RU2294043C2 - Overcurrent protective device - Google Patents

Abstract

FIELD: microelectronics; protection of wire communication equipment against heavy currents due to occurrence of unwanted voltages in communication line.

SUBSTANCE: proposed protective device has switching unit transferred from low-resistance state to current-limiting mode in response to signal coming from overcurrent control unit or from current-limiting mode to high-resistance state in response to signal arriving from unit controlling overvoltage with respect to peak value of AC or DC voltage and overvoltage with respect to RMS value of AC voltage. Switching unit uses inertia optoelectronic switch circuit arrangement with normally closed contacts. Protective device is inserted in series with communication line. Circuit arrangement of communication-line overcurrent protective device units can be optimized for each polarity of emergency voltages or separately for DC and DC overcurrent levels.

EFFECT: enhanced operating reliability.

1 cl, 4 dwg

Description

The invention relates to the field of microelectronics and can be used to protect wired communication equipment from dangerous currents caused by the ingress of extraneous voltages in the communication line.

It is known that a protection device consisting of a switching unit is included in a communication line break, which, upon a signal from a current control unit during overcurrent, switches from a low-impedance state to current limiting mode, and according to a signal from a voltage control unit during overload, an amplitude value of AC or DC voltage - from current limiting mode to high resistance state. The switching unit of such a protection device can be made according to the electric circuit on bipolar transistors [1] or on field effect transistors with an induced channel [2].

The aim of the invention is to improve the technical characteristics of the protection device against current overloads, increasing the reliability of its operation.

This goal is achieved by the fact that, in the protection device included in the communication line break, the switching unit is made according to the electrical circuit of an inertial optoelectronic switch with normally closed contacts. The switching unit, upon a signal from the current monitoring unit during overcurrent, switches from the low-impedance state to the current limiting mode, and according to the signal from the voltage monitoring unit during overloads according to the amplitude value of the alternating or direct voltage and when overloaded by the effective value of the alternating voltage, from the current limiting mode in a high resistance state.

The figure 1 presents a structural diagram of the proposed protection device, and in figure 2 its current-voltage characteristic. The protection device 2 included in the breaking of the communication line 1 consists of a switching unit 3 made according to the electrical circuit of an inertial optoelectronic switch with normally closed contacts, a voltage control unit 4, a current control unit 5.

Figure 2a shows the I-V characteristic of a DC protection device 2. When 1 current flows in the communication line with an amplitude in the range of values from zero to | I1 | the switching unit 3 is in a low-impedance state and the I – V characteristic of the protection device 2 is almost linear. If the current amplitude in the communication line 1 is exceeded, | I1 | the current control unit 5 generates a signal 6, by which the switching unit 3 enters the current limiting mode. If the DC voltage drop across the protection device 2 exceeds the value of U1, then the switching unit 3 by signal 7 from the voltage monitoring unit 4 will go into a high-resistance state.

If on alternating current the effective value of the voltage drop across the protection device 2 exceeds U1, then the switching unit 3, by signal 7 from the voltage monitoring unit 4, will go into a high-impedance state, and the I – V characteristic of the protection device 2 will take the form shown in figure 2b. In a high-resistance state, the protection device 2 dissipates a small amount of power, which ensures high reliability of its operation in emergency mode, for example, if an extraneous voltage of the AC mains with an effective voltage value of more than U1 gets into the communication line.

The figure 3 presents an example of an electrical circuit diagram of one of the possible options for the practical implementation of the inventive device for protecting the communication line from current overloads, explaining its operation in the case of unipolar voltage. The current control unit 5 is made on the resistor R1 and the diode VD1, and the voltage control unit 4 is on the resistor R2. The switching unit 3 consists of a LED VD2, photodiodes VD3-VD (3 + n), a resistor R3 and a field effect transistor with integrated channels VT1.

The scheme works as follows. When 1 current flows in the communication line in the range of values from zero volts to I1, the field-effect transistor with an integrated channel VT1 is in a low-resistance state. If the current in the communication line 1 exceeds the value of I1, then the voltage drop across the resistor R1 will be higher than the threshold for switching on the diode VD1 and the LED VD2 connected in series. When current flows through the VD2 LED, a light stream is emitted, illuminating the matrix of n series-connected VD3-VD (3 + n) photodiodes, which generates photo-emf, creating a voltage on resistor R3 sufficient to control the gate of the field-effect transistor with an integrated channel VT1. The larger the current flowing through the VD2 LED, the more the blocking voltage is applied between the gate and the source of the field-effect transistor with integrated channel VT1, the higher its output resistance, while the current in communication line 1 decreases. Due to such negative feedback, the switching unit 3 provides a current limiting mode. The value of resistor R2 is selected so that when the line 1 is overloaded, when the constant voltage or the actual value of the alternating voltage on the protection device 2 exceeds U1, a current will flow through the VD2 LED, which will reliably lock the field-effect transistor with the built-in channel VT1, transferring the switching unit 3 to a high resistance state. The described mode of operation corresponds to the current-voltage characteristic shown in figure 2A. The value of the resistor R3 is selected so that when the line 1 is overloaded, when the effective value of the AC voltage drop on the protection device 2 exceeds U1, the recovery time of the low-resistance state of the field-effect transistor with the built-in channel VT1 is longer than the alternating voltage half-cycle. Such an inertia of the optoelectronic switch ensures that the switching unit 3 is transferred to the high-resistance state described by the I – V characteristic shown in FIG. 2b.

Known circuitry solutions can significantly improve the characteristics of the above embodiment of the practical implementation of the inventive device for protecting the communication line from current overloads. Reducing the resistance of the protection device in a low-impedance state will allow, for example, a contactless current monitoring unit or using the property of a field-effect transistor with an integrated channel VT1 to enter saturation mode, providing a current limiting mode without using a resistor R1. The accuracy of setting the voltage value U1, above which the switching unit 3 goes into a high-resistance state, will significantly increase if the zener diode is connected in series with the resistor R2, and replacing the resistor R2 with a current source will ensure the reliability of the protection device with minimal overloads. On alternating current, it is effective to use a capacitor voltage in the control unit instead of the resistor R2. If necessary, the circuitry solutions of the units of the communication line protection device can be optimized for each of the polarities of the emergency voltage or separately for the levels of overloads for direct and alternating current.

Information sources

1. US patent No. 4475012, CL. H 04 M 1/31, publ. 10/02/84.

2. US patent No. 5198957, CL. H 02 H 9/04, publ. 03/30/93.

Claims (1)

A current overload protection device included in a communication line break consisting of a switching unit, which, upon a signal from a current control unit during current overload, switches from a low-impedance state to current limiting mode, and according to a signal from a voltage control unit during voltage overload, from mode of limiting the current to a high-resistance state, characterized in that the switching unit is made according to the electrical circuit of an inertial optoelectronic switch with normally closed contacts on field-effect transistors with built-in nnym channel, transition time from which a low-impedance off state half cycle longer sequence of alternating voltage when the voltage overload.

Images