JPH01303053A - Low voltage detection circuit - Google Patents

Abstract

PURPOSE:To cause no output interruption, by supplying the voltage applied to transistors through a switching circuit and a delay circuit ON-OFF controlled from a constant voltage power source depending on the control signal. CONSTITUTION:A low voltage detection circuit 10 is equipped with a transistor(Tr) 13 whose emitter is connected to earth through a Zener diode 12, an electrolytic capacitor 15, the 2nd Tr 17 and the 3rd Tr 20 and is composed of an SCR 24 and an output terminal 25. A switching circuit A is composed of an FET 29 into whose drain constant voltage Vc is inputted, etc., through a resistor 26 and a protection diode 27 and of a Tr 32. When the power supply is put to work, no low voltage detection circuit 10 will be operated before the output voltage of the output to detect the voltage drop comes to lead, and that in detecting this voltage drop the output can immediately be interrupted, while no circuit 10 will work when the signal to detect the voltage drop is in an OFF state and no output from its output terminal will be interrupted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects when the output voltage from a switching regulator, etc. drops or becomes zero, and cuts off the output of the switching regulator, etc. The present invention relates to a low voltage detection circuit.

[Conventional technology and problems] Conventionally, for example, in switching regulators, etc.
The desired output voltage is obtained by pulse-controlling the input DC voltage, but if this output voltage drops or becomes zero due to a short circuit, damage, etc., this is detected by the low voltage detection circuit. The switching regulator, etc. is protected by detecting the above, cutting off the output to the control circuit that performs the pulse control, and stopping the oscillation of the control circuit, thereby cutting off the output of the switching regulator, etc. There is.

As such a low voltage detection circuit, for example, one having the configuration shown in FIG. 3 is known. That is, in FIG.
The low voltage detection circuit 1 includes an I transistor 3 to which an output voltage from a switching regulator (not shown) or the like is inputted to its base via an input terminal 2, an emitter of the transistor 3 whose +4 rule is 8, and a negative side of which is input to the emitter of the transistor 3. An electrolytic capacitor 5 is connected to the collector of 3 and a constant voltage Vc is applied to the →− side through a resistor 4, and the − side of this electrolytic capacitor 5 is connected to a Zener diode 6 with a predetermined Zener voltage and a gate through the resistor. 5CR7, which is connected to
and the output terminal 8 connected to the anode side of this 5CRT.
It is composed of.

According to the low voltage detection circuit 1 configured in this way, when the output voltage of the switching regulator or the like input to the input terminal 2 is equal to or higher than the reference voltage,
The signal of H level will be input to the head of
Therefore, since the emitter and collector of this transistor 3 are on, a constant voltage ■ is input to the + side of the electrolytic capacitor 5. flows to the ground via the transistor 3, so no signal is input to the gate of 5CR7, and therefore this 5CR7 is in a non-conducting state, so the 5C
The constant voltage Vc input to the anode side of R7 is input from the output terminal 8 to a control circuit that performs pulse control such as a switching regulator (not shown), and this input causes the control circuit to continue operating, and the switching regulator etc. are output continuously.

Here, when the output voltage of the switching regulator, etc. decreases due to a short circuit or damage to the load, or becomes zero, the output voltage applied to the input terminal 2 decreases, so that the output voltage remains at the predetermined level. When the voltage drops below the voltage, a signal of I7 level is applied to the heath of transistor 3, and therefore, the emitter and collector of transistor 1 to transistor 3 are turned off, and the electrolytic capacitor 5
is constant voltage ■. Each time it is charged by the current from
When the charging voltage of the electrolytic capacitor 5 exceeds the predetermined Zener voltage of the Zener diode 6, a current flows from the electrolytic capacitor 5 to the gate of 5CR7 via the Zener diode 6 and the resistor.
Since the anode of 5CR7 becomes conductive between the anode and 1', a constant voltage (2) is input to the anode side of this 5CR7. is the 5C
It will be connected to ground via R7, and thus no signal will be output to the control circuit (not shown), so this control? The operation of the ffU circuit is stopped, and the output of the switching regulator and the like is cut off.

However, the low voltage detection circuit configured in this way]
, the time constant is determined by the resistor 4 and the electrolytic capacitor 5 so that the low voltage detection circuit 1 does not operate and cut off the output of the switching regulator, etc., when the power is turned on, before the output voltage of the switching regulator, etc. rises. It has a delay time.

Therefore, even if the output voltage drops or becomes zero due to an abnormality, S(, R7 becomes conductive and the signal input to the control circuit is stopped after the delay time described above has elapsed. Since the output of the switching regulator, etc. is cut off by stopping the switch, even if a sudden accident such as a load short circuit occurs, the output of the switching regulator, etc. will be cut off only after a predetermined delay time has elapsed.

Furthermore, in the case of a short-circuit accident, it is common for the short-circuit state to occur after a number of short-circuit and open circuits, rather than the short-circuit state at -. On the other hand, in the low voltage detection circuit 1 configured as described above, devices such as a switching regulator may be destroyed due to the presence of the delay time.

In addition, when the signal to be detected is on/off controlled by an on/off control signal, even when the signal to be detected is turned off by the on/off control, the voltage detection circuit detects this and the signal is turned off. There is also a problem in that each time the output is cut off, the signal is no longer turned on even after the on control is performed.

[Purpose of the invention]

In view of the above points, the present invention is designed to operate before the output voltage of the signal that should detect a voltage drop rises when the power is turned on (in addition, when a drop in the output voltage is detected, the output is immediately shut off). It is an object of the present invention to provide a low voltage detection circuit which is capable of detecting a signal to be detected and which does not cut off the output in the off state when the signal to be detected is on/off controlled.

[Means and actions to solve the problem] The above purpose is to
According to the present invention, a signal for detecting a voltage drop is input to the emitter.

A transistor to which a predetermined voltage is applied between the collectors, an output terminal to which a constant voltage is supplied, and ground, and the collector of the transistor is connected to the gate via a Zener diode, and a constant voltage is input. and a switching element connected between the output terminal and ground, and the predetermined voltage applied to the transistor is controlled based on a control signal for controlling on/off the signal to be detected from the constant voltage power supply. The signal is supplied through a switching circuit and a delay circuit that are controlled on and off, and when the signal to be detected falls below the reference voltage, the switching element becomes conductive and drops the constant voltage to ground, thereby reducing the output. This is achieved by a low voltage detection circuit that cuts off the output from the terminal, but does not cut off the output from the output terminal by not supplying a predetermined voltage to the transistor when the signal to be detected is off.

According to this invention, first, when the power is turned on, a predetermined voltage is applied between the emitter and collector of the transistor after a predetermined delay time has elapsed from the constant voltage power supply via the delay circuit, so that the signal to be detected reaches the predetermined voltage. Before the low voltage detection circuit starts up, the specified voltage is not applied between the emitter and collector of the transistor, so even if this transistor turns off, no signal is input to the gate of the switching element, so The switching element is in a non-conducting state, and the constant voltage output from the output terminal is not cut off, but
After that, when a predetermined voltage is applied to the transistor, if the signal to be detected is equal to or higher than the reference voltage, the transistor is on, so the predetermined voltage passes through the transistor and falls to the ground, so the switching element No signal is input to the gate, so the switching element is in a non-conducting state, and a constant voltage continues to be output from the output terminal. Furthermore, if the voltage of the signal to be detected in this state drops due to a short circuit or breakdown of the load and becomes below the reference voltage, the voltage of the transistor becomes L level, which turns off the transistor. Therefore, this switching element becomes conductive, and the constant voltage applied to the output terminal passes through the switching element and falls to the ground, so the output from this output terminal is output without any delay time. When the signal to be detected is in the off state due to the on/off control signal, the switching circuit is turned off by the on/off control signal, and the predetermined voltage is not applied to the transistor. Therefore, the output from the output terminal will not be cut off.

Thus, when the power is turned on, the low voltage detection circuit according to the present invention does not operate before the output voltage of the output whose voltage drop is to be detected rises, and when it detects this output voltage drop, it immediately shuts off the output. Furthermore, when the signal to be detected is in the OFF state, the low voltage detection circuit does not operate and the output from its output terminal is not cut off.

〔Example〕

The present invention will be described below based on embodiments shown in the drawings.

The first part shows an embodiment of the low voltage detection circuit according to the present invention, and this low voltage detection circuit 10 has an output voltage from a switching regulator (not shown), etc. input from an input terminal 11 to its base via a resistor. and a transistor 13 whose emitter is connected to ground via a Zener diode 12, and a constant voltage (2). An electrolytic capacitor 15 is applied to the + side via a switching circuit A and a resistor 14, which will be described later, and the + side of this electrolytic capacitor 15 is connected to the base via a Zener diode 16 with a predetermined Zener voltage, and the emitter is connected to the ground. The connected second transistor 17 and the above constant voltage VC are connected to the base.
is inputted through the resistor 8, the collector of the second transistor 17 is connected through the resistor 9, and the constant voltage 2 is inputted to the emitter of the third transistor 20. This third transistor 2
The collector of the first transistor 13 is connected to the ground via a capacitor 21, and is also connected to the collector of the first transistor 13 via a resistor 22.
~The collector of the transistor 13 is a Zener diode 23
and 5CR24 input to the anode via a resistor,
The output terminal 25 is connected to the anode side of this 5CR2,'I and the collector of the third transistor 20 is connected via a resistor.

Further, the swinging circuit A has a constant voltage (2) applied to the drain via a 26° resistor and a protection diode 27.

FET 2 to which is input and whose source is connected to ground, and to which an on/off control signal for controlling the on/off of the signal to be detected is input from the input terminal 28.
9 and the drain of this FET 29 via the resistor 30,
The bases are each connected to a constant voltage (2) via a resistor 31, and the emitter is connected to a constant voltage (2). and a transistor 32 whose collector is connected to the resistor 4, respectively.

The low voltage detection circuit IO according to the present invention is configured as described above, and when the power is turned on and when the on/off control signal input to the input terminal 28 is turned on (see FIG. 2 (A)). , FET29 is turned on and constant voltage ■. rises instantaneously, so the signal input to the base of the transistor 32 becomes L level, so the transistor 32 is turned on, and therefore the voltage becomes constant. The electrolytic capacitor 15 is charged by the current from the electrolytic capacitor 1.
When the charging voltage of the transistor 5 becomes higher than the Zener voltage of the Zener diode 1G, a current flows from the electrolytic capacitor 15 to the base of the transistor 17 via the Zener diode 16, and as a result, the base of the transistor 17 becomes H level and the transistor 17 is turned on, the transistor 20 is also turned on, and since there is a Zener diode 12, even if the transistor 13 is turned on, no current flows to the ground through the transistor 13, so the capacitor 21 is instantly charged. will be done.

In this way, after a predetermined delay time L r , a predetermined voltage is applied to the collector of the transistor 13 via the resistor 22, and thus the low voltage detection circuit 10 becomes operational.

Note that the above-mentioned predetermined delay time is determined by taking into account the rise time of the output voltage of the signal of the Suinochinda regulator, etc. that generates the signal to detect the voltage drop (see Fig. 2 (B)). After the output voltage rises and falls, a predetermined voltage is applied to the collector of the transistor 13. Therefore, before the signal to be detected rises to a predetermined voltage, the low voltage detection circuit 10 is in a non-operating state because the predetermined voltage is not applied between the emitter and collector of the transistor 13 (see Fig. 2 (C). ), the base of the transistor 13 becomes 1-Leher, so that 8.1
~Even if transistor 13 is turned off, no signal is input to the gate of 5CR24, so this SCR244;l
It is in a non-conductive state, and the output of the predetermined voltage from the output terminal 25 is not cut off (see FIG. 2(D)).

When a predetermined voltage is applied to the collector of the transistor 13, if the signal to be detected is higher than the reference voltage, the signal is input from the input terminal 11 via the resistor to the base of the transistor 13. Since the signal is H level, the 1-range disk 13 is on and the predetermined voltage passes through the transistor 13 and falls to ground, so the voltage at the collector of this transistor 13 is low;
Due to the action of the Zener diode 23, no signal is input to the gate of the 5CR 24, so the 5CR 24 is in a non-conducting state, and the predetermined voltage continues to be output from the output terminal 25 (see FIG. 2(D)).

When the on/off control signal input to the input terminal 28 turns off, the FET 29 turns off, and therefore the transistor 3
2 is also turned off, so the predetermined voltage is no longer applied to the collector of the transistor 13, and the low voltage detection circuit 10 becomes inoperative (see FIG. 2C). In this case, since no signal is input to the gate of 5CR24, 5CR24 is in a non-conductive state, but the output terminal 25
Since the predetermined voltage is not applied to the output terminal 25,
There will be no output from. When the on/off control signal input to the input terminal 28 is turned on again, the above operation is repeated, and the present low voltage detection circuit 10 becomes operational again (see FIG. 2(C)).

If the signal to be detected falls below the reference voltage due to a voltage drop due to a short circuit or breakdown of the load, the signal input from the input terminal 11 to the base of the transistor 13 via the resistor becomes L level, and this causes Since the transistor 13 is turned off, the predetermined voltage is applied to the Zener diode 2.
3 to the gate of 5CR24, therefore, 5CR24 becomes conductive, and the output terminal 25
Since the constant voltage applied to the output terminal 25 falls to the ground through the 5CR 24, the output from the output terminal 25 is immediately cut off without any delay time (see FIG. 2(D)).

Therefore, when the output terminal 25 of the present low voltage detection circuit 10 is input to the control circuit as a signal for operating the control circuit for performing pulse control of the input voltage of a switching regulator, for example, When the output voltage of the switching regulator drops due to some reason such as a short circuit or breakdown of the load, the low voltage detection circuit 10 detects this and immediately detects the voltage drop at its output terminal 25.
This stops the oscillation of the control circuit (see Fig. 2 (D)) and interrupts its pulse control, so that the switching regulator immediately stops when the output voltage drops. The output is cut off, and damage to the switching regulator and the load circuit can be prevented.

〔Effect of the invention〕

As described above, according to the present invention, a transistor to which a signal to detect a voltage drop is inputted to the base and a predetermined voltage applied between the emitter and the collector, an output terminal to which a constant voltage is supplied, and a ground the collector of the transistor is connected to the gate via a Zener diode, and the switching element is connected between the ground and an output terminal to which a constant voltage is input; A predetermined voltage applied to the circuit is supplied from a constant voltage power supply via a switching circuit and a delay circuit that are controlled on and off based on a control signal that controls on and off the signal to be detected, and this signal to be detected is a reference signal. When the voltage falls below the voltage, the switching element becomes conductive and drops the constant voltage to ground, thereby cutting off the output from the output terminal, but when the signal to be detected is off, a predetermined voltage is supplied to the transistor. Since the low voltage detection circuit is configured so that the output from the output terminal is not cut off by not switching on the power, first, when the power is turned on, the constant voltage power supply is connected to the emitter and collector of the transistor after a predetermined delay time has passed through the delay circuit. Since a predetermined voltage is applied between the low voltage detection circuit and the emitter of the transistor before the signal to be detected rises to the predetermined voltage.

Since a predetermined voltage is not applied between the collectors, no signal is input to the gate of the switching element even if this transistor is turned off. Therefore, the switching element is in a non-conducting state, and the constant voltage from the output terminal is not applied. Output is not cut off.

However, when a predetermined voltage is subsequently applied to the transistor, if the signal to be detected is equal to or higher than the reference voltage, the transistor is on, and the predetermined voltage passes through the transistor and falls to ground, causing switching. No signal is input to the gate of the element, so the switching element is in a non-conducting state, and a constant voltage continues to be output from the output terminal. Furthermore, if the voltage of the signal to be detected in this state drops due to short-circuiting or destruction of the load and becomes below the reference voltage, the bases of the transistors 1 to 17 become I7 level, which turns off the transistors, so the predetermined voltage becomes Therefore, the switching element becomes conductive, and the constant voltage applied to the output terminal passes through the switching element and falls to the ground, so the output from this output terminal becomes When the signal to be detected is in the off state by the on-off control signal, the switching element is turned off by the on-off control signal, and the predetermined voltage is not applied to the transistor. , the output from the output terminal will not be cut off as described above.

Thus, according to the present invention, when the power is turned on, the output does not operate before the output voltage of the output whose voltage drop is to be detected rises, and when a drop in the output voltage is detected, the output can be immediately shut off. This can prevent damage to the Swissindustry regulator, etc. that outputs the signal to be detected, and when the signal to be detected is in the OFF state, the wooden voltage detection circuit is not activated, and the output terminal is Since the output of the voltage detector is not cut off, an extremely excellent low voltage detection circuit can be provided, which does not cause the wooden voltage detection circuit to malfunction and cut off its output due to the on/off state of the signal to be detected. .

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the low voltage detection circuit according to the present invention, and Fig. 21m (A) to (D) do not show the operation timing of the low voltage detection circuit of Fig. 1, but are time charts 1. . FIG. 3 is a circuit diagram showing an example of a conventional low voltage detection circuit. 10...Low voltage detection circuit; 11.28...Input terminal; 12.16.23...Zener diode; 13
゜17.20.32...Transistor; 14.1
8゜1.9, 22, 26, 30.3]...Resistance; 1
5... Electrolytic capacitor; 21... Capacitor;
24...SCR. 25... Output terminal; 27... Protection diode;
29...FET. Patent applicant: Stanley Electric Co., Ltd. Representative: Patent attorney Kodo Hirayama: Patent attorney Tamotsu Kaizu Three procedural amendments (M'R) July 25, 1999 Commissioner of the Patent Office Yoshi 1) Moon Takeshi 1. Indication of the case Patent Application No. 21027 of 1988 2. Name of the invention Low voltage detection circuit 3. Relationship with the case by the person making the amendment Patent applicant address 2-9-13 Nakameguro, Meguro-ku, Tokyo Name name
(230) Stanley Electric Co., Ltd. 4, Agent address: 1, Shinjuku, Shinjuku-ku, Tokyo 160. -1.3-12
Neutral building 2nd floor Telephone 03 (352) 1808 Heisei 1
June 12, 1999 (Delivery address: July 4, 1999) 6, [Brief explanation of drawings] column 7 of the specification subject to amendment, Contents of the amendment

Claims (1)

[Claims] A transistor is connected between the base of which a signal to detect a voltage drop is input and a predetermined voltage is applied between the emitter and collector, and the output terminal to which a constant voltage is supplied and ground, and whose collector is a Zener. The transistor includes a switching element connected to the gate via a diode and between an output terminal to which a constant voltage is input and the ground, so that the predetermined voltage applied to the transistor is supplied from the constant voltage power supply. The switching element is supplied through a switching circuit and a delay circuit that are controlled to turn on and off based on a control signal that controls on/off the signal to be detected, and when the signal to be detected falls below a reference voltage, the switching element becomes conductive. Therefore, by dropping the constant voltage to ground, the output from the output terminal is cut off, but
A low voltage detection circuit, characterized in that when the signal to be detected is off, a predetermined voltage is not supplied to the transistor, so that output from the output terminal is not cut off.