to the power supply terminal 11, and the cathode is connected to the connection point between the light emitting diode 14 and the resistor 15. The forward ON voltage V _F2 of this erroneous lighting prevention diode 20 is set lower than the above-mentioned light emission start voltage V _F1 (V _F2 < V _F1 ), and when the motor rotation is stopped, the above-mentioned V _F1 is applied to the power supply terminal 11. When a voltage higher than
By turning on, the voltage between the terminals of the light emitting diode 14 is suppressed to approximately V _F2 or less, thereby preventing erroneous lighting. Therefore, as long as the motor is not driven to rotate, even if the power supply voltage increases, the light emitting diode 14
will not be erroneously lit, and the reliability of the light emitting display can be improved.

Note that the present invention is not limited to the above-mentioned embodiments. For example, the DC power supply voltage V _DC , the light emission starting voltage V _F1 of the light emitting diode, the forward voltage V _F2 of the erroneous lighting prevention diode, etc. are as described above. Various changes can be made within the range that satisfies each condition.

[Effect of idea]

According to the embodiment of the present invention, when the back electromotive force of the motor coil is used to drive the light emitting diode, the light emitting diode lights up while the motor is stopped because the power supply voltage becomes equal to or higher than the light emission starting voltage of the light emitting diode. By turning on the diode connected in parallel to the series circuit of the motor coil and the light emitting diode, the above-mentioned false lighting can be prevented, and misidentification of operation can be prevented. reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention;
FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a waveform diagram for explaining the operation of the circuit shown in FIG. 1, 11...Power terminal, 2A, 2B, 12A,
12B...Motor drive transistor, L1, L
2, L3, L4, L5, L6...Motor coil,
4, 14... Light emitting diode, 5, 15... Resistor, 10, 20... Diode for preventing erroneous lighting.

Claims (1)

[Scope of utility model registration request] A series circuit of a motor coil and a motor drive switching element connected to a power supply voltage terminal to which power supply voltage V _DC is supplied, one end connected to the connection point of these motor coil and motor drive switching element, and the other end connected to the connection point of the motor coil and motor drive switching element. is connected to the power supply voltage terminal, and the light emitting diode is driven to be lit by a voltage obtained by the power supply voltage V _DC and the back electromotive voltage −V _M generated in the motor coil. , the light emission starting forward voltage of the light emitting diode connected in parallel to the series circuit of the light emitting diode and the motor coil;
A circuit for preventing false lighting of a light emitting diode, comprising a diode for preventing false lighting having a forward voltage V _F2 lower than V _{F1 (V F2 <} V _F1 ).