JPH0594885A - Wire breaking detection circuit - Google Patents

Abstract

PURPOSE:To allow breaking of wire to be detected with little power consumption for low impedance loads. CONSTITUTION:One end of a lamp 2 is connected to the positive electrode of a DC power source 3 while the other end is grounded via an inductance 4. An oscillating circuit is provided as an AC signal source and its output terminal is connected to between a lamp 2 and the inductance 4 via a resistance 6. Since the impedance of the lamp 2 is small, no AC signal is generated in the inductance 4 when there is no wire broken in the lamp 2 while such a signal is generated in the inductance 4 when there is a wire broken in the lamp 2. Breaking of wire is detected by determining whether or not an AC signal is found at a detection terminal 7 connected to between the lamp 2 and the inductance 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to provide a novel disconnection detection circuit capable of reducing the power loss at the time of detection. For example, the disconnection of a lamp is detected and displayed, or the disconnection is detected. It can be widely applied to applications such as cutting off power supply to a circuit so that unnecessary power is not consumed later.

[0002]

2. Description of the Related Art A method of detecting the presence or absence of a current flowing through a lamp is generally used for detecting a low impedance load such as a lamp disconnection, as shown in FIG.

That is, a resistor b is connected in series to the lamp a, which is grounded, and a power supply voltage is supplied from a direct current power source c to the lamp a. The lamp current i is voltage-converted by the resistor b and taken out from a detection terminal d. In this case, it is determined that the lamp a has broken because the lamp current i has become zero.

[0004]

However, the above-mentioned method has a problem in that when the value of the lamp current i is large, the resistance loss becomes large, which violates the demand for power saving.

In particular, in battery-powered portable equipment, for example, portable liquid crystal projector devices, there is a restriction that the capacity of the battery cannot be increased unnecessarily in order to meet the demand for size reduction and weight reduction. There is a circumstance in which the power loss due to the detection of the burnout of the light cannot be ignored.

[0006]

Therefore, in order to solve the above-mentioned problems, the present invention connects an inductance in series to a low impedance load that receives power from a DC power supply and grounds one end thereof, A signal from an AC signal source is supplied to the inductance, and it is detected whether or not the low impedance load is disconnected depending on the presence or absence of the AC signal generated in the inductance.

[0007]

According to the present invention, an inductive load (inductance) is connected in series to a low impedance load without connecting a resistive load in series, and the low impedance load is controlled by whether an AC signal is generated or not. Since it is detected whether or not the wire is disconnected, the resistance loss can be reduced, and the wire disconnection can be detected without waste in terms of power consumption.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The disconnection detection circuit of the present invention will be described below with reference to the illustrated embodiments.

FIG. 1 shows a basic configuration 1 of the disconnection detection circuit according to the present invention.

The lamp 2 has one end connected to the positive electrode of the DC power supply 3 and the other end grounded via the inductance 4.

An oscillating circuit 5 is provided for receiving a power supply voltage from the DC power supply 3 to generate a predetermined AC signal.

The output terminal of the oscillation circuit 5 is connected between the lamp 2 and the inductance 4 via the resistor 6, and the terminal voltage of the inductance 4 is taken out from the detection terminal 7.

FIG. 2 is a circuit diagram in which the oscillation circuit 5 is replaced with an equivalent AC signal source 8 in order to explain the operation of the above circuit.

A detecting section 9 shown by a chain double-dashed line in the figure comprises an AC signal source 8, a resistor 6 and an inductance 4, and a disconnection detection signal is taken out from a detection terminal 7.

When the lamp 2 is not broken, the impedance of the lamp 2 is small, so that the AC signal is not taken out from the inductance 4 as shown in the equivalent circuit of FIG.

However, if the lamp 2 is broken, the lamp shown in FIG.
As shown in the equivalent circuit of (b), the resistance 6 and the inductance 4 are connected in series to the AC signal source 8,
The AC signal comes to be output from the detection terminal 7 as the terminal voltage of the inductance 4.

That is, assuming that the AC signal is taken out to the detection terminal 7 only when the lamp 2 is broken and the inductance 4 is an ideal inductance without resistance, the potential of the detection terminal 7 becomes zero when the lamp is not broken, and the lamp current is reduced. There is no resistance loss of the inductance.

FIG. 4 shows an example of a circuit in which the disconnection detection signal is converted into a direct current and used as a signal for displaying the disconnection.

An AC signal detected when the lamp 2 is burnt out is converted into a DC signal by the rectifying circuit 10 and then sent to the LED driving transistor as a base signal.

The rectifier circuit 10 is composed of capacitors 11 and 12 and diodes 13 and 14, and the terminal voltage of the capacitor 12 is divided by resistors 15 and 16 to generate N.
It is designed to be added to the base of the PN transistor 17, and an LED is provided on the collector side of the NPN transistor 17.
18 and a resistor 19 are provided.

Therefore, when the lamp 2 is disconnected, the AC voltage generated in the inductance 4 is converted into a DC voltage and becomes an ON signal to the NPN transistor 17, and the lamp 2
Disconnection is displayed by the LED 18.

5 and 6 show an application example of the disconnection detection circuit.

FIG. 5 shows an example in which when the lamp is burnt out, the relay contact that has been held until then is cut off to cut off the power supply to the lamp and other circuit parts that are being supplied with power from the same power source. It is a thing.

The a-contact 20a of the relay 20 is connected to the power supply line 2
1, which determines whether or not to supply power to the lamp 2 and other circuit parts 22 in the subsequent stage.

The coil 20b of the relay 20 is connected to the collector of an NPN transistor 23 whose emitter is grounded, and its base is connected to a power supply line 21 via a resistor 24 and a power switch 25.

Therefore, when the NPN transistor 23 is turned on and the relay 20 is held by turning on the power switch 25, the power supply voltage is supplied to the lamp 2 and other circuit portions 22.

In the lamp circuit portion, an inductance 4 is connected in series to the lamp 2, and an output signal of the oscillation circuit 5 is added to the inductance 4 via a resistor 6. Between the lamp 2 and the inductance 4, The disconnection detection signal taken out from is sent to the base of the NPN transistor 27 via the rectifier circuit 26.

The collector of the emitter-grounded NPN transistor 27 is connected to the base of the NPN transistor 23. Therefore, when disconnection of the lamp 2 is detected,
The NPN transistor 27 is turned on to turn off the NPN transistor 23, the relay contact 20a is released, and the supply of the power supply voltage to the lamp 2 and other circuit portions 22 is cut off.

FIG. 6 shows an example in which an output pulse of a PWM (pulse width modulation) section which constitutes a switching regulator is used as an AC signal.

In the circuit diagram, the part related to the holding of the relay 20 and the part for releasing the holding of the relay when the disconnection is detected are exactly the same as those in the circuit diagram of FIG. In this configuration, the AC signal associated with is added to the inductance 4.

That is, the primary coil 30a of the transformer 30
Has one end connected to the power supply line 21 and the other end provided with an NPN transistor 31. The NPN transistor 31 is switching-controlled by the PWM unit 29, and rectification extracted from one of the secondary side coils 30b and 30b 30b. Previous AC signal is capacitor 32, resistor 33
Is added to the inductance 4 via.

In the above-mentioned circuit, it can be considered that the lamp 2 corresponds to a backlight when the liquid crystal type projector device is taken as an example, and the other circuit section 22 includes a processing circuit for video and audio. This is to prevent waste of power consumption by cutting off the power supply to the processing circuit for video and audio when the backlight is broken.

[0033]

As is apparent from the above description, according to the present invention, whether or not the low impedance load is disconnected by detecting the AC signal that should occur in the inductance when the low impedance load is disconnected. Since it is possible to determine the power consumption, it is possible to save power for detection of disconnection. Therefore, it is effective to apply this to a load control circuit having a limited power supply capacity.

The above-described embodiment is merely an example of the implementation of the present invention, and the technical scope of the present invention is not construed narrowly by this example alone. Not limited to disconnection detection, motor coil disconnection detection, etc.
It can be widely applied to circuits using low impedance circuit components.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a disconnection detection circuit according to the present invention.

FIG. 2 is an equivalent circuit diagram of FIG.

3A is an equivalent circuit diagram when there is no disconnection, and FIG. 3B is an equivalent circuit diagram when there is disconnection.

FIG. 4 is a circuit diagram showing a display example after detection of disconnection.

FIG. 5 is a circuit diagram showing an application example of the present invention.

FIG. 6 is a circuit diagram showing an application example different from that of FIG.

FIG. 7 is a circuit diagram showing a conventional disconnection detection example.

[Explanation of symbols]

 1 Disconnection detection circuit 2 Low impedance load 3 DC power supply 4 Inductance 5 and 8 AC signal source

Claims (1)

[Claims] 1. A low impedance load, which receives power from a DC power supply, is connected in series with an inductance, one end of which is grounded, and a signal from an AC signal source is supplied to the inductance. A disconnection detection circuit, which is configured to detect whether or not a low impedance load is disconnected depending on the presence or absence of a signal.