JPS6291007A - Power source voltage detecting circuit - Google Patents

Abstract

PURPOSE:To ensure muting at power source application and power source interruption by using a Zener current flowing to a Zener diode provided to a constant voltage circuit so as to detect power source voltage fluctuation. CONSTITUTION:A detection resistor 13 connected to an anode of a Zener diode 9 of a constant voltage circuit and detecting a current flowing to the Zener diode 9 and a common emitter detection transistor (TR) 14 whose base is connected to a connection point A between the anode of the Zener diode 9 and the detection resistor 13 and whose collector receives a power source voltage are provided. In detecting the Zener current flowing to the Zener diode 9, the power source voltage fluctuation is detected while a constant voltage is generated from the constant voltage circuit, the TR 14 is turned on when the power source voltage is a prescribed value or over and the TR 14 is turned of when the power source voltage is below the prescribed value.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Industrial Application Field The present invention relates to a power supply voltage detection circuit that detects the power supply voltage of a device equipped with a constant voltage circuit. The present invention relates to a power supply voltage detection circuit suitable for use in a muting circuit for minimizing noise.

(B) Prior Art It is known that noise is generated due to transient phenomena when power is turned on or turned off in an audio device.

Therefore, for example, the sound equipment is
A meeting circuit is provided which operates when the power is turned on and when the power is turned off, as described in the above publication. This type of muting circuit includes a muting control means that detects voltage fluctuations and controls the on/off of a common-emitter muting transistor whose collector is connected to a signal transmission path through which an acoustic signal is transmitted. The muting control means turns on the muting transistor when the power is turned on and when the power is turned off to prevent noise from being emitted from the speaker, so-called muting.

el Problems that the invention attempts to solveHowever,
The muting control means provided in the above-mentioned meeting circuit controls the muting transistor by detecting fluctuations in the operating voltage of the acoustic device, which is regulated to a constant voltage via the constant voltage circuit. Due to the time constant of the voltage circuit, the muting operation is not performed immediately when the power is turned on or turned off, and noise may occur until the muting operation is completed. However, if the muting transistor is controlled by detecting fluctuations in the unregulated power supply voltage from the power supply circuit using the miniting control means, the muting transistor will not be affected by the ripple component superimposed on the power supply voltage. This is not desirable as there is a risk that the system may malfunction.

The present invention aims to provide a power supply voltage detection circuit suitable for constructing a muting circuit which has been constructed in view of the above points.

A power supply voltage detection circuit according to the present invention includes a transistor in which a collector-emitter path is inserted in a power supply line and a Zener diode for controlling the collector current of the transistor. a constant voltage circuit for constant voltage; a detection resistor connected to the anode of the Zener diode to detect the current flowing through the Zener diode; and a base connected to the connection point between the anode of the Zener diode and the detection resistor. The device is characterized in that it is provided with a common emitter type detection transistor whose collector is supplied with a power supply voltage 7JD.

(4) Function The present invention detects fluctuations in the power supply voltage while a constant voltage is being generated from the constant voltage circuit by detecting the Zener current flowing through the Zener diode provided in the constant voltage circuit, and The detection transistor is turned on when the voltage is greater than a predetermined value, and the detection transistor is turned off when the power supply voltage is less than a predetermined value.

(v) Example The diagram shows an example in which the power supply voltage detection circuit according to the present invention is used in a radio receiver, where ■ indicates an AC power supply (2), a power switch (3), a power transformer (4), and a rectifier circuit. (5)
The power supply circuit consists of a power supply line (transistor (8) with a collector-emitter path inserted in the blade, a Zener diode (9) whose cathode is connected to the base of the transistor (8), and the Zener diode (9). ) to gradually increase the voltage applied to the cathode of the zener diode (9) and to prevent noise from occurring when the Zener diode (9) is turned on. The voltage circuit (3) is a detection resistor inserted between the anode and ground of the Zener diode (9) of the constant voltage circuit (A9), and the α6 base is connected to the Zener diode (9).
The collector is connected to the input terminal B of the constant voltage circuit 9) via the resistor α9 at the connection point A between the anode of 9) and the detection resistor α3).
A common emitter detection transistor connected to (1
0 is a tuner circuit that converts the radio waves received by the antenna into an intermediate frequency, selectively amplifies them, detects them, and extracts the acoustic signal from the output terminal α. (19 is a collector-emitter path between the output terminal U and the ground. A muting transistor is inserted, ■ is a driving transistor that drives the muting transistor, and ri is a resistor (22 and @) and a capacitor (product), and is used to control the on-time of the driving transistor (■). The constant circuit (to) is a control transistor whose base is connected to the collector of the detection transistor α and whose collector is connected to the time constant circuit, and which controls the drive transistor (2).Here,
The tuner circuit (10 indicates a desired broadcast frequency) is stored in advance in a memory (G) constituted by an integrated circuit provided in the tuner circuit C16, and corresponds to the memory in which the desired broadcast frequency is stored at the time of reception. It has a preset tuning function that allows you to receive the desired broadcast frequency by simply pressing a channel switch (not shown).
6) is provided with an inhibit signal (5) which inhibits the write operation of the stored contents of the memory 126) by marking the rLJ signal (inhibitory signal). Further, the tuner circuit west has a muting output terminal @ which generates an rHJ signal when changing the number of broadcasting station waves to be shifted from the - channel to another channel.

First, minting when the power is turned on will be explained.

Now, when the power switch (3) is turned on, the power supply circuit generates a positive power supply voltage at the output terminal. The power supply voltage is smoothed by a capacitor (c) and is also connected to the input terminal B of the constant voltage circuit
Therefore, the capacitor aυ of the time constant circuit of the constant voltage circuit 4 starts charging in accordance with the charging time constant of the time constant circuit υ. Therefore, no current flows through the Zener diode (9) until the terminal voltage of the capacitor αυ becomes different from the Zener voltage of the Zener diode (9), so the detection transistor side is in an off state. Further, the power supply voltage generated from the power supply circuit is immediately applied to the collector of the detection transistor (14) via the resistor, but since the detection transistor is in the off state, the power supply voltage is applied to the collector of the detection transistor (14) via the resistor. is applied to the base of the control transistor (c).

On the other hand, the transistor (8) of the constant voltage circuit (2) turns on before the terminal voltage of the capacitor αυ reaches the Zener voltage of the Zener diode (9). The power supply voltage generated from (g) is applied to the circuit through the transistor (8). Therefore, the capacitor C2 of the time constant circuit
4) +-! Since it is gradually charged through the resistors @ and @, a base current flows through the drive transistor (2), and the drive transistor (2) is turned on.

Then, eventually, the capacitor of the time constant circuit @
By being charged, the control transistor to which voltage is already applied to the base is turned on before the drive transistor (2) is turned off. Therefore, the drive transistor 4 continues to be in the on state.

When the charging of the capacitor circle in the constant voltage circuit progresses and the terminal voltage of the capacitor αυ reaches the Zener voltage of the Zener diode (9), the Zener diode (9) turns on, so the Zener diode (9) A current flows through, and a voltage is generated at one end (point A) of the detection resistor α3. Here, when the detection resistor is used, the resistance value is such that a voltage sufficient to turn on the detection transistor α4 is generated at point A by the current value flowing through the Zener diode (9) in a steady state. Therefore, when the steady state is reached, the voltage generated at point A causes the detection transistor (
14 is turned on. Therefore, the voltage to the point becomes the base-emitter voltage V□ of the detection transistor I, and since the voltage drop across the Zener diode (9) is the Zener voltage, the cathode of the Zener diode (9) The voltage generated at transistor (8) becomes constant and
A constant voltage is generated at the emitter of. Further, when the detection transistor αa is turned on, the base voltage of the control transistor (b) becomes approximately the ground potential, and the control transistor C is turned off.

When the control transistor (c) is turned off, the capacitor (2) in the time constant circuit starts charging in accordance with the charging time constant, so that the drive transistor continues until the terminal voltage of the capacitor (124) reaches a predetermined value. ■ turns off after continuing to be on. When the driving transistor (2α is turned off), the muting transistor (Lo) is not applied with a base voltage (so the muting transistor αl is turned off. In other words, the muting transistor (11 is turned off when the detection transistor I is turned on). It turns off with a delay of the charging time until the terminal voltage of the capacitor 04) in the time constant circuit reaches a predetermined voltage.

On the other hand, the constant voltage generated from the constant voltage circuit (S) is marked as the operating voltage of the tuner circuit αQ when the Zener diode (9) turns on, that is, when the detection transistor side turns on. In an unstable state where the operating voltage of the tuner circuit (161) is not constant, the miniaturing transistor α9 is in an on state.

Therefore, when the power is turned on, the muting transistor α9 is turned on immediately when the power switch (3) is turned on, and remains on until a constant voltage is generated from the constant voltage circuit 4. Generated noise can be reliably prevented.

Next, a meeting when the power is cut off will be explained.

Now, when the power switch (3) is turned off, the power supply voltage generated from the power supply circuit (power) gradually decreases due to the time constant of the power supply circuit.Even if the power supply voltage decreases to a certain extent, the constant voltage circuit ( If the terminal voltage of the capacitor συ is equal to or higher than the Zener voltage of the Zener diode (9), a constant voltage is generated at the emitter of the transistor (8), but the current flowing through the Zener diode (9) is higher than the Zener voltage of the Zener diode (9). Since it gradually decreases in accordance with the terminal voltage of IIJ, the voltage generated at point A eventually becomes less than the rising voltage v of the detection transistor mill.Therefore, the detection transistor a turns off, and the control transistor C2S is turned on. When the control transistor C5) is turned on, the capacitor (24) of the time constant circuit CD is instantly discharged,
At the same time, the driving transistor (2Q) turns on, so the muting transistor (I9) turns on.
The muting transistor (1'J is a constant voltage circuit) remains on until the voltage generated at the emitter of the transistor (8) is almost eliminated. therefore,
The meeting transistor H is a constant voltage circuit (6)
It turns on when a constant voltage is being generated from the constant voltage circuit, and the on state continues until almost no voltage is generated from the constant voltage circuit, so when the power is cut off, the tuner circuit αω
The noise generated from the noise is reliably prevented.

The tuner circuit (16) has a muting output terminal that generates an "H" signal when changing the broadcast frequency, so the control transistor (to) is turned on when changing channels. Therefore, as in the case of power cutoff described above, drive transistor (2) is turned on and muting transistor (alpha)9 is turned on, so that inter-office noise generated at a frequency where there is no broadcast radio wave is also muted.

By the way, in the circuit shown in the figure, in addition to the base of the control transistor (to) being connected to the collector of the detection transistor (14) via a resistor (to), there is also a memory for preset tuning provided in the tuner circuit u0. The base of a transistor Gυ whose collector is connected to the inhibit terminal (5) of (to) is connected via a voltage dividing circuit. For that reason,
The memory (to) turns on/off the transistor c3υ.
Depending on the off state, the operation of importing the memory contents is prohibited. First, when the power is turned on, the transistor Gυ is driven by the on/off of the detection transistor I, and as described in the explanation of muting above, after the power is turned on. , is in the off state, so the power supply voltage divided by the resistor α9 and the voltage divider circuit is applied to the base of the transistor 61).

On the other hand, before the detection transistor I is turned on, a non-regulated voltage is generated at the emitter of the transistor (8) of the constant voltage circuit (2);
Since the voltage is applied to the collector of the circuit via a time constant circuit consisting of a resistor and a capacitor (2), the voltage is applied to the collector of the circuit after the power is turned on due to the charging time constant of the time constant. The rLJ signal is applied to the inhibit terminal (5) of the memory (26) of the cheese circuit σθ. Then, by charging the capacitor c34 connected to the time constant,
When the collector voltage of the transistor C31) reaches a predetermined value, the transistor 3υ is turned on and the capacitor (b) is discharged. At this time, the memory (to)
The "L" signal should still be applied to the inhibit terminal □□□ of the
Since the transistor 01) is turned on while the J signal is applied, the inhibit terminal continues to be
L” signal will be applied. Eventually, the detection transistor Q41 turns on, so the transistor G1)
is turned off, and the capacitor (b) of the time constant circuit 9) is charged by the charging time constant. In this case, the base voltage of the transistor GD is approximately the ground potential, and the transistor Gυ is not turned on, so that the capacitor (b) is sufficiently charged, and after a predetermined period of time, the inhibit terminal of the memory track is closed. The rHJ signal is applied and the nuclear memo'
The write operation inhibition state of J-(26) is released.

At this time, since the detection transistor side is in an on state, that is, a constant voltage is being generated from the constant voltage circuit, the tuner circuit cLω is in a steady state. Therefore, in a state where a constant voltage is not applied to the tuner circuit (1, 61) and the contents of the memory (1) cannot be reliably written, the write operation of the memory (1) is prohibited.

Next, what happens when the power is cut off will be explained.

When the power is cut off, the detection transistor α4 is turned off while a constant voltage is being generated from the constant voltage circuit set. When the detection transistor a is turned off, the power supply voltage is applied to the base of the transistor 0v via the resistor and the voltage dividing circuit. At this time, since a constant voltage is still applied to the collector of the transistor 0υ, the transistor Gυ
turns on. Therefore, when the tuner circuit αe is in a steady state, that is, before the operating voltage of the memory (to) drops, the rLJ signal is applied to the inhibit terminal (5) of the memory (to). 'J-
Writing of the memory contents of fi is prohibited. For that reason,
If the memory +26) is provided with a backup capacitor (not shown) serving as a backup power source, the stored contents of the memo IJ-0'6) will be reliably retained.

(G) Effects of the Invention As stated above, according to the present invention, fluctuations in the power supply voltage are detected by detecting the Zener current flowing through the Zener diode provided in the constant voltage circuit. While a constant voltage is being generated from the circuit, it is possible to detect increases and decreases in the power supply voltage when the power is turned on and when the power is turned off.

Further, if the power supply voltage detection circuit according to the present invention is used in a muting circuit of an audio device or a circuit that generates an inhibit signal for an integrated circuit as in the embodiment, it can be used to perform muting and integration during power-on and power-off. It is possible to reliably inhibit the operation of the circuit.

[Brief explanation of drawings]

The figure is a circuit diagram showing one embodiment of the present invention. Explanation of main drawing numbers: power supply circuit, hereafter: constant voltage circuit, (9)
...Zener diode, α3...detection resistor, I
...Detection transistor, αe...Tuner circuit,
a9... Muting transistor, ■...
Drive transistor, (c)...control transistor,
I26)...Memory, Punishment...Inhibit terminal, C31) - Transistor.

Claims (1)

[Claims] (1) A constant voltage circuit that includes a transistor with a collector-emitter path inserted in the power supply line and a Zener diode for controlling the collector current of the transistor, and is connected to the anode of the Zener diode and a constant voltage circuit that makes the power supply voltage constant. a detection resistor for detecting the current flowing through the Zener diode, and a common-emitter detection transistor whose base is connected to a connection point between the anode of the Zener diode and the detection resistor and whose collector is applied with a power supply voltage. detects fluctuations in the power supply voltage by detecting the Zener current flowing through the Zener diode, turns on the detection transistor when the power supply voltage is above a predetermined value, and turns on the detection transistor when the power supply voltage is less than the predetermined value. A power supply voltage detection circuit characterized in that the detection transistor is turned off.