JPS6326433B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention provides a method for cutting off the output of a DC stabilized power supply when the output voltage of the power supply is abnormally changed (abnormal drop or rise in output voltage). The present invention relates to an alarm circuit that prevents the spread of a failure and outputs an alarm, and particularly relates to an alarm circuit that has a simplified circuit configuration.

(b) Background of the Technology In recent years, a large number of alarm circuits have been used for maintenance of various devices, but with the development of communication technology, the above-mentioned alarm circuits are no exception, and miniaturization is required.

(c) Prior art and problems An example of a conventional alarm circuit will be explained using FIG.

FIG. 1 is a block diagram of a conventional alarm circuit.
In the figure, 1 is a DC voltage input terminal, 2 is a circuit breaker, 3 is a DC-DC converter, 4 is a constant voltage stabilizing circuit, 5 is an overvoltage detection section, 6 is a low voltage detection section, 7, 8, and RLX are Relay, 9 is output terminal, 1
0 is the alarm output terminal, 7', 7'' are the contacts of relay 7,
8' and 8'' are contacts of relay 8, X ₁ , X ₁ ', and X ₂ are contacts of relay RLX, R ₁ to R ₅ are resistors, ZD ₁ and ZD ₂ are Zener diodes, and TR ₁ and TR ₂ are transistors. ,
_L1 is a trip coil.

The DC input voltage V applied to the input terminal 1 passes through the circuit breaker 2 to the DC-DC converter 3.
is added to the current, converted to DC, and output. Then, by applying this DC voltage to the constant voltage stabilizing circuit 4, a stabilized DC voltage is obtained at the output terminal 9.

Now, if the DC voltage appearing at the output terminal 9 drops abnormally due to a short circuit in the load connected to the output terminal 9 or other causes, the low voltage detection section 6 has a circuit that detects this and outputs an alarm. be. When the DC voltage at the output terminal 9 drops below a certain value, the current flowing through the relay 8 included in the low voltage detection section 6 becomes below the operating current value, and the contacts 8' and 8'' of the relay 8 are closed. , At this time, contact _X1 of relay RLX and
Since _X1 ' is closed, trip coil _L1 detects an overcurrent, turns off circuit breaker 2, reduces the DC voltage appearing at output terminal 9 to zero, and current flows to alarm output terminal 10, causing an alarm. is output.

Further, when the DC voltage appearing at the output terminal 9 abnormally increases for some reason, the overvoltage detection section 5 is a circuit that detects this and outputs an alarm. now,
When the DC voltage at the output terminal 9 rises above a certain value, the current flowing through the relay 7 included in the overvoltage detection section 5 reaches the operating current value, contacts 7' and 7'' of the relay 7 close, and when operating, , contacts X ₁ and X ₁ ′ of relay RLX are closed, so trip coil L ₁ detects the overcurrent and circuit breaker 2
is turned off, the DC voltage appearing at the output terminal 9 is reduced to zero, and current flows to the alarm output terminal 10 to output an alarm.

As described above, the conventional alarm circuit is provided with a low voltage detection section and an overvoltage detection section, and an alarm is outputted both in the case of low voltage and in the case of overvoltage, thereby reducing the DC voltage appearing at the output terminal to zero.

However, in the configuration of such a conventional alarm circuit, a low voltage detection section and an overvoltage detection section are provided, and two relays are also used, which has the disadvantage that the structure becomes large.

(d) Purpose of the Invention The purpose of the present invention is to eliminate such conventional drawbacks and simplify the circuit configuration.

(e) Structure of the invention When the output voltage of a power supply that is supposed to supply a constant voltage to a load becomes overvoltage or low voltage, an alarm circuit that outputs an alarm outputs a voltage higher than the constant voltage at the output terminal of the power supply. A first series circuit consisting of a first Zener diode and a diode, which becomes conductive when it appears, and a second series circuit consisting of a first transistor, a relay, and a second transistor are connected in parallel, and the first The transistor is connected to the second transistor by a second Zener diode that becomes conductive at a voltage equal to or lower than the current value of the relay.

(f) Embodiment of the Invention An embodiment of the alarm circuit of the present invention will be described with reference to FIG.

FIG. 2 is a block diagram of the alarm circuit of the present invention. In the figure, the same devices as in Figure 1 are given the same numbers, ZD ₃ and ZD ₄ are Zener diodes, TR ₃ and TR ₄ are transistors, R ₆ and
R ₇ is a resistor, D ₁ to D ₃ are diodes, 11 is an alarm circuit, 12 is a relay, and 12' is a contact point of the relay 12.

In normal operation, as explained in the prior art, the DC input voltage V applied to the input terminal 1 is applied to the DC-DC converter 3 via the circuit breaker 2, where it is converted into DC and output. Ru. and,
By applying this DC voltage to the constant voltage circuit 4, a stabilized DC voltage is obtained at the output terminal 9.

Now, the load connected to the output terminal 9 is short-circuited, or
If the DC voltage appearing at the output terminal 9 drops below a certain value due to other causes, the current flowing through the relay 12 becomes below the operating current, and the contact 1 of the relay 12
2′ and 12″ are closed, contacts _{X 1} and
Since _X2 ' is closed, trip coil _L1 detects an overcurrent, turns off circuit breaker 2, reduces the DC voltage appearing at output terminal 9 to zero, and current flows to alarm output terminal 10. An alarm is output.

Additionally, if the DC output voltage of the constant voltage stabilizing circuit rises above a certain value for some reason, the Zener diode ZD ₁ becomes conductive, generating a bias voltage that turns on the transistor TR _{1 .}
turns on. As a result, R ₇ , D ₄ ,
The current flowing into the base of the transistor TR ₄ via D ₅ and ZD ₄ now flows into the collector of the transistor TR ₃ , turning off the transistor TR ₄ . As a result, the current flowing through the relay 12 becomes less than the operating current of the relay 12, and the relay 12 becomes lower than the operating current of the relay 12.
2 contacts 12' and 12'' close.This relay 1
2 contacts 12' and 12'' close, the trip coil _L1 detects an overcurrent, turns off the circuit breaker 2, reduces the DC voltage appearing at the output terminal 9 to zero, and closes the alarm output terminal 10.
Current flows and an alarm is output. Furthermore, in this case, the Zener diode ZD ₃ quickly reaches a saturated state and draws current, so the influence on the load can be avoided as much as possible.

That is, according to the present invention, it is possible to provide an alarm circuit using only one relay.

In addition, in the above alarm circuit 11, an NPN transistor or a field effect transistor is used instead of a PNP transistor, an electronic switch is used instead of a mechanical switch such as a relay,
If the input power source is AC, use an AC-DC converter instead of a DC-DC converter, insert the circuit breaker on the output side of the DC-DC converter, omit the constant voltage stabilizing circuit, and use DC. - Diode D ₁ that detects voltage from the output of the DC converter
Modifications of the embodiment shown in FIG. 2 may be considered, such as inserting a resistor in parallel to the series circuit of D3 and _D3 , but the above-mentioned operation is possible in either case.

(g) Effect of the invention As explained above, the alarm circuit of the present invention does not have a low voltage detection section and an overvoltage detection section, unlike conventional alarm circuits, and only one relay is provided.
The configuration can be simplified with just 1.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a conventional alarm circuit, and FIG. 2 is a configuration diagram of an alarm circuit of the present invention. In the figure, 1 is a DC voltage input terminal, 2 is a circuit breaker, 3 is a DC-DC converter, 4 is a constant voltage stabilizing circuit, 5 is an overvoltage detection section, 6 is a low voltage detection section, 7, 8, 12 is the relay, 9 is the output terminal, 1
0 is alarm output terminal, 11 is alarm circuit, ZD ₁ to
ZD ₄ is a Zener diode, TR ₁ to TR ₄ are transistors, R ₁ to R ₇ are resistors, D ₁ to D ₅ are diodes, and L ₁ is a trip coil.

Claims (1)

[Claims] 1. In an alarm circuit that outputs an alarm when the output voltage of a power supply that is supposed to supply a constant voltage to a load becomes overvoltage or undervoltage, continuity occurs when a voltage higher than the constant voltage appears at the output terminal of the power supply. The first
A first series circuit consisting of a Zener diode and a diode, and a second series circuit consisting of a first transistor, a relay, and a second transistor are connected in parallel, and the first transistor and the second transistor are connected in parallel. An alarm circuit characterized in that the alarm circuit is configured by connecting a second Zener diode which becomes conductive at a voltage lower than the sensing current value of the relay.