JPH08110360A - Signal generation circuit - Google Patents

Abstract

PURPOSE: To provide a circuit for generating a specific signal as fast as possible after detecting a specific state change with a circuit in a simple configuration. CONSTITUTION: The signal generation circuit consists of a first voltage comparison circuit 11 for comparing the voltage across the capacitor of a time constant circuit which is constituted by a first resistance impedance 3 and a capacitor 4 with a first reference voltage 12 and a second voltage comparison circuit 21 for comparing a second reference voltage 22 which is higher than the voltage 12 with the voltage across the capacitor 4. In a signal generation circuit with the output signal of the circuit 11 as a main signal, a serially connected circuit of a constant voltage control element 7, a second resistance impedance 8, and a rectification element 9 is connected in parallel with the impedance 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a signal generating circuit for outputting a specific signal.

[0002]

2. Description of the Related Art In a DC power supply device which is used for various purposes after inputting a commercial power supply and transforming / rectifying, the rectified voltage disappears when the commercial main power supply is cut off, so that it is convenient to be able to generate a notice signal thereof. . An example of a circuit used for that purpose is shown in FIG.

In FIG. 3, an auxiliary power source 1 (Vc) is provided as an operating power source for the signal generating circuit and is always turned on. The resistor 2 and the resistor 3 divide the DC voltage of the auxiliary power supply 1, and the capacitor 4 and the resistor 3 form a time constant circuit. A connection point 5 indicates a connection point between the capacitor 4 and the resistor 3. The relay contact 6 indicates a relay contact for turning on / off the main power supply, which will be described later.

A terminal 10 is, for example, a relay signal terminal for turning on / off the main power source (not shown). The first voltage comparison circuit 11 compares the DC voltage V1 of the DC voltage source 12 with the voltage v across the capacitor 4 and generates an output signal when the voltage v exceeds V1 or drops from V1. To do. The DC voltage V1 is the first reference voltage.

The terminal 20 is an output terminal for a notice signal different from the output signal. The second voltage comparison circuit 21 compares the DC voltage V2 of the DC voltage source 22 with the voltage v across the capacitor 4, and when the voltage v exceeds the voltage V2 or drops from V2, a warning signal is issued. Output. The DC voltage V2 is used as the second reference voltage, and a value higher than the first reference voltage V1 is selected and set.

Next, the operation of FIG. 3 will be described. Relay contact 6
When is closed, the connection point 5 between the resistor 2 and the resistor 3 is grounded, so that the electric charge charged in the capacitor 4 is discharged and is not accumulated thereafter. When the relay contact 6 is operated from close to open at time t _O , the capacitor 4 is started to be charged by the auxiliary power supply 1 via the resistors 2 and 3. Figure 4 (A)
FIG. 4 is a diagram showing a voltage change across the capacitor 4 at that time. In FIG. 4A, the horizontal axis represents time t and the vertical axis represents voltage v.
Indicates. The voltage v rises from a "zero" value when the relay contact 6 is opened according to a time constant determined by the resistor 3 and the capacitor 4. When V1 is reached at time t ₁ , an output is generated from the first voltage comparison circuit 11 and the terminal 10
Obtained from Therefore, a commercial power supply (not shown) can be turned on by passing the output signal to the relay.
For example, the time t _P is the ON time. The waveform (“L” → “H”) shown in FIG. 4B is the output of the first voltage comparison circuit 11.

The voltage v further rises and V2 is reached at time t ₂ .
When it reaches, another signal is generated from the second voltage comparison circuit 21 and is obtained from the terminal 20. Since this signal is generated after the signal for turning on the commercial power source is generated, it can be used to confirm the generation of the ON signal. FIG.
The waveform (“H” → “L”) shown in (C) is the second comparison circuit 21.
Is the output of. This confirmation signal is when the power is turned on,
For example, when power is supplied to the semiconductor memory, it can be used to disconnect the memory power backup circuit. After the confirmation signal is output, the voltage v further rises gradually with the passage of time, reaches the voltage Vc of the auxiliary power supply 1, and is saturated.

Next, when the relay contact 6 is closed, the commercial power source is turned on.
It can be controlled off. Time t _CAt relay connection
If point 6 is closed, is the connection point of resistors 2 and 3 grounded?
As a result, the accumulated charge of the capacitor 4 is rapidly discharged. relay
Changes in voltage v across capacitor 4 when contact 6 is closed
The conversion is as shown in the latter half of Fig. 4 (A). That is, the voltage v
The voltage Vc of the auxiliary power source suddenly starts to fall at time t₃To
When the voltage V2 is reached, the second voltage comparison circuit 21
A change output of "L" → "H" is generated.

[0009] Then, when reaching the voltage V1 at time t _4, the first voltage comparator circuit 11 generates a change in the output of "H" → "L". The upcoming signal acts to turn off the main power supply. For example, it is turned off at time t _f . Therefore, the output of the second voltage comparison circuit 21 described above can be recognized as a notice signal for turning off the main power supply. FIG.
The operation signal of the second voltage comparison circuit in (C) is
It is called an L signal (power fail logic). The warning signal is, for example, for the backup power supply of the semiconductor memory, when the sensor on the primary side of the commercial power supply detects an abnormality of the commercial power supply,
It is to turn on the backup power.

[0010]

[Problems to be Solved by the Invention] In FIGS. 4 (B) and 4 (C),
Although PFL signal is the meaning of the warning signal for the main power supply off, as shown in FIG. 4, the generation of the waveform change time t ₃
Looking at, the time difference from the time t _C when the relay contact 6 is closed to the time t ₃ when the output of the second voltage comparison circuit is generated is relatively large. That is, in order to have the meaning of the advance notice signal, it is necessary to reduce the time interval between them. For that purpose, it is necessary to select the second reference voltage >> the first reference voltage as the magnitude of the reference voltage. However, when making the selection, the meaning of the notice signal can be fulfilled, but the meaning of the confirmation signal is lost. It is the output change t of the first voltage comparison circuit.
_This is because the change t ₂ of the output of the second voltage comparison circuit can be obtained by taking an extremely longer time after ₁ than in the case of FIG. 4 (A).

Therefore, as another concept, a third voltage comparison circuit is used, and the reference voltage V3 for the comparison is the second voltage.
It has been proposed to use a third reference voltage that is higher than the reference voltage V2. When the confirmation signal for turning on the power is initially obtained, the second voltage comparison circuit is used as usual. At this time, the third voltage comparison circuit is not connected. The third voltage comparison circuit is used for the notice signal, and the second voltage comparison circuit is not connected at that time. In this way, t in FIG.
The interval of _C, t ₃ can be made long to have the meaning of a power-off warning signal.

In this way, when the notice signal generation time is adjusted only by selecting the reference voltage, the notice signal and the confirmation signal cannot be compatible with each other. Further, it is convenient to prepare three voltage comparison circuits, but the device becomes large and the method of use becomes complicated due to the presence or absence of connection, and it is easy to make a mistake.

It is therefore an object of the present invention to remedy these drawbacks of the prior art and to provide a circuit with a simple construction which is capable of generating a signal as soon as possible after detecting a predetermined state change. .

[0014]

A first voltage comparison circuit 11 for comparing a voltage across a capacitor 4 of a time constant circuit composed of a first resistive impedance 3 and a capacitor 4 with a first reference voltage V1, and a first reference A second reference voltage value V2, which is higher than the voltage V1, is compared with the voltage across the capacitor 4.
In the signal generating circuit which is composed of the voltage comparison circuit 21 and uses the output signal of the first voltage comparison circuit 11 as a main signal, the present invention provides a constant voltage control element 7, a second resistive impedance 8
A series connection circuit of the rectifying element 9 is connected in parallel with the first resistive impedance 3.

[0015]

When the capacitor of the time constant circuit starts charging, the charging voltage is compared with the first reference voltage and the second reference voltage by the first and second voltage comparison circuits, respectively, and the first voltage comparison circuit The use of the output signal as the main signal of the signal generating circuit is the same as in the prior art.

Next, when a predetermined state change is detected, the capacitor is discharged. The electric charge accumulated in the capacitor passes through the constant voltage control element, the second resistive impedance, and the rectifying element, and abrupt discharge is started. An output signal is generated from the second voltage comparison circuit when the voltage across the capacitor drops below the second reference voltage. Since the two resistive impedances are connected in parallel, the discharge time constant is smaller than when the capacitor was initially charged, and the discharge is more rapid, which is more rapid than in the case of a single resistive impedance as in the prior art. Become. Therefore, the generation of the output signal from the second voltage comparison circuit is accelerated. If this signal is used as a notice signal for the output signal of the first voltage comparison circuit, it can be widely used.

After that, by disconnecting the connection of the resistive impedance connected in parallel by the operation of the constant voltage control element, the capacitor discharge becomes gentle. The output generation of the first voltage comparison circuit may be the same as the conventional one.

[0018]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention. In FIG. 1, many configurations similar to those of the related art exist. That is, the auxiliary power source 1, the resistor 2, the resistor 3, the capacitor 4, the relay contact 6, the terminal 10, the first voltage comparison circuit 11, the DC voltage source 12, the terminal 20, the second voltage comparison circuit 2
1, a DC voltage source 22, and the connection configuration thereof is the same as that of FIG.

In FIG. 1, the voltage control element 7 is a Zener diode, the Zener voltage of which is the second reference voltage V2.
And select approximately the same as. Let the Zener voltage be V _D. The forward potential drop of the rectifying element 9 is V _F. Voltage V2
It is sufficient to satisfy V2> V _D + V _F as a relationship with. The second resistance impedance 8 is selected to be extremely small by comparing its resistance value with the resistance value of the first resistance impedance 3.

In the operation of FIG. 1, a confirmation signal corresponding to the output signal of the terminal 10 can be output from the terminal 20 by initially closing and then opening the relay contact 6, and the above is the same as the conventional technique. is there.

Next, when the relay contact 6 is opened and closed, the characteristic operation of the present invention is performed. That is, when the primary side sensor detects that the commercial power supply is cut off due to a power failure in the commercial power supply circuit, the relay contact 6 is immediately closed.
The electric charge accumulated in the capacitor 4 was sufficiently large, and the DC voltage had a voltage value substantially equal to the voltage Vc of the auxiliary power supply 1. Since the relay contact 6 is grounded, the electric charge of the capacitor 4 is rapidly discharged by both the path passing through the resistor 3 and the path passing through the Zener diode 7, the resistor 8 and the diode 9. Since the value of the resistor 8 is smaller than that of the resistor 3, the discharge amount is much larger than that when only the resistor 3 is used. Therefore, the voltage v of the capacitor 4 drops to V2.

FIG. 2 is a diagram showing the time variation of the voltage across the capacitor 4. The time is plotted on the horizontal axis, and the time t _C indicates the time when the relay contact 6 is closed. The time when the voltage v across the capacitor 4 becomes equal to V2 is t ₅
If so, the time is newer in time, that is, closer to t _C , as compared with t ₃ shown in FIG. Therefore, in the case where the commercial power supply is rectified to supply power to the semiconductor memory, for example, as described above, the output signal of the second voltage comparison circuit 21 may be automatically used to switch the power supply system to the backup power supply. Therefore, the second voltage comparison circuit 21
The output signal of can be used as a notice or warning signal of the operation caused by the output signal of the first voltage comparison circuit 11.

In FIG. 2, the voltage v across the capacitor 4 continues to drop, but the discharge path is only the path of the resistor 3. This is because the Zener diode 7 operates. Then, at time t ₆ , the voltage V1 of the first reference power supply
Reach Time t ₆ is earlier than t ₄ in FIG. Then the time difference between t ₃ and t ₄ in FIG. 4, when comparing the time difference between t ₅ and t ₆ in FIG. 2, both the time difference is equal.

[0024]

As described above, according to the present invention, it is possible to easily output the output signal of the second voltage comparison circuit earlier than the conventional one, and therefore it is useful when using the output signal. The circuit configuration therefor is not complicated and is practical.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing a temporal change of a voltage across a capacitor in the circuit of FIG.

FIG. 3 is a diagram showing a circuit configuration as a conventional technique.

4 is a diagram showing a temporal change in voltage across a capacitor of the circuit of FIG. 3 and a change in output signal at a terminal.

[Explanation of symbols]

 1 Auxiliary power supply 2 Resistive impedance 3 Resistive impedance 4 Capacitor 6 Relay contact 7 Constant voltage control element 8 Resistive impedance 9 Rectifier element 10 Terminal 11 First voltage comparison circuit 12 DC voltage source 20 Terminal 21 Second voltage comparison circuit 22 DC Voltage source

Claims (3)

[Claims] 1. A first voltage comparison circuit for comparing a voltage across a capacitor of a time constant circuit composed of a first resistive impedance capacitor with a first reference voltage, and a second reference voltage value higher than the first reference voltage. A second voltage comparison circuit for comparing the voltage across the capacitor, and a signal generation circuit having an output signal of the first voltage comparison circuit as a main signal, wherein a constant voltage control element, a second resistive impedance, and a rectifying element are provided. A signal generation circuit, wherein the serial connection circuit of is connected in parallel with the first resistive impedance. 2. The signal generating circuit according to claim 1, wherein the value of the second resistive impedance is selected to be extremely smaller than the value of the first resistive impedance. 3. A signal generating circuit, wherein a zener diode having a zener voltage lower than a second reference voltage is used as the constant voltage control element according to claim 1.