JPS60185409A - Muting circuit - Google Patents

Abstract

PURPOSE:To improve the reliability and to miniaturize the titled circuit by using a circuit for time constant circuit at power supply ON and a capacitor for integration circuit at power supply OFF in common so as to constitute an electronic muting circuit. CONSTITUTION:A constant current source 1a charges a capacitor C at power ON, a level detection circuit 5 detects a potential at a point A, and when the potential reaches a voltage V1 decided by a muting time t1, an output signal is generated from a level detection circuit 5 and a Schmitt circuit 6 and operates gate circuits 2a, 2b nearly at the same time. Thus, the capacitor C is charged from a constant current source 1b in addition to the constant current source 1a by the gate circuit 2 and the potential rises with a larger slope. Further, an output of a pulse generating cirlcuit 3 is inputted to the gate circuit 2 by the operation of the gate circuit 2b and the output reaches a DC voltage +Vcc while being charged at a power supply voltage 0V. The gate circuit 2b is operated at power OFF even with a voltage of the muting level voltage V1, a signal of the pulse generating cirlcuit 3 is inputted to the gate circuit 2 so as to discharge the capacitor C.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a muting circuit that operates when a power supply voltage is turned on or off, and particularly to a circuit for obtaining a micoding output.

Conventionally, in audio signal amplifiers such as stereo amplifiers, a separate switch from the power switch was installed in the mi-coating circuit to prevent transient noise that occurs when the power is turned on and off, or the circuit shown in Figure 1 was used. The all-electronic circuit shown was used. That is, in FIG. 1, C1 is a muting time constant capacitor, and C2 is an integrating capacitor. [・When the power is turned on to the lance T, a negative DC voltage is generated on the secondary side of the lance T by the diode D,
The base of the transistor Q1 is kept at a sufficiently low potential through the resistors R3 and R4, the transistors Q1 and Q1 are turned off, and the capacitor C1 for the micoating time constant is charged, and the potential at point 2 is determined by the time constant determined by the resistor R1. "Stand by"
Two. The muting output is detected from the 0 point, and the circuit is activated when it rises to a predetermined voltage. Further, when the power is turned off, the negative DC voltage disappears, and the integrating capacitor C2 is discharged via the resistors R2, R3, and R4. This discharge current turns on the transistor Q1, and the time constant capacitor C1 is immediately discharged, thereby preventing transient noise.

However, since the circuit in Figure 1 is entirely electronic, it is reliable but requires one capacitor each for time constant and integration, and the circuit operates from the power on for the time constant capacitor. Since it takes several seconds for the power to turn off, a device with a human body size is required, and the operating time when the power is turned off is not sufficiently short. In addition, a device with a separate switch not only requires two capacitors, but also has various problems such as the capacity, durability, and selection of the mounting position of the switch.

The present invention solves the above-mentioned problems, and embodiments thereof will be described below with reference to the drawings.

Fig. 2 is a diagram showing the operating principle of the present invention. In Fig. 2, 1 is a constant current source that charges the capacitor C, and 3 detects the L/L level of the power supply voltage applied to the 0 point and compares it with the power supply frequency. A pulse generating circuit 2 generates a pulse for a sufficiently short period of time, and 2 is a gate circuit operated by a signal from the pulse generating circuit 3. One end is connected to the 0 point via a resistor R, and the other end is connected to a ground point. ing.

When the power supply is turned on and the power supply voltage shown in FIG. 3(A) is applied to the 0 point, the -th pulse is output from the pulse generating circuit 3, and the circuits 1 to 2 are turned on. Thereafter, the pulse generating circuit 3 generates a pulse at a frequency twice the power supply frequency for the zero point output voltage as shown in FIG. 3(b).

On the other hand, the point potential rises linearly to the DC voltage +VCC due to the constant current source 1, but since the gate circuit 2 causes discharge to occur in a very short time via the resistor R when the power supply voltage is OV, as shown in FIG. )become that way. Here, the miscoating level is detected from the 0 point, and a predetermined circuit is set to operate when the voltage reaches or exceeds the voltage V1 determined by the operating time t1. (Ti is usually several seconds as shown in above) If the power is turned off at 13 in Figure 3, the pulse 3- generating circuit 3 will continue to be powered for a predetermined period of time, so it will maintain its operating state. It detects zero volts of the power supply and outputs a signal. During this period, Goo 1~Circuit 2
is in the on state, and the charge on the capacitor C is rapidly discharged through the resistor.

FIG. 4 shows an embodiment of the present invention, and the same parts as in FIG. 2 are denoted by the same reference numerals. 1a and 1b are constant current sources for charging the capacitor C, and 4 is a signal generation circuit. It consists of Schmitt circuits 1 to 6 which generate triggered signals. or,
Reference numerals 2a and 21) are gate circuits which operate depending on the outputs of the level detection circuit 5 and Schmitt circuit 6, respectively.

When the power is turned on, the capacitor C is charged by the constant current source 1a, and the level detection circuit 5 detects the thermal potential. An output signal is generated from the circuit 6, and the gate circuits 2-4 = a and 2b are operated almost simultaneously. Therefore, by gate circuit 2, capacitor C is connected to constant current source 1b in addition to constant current source 1a.
Charging is also carried out from the top, and it rises due to an even larger slope. In addition, when circuits 1 to 2b operate, the output of the repulse YV circuit 3 [Fig. 5 (b)] is input to the gate circuit 2, and as described above, when the power supply voltage is While discharging, the DC voltage rises to +VCC [Figure 5 (c)]. When the power is turned off, the output of the level detection circuit 5 is generated when the muting level voltage V1 or less is reached, and the gate circuit 2a is opened, so no current flows from the constant current source 1b, but the Schmitt circuit 6 is used as a level detection circuit. Since the output is generated due to the hysteresis characteristic until the output of circuit 5 drops to a certain set level, the gate circuit 2b operates even when the muting level voltage v1 is lower than that, and therefore the signal of the pulse generation circuit 3 is (above), the capacitor C is discharged. In FIG. 4, the Schmitt circuit 6 may be replaced with a flip-flop to perform the same operation.

As described above, according to the present invention, since it is a purely electronic system that does not use mechanical means such as switches, reliability is not only improved, but also the constant circuit capacitor when the power is turned on and the Since one integral circuit capacitor can be used in common, the cost is low, and everything except the capacitor can be incorporated into the IC, making it easy to reduce the size of the integrated circuit. In addition, it is desirable that the capacitor has a small capacity for use in an integrating circuit, and even when used as a time constant, the slope of the rise can be changed by varying the current value of the constant current source.
There is no need to use large capacity capacitors compared to conventional methods. Furthermore, when the pulse width of the pulse generating circuit cannot be narrowed sufficiently compared to the power supply frequency, the rising voltage during charging may become smaller than the falling voltage during discharging, and the capacitor charging voltage may not rise. According to this, the signal generating circuit 4 and the gate circuit 21) do not input pulses to the circuits 1 to 2 until the muting voltage is reached, so the inconvenience described in (a) above is eliminated.

[Brief explanation of the drawing]

Fig. 1 shows a conventional micoding circuit, Fig. 2 shows a circuit showing the operating principle of the present invention, Fig. 3 shows the operating waveforms of Fig. 2, and Fig. 4 shows a circuit showing the operating principle of the present invention.
The figure shows an embodiment of the present invention, and FIG. 5 shows the operating waveforms of FIG. 4. 1.1a, 1b... Constant current source 2.2a, 2b... Goo 1-circuit 3...
...Pulse generation circuit 4...Signal generation circuit 5.
...Level detection circuit 6 ...Schmidts 1
Circuit patent applicant Pioneer Corporation 7- 10Vcc 8- 3rd decoy

Claims (2)

[Claims] (1) In a power supply muting circuit operated by a capacitor charging voltage, the first circuit that charges the capacitor→no
and a second current level, a pulse generation circuit that generates a pulse at the zero level of the AC power supply voltage, and a signal generation circuit that detects the charging voltage of the capacitor and generates an output at a predetermined potential. a first gate circuit that controls signal transmission of the pulse generation circuit by the output of the signal generation circuit;
a second gate circuit that is turned on by the output signal of the circuit and controls the discharging of the charge charged in the capacitor; and a second gate circuit that controls the output of the second constant current source to the condenser 4 by the output of the signal generation circuit. A third goo 1-circuit and a muting circuit. (2) The muting circuit according to claim 1, wherein the signal generating circuit is comprised of a level sending circuit and a signal transmitting circuit.