JPS6040011Y2 - Muting control signal generation circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting control signal generation circuit, and more particularly to a muting control signal generation circuit when power is turned off in audio equipment.

In audio equipment, a so-called pop sound or the like is generated when the power is turned on or off, so a muting circuit is used to necessarily cut off the sound output.

In other words, when the power is turned on or off, the power supply voltage rises or falls with a certain time constant, during which the entire circuit becomes unstable and generates popping noises.
It is necessary to operate the muting circuit instantly in response to power on/off operations.

The above object can be achieved by providing a voltage rise detection circuit that detects the rise of the power supply voltage when the power is turned on and releases muting when this voltage reaches a predetermined value.

However, when the power is off, there is a method to obtain a muting control signal by detecting the rise of the power supply voltage. , it takes a long time for this voltage to drop below a predetermined value.

Therefore, the muting function when the power is turned off cannot be sufficient.

Therefore, there is a method of applying muting that takes advantage of the fact that the potential state of the line opposite to the ground line of the secondary winding of the power transformer immediately reaches the zero position when the power is turned off.
In equipment where a DC voltage such as double voltage or triple voltage is obtained from the output of the secondary winding of a transformer using a voltage doubler rectifier circuit, the connection configuration is such that the secondary winding is floating above the ground potential. This 2.
The potential of the next winding does not immediately become zero when the power is turned off, so complete muting cannot be obtained.

The purpose of the present invention is to provide a muting control signal generation circuit that can achieve good muting when the power is turned off in audio equipment having a power supply circuit with a floating configuration in which the secondary winding of the power transformer is floating from the ground W. be.

The muting control signal generation circuit of the present invention detects the AC ripple component at a predetermined circuit connection point in a rectifier circuit that rectifies the output of the secondary winding of a power transformer that is floating with respect to the ground potential. A detection signal is generated when the minute runs out, and this detection signal is used to apply muting.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which the output of the secondary winding L2 of the power transformer T is rectified by the double voltage rectifier circuit 1, and then the DC voltage is B
This shows the case where you get .

The voltage doubler rectifier circuit 1 has a series connection configuration of capacitors C1 and C2 and rectifier diodes D1 and D2, and the positive terminal of the capacitor C1 is connected to one end of the secondary winding L2 of the transformer T via the diode D□. The series connection point A of the capacitors C1 and C2 is directly connected to the other end of the secondary winding L2, so that the secondary winding is floating with respect to the ground potential.

゛ In order to detect the AC ripple at this series connection point A, the point A is connected to the ripple component detection circuit 3 via a DC blocking capacitor C3.

The detection circuit 3 consists of a circuit that smooths and rectifies the AC component at the circuit connection point A from which the DC component has been removed by the capacitor C3, and includes rectifier diodes D3. D, smoothing capacitor C
1 and resistors R□ and R2.

This detection output, which is a rectified and smoothed output, is an input to a muting control signal generation circuit 4, and this circuit 4 is connected between a switching transistor Q1 controlled by the detection output, this collector, and a stabilized power supply 1B. It is composed of a collector resistor provided and a diode D as a unidirectional element.

In this configuration, when the power switch S1 is on and AC power is applied to the primary winding L1 of the power transformer T□, an AC ripple component naturally occurs at the circuit connection point A in the rectifier circuit 1. Therefore, this ripple component is detected by the detection circuit 3, and a DC voltage corresponding to the ripple component is generated as the base control signal of the transistor Q.

Therefore, since the switching transistor Q□ is turned on, no signal is generated at the control output terminal OUT by the diode 8.

Next, when the power switch S□ is turned off, the AC ripple component at the circuit connection point A immediately disappears, so the detection output of the detection circuit 3 also becomes zero level, and the transistor Q□ is controlled to be turned off.

Therefore, the stabilized power supply 1B is led out to the output terminal OUT via the unidirectional diode D5.

This is because even if the power switch S1 is turned off, DC output is generated from the stabilizing circuit 1 for a predetermined period of time due to the action of the capacitor of the rectifying circuit 1, and after a predetermined period of time, the output of the stabilizing circuit 2 is also generated. Since the signal disappears, a muting control signal as shown at the output terminal ωπ in the figure is generated.

A predetermined muting circuit (not shown) may be activated by this output signal.

FIG. 2 is a diagram showing a part of another embodiment of the present invention, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.

In this example, a triple voltage rectifier circuit is used as the rectifier circuit 1, and another capacitor C5 is used in addition to the series-connected capacitors C1 and C2, and diodes D6 to D8 charge these capacitors q. This is a rectifier diode.

The signal is then input from a series connection point A between capacitors C1 and C2 to a ripple component detection circuit 3 shown in FIG. 1 via a DC blocking capacitor C3.

Also, the connection point A' between the capacitor C5 and the diode D6
Of course, the AC ripple command may be derived from .

It is clear that in this example as well, the same operation as in FIG. 1 is performed and the intended muting when the power is turned off becomes possible.

According to the present invention, in a device in which the secondary winding of the power transformer is floating with respect to the ground potential, muting can be performed accurately when the power is turned off with an extremely simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIG. 2 is a partial circuit diagram showing another embodiment of the present invention. Explanation of symbols of main parts, 1... Voltage doubler rectifier circuit,
3... Ripple component detection circuit, 4...
Muting control signal generation circuit, T...power transformer, h...secondary winding.

Claims (1)

[Scope of utility model registration request] Muting control for audio equipment comprising a power transformer having a secondary winding floating with respect to ground potential, and a rectifier circuit that rectifies the output of the secondary winding of the power transformer to obtain a DC voltage. The signal generating circuit includes ripple detection means for detecting a ripple component at a predetermined circuit connection point of the rectifier circuit and generating a predetermined detection signal when the ripple component disappears, and the predetermined detection signal A muting control signal generation circuit that generates a muting control signal using.