JPS6042499Y2 - Muting signal generation circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a muting signal generation circuit for muting pop sounds when power is turned on and off.

The object of the present invention is to provide a muting signal generation circuit for muting pop sounds when power is turned on and off with a simple configuration.The present invention will be explained below with reference to embodiments.

The figure is a circuit diagram of a muting signal generation circuit according to an embodiment of the present invention, and shows an example of application to a three-band car stereo device.

In the figure, 10B is a battery power supply terminal, 1 is a stabilized power supply circuit, and 2 is a receiving band changeover switch. Similarly, when the movable contact co is brought into contact with the fixed contact CB, the output voltage of the stabilized power supply circuit 1 is supplied to the tuner for medium wave broadcast reception, so that the output voltage of the circuit 1 is supplied. Movable contact C0
When the fixed contact Cc is brought into contact with the fixed contact Cc, the output voltage of the stabilized power supply circuit 1 is supplied to the tuner for receiving long wave broadcasting, and the band can be switched by switching the changeover switch 2. .

Therefore, for example, when the movable contact C0 is brought into contact with the fixed contact CA, FM broadcasting is received.

In the car stereo device configured as described above, when the selector switch 2 is changed over, pop noises are generated due to voltage fluctuations and the like.

Therefore, in one embodiment of the present invention, the fixed contact C8 of the change-over switch 2 is connected to the base of the transistor Tr□ and the base of the transistor Tr2 through a time constant circuit 3 in which a resistor R□ and a capacitor C□ are connected in series.

The transistors Tr and Tr2 are mutually complementary transistors, and for example, the transistor Tr1 is
The PN transistor Tr2 is a PNP transistor connected in parallel.

On the other hand, the output voltage of the movable contact CO, that is, the stabilized power supply circuit 1, is applied to the collectors of the transistors Tr1 and Tr2 through the resistor R2, and also to the base of the transistor Tr3.

The low loss B2 acts as a collector load for the transistors Tr1 and Tr2, and also acts as a bias resistance for the transistor Tr3.

In addition, the collector output of transistor Tr3 is connected to diode D.
1 to the muting switch circuit as a muting signal voltage.

Note that the resistor R3 is a collector load resistance of the transistor Tr3.

Further, a load is applied from the fixed contact CB through the diode D2, and a resistor R4 is connected from the fixed contact CB to the ground.
Connect.

Note that the variable resistor VR and the capacitor C2 are an equivalent resistance and a decoupling capacitor of a tuner for medium wave reception as a load.

The same applies to the equivalent resistances and decoupling capacitors of the FM and long-wave reception tuners, but they are omitted.

The output voltage of the stabilized power supply circuit 1 output from the fixed contact Ca of the changeover switch 2 changes every time the band is switched.

First, when the changeover switch 2 is switched from fixed contact CA to fixed contact CB, the output voltage from fixed contact CB changes from zero to the stabilized output voltage value, and when switched from fixed contact C8 to fixed contact Cc, the output voltage from fixed contact CB changes. The output voltage from varies from the regulated output voltage value to zero.

Also, from fixed contact CA to C9 side, and vice versa, fixed contact C6C
Even when switching to the A side, the fixed contact CB is always relayed.

Therefore, as described above, the output voltage from the fixed contact CB will vary every time the band is switched.

First, a case without the diode D2 and the resistor R4 will be described.

When the movable contact Co and the fixed contact CB are currently in contact, only for a certain period of time Wio determined by the time constant T, (R1xC□) of the time constant circuit 3 from the time when the movable contact C8 contacts the fixed contact CB. , transistors Tr□ and Tr
A voltage is applied to the base of 2.

Therefore, the transistor Tr□ is turned on only during the above-mentioned fixed time fa7rto, and the saturation voltage V(,2) of the transistor Tr□ is applied to the base of the transistor Tr3.

Therefore, in the transistor Tr3, the movable contact CO is the fixed contact C.
The transistor Tr3 is turned off for a predetermined period of time T1o from when it contacts B, and the collector voltage of the transistor Tr3 is output as a muting signal to the muting switch circuit through the diode D1, and muting is applied.

When the predetermined time T1o has elapsed, the transistor Tr
, returns to the off state, and the bias voltage is applied to the transistor Tr3 by the resistor R2, and the transistor Tr3 returns to the on state, and the muting signal disappears.

Furthermore, when the movable contact C8 is switched from contacting the fixed contact C8 to contacting the fixed contact CA or C8, the output voltage from the fixed contact CB fluctuates from the stabilized voltage to zero. .

When the output voltage from the fixed contact CB fluctuates in the zero direction, the charge stored in the capacitor C1 is transferred to the transistor Tr.
The emitter-base of 2 is discharged through the path of resistor R□.

The transistor Tr3 is turned on only during this discharge time T1o, the collector voltage of the transistor Tr3 rises, and is output as a muting signal to the muting switch circuit through the diode D1, so that muting takes place only during the discharge time T2o. Become.

Therefore, muting is applied only for a certain period of time T1o and T20 after the movable contact C8 is switched, and the occurrence of pop noise is suppressed.

In addition, by connecting the transistors Tr□ and Tr2 in parallel, the transistors Tr and T
This helps prevent r2 from reverse voltage breakdown.

However, since there is no diode D2 and resistor R1, when the changeover switch 2 is switched from fixed contact CA to C, or from Co to CB, the output voltage from fixed contact CB will change due to the time constant of capacitor C2 and variable resistor VR. The rising waveform becomes dull.

Also, when the changeover switch 2 is changed from the contact CB to CA and from CB to Cc, the falling waveform of the output voltage from the fixed contact CB is also blunted due to the discharge time constant of the capacitor C2 and the variable resistor 8.

Therefore, the time when the transistor Tr□ turns on is delayed from the time when the selector switch 2 is switched, and the transistor Tr2
The time when the switch is turned on is delayed from when the changeover switch 2 is switched, and there may be cases where the pop sound when the changeover switch 2 is switched cannot be completely removed.

Here, since the diode D2 and the resistor R4 are connected, at the moment when the changeover switch 2 is switched and the movable contact Co contacts the fixed contact CB, the forward voltage drop of the fixed contact CB is at least equal to the forward voltage drop of the diode D2. The output voltage rises and turns on the transistor Tr1.

Also, move the movable contact CO from the fixed contact CB to the other fixed contact C.
When switching to A or C8, the output voltage from fixed contact CB is approximately R4×vo/(R1+R4
), the capacitor C1 immediately starts discharging and turns on the transistor Tr2.

Here, ■c is the charging voltage of the capacitor C0.

Therefore, the delay in the operation of transistors Tr, Tr2 due to the load effect of the load connected to fixed contact C8 is eliminated.
A muting signal is generated simultaneously with switching of the changeover switch 2.

For this reason, muting is applied at the same time as the selector switch 2 is switched, and pop noises can be completely suppressed.

As explained above, according to the present invention, the muting signal can be generated for a predetermined time without delay from the time when the power is turned on or off by switching the changeover switch, and the generation of pop noise can be suppressed.

Further, the circuit configuration for this purpose is also simple.

In addition, as mentioned above, if the output voltage from the fixed contact of the center that always passes through during switching is detected, it is possible to generate a muting signal for band switching, and only one muting signal generation circuit is required for each band switching. A muting signal can be obtained.

[Brief explanation of the drawing]

The figure is a circuit diagram of an embodiment of the present invention. 1... Stabilized power supply circuit, 2... Changeover switch, 3... Time constant circuit, Tr□, Tr2 and Tr3... Transistor.

Claims (1)

[Scope of utility model registration request] A changeover switch has at least two fixed contacts to which a load such as a tuner is connected, and supplies a power supply voltage to the load by switching a movable contact; a first transistor connected in parallel and complementary to the first transistor; A second transistor is connected between the bases of the first and second transistors and a fixed contact through which the movable contact of the changeover switch always passes each time the movable contact of the changeover switch is switched, and is connected to a power supply via the changeover switch. a time constant circuit consisting of a first resistor and a capacitor to which a voltage is supplied;
a third transistor that is driven by the output of the transistor to perform on/off operations; a diode connected between the power supply terminal and the load; and a diode connected between the power supply terminal and the reference terminals of the first and second transistors. A muting signal generating circuit comprising: a second resistor connected between said third transistors, and an output of said third transistor being used as a muting signal.