JPS584250Y2 - transient killer circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a transient killer circuit in an audio amplifier for eliminating shock noise when the power is turned on.

The transient killer circuit in conventional audio amplifiers is a method that short-circuits the input signal line of the audio amplifier for a certain period of time immediately after the power is turned on and off, or a method that connects the amplifier output and the load to the output side of the audio amplifier 1 as shown in (speaker)
A relay 2 is installed to intermittent the
By keeping the output signal line open for a certain period of time immediately after, the shock noise when the power is turned on is removed, and by immediately opening the relay 2 and opening the output signal line immediately after the power is turned off. , power off
A method was adopted to eliminate the shock noise caused by the time.

The present invention provides a novel transient killer circuit that is fundamentally different from such conventional methods and has an extremely simple configuration.

The present invention is a negative feedback amplifier in which the amplification gain is controlled by the amount of feedback, when the feedback amount is turned on.

It is characterized in that by increasing the amplification gain for a certain period of time immediately after turning off or stopping the power supply, the amplification gain is significantly lowered and the shock noise when the power is turned on is substantially eliminated.

A typical embodiment will be described below with reference to FIG.

FIG. 2 shows an embodiment that eliminates the shock sound when the power is turned on.

In the figure, reference numeral 3 denotes a well-known negative feedback type audio amplifier of two power supply type, the output of which is fed back to the input side through a feedback circuit 4.

That is, feedback resistors R2 and R3 are connected in series to the output terminal of the amplifier 3, and the ground terminal of the feedback resistor R3 is configured to be grounded through a capacitor and a switchable transistor Q3, and the feedback resistor R2t connected in series is
The connection point of Ra is input to the input transistor Q1 of the differential amplifier.
The amplifier output is connected to the base of the other transistor Q2 paired with the transistor Q2, and the amplifier output is divided by a feedback resistor R2tRs and fed back to the input side.

The base of the switching transistor Q3 is supplied with a 10B power source obtained from the power supply circuit 6.
As provided as its emitter output through 4,
The emitter of the control transistor Q4 is connected, and its collector is connected to the power supply circuit 6.

The base of this control transistor Q4 is connected to the power supply O
When the transistor Q3 is connected in parallel to the power supply circuit 6 and has a relatively large time constant (several tens of seconds) so that the switching transistor Q3 is kept in the cut-off state for a certain period of time immediately after N and its emitter output is used to keep the switching transistor Q3 in the cut-off state. It is connected to a connection point between a series-connected resistor R1 and a capacitor C1 that constitute a constant circuit (charging circuit) 5, and is configured to be controlled by the terminal voltage (charging voltage) of this capacitor C1.

That is, the switching transistor Q3 maintains the cut-off state for a certain period of time immediately after the power is turned on by the output of the time constant circuit 5 and the control transistor Q4 controlled by the time constant circuit 5, and maintains the ground side terminal of the feedback resistor R3 in the open state. ,
Thereafter, conduction is established, and the ground terminal of the feedback resistor R3 is controlled to be grounded through the capacitor and the switching transistor Q3.

According to the above configuration, when the power switch 7 is turned on, 10B power is supplied to the time constant circuit 5, and the capacitor C1 is charged through the resistor R1, and the terminal voltage thereof gradually increases. The emitter potential of Q4 also gradually increases.

Then, after a certain period of time has elapsed, the terminal voltage of capacitor C1 reaches a predetermined voltage, and the emitter potential of control transistor TIN also reaches a predetermined voltage.
The ground side terminal of No. 3 is grounded through a capacitor and a switching transistor Q3.

That is, the ground terminal of the feedback resistor R3 is held open for a certain period of time immediately after the power is turned on, and the output of the amplifier 3 is fed back to the input side only through the feedback resistor R2.
In other words, since the amount of feedback is significantly larger than during normal operation (set to 25 dB in the example), the amplification gain of amplifier 3 is temporarily significantly reduced, and the shock noise when the power is turned on is significantly suppressed and is virtually ignored. It can be removed as much as possible.

Then, after a certain period of time has elapsed, when the ground side terminal of the feedback resistor R3 is grounded through the capacitor and the switching transistor Q3, the output of the amplifier 3 is connected to the feedback resistor R2t R.
Since the voltage is divided by s and fed back to the input side, a predetermined amplification gain is obtained and normal operation is achieved.

As described above, the present invention reduces the feedback amount of the negative feedback amplifier to the power supply O
Not only is this a new type of transient killer circuit that significantly reduces the amplification gain by increasing the amplitude for a certain period of time immediately after N, virtually eliminating the shock sound when the power is turned on, but it also uses a feedback resistor that controls the amount of feedback. It has the practical advantage of being an extremely simple configuration that only requires switching.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of a conventional transient xy circuit, and FIG. 2 is a diagram showing the configuration of the transient killer circuit of the present invention. 3 is an amplifier, 4 is a feedback circuit, 6 is a power supply circuit, 5 is a time constant circuit, R2t R3 is a feedback resistor, Q3 is a switching transistor, R1 is a resistor, and C1 is a capacitor.

Claims (1)

[Scope of utility model registration request] In a negative feedback amplifier in which the amplification gain is controlled by the amount of feedback, a feedback resistor R2°R3 is connected in series to the output terminal of the amplifier 3, and the feedback is fed back to the input side from the connection point of both feedback resistors R2 and R3. A feedback circuit 4 configured to be grounded through the ground side terminal of the resistor R3 and a switching transistor Q3, and a power supply circuit 6 that obtains a predetermined power supply voltage.
A time constant circuit 5 is provided, which charges the power supplied from the power supply circuit 6 through a resistor R1 to a capacitor C1 connected in series with the resistor R1, and controls the switching transistor Q3 to turn on and off based on the terminal voltage of the capacitor C1. , a transient characterized in that the switching transistor Q3 is held in a cut-off state for a certain period of time immediately after the power is turned on, and the ground side terminal of the feedback resistor R3 is opened to increase the amount of feedback, thereby reducing the amplification gain. killer circuit.