JPH0212758Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention relates to an audio/alarm switching circuit used, for example, in a radio with a clock alarm.

(b) Prior art and its problems In general, in audio equipment such as radios and televisions, while deriving an audio output signal,
When a time signal or some kind of notification event occurs,
Some devices have an alarm function to notify this and output a warning sound or the like.

The audio/alarm switching circuit used in this type of equipment uses a phase-shifted oscillator as an alarm sound generating circuit. Phase-shifted oscillators are used because their circuit configuration is simpler than multivibrators and LC oscillators, but in any case, they are unstable due to changes in ambient temperature, and the pitch of the oscillator remains constant. There was a problem that it wasn't. Furthermore, this type of conventional audio/alarm switching circuit is constructed by separately providing a circuit for stabilizing the oscillation circuit in addition to an alarm oscillator, audio/alarm switching circuit, audio output, and mute circuit. Therefore, the disadvantage was that the circuit as a whole became complicated.

(c) Purpose of the invention Therefore, the purpose of this invention is to create an audio alarm whose circuit can be constructed relatively easily, which does not operate unstable due to temperature etc., and which can output an alarm sound with a constant pitch. The present invention provides a switching circuit.

(d) Structure of the invention In order to achieve the above object, the audio/alarm switching circuit of this invention includes a phase-shifting oscillator consisting of a first transistor and a phase-shifting circuit, a switch for switching audio and alarm, and a switch for switching between audio and alarm. When turned on to the audio side, it is turned off, and when turned on to the alarm side, it is turned on, muting the audio signal, and biasing the base of the first transistor by the voltage between the base and emitter, and shifting the phase. The second transistor energizes the first transistor of the phase-shifted oscillator, and an output circuit that derives either an audio signal or an oscillation signal from the phase-shifted oscillator.

In this audio/alarm switching circuit, when the switch is turned on to the audio side, the second
The transistor is turned off, the audio signal is directly output from the output circuit, and the oscillator stops oscillating. When the switch is turned to the alarm side, the second transistor Q2 is turned on, muting the audio signal, and
A bias current flows through the first transistor of the phase-shifted oscillator due to the voltage VBE of the second transistor, the phase-shifted oscillator oscillates, and its output is outputted as an alarm signal from the output circuit. Also, the VBE of the second transistor decreases as the temperature rises,
Since it operates in the direction of lowering the base current of the first transistor, it compensates for the increase in the collector current of the first transistor due to temperature rise, and it is possible to obtain a stable oscillator output even with respect to temperature. .

(e) Examples This invention will be explained in more detail below using examples.

The drawing shows one embodiment of this invention.
It is a connection diagram of an alarm switching circuit.

This embodiment audio/alarm switching circuit is as follows:
A phase-shifted oscillator 1, a switch 2 for switching between alarm and audio, a mute circuit 3 for muting the audio signal and energizing the phase-shifting oscillator 1, and deriving an audio signal or an oscillation signal from the phase-shifting oscillator 1. It is composed of an output circuit 4 that performs the following steps.

The phase-shifting oscillator 1 includes an NPN transistor (first transistor) Q1, capacitors C1, C2, C3 and a resistor R1, which constitute a phase-shifting circuit.
R2, this phase-shifted oscillator 1
The circuit itself is similar to a well-known circuit.

Switch 2 can be switched between alarm (ALARM) and audio (AUDIO), and when common terminal C is turned on to the alarm side,
Power supply voltage Vcc passes through switch 2 to mute circuit 3
When the common terminal C is connected to the audio side, no voltage is applied to the mute circuit 3 via the switch 2, and the mute circuit 3 is opened. Although the switch 2 is shown schematically, it may use either a contact or non-contact circuit, and may be operated manually or automatically in response to some control signal. Good too.

The mute circuit 3 has an audio signal input terminal 5
capacitor C4, resistor R4, transistor (second transistor) Q2 whose emitter is connected to ground, one end connected to common terminal C of switch 2, and the other end connected to the base of transistor Q2. The base of this transistor Q2 is connected to the transistor Q1 of the phase-shifted oscillator 1 via the resistor R6.
connected to the base of.

The output circuit 4 also includes a signal output terminal 6, a resistor R
7, R8, a capacitor C5, etc., one end of the resistor R7 is connected to the collector of the transistor Q2, and the other end is connected to the output terminal 6. Further, one end of the capacitor C5 is connected to the collector of the transistor Q1 of the phase-shifted oscillator 1, and is also connected to the output terminal 6 via a resistor R8.

Next, the operation of the embodiment circuit connected as described above will be explained.

First, when the common terminal C of the switch 2 is connected to the audio side, the base of the transistor Q2 is in an open state, so it is off, and therefore the audio signal input to the input terminal 5 is
It is directly derived from the output terminal 6 via the capacitor C4 and resistors R4 and R7. On the other hand, since the transistor Q2 is off, the bias current does not flow through the transistor Q1 of the phase-shifted oscillator 1, and the phase-shifted oscillator 1 does not oscillate.

On the other hand, when the common terminal C of switch 2 is turned on to the alarm side, the power supply voltage Vcc is applied to the base of transistor Q2 via switch 2 and resistor R5, so transistor Q2 is turned on, and therefore the input The audio signal input to the terminal 5 is muted because it is pulled to the low level on the collector side of the transistor Q2 of the resistor R4.

Furthermore, base bias is applied to the transistor Q1 of the phase-shifting oscillator 1 by the base-emitter voltage VBE of the transistor Q2, and the oscillation of the phase-shifting oscillator 1 is started. As a result, the oscillation signal of the phase-shifted oscillator 1 is output from the output terminal 6 from the collector of the transistor Q1 via the capacitor C5 and the resistor R8. If an output amplifier, a speaker, etc. are connected to the output terminal 6, the oscillation signal of the phase-shifted oscillator 1 will be derived as an alarm signal.

In addition, in general, the collector current of a transistor IC
changes with temperature. That is, as the temperature rises, the DC amplification factor increases and the collector current IC increases. However, in this embodiment circuit, as the temperature rises, the base-emitter voltage VBE of transistor Q2 decreases, which acts to suppress the current of transistor Q1, and as a result, suppresses the increase in collector current IC and performs temperature compensation. become.

(f) Effects of the invention According to this invention, the base-emitter voltage VBE of the second transistor is used to energize the phase-shifted oscillator, so it is stable against changes in ambient temperature. You can get an alarm circuit. Furthermore, since the transistor for stabilizing the phase-shifted oscillator is also used for muting the audio signal, a very simple configuration can be obtained as a whole circuit.

Moreover, the switch can directly turn on and off the DC voltage.
By turning off, the alarm and audio signals can be switched, which simplifies the circuit configuration.

In addition, a phase-shifted oscillator is used to generate the alarm signal, and other circuit parts can be composed of transistors, resistors, and transistors.
An audio/alarm switching circuit suitable for IC implementation can be obtained.

[Brief explanation of the drawing]

The drawing shows one embodiment of this invention.
It is a connection diagram of an alarm switching circuit. 1: phase-shifted oscillator, 2: switch for audio/alarm switching, 3: mute circuit, 4: output circuit, Q1: first transistor, Q2: second transistor.

Claims (1)

[Scope of utility model registration request] A phase-shifting oscillator consisting of a first transistor and a phase-shifting circuit, and a switch that switches between audio and alarm.When this switch is turned on to the audio side, it is turned off, and when it is turned on to the alarm side, it is turned on and outputs the audio signal. Along with Miyuto,
a second transistor that base-biases the first transistor by a base-emitter voltage and energizes the first transistor of the phase-shifting oscillator; and an audio signal and oscillation from the phase-shifting oscillator. An audio alarm switching circuit consisting of an output circuit that derives one of the signals.