JPH0737192Y2 - Fire alarm receiver power circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a power supply circuit of a receiver in a fire alarm system.

[Prior Art] Conventionally, in a fire alarm system, a standby power source such as a battery is installed together with a regular power source such as a commercial power source from the viewpoint of ensuring the reliability of the facility. That is, as shown in FIG. 2, the receiver in the fire alarm equipment is provided with a switching regulator 1 for obtaining a predetermined DC power source from a commercial power source as a regular power source, and a battery 2 for a standby power source, as power sources,
The switching connection of these two power sources to the load 3 is made by a power source switching relay 4 energized by a regular power source.
Power is normally supplied to the load 3 from the switching regulator 1, which is the normal power supply, through the switching contact 5 of the power supply switching relay 4, which is energized by the switching regulator 1. Then, when the power supply from the regular power supply is stopped due to a power failure or the like, the power supply switching relay 4 is deenergized, and the switching contact 5 is switched to supply the power to the load from the battery 2 which is the standby power supply.

[Problems to be Solved by the Invention] In the conventional configuration as described above, the load 3
When a short-circuit accident occurs on the power supply side, the power switching relay 4
Is temporarily de-energized from the voltage drop across it, switching the switching contact 5 to the battery 2 side. Then, an excessive current flows from the battery 2 to the load 3 via the switched contact 5, and the fuse 6 provided on the way is blown. Further, when the switching contact 5 of the power source switching relay 4 is switched to the battery 2 side, the voltage drop is restored, and the switching regulator 1 is energized again to switch the switching contact 5 to the switching regulator 1 side. The power switching relay 4 is deenergized again due to a short-circuit accident on the load 3 side, and switches the switching contact 4 to the battery 2 side again.

In this way, the power source switching relay 1 is repeatedly energized and deenergized, and the switching contact 5 is melted and damaged.

Therefore, in order to repair a receiver that has caused a short circuit accident, it is needless to say that the cause of the short circuit is removed, but the fused fuse 6 and the melted switching contact 5 or the power source switching relay 4 as described above are removed. Will have to be replaced.

[Means for Solving the Problems] The power supply circuit according to the present invention comprises a current monitoring circuit for monitoring the current flowing from the common power supply to the switching contact, and a current limiting circuit for limiting the current flowing from the common power supply to the switching contact. ,
This problem is solved by driving this current limiting circuit by a current monitoring circuit.

[Operation] That is, the power supply circuit according to the present invention is
An overcurrent generated by a short-circuit accident that occurs on the load side is monitored by a current monitoring circuit, and when an overcurrent is detected, the current limiting circuit limits the current to the load side while continuing to energize the power supply switching relay. Prevents the contact from switching to the standby power supply side.

[Embodiment] FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit according to the present invention. As a conventional power supply, a switching regulator 1 which obtains a predetermined DC power supply from a commercial power supply and uses it as a regular power supply And a battery 2 serving as a standby power source, and switching connection of these two power sources to the load 3 is performed by a power source switching relay 4 energized by a regular power source. Power is normally supplied to the load 3 from the switching regulator 1, which is the normal power supply, through the switching contact 5 of the power supply switching relay 4, which is energized by the switching regulator 1. Then, when the power supply from the regular power supply is stopped due to a power failure or the like, the power supply switching relay 4 is deenergized, and the switching contact 5 is switched to supply the power to the load from the battery 2 which is the standby power supply.

Although the above-mentioned configuration is similar to the conventional power supply circuit, in the power supply circuit according to the present invention, further, the current monitoring circuit 7 for monitoring the current flowing from the switching regulator 1 which is the regular power supply to the switching contact 5, and the switching regulator 1 A current limiting circuit 8 for limiting the current flowing from the switching contact 5 to the switching contact 5 and a display 9 are provided. More specifically, the current monitoring circuit 7 includes a resistor 10 inserted in an electric path from the switching regulator 1 to the switching contact 5, a transistor 11 and resistors 12 and 13 which are switched by a potential difference generated between both ends of the resistor 10. And a switching circuit. The current limiting circuit 8 is composed of a transistor 14 inserted in the electric path from the switching regulator 1 to the switching contact 5 and a switching circuit composed of resistors 15 and 16. The output of the current monitoring circuit 7 is input to the current limiting circuit 8 via the backflow prevention diode 17 and also to the light emitting diode 19 as a display via the inverter 18. In addition,
In the above-mentioned embodiment, the indicator 9 made of the light emitting diode as described above is used as the display 9, but the same effect can be expected sufficiently even if an acoustic device such as a buzzer is used.

Now, in the power supply circuit according to the present invention configured as described above, the power supply switching relay 4 is normally energized by the switching regulator 1 so that the switching contact 5 becomes the normal power supply side, and the power supply to the load 3 is supplied to the switching regulator. 1
Starting from As long as the load 3 is operating normally, the transistor 10 does not turn on because the current more than the predetermined value does not flow through the resistor 10 of the current monitoring circuit 7, and therefore the transistor 14 of the current limiting circuit 8 is in the on state. The power is continuously supplied and the light emitting diode 19 is not turned on.

When the power supply from the switching regulator 1 is stopped due to a power failure or the like, the power supply switching relay 4 is deenergized, and the switching contact 5 is switched to supply power to the load from the battery 2 which is a standby power supply. Of course, since no current flows through the light emitting diode 19, it does not light up.

When a short-circuit accident occurs on the load 3 side, an excessive current of a predetermined value or more flows through the resistor 10 of the current monitoring circuit 7 to cause a transistor failure.
11 is turned on, so that the transistor 14 of the current limiting circuit 8
Is turned off to stop the power supply and turn on the light emitting diode 19 to indicate that the load 3 is short-circuited. However, since the power switching relay 4 continues to be energized by the switching regulator 1, the switching contact 5
Does not switch to the battery 2 side, which is the standby power source. Therefore, since the power source switching relay 4 is not repeatedly energized / deenergized, the switching contact 5 is not melted and damaged, and no current flows from the battery 2, so that the relay 2 is The provided fuse 6 is not blown.

In the above-described embodiment, the occurrence of the short-circuit accident on the load side can be notified by providing the indicator light including the light emitting diode 19. However, even without such an indicator, the switching contact 5 is melted and damaged. The initial objective of preventing blown fuse 6 is achieved.

[Effects of the Invention] As described above, the power circuit of the fire alarm receiver according to the present invention has a current monitoring circuit that monitors the current flowing from the regular power source to the switching contact and a current limiting circuit that limits the current flowing from the regular power source to the switching contact. Since the current limiting circuit is driven by the current monitoring circuit, the power switching relay will not be deactivated even if a short-circuit accident occurs on the load side. There is no melting damage due to repeated operation, and there is no melting of the fuse due to excessive current from the standby power supply.

Furthermore, since a display device driven by the current monitoring circuit is provided, when a short-circuit accident occurs on the load side,
The occurrence can be confirmed quickly.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a power supply circuit of a fire alarm receiver according to the present invention, and FIG. 2 is a circuit diagram showing a power supply circuit of a conventional fire alarm receiver. It is indicated by the same reference numeral. 3 ... Load, 1 ... Regular power supply (switching regulator), 2 ... Standby power supply (battery), 5 ... Switching contact, 4 ... Power supply switching relay, 7 ... Current monitoring circuit, 8 ... Current limiting circuit,
9 ... Indicator (light emitting diode)

Claims (4)

[Scope of utility model registration request] 1. A switching contact for switching a power supply path to a load between a regular power source such as a commercial power source and a standby power source such as a battery is switched and connected by a power source switching relay energized by the regular power source. In the power circuit of the fire alarm receiver, a current monitoring circuit for monitoring the current flowing from the regular power source to the switching contact and a current limiting circuit for limiting the current flowing from the regular power source to the switching contact are provided. A power supply circuit of a fire alarm receiver characterized in that a current limiting circuit is driven by the current monitoring circuit. 2. A switching contact for switching a power supply path to a load between a regular power source such as a commercial power source and a standby power source such as a battery is switched and connected by a power source switching relay energized by the regular power source. In the power circuit of the fire alarm receiver, a current monitoring circuit that monitors the current flowing from the regular power source to the switching contact, a current limiting circuit that limits the current flowing from the regular power source to the switching contact, and an indicator. A power supply circuit for a fire alarm receiver, characterized in that the current limiting circuit and the indicator are driven by the current monitoring circuit. 3. The power circuit of the fire alarm receiver according to claim 2, wherein the indicator is an indicator lamp. 4. The fire alarm receiver power supply circuit according to claim 2, wherein the display is an acoustic device.