JPH0537250Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a power on/off detection circuit, and particularly to a power on/off detection circuit that allows mute circuits, reset circuits, etc. to operate quickly and reliably.

(Prior Art) The circuit operation when a conventional power on/off detection circuit is connected to a muting circuit of a vehicle-mounted stereo device will be described with reference to FIGS. 2 to 4. Second
The figure is a circuit diagram showing main parts of a conventional power on/off detection circuit and a mute circuit, and FIGS. 3 and 4 are voltage waveform diagrams for explaining the operation of the circuit shown in FIG. 2.

As shown in FIG. 2, the conventional power on/off detection circuit 11 consists of an NPN transistor for voltage detection.
Q ₁ , resistors R ₂ , R ₃ , R ₁₈ and Zener diode
It is composed of D ₁ .

When the power switch _S1 of the in-vehicle stereo device (hereinafter referred to as car stereo) and/or the car accessory (hereinafter referred to as ACC) switch _S2 is in the off state (power off), the voltage detection transistor _Q1 is off. . Therefore, the switching NPN transistor _Q10 of the miute transistors _Q8 and _Q9 of the miute circuit is on, and the NPN transistor _Q5 is off.
NPN transistor Q ₆ is on, PNP transistor
_Q7 is on and NPN miute transistor
Both Q ₈ and Q ₉ are on. Therefore, Miyut is in effect.

12a is line amplifier for Lch, 12b is Rch
This is a line amplifier for. miute transistor
By Q ₈ and Q ₉ , the respective line amplifiers 12a,
The output of 12b is muted.

Furthermore, when both switch S ₁ and switch S ₂ are turned on (power on), a voltage Eb obtained by subtracting Zener voltage E ₂ of Zener diode D _{1 from battery voltage E 1} of battery ₂ is applied to point b, and the transistor _Q1 turns on. Therefore, the transistor Q ₁₀ is turned off, and current is supplied to the capacitor C ₁ via the resistor R ₉ to start charging. When capacitor C ₁ is fully charged, transistor Q ₅ in the miute circuit is turned on, transistors Q ₆ and Q ₇ are both turned off, and miute transistors Q ₈ and Q ₉ are turned on.
Both are turned off. Therefore, the miute is released.

Furthermore, when switch S ₁ and/or switch S ₂ turns off from this state (power on → off), voltage Eb at point b becomes zero, and transistor Q ₁
turns off and transistor _Q10 turns on. At this time, capacitor _C1 is instantaneously discharged via resistor _R8 , which has a small resistance value. Therefore, transistor Q ₅ in the miute circuit is turned off, transistors Q ₆ and Q ₇ are both turned on, and miute transistors Q ₈ and Q ₉ are turned on.
both turn on. As a result, Miyut becomes effective.

Next, the above process will be explained in more detail.

When both switch _S1 and switch _S2 are turned from on to one or both are turned off, the voltage Ea at point a in FIG. 2 follows a downward curve Ea as shown in FIG. 3A. The reason why voltage Ea does not drop suddenly is because capacitor _C2 is discharged. The voltage Eb at point b is the voltage obtained by subtracting the Zener voltage _E2 from the voltage Ea at point a, and follows a downward curve Eb as shown in FIG. 3A. Theoretically, a transistor turns on if the base voltage is higher than 0.6V.
It turns off if it is lower than 0.6V. However, due to the characteristics of a transistor, it does not turn completely on or completely off at 0.6V, and when the base voltage is around 0.6V, the transistor is in an intermediate state. Therefore, b
As the voltage Eb at the point decreases, the transistor
The voltage Ec at point c, which is the base voltage of Q ₁ , decreases,
Even when the voltage reaches around 0.6V, transistor _Q1 does not instantly change from the on state to the off state. And the voltage
Since the voltage drop across Eb is gradual, the voltage Ec at point c remains around 0.6V for a considerable period of time, so transistor _Q1 turns off after a long period of time in the intermediate state. Therefore, the voltage Ed at point d follows a gradual rising curve Ed as shown in FIG _.
It also turns on after going from the off state to the intermediate state for a while.

Even when reaching the transistor Q ₇ via the transistors Q ₅ and Q ₆ , the voltage Ee at the point e, which is the collector voltage of the transistor Q ₇ , follows the same rising curve as the voltage Ed at the point d. Q ₈ and Q ₉ cannot be turned on instantly from off at the rising edge of voltage Ee at point e, and the effect of the mute is delayed when the power is turned off.

Contrary to the above, when switch S ₁ and/or switch S ₂ is in the OFF state, switch S ₁ and switch S ₂
When both are turned on, other circuits connected to the battery 2 start operating, causing the load to fluctuate. Therefore, as shown in the rising curve Ea in Figure 4A,
The voltage Ea at point a temporarily and rapidly drops during the rise. Along with this, the voltage Ec at point c also drops temporarily and rapidly, as shown by the rising curve Ec in FIG. 4A. As a result, the transistor _Q1 , which was previously only turned on, momentarily turns off, and the voltage Ed at point d temporarily and rapidly rises while falling, as shown in FIG. 4B. A similar voltage change occurs at point e, and the mute transistors Q ₈ and Q ₉ , which were previously off, are turned on momentarily. This caused the mute circuit to operate unstable.

(Problem to be solved by the invention) Originally, the Mute circuit was designed to instantly activate the Mute when the car stereo's power switch _S1 and/or the car's ACC switch _S2 were turned off (power off). , when switch S ₁ and switch S ₂ are both in the on state (power on), the capacitor
This is to ensure that the miute is released after a predetermined time determined by the capacity of _C1 .

However, as mentioned above, in the conventional mute circuit, the conventional power on/off detection circuit connected to the mute circuit does not accurately detect the power on/off operation. was carried out late. Furthermore, when both the switch _S1 and the switch _S2 were turned on, the mute-off operation of the mute circuit, which should be performed after a predetermined period of time, could not be reliably performed.

(Means for Solving the Problems) Therefore, in order to solve the above problems, the present invention provides that a first DC power supply line having a switch is connected to the base via a first voltage dividing resistor, and The second DC power supply line is connected to the collector and the emitter is grounded.
, a second transistor for switching having the same polarity as the first transistor, the collector of which is connected to the base and the emitter of which is grounded; a third transistor for switching the voltage dividing resistor, which has the same polarity as the first transistor and whose collector is connected to the collector through the voltage dividing resistor 2 and whose emitter is grounded; and the base of the third transistor is connected to the collector. and a collector of the second transistor is connected to the base, and the second DC power supply line is connected to the emitter of the third transistor. The present invention provides a power on/off detection circuit comprising a fourth transistor and a diode having a collector connected to a cathode of the second transistor and an anode connected to an external circuit. .

(Example) A power on/off detection circuit according to the present invention will be described in detail below with reference to FIG. FIG. 1 is a circuit diagram showing an embodiment of the power on/off detection circuit and a main part of the mute circuit of the present invention. Note that the same parts as in the conventional example are given the same reference numerals, and specific explanations of those parts will be omitted.

First, the circuit configuration of the power on/off detection circuit 1 of this embodiment will be explained. Power is supplied from battery 2, and the car stereo power switch _S1
A first DC power supply line having an ACC switch _S2 is connected to the base of a voltage detection NPN transistor _Q1 whose emitter is grounded via a Zener diode _D1 and a first voltage dividing resistor _R1 . The connection point between the anode of the Zener diode _D1 and the voltage dividing resistor _R1 is grounded via the resistor _R2 . A second DC power line supplied with power from the battery 2 is connected to the collector of the transistor _Q1 via a resistor _R3 .

The base of the emitter-grounded NPN transistor _Q2 , which is used for switching the miute transistors _Q8 and _Q9 , is connected to the collector of the transistor _Q1 and the resistor _R3.
and also the transistor Q ₂
The collector of is connected to the cathode of diode _D2 . The anode of this diode D ₂ is connected to the miute circuit.

The collector of the NPN transistor Q ₃ for switching the voltage dividing resistor whose emitter is grounded is connected to the connection point between the first voltage dividing resistor R ₁ and the base of the transistor Q ₁ via the second voltage dividing resistor R ₄ . There is. Also, the base of transistor _Q3 is connected to the transistor through resistor _R5 .
PNP digital transistor _Q4 driving _Q3
connected to the collector.

The base of this digital transistor _Q4 is connected to the collector of transistor _Q2 , and the emitter is connected to the second DC power supply line. The digital transistor _Q4 is a resistor as shown in Figure 1.
R ₆ and resistor R ₇ .

Next, the circuit operation of this embodiment will be explained. Since the basic operation is the same as that of the conventional example, detailed explanation thereof will be omitted here.

The transistor Q ₂ of this embodiment is similar to the transistor Q ₁₀ of the conventional example, and is composed of the mute transistors Q ₈ ,
In addition to being a switching transistor for _Q9 ,
It is also the drive transistor for transistor _Q4 . Diode D ₂ is intended to prevent current from the base of transistor Q ₄ from being supplied to capacitor C ₁ .

First, when switch S ₁ and/or switch S ₂ is off (power off), transistor Q ₁ is off and transistor Q ₂ is on, so transistor Q ₃ and transistor Q ₄ are on. The base of transistor Q ₁ is grounded by voltage dividing resistor R ₄ . Also, since transistor Q ₂ is on in the miute transistors Q ₈ and Q ₉ ,
Both are on. Therefore, Miyut is in effect.

Next, when switch _S1 and switch _S2 are both turned on, transistor _Q1 is turned on and transistor _Q2 is turned off, so transistor _Q4 is turned off, and thus transistor _Q3 is turned off.
To explain this process, at the moment both switches S ₁ and S ₂ are turned on (power on), the voltage at point b is
Eb is divided by voltage dividing resistors R ₁ and R ₄ , and the divided voltage Ec is applied to the base of transistor Q ₁ . Then, when the voltage Ec at point c becomes 0.6V or higher, transistor Q ₁ turns on, and transistor Q ₂
is turned off. Therefore, the transistor _Q4 is turned off, the voltage dividing resistor switching transistor _Q3 is turned off, and the resistor connected to the base of the transistor _Q1 is turned off.
R ₄ is open from ground. Therefore, at this time,
Even if other circuits connected to battery 2 start operating and the load increases and the voltage Eb at point b drops instantaneously, the voltage Ec at point c does not drop due to the voltage dividing resistor _R4 , so the transistor Do not descend until it is no longer possible to keep Q ₁ on. By this,
Since transistor Q ₁ can remain on and transistor Q ₂ can remain off, as in the conventional example,
Miut transistor Q ₈ which was only off once,
Since _Q9 does not turn on momentarily, the mute circuit can reliably perform the mute-off operation after a predetermined period of time after the power is turned on. However, the voltage at point c
If Ec drops to the point where the base current can no longer flow through transistor Q ₁ , it will no longer be possible to keep transistor Q ₁ on, so the resistance values of voltage dividing resistors R ₁ and R ₄ should be adjusted, taking into full consideration the instantaneous voltage drop at point b. Determine.

Next, when the switch _S1 and/or the switch _S2 is turned off (power on→off), this embodiment performs the circuit operation opposite to the above. First, the voltage at point b
When Eb drops, transistor _Q1 cannot maintain a fully on state and becomes an intermediate state, a half-on state. Then, a slight voltage is generated at point d, and transistor _Q2 changes from off to half on. This turns on transistor _Q4 and turns on transistor _Q3
is also turned on, so the voltage dividing resistor _R4 is grounded. At this time, c which is the base voltage of transistor _Q1
The voltage Ec at the point is divided by voltage dividing resistor _R1 and voltage dividing resistor _R4 , so it drops rapidly and the transistor
Q ₁ turns off instantly. Here, even if the voltage Ea at point a rises a little and the voltage Eb at point b rises a little, the voltage Ec at point c will be the same as the voltage Eb at the voltage dividing resistor R ₁ ,
Since the voltage is divided by _R4 , it hardly increases. Therefore, transistor Q ₁ can be stably maintained off.

Therefore, when the power is turned off, the transistor Q ₁ is instantly turned off and the transistor Q ₂ is turned on instantly, so the mute transistors Q ₈ and Q ₉ are also turned on instantly, and the mute is immediately applied.

Although the case where the power on/off detection circuit of the present invention is connected to a mute circuit has been described here, it may also be connected to a reset circuit or the like. Further, the digital transistor _Q4 may be composed of a general transistor and a resistor.

(Effects of the invention) As described above, the power on/off detection circuit according to the invention turns off the power by switching the resistance value of the voltage dividing resistor that divides the base voltage applied to the base of the voltage detection transistor. Sometimes, the base voltage can be dropped rapidly and quickly passed near the threshold voltage of the voltage sensing transistor, so the voltage sensing transistor can be turned off instantaneously, thus turning off the power off state instantly and quickly. Can be detected stably. Furthermore, when the power is turned on, there is no risk of the voltage detection transistor malfunctioning even if the base voltage of the voltage detection transistor fluctuates around the threshold voltage.
The power-on state can be accurately detected without being affected by voltage fluctuations.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the power on/off detection circuit of the present invention and main parts of a mute circuit, and Fig. 2 is a circuit diagram showing main parts of a conventional power on/off detection circuit and a mute circuit. , 3 and 4 are voltage waveform diagrams for explaining the operation of the circuit shown in FIG. 2. 1...Power on/off detection circuit, 2...Battery, 12a, 12b...Line amplifier, C ₁ , C ₂
... Capacitor, D ₁ ... Zener diode,
D ₂ ... Diode, Q ₁ to Q ₃ , Q ₅ , Q ₆ , Q ₈ , Q ₉ ...
...NPN transistor, Q ₄ ...Digital transistor, Q ₇ ...PNP transistor, R ₁ to R ₁₇ ...
Resistance, S ₁ , S ₂ ... switch.

Claims (1)

[Scope of utility model registration request] A first DC power line having a switch is a first
is connected to the base through a voltage dividing resistor, and
a first transistor for voltage detection, the collector of which is connected to a second DC power supply line and whose emitter is grounded; and the first transistor whose collector is connected to its base and whose emitter is grounded; a second transistor for switching having the same polarity as the transistor; and a second transistor for switching having the same polarity as the first transistor, the base of which is connected to the collector via a second voltage dividing resistor, and the emitter of which is the same as the first transistor. a third transistor for switching the polarity dividing resistor; the base of the third transistor is connected to the collector;
The collector of the transistor is connected to the base,
and a fourth transistor having a polarity opposite to that of the first transistor for driving the third transistor, the emitter of which is connected to the second DC power supply line, and the collector of the second transistor is connected to the cathode. 1. A power on/off detection circuit comprising a diode having an anode connected to an external circuit.