JPH06101924B2 - Short circuit alarm circuit - Google Patents

Description

DETAILED DESCRIPTION [Outline] An alarm circuit characterized by detecting a short circuit of a power supply circuit by a change in an inrush current when a power supply is turned on by using a delay due to charging of a capacitor.

[Industrial application field]

The present invention relates to a short circuit alarm circuit for a power supply circuit with an inrush current suppression circuit.

The alarm circuit also notifies the power supply circuit of its normal and abnormal operation,
It is important from the viewpoint of maintenance, and it is desirable that the error can be accurately and accurately displayed.

[Conventional technology]

FIG. 3 shows a short-circuit alarm circuit of a conventional power supply circuit. This power supply circuit is a DC-DC converter used in a telephone exchange, and outputs a divided voltage Vin as a DC voltage Vout and outputs it.
A transformer T is used for insulation of input and output. Switching transistor Q ₄ is turned on / off to interrupt a direct current, and a voltage induced on the secondary side of transformer T is diode-converted.
And rectified by D _5, D ₆ to a DC voltage Vout. L is an inductance and C ₃ is a capacitor, which form a smoothing circuit. C _{2 is} also a capacitor and supplies power when transistor Q ₄ is on.
Supply current with Vin. CNT is a control circuit, output voltage
Monitor Vout and control the on / off period of Q ₄ so that Vout is constant.

Since this circuit contains a large-capacity capacitor C ₂ , a large inrush current occurs when the power is turned on, and a resistor R ₆ is inserted to suppress this. Resistor R ₆ is contact K1 of relay K1
It is inserted and removed by a, and K1a is opened and inserted at startup, and K1a is closed and short-circuited during converter operation. When a large inrush current flows when the power is turned on, a sufficient voltage is generated across the resistor R ₆ to turn on the transistor Q ₃ , and when Q _{3 is} turned on, the transistor Q ₃ turns on.
Q ₁ and Q ₂ are off, relay K 1 is deenergized, so contact K ₁ a remains open. When the charge of the capacitor C ₂ progresses and the inrush current decreases, the transistor Q ₃ turns off,
Q _1, Q ₂ is turned on. When Q ₂ turns on, relay K1 is energized, closing contact K1a. The converter is now ready for operation.
The control circuit CNT lights up the light emitting element (light emitting diode) PC ₁ during normal operation, and the output light of PC ₁ enters the light receiving element (phototransistor) PC ₂ and turns it on, so that the transistor Q ₁ turns on. Thyristor as long as normal operation continues
D ₁ never turns on.

Light-emitting element D ₀ is for alarm, capacitor C ₂ , transistor Q ₄
When the fuse F is blown and the contact Fa is closed, an excessive current flows in the circuit due to a short circuit, etc. Also, it lights up when the light emitting element PC ₁ goes out due to abnormal operation of the converter.

Note that D ₂ and D ₃ are diodes, D ₄ is a zener diode, C ₁ is a capacitor, and R _{1 to} R ₅ are resistors.

[Problems to be solved by the invention]

In this conventional circuit, when powered on and replace a blown fuse, the resistance R ₆ open the contact K1a this time is inserted inrush current at power-on is limited by the resistor R _6. However, since the capacitor C _{2 and the} like are in a short-circuited state, a state in which a large current continues to flow continues, and a voltage for turning on Q ₃ continues to be generated across R ₆ . Therefore, the contact K1a is not closed and the fuse F is not blown, so that the light emitting element D ₀ may not generate an alarm.

The present invention is intended to improve such points and surely generate an alarm when an abnormal current flows.

[Means for solving problems]

The present invention, as shown in FIG. 1, has an inrush current suppressing resistor (R ₆ ).
When the relay circuit (Q ₃ the resistance response to inrush current to a voltage generated in (R ₆₎ is to short the resistor (R ₆₎ when reduced,
And Q _2, K1, K1a), when the excessive current flows through the fuse in the circuit to blow, and the circuit alarm circuit of the power supply circuit and a device (D ₀₎ the circuit operates to generate a warning when the abnormality,
The resistor is connected a series circuit of a capacitor in parallel with (R ₆₎ (C ₄₎ and zener diode (D _7), said alarm device when a persistently high voltage to the resistor (R ₆₎ occurs ( It is characterized by the provision of circuits (R ₇ , D ₈ , Q ₅ ) for operating D ₀ ).

[Action]

When the circuit is short-circuited and an excessive current flows, it rises largely like an inrush current when the power is turned on, but it does not decrease rapidly and the large current continues. Therefore, inrush current suppression resistor R ₆
If a capacitor is connected to the resistor so that the voltage of the resistor does not rise so much with an inrush current and rises with an excessive current due to a short circuit, the former will not give an alarm, and the latter will give an alarm. .

〔Example〕

FIG. 1 shows an embodiment of the present invention. The same parts as those in FIG. 3 are designated by the same reference numerals. As is clear from a comparison between the two, in the present invention, a series circuit of a small capacity capacitor C ₄ and a Zener diode D ₇ is connected in parallel with the inrush current limiting resistor R ₆ .
Further, a transistor Q ₅ is connected in parallel to the thyristor D _1, and the base of this Q ₅ is driven by the voltage of the resistor R ₆ via the resistor R ₇ and the Zener diode D ₆ . The Zener diode D ₇ is a protection diode for surely turning on Q ₃ when the power is turned on.

The operation of FIG. 1 will be described with reference to FIG. 2. In the normal state, the inrush current I has a large value at first, as shown in (a), but decreases rapidly with the elapse of time t. The voltage V _R6 generated in the resistor R ₆ rises gently due to this inrush current, starts decreasing due to the decrease of the inrush current due to the time constant of the capacitor C ₄ , and becomes 0 when the relay K1 closes the contact K1a. Eventually not reach the breakdown voltage V _D8 of zener diode D _8, the diode D ₈ is turned off, thus Q ₅ is turned off.

On the other hand, at the time of abnormality, it becomes as shown in (b), and the inrush current I does not decrease even after the time t has elapsed. Therefore capacitor C ₄
Charging progresses, the voltage of the resistor R ₆ rises and finally exceeds the breakdown voltage V _D8 , the zener diode D ₈ is turned on, the transistor Q ₅ is turned on, and the light emitting device D ₀ is turned on to issue an alarm. Note that V _Q2 and V _Q5 are the collector-emitter voltages of the transistors Q ₂ and Q ₅ . The time constant of C ₄ , that is, the charging time is set to the time when the voltage across R ₆ becomes V _D8 or less.

〔The invention's effect〕

As described above, according to the present invention, in a power supply circuit with an overcurrent warning circuit and an inrush current suppression circuit, an overcurrent due to a circuit failure can be reliably warned, which is very effective.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining operation, and FIG. 3 is a circuit diagram showing a conventional example. In FIG. 1, R _{1 to} R ₇ are resistors, C _{1 to} C ₄ are capacitors, Q _{1 to} Q ₄ are transistors, D ₀ is a light emitting element (LED), D ₁ is a thyristor, D ₂ and D ₃ are diodes, D ₄ , D ₇ , and D ₈ are Zener diodes, K1 is a relay, and K1a is a relay contact.

Claims (1)

[Claims] 1. An inrush current suppressing resistor (R ₆ ) and the resistor (R ₆ )
The relay circuit (Q ₃ , Q ₂ , K1, K1a) that short-circuits the resistor (R ₆ ) when the inrush current is reduced in response to the voltage generated at element circuit operation generating an alarm when an abnormality in the circuit alarm circuit of the power supply circuit and a (D _0), and a capacitor (C ₄₎ in parallel with the resistor (R _6), the resistor (R ₆₎ circuit alarm circuit, characterized in that persistently high voltage provided circuit said to operate the alarm device (D ₀₎ when generating _{(R 7, D 8, Q} 5) to.