JPH0212737Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a muting drive circuit for a cassette deck, and particularly to one that utilizes the output of a logic gate circuit.

(Prior art) Conventionally, when the power switch is turned on, the muting semiconductor element is turned on to short-circuit the output signal, and after a predetermined period of time has elapsed after mutating,
Muting is canceled by turning off the muting semiconductor element. When the power switch is turned off, the muting semiconductor element is immediately turned on.
The system uses muting to eliminate click noise.

However, in the above-mentioned conventional muting drive circuit, it takes some time for the muting semiconductor element to be completely turned on immediately after the power switch is turned on, and there is a possibility of outputting click noise when the power switch is turned on. In addition, since there are no parts that are shared with other circuits and the muting circuit is configured independently, it has the disadvantage that the number of parts is large and the circuit is complicated.

(Purpose of the invention) The purpose of the invention is to eliminate the above-mentioned drawbacks of the conventional circuit, completely eliminate click noise when turning on and off the power switch, and simplify the circuit configuration by using this circuit in common with other circuits. In addition to
An object of the present invention is to provide a muting drive circuit using a C-MOS logic gate circuit with low power consumption.

(Structure of the idea) The configuration of the present invention will be explained using FIG. 1.

C
-supplied to the input terminal a of the MOS logic gate circuit 7;
From battery 1 to ignition SW2 and
Connect the power source led through POWER SW3 to C-
Connected to the input terminal b of the MOS logic gate circuit 7,
The output of the C-MOS logic gate circuit 7 is inverted by the C-MOS logic gate circuit 8, and the output is connected to the drive terminal CE (chip enable) of the microcomputer or
Connect to INH (inhibit). The signal path connected to CE (INH) is further connected to the input terminal a of the C-MOS logic gate circuit 15 via a time constant circuit of a resistor 9 and a capacitor 10, and the ignition signal is connected to the input terminal a of the C-MOS logic gate circuit 15.
The signal path led from SW2 to POWER SW3 is further connected to an input terminal b of a C-MOS logic gate circuit 15 via a time constant circuit of a resistor 13 and a capacitor 14. The input terminals a and b of the C-MOS logic gate circuit 15 are connected to the anode sides of the diodes 11 and 12, respectively, and the cathodes of both are connected to the output line of the POWER SW 3, and the resistor 1
It is grounded via 6. The output of the C-MOS logic gate circuit 15 becomes the output of the muting drive circuit.

(Operation of the invention) The circuit of the invention is shown in Fig. 1, and the time chart of the potential at each point A to F in the circuit diagram is shown in Fig. 2 a and b.
This is shown and explained below.

The C-MOS logic gate circuit 15 is a system
Muting output is always generated when OFF (point F), and when ignition SW2 is turned ON (A
point), the input terminal b of the C-MOS logic gate circuit 15 by the time constant circuit of the resistor 13 and the capacitor 14.
gradually becomes H, and by inserting a cassette tape, POWER SW3 is also turned on, and C-MOS
Set the input terminal b of the logic gate circuit 7 to H (B
point). Since the input terminal a of the C-MOS logic gate circuit 7 is always backed up, it is driven at the same time as the input terminal b is applied, and the output of the C-MOS logic gate circuit 7 is inverted from H to L. The inverted output is further inverted by the C-MOS logic gate circuit 8 and becomes H (point C). When point C becomes H, the control terminal CE (INH) of the microcomputer turns ON, and
The microcomputer is driven. The above circuit will work as a microcomputer drive circuit. Furthermore, the microcontroller
The output signal led to the CE (INH) terminal gradually becomes H (point D) by the time constant circuit of the resistor 9 and the capacitor 10, and is applied to the input terminal a of the C-MOS logic gate circuit 15. Input terminal b of the C-MOS logic gate circuit is turned on when ignition SW2 is turned on.
Since it has already become H (point E), C-
The MOS logic gate circuit 15 is delayed by the time constant circuit of the resistor 9 and the capacitor 10 from when the POWER SW 3 is turned on, and changes the mute output signal from H to L.
(point F) and cancel mutating.

Next, POWER SW3 or ignition SW2
When the input terminals a (point D) and b (point E) of the logic gate circuit 15 are turned off, the diodes 11 and 1
2, the input terminals a and b of the C-MOS logic gate circuit 15 immediately become L, the output is inverted to H (point F), and muting occurs.

Figure 2b shows a time chart of the potential at each point A to F in Figure 1 when the ignition SW2 is turned ON and OFF while the POWER SW3 is in the ON state, and in particular, the time chart for the points D to F. As is clear from the chart, by providing time constant circuits in each of the logic gate circuits 7, 8 and 15, there is no click noise even when the ignition switch 2 is turned on and off while the power switch 3 is on. does not occur, and 2
By aligning the delay times of the two time constant circuits, the
This makes it possible to make the time required to cancel muting the same as when turning POWER SW2 ON and OFF.

In the conventional technology, since muting is applied at the same time as the power switch is turned on, it takes some time for the muting transistor to turn on, and this time difference may cause a clicking noise to be output when the power switch is turned on.

In this invention, since muting is applied from the OFF state of the system, it is possible to completely eliminate the clicking noise when the power switch is turned ON. Furthermore, it is no longer affected by the instability of the rising edge of the muting transistor.
Click noise when the power is turned off can also be eliminated by preventing the stabilized power supply output from dropping suddenly.

In addition, since the circuit configuration is shared with the microcomputer drive circuit, the number of components is small, and C-MOS logic gate circuits are used for elements that require backup current and elements that constantly output muting signals when the system is OFF, resulting in low consumption. It has the advantage of requiring very little current.

Furthermore, in this invention, when the cassette is inserted and POWER SW3 is in the ON state, the ignition is turned on.
No clicking noise occurs even when SW2 is turned on and off, making it ideal as a muting drive circuit for automobile stereos.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 shows a time chart of the potentials at points A to F in FIG. Then, the POWER SW is turned on. Figure 2b shows the state where the POWER SW is turned on.
After that, turn on the ignition switch,
Alternatively, it is a diagram showing a state in which they are turned on at the same time. 2...Ignition SW, 3...POWER
SW, 7, 8...C-MOS logic gate circuit for microcomputer drive, 9...Resistor for time constant circuit, 10...
Capacitor for time constant circuit, 11, 12...Discharging diode, 15...C-MOS logic gate circuit for generating muting signal.

Claims (1)

[Scope of utility model registration request] a first logic gate circuit connected to a power supply via an ignition switch and generating a muting signal; a power switch connected after the ignition switch and turned on when a cassette is inserted; A muting drive circuit comprising a second logic gate circuit connected to the circuit and driving the first logic gate circuit, the first logic gate circuit always generating a muting output when the power switch is OFF, and the second logic gate circuit. a first time constant circuit connected between the input signal path of the gate circuit and the ignition switch and in parallel with the power switch; an output signal path of the second logic gate circuit; A muting drive circuit comprising: a second time constant circuit provided between the input signal path and the input signal path.