RU2275670C1 - Overload protection block for use in electric power circuits - Google Patents

Abstract

FIELD: engineering of radio-electronic equipment for providing resistance to interference.

SUBSTANCE: overload protection block for utilization in electric power circuits contains stabilitron-resistor threshold device connected to it output and transistor, input of which is connected to output of stabilitron-resistor threshold device, second stabilitron-resistor threshold device, stabilitron of which is connected to stabilitron of first stabilitron-resistor threshold device, and second transistor, connected serially with first transistor, while input of second transistor is connected output of second stabilitron-resistor threshold device, while resistor of second stabilitron-resistor threshold device is connected to common point of serially connected transistors, which are connected between outputs of protection block. Also, block has two additional resistors, connected in parallel to first and second transistors.

EFFECT: increased reliability of block operation during protection from overloads by voltage.

2 cl, 2 dwg

Description

The overvoltage protection unit in power circuits belongs to the field of electrical engineering and can be used in electronic equipment (CEA) devices to provide noise immunity and resistance of CEA to the effects of powerful impulse noise along power circuits.

Known devices designed to reduce interference, such as low-pass filters in power circuits [1]. In circuits that themselves create interference, nonlinear devices are used to reduce the generated interference, for example, a diode connected in parallel with an inductance [2]. These devices are extremely simple and quite effectively limit interference.

However, they are not applicable for suppressing or limiting impulse noise arising in the power supply circuits of switching devices, when, for example, automation switches off overload or (especially) short circuit in the load. In addition, overvoltage sources in the REA power supply circuits can also be located outside the REA. In particular, it can be pulses of discharge of static electricity.

Known blocks of overvoltage protection in power circuits using non-linear resistances, zener diodes or special limiting diodes (actually working also on the principle of a zener diode) [3]. To protect against pulsed high-power interference, parallel voltage limiters are used using, for example, a thyristor, the control electrode of which is connected through a zener diode to the thyristor anode [4]. Other controllable elements can be used to protect against impulse noise.

The closest in technical performance and the achieved result can be recognized as a device for surge protection [5], the principle of which is based on the formation of shunt current pulses in the circuit in which the surge pulses occur.

This device is made in the form of a parallel voltage limiter containing a zener-resistor threshold device and a transistor, the control input of which is connected to the output of the zener-resistor threshold device, and the output is parallel to the power buses. The device ballast is the integrated resistance of the power circuits.

However, it (with its utmost simplicity) has reduced functional reliability: when the zener diode or transistor breaks in the circuit, the overvoltage protection function disappears, and when the transistor closes in the circuit, the supply voltage disappears. And another thing: this device can generate an overload current pulse when the power is turned on, if this voltage exceeds the stabilization voltage of the zener diode. In addition, a shunt current pulse will not be generated if the time constant for establishing the interference voltage is greater than the time constant for charging the capacitor.

The objective of the proposal is to increase the reliability of the unit while protecting against voltage overloads.

This problem is solved in that in the block of protection against voltage overloads in the power supply circuits, containing a zener-resistor threshold device and a transistor connected to its output, the input of which is connected to the output of the zener-resistor threshold device, and the output is connected to the output of the block a second zener diode threshold device, the zener diode of which is connected to a zener diode of the first zener diode threshold device, and a second transistor connected in series with th transistor, the input of the second transistor connected to the output of the second resistor-zener threshold device, and the second resistor is a resistor-zener threshold device connected to the common point of the serially connected first and second transistors. In addition, the overvoltage protection unit in the power supply circuits is equipped with two additional resistors connected in parallel to the first and second transistors.

Figures 1 and 2 are diagrams of a surge protection unit in power circuits.

The drawings show:

VT1 and VT2 are transistors providing overvoltage protection;

Zener diodes VD1, VD2 and resistors R1 and R2, forming sequential zener-resistor threshold devices;

U0, U1, U2 - points on the circuit of the proposed device and the corresponding voltage on them (see below).

In Fig.2, additional resistors R3 and R4 are each connected in parallel to transistors VT1 and VT2, respectively.

Made block (Fig.1 and 2) as follows.

Surge protection is subject to a circuit (not shown in the drawings) connected to the terminals U0 (common bus) and U2 (power bus). The Zener diodes VD1 and VD2 of the Zener diode threshold devices VD1-R1 and VD2-R2 are connected to the output U2 (power bus). Resistor R1 of one zener diode threshold device VD1-R1 is connected to a power bus, and resistor R2 of a second zener diode threshold device VD2-R2 is connected to a common point U1 of transistors VT1 and VT2 connected in series. Two transistors VT1 and VT2 connected in series (preferably field-effect transistors, for high-voltage circuits - IGBT type transistors; bipolar transistors can be used, for which measures must be taken to limit the base currents; thyristors can be used to control “disposable” systems) between pins U0 and U2. The outputs of the zener-resistor threshold devices (common points of the zener diodes and resistors of each such device) are connected to the control inputs of the transistors. The common point of two series-connected transistors forms a technological point (terminal U1), which is used to test the operability of series-connected transistors VT1 and VT2 at the stage of manufacturing and tuning. In figure 2, these transistors are shunted by resistors R3 and R4. If the resistances R3 and R4 are equal, the potential at the point U1 is equal to half the supply voltage of the REA. In this case, the voltage at the Zener diode VD2 is half that of the Zener diode VD1 (almost all the time - until the appearance of short-term overvoltage pulses in the power circuits of the REA).

The block works as follows.

As long as the voltage between the terminals U2 and U0 (the supply voltage of the electronic equipment) does not exceed the stabilization voltage of the zener diodes VD1 and VD2, the zener diodes are closed, the voltage at the control inputs of the transistors (on resistors R1 and R2) is equal to zero. In this case, both transistors VT1 and VT2 connected in series are closed and there is no current through them (at least the total current does not exceed the sum of the leakage currents of the Zener diodes and transistors; for the unit, this is the standby mode). If in the block shunting reasonably high-resistance resistors R3 and R4 are used (figure 2), then a slight additional current flows through them.

When a pulsed noise occurs, in which the sum of the supply voltage and the interference pulse exceeds a predetermined level, the zener diode VD1 starts to pass current, a voltage is applied to the resistor R1, which is applied to the control input of the transistor VT1, it opens, and the voltage at the point U1 decreases to zero, the zener diode VD2 also begins to pass current, a voltage is allocated to resistor R2, which is applied to the control input of transistor VT2. At this moment, both transistors VT1 and VT2 open and form a shunt between the terminals U0 and U2. Moreover, the higher the emission of the interference pulse, the greater the control voltage and the stronger the transistors open. The current amplitude is limited only by the internal dynamic resistance of the interference source (for this, transistors VT1 and VT2 must have the necessary parameters for voltage and output current). At the end of the interference pulse, the zener diodes are closed, the voltage from the control inputs of the transistors is removed, they are also closed, and the unit again goes into standby mode.

Parallel connection of the control circuits of transistors VT1 and VT2 (zener-resistor threshold devices VD1-R1, VD2-R2) according to the function performed and the serial connection of the transistors VT1 and VT2 in the block can improve its reliability and avoid unexpected short circuits in the protection circuit, unlike from the prototype, in which only one transistor is used, at the closure of which the equipment becomes inoperative. In the proposed block, any one failure can only lead to failure of the protection, but never lead to a failure of the type of short circuit in the power circuit. If necessary, to block faults of an open type block, such blocks can be connected in parallel.

In the proposed unit, the Zener diodes VD1 and VD2 should be installed with a minimum excess of the stabilization voltage U _stub over the maximum possible supply voltage U _{pit.max of the} protected REA (with the necessary allowance for the voltage at the control inputs of the controlled elements). This allows, under conditions of any interference, to ensure the rated mode of operation of the protected equipment and to provide it with an estimated service life and service life.

The unit can be used both independently to protect CEA along power supply circuits, for example, as a part of a stand, and as part of a protected CEA as its integral part.

The proposed set of features in the proposed by the author of the overvoltage protection in the power supply circuit has not been met before to solve the problem and does not follow explicitly from the prior art, which allows us to conclude that the technical solution meets the criteria of "novelty" and "inventive step". Standard zener diodes can be used as elements for the implementation of the device, and field effect transistors for low voltage circuits or IGBT transistors for high voltage power supply systems can be used as controlled elements.

Information sources

1. Power sources CEA. Directory. Ed. G.S. Naivelt. M., "Radio and Communications", 1985, p.160, Fig.4.19.

2. Kazakov L.A. REA electromagnetic devices. Directory. Moscow, "Radio and Communications", 1991, p.305, Fig. 10.7, a.

3. Overvoltage protection circuit. UK application No. 2046539, H 02 H 9/04.

4. Surge protection device. RF application No. 93054916, N 02 H 9/04.

5. Device for surge protection. RF patent No. 1705947, H 02 H 9/04.

Claims (2)

1. The overvoltage protection block in the power supply circuits, comprising a zener-resistor threshold device connected to its output and a transistor, the input of which is connected to the output of a zener-resistor threshold device, characterized in that a second zener-resistor threshold device, a zener diode, is additionally introduced into it which is connected with the zener diode of the first zener diode threshold device, and a second transistor connected in series with the first transistor, the input being second of the first transistor is connected to the output of the second zener-resistor threshold device, and the resistor of the second zener-resistor threshold device is connected to a common point of the transistors connected in series, which are connected between the output terminals of the block. 2. The overvoltage protection block in the power supply circuits according to claim 1, characterized in that two additional resistors are connected to it, connected in parallel to the first and second transistors.

Images