RU1772834C - Method of chatterless load switching by reed relay - Google Patents

Abstract

Usage: switching equipment. SUMMARY OF THE INVENTION: To eliminate the influence of the reed switch contacts vibration on the current curve, a time delay between the moment the reed switch is triggered and the moment the transistor switch is unlocked is achieved by increasing the control current of the transistor switch. Zil.

Description

The invention relates to the field of electrical circuit control and can be used in reed relays to eliminate the effect of the bounce of their contacts on the load circuit.

There is a known method of no-bounce load switching by a reed relay based on its optimal control, in which the current in the reed switch control winding is initially increased to the maximum permissible value, and then it is abruptly reset to the lowest level, choosing at the same time the switching moment so that the contact of the reed switch part collision with a predetermined speed selected from the condition that there is no rebound (1).

The disadvantages of this method are the complexity of its implementation, which involves the introduction of a pulse generator, an amplifier-inverter, stabilizing elements, etc., into the relay circuit, and also that it predetermines a limited (albeit increased compared to conventional relays) speed, caused by increase in time to the first (and last in this case) collision of contacts and the impossibility of using forced excitation

The last drawback is free of the method of loadless switching of the load by delaying the signal from the relay output circuit for a time exceeding the interval between adjacent collisions of the contacts

(2).

The delay is accomplished by repeatedly inverting and integrating bounce pulses using transistor switches. RC circuits forcing means, therefore, the circuit implementation of the method is quite complex.

The purpose of the invention is to simplify the method.

This goal is achieved by the fact that in the method of loadless switchover of the load by a reed relay, including supplying a control signal for the operation of the reed switch, the contacts of which switch the control circuit of the transistor key, providing a time delay between the moment the reed switch operates and the moment the transistor switch operates, and the subsequent operation of the transistor switch commuting load current, the specified time delay between the moment of operation of the reed switch and the moment of operation of the transistor yucha provide by increasing the control current sJ 4J H) 00

w

-

E

the transition of the transistor to the value defined by the expression:

B 1B.fehr (112 / rs),

where 1c. gr is the boundary current of the control transition of the transistor switch;

tia is the value of the time delay determined by the duration of the bounce of the contacts of the reed switch;

t $ is the time constant of the semiconductor key in the saturation region.

Achieving this goal became possible thanks to the use of a specific feature of the semiconductor key of an element, in particular, a bipolar transistor: a proportional dependence of the absorption time of its minority carriers on the magnitude of the control (base) current at the start of locking.

In FIG. 1 is a schematic implementation of the inventive method; 4 in FIG. 2 and 3, respectively, theoretical and experimental oscillograms of the switching process.

To implement the method, a circuit containing a reed relay 1, a transistor 2, a resistor of its base circuit 3 can be used.

The principle of operation of the device is extremely simple: when the contacts of the reed relay on the basis of transistor 2 are closed, the unlocking potential appears and a current begins to flow in the load; de-energizing the windings of relay 1 returns the circuit to its original state.

The proposed method is based on the following considerations.

A bipolar transistor is, in a sense, an inertial device and neglecting the rise times tH and fall times tc. we can assume that the duration of its output signal exceeds the duration of the input signal at the time of resorption tp (see the upper and middle fragments of Fig. 2).

It is easy to see that the value of tp depends on the magnitude of the base current IB; the larger the IB, the wider the thickness of the formed base layer and the longer it takes to absorb it; formally, this dependence is expressed as follows:

tp zs In

B-IB IK / B-IB

(t)

where TS is the transistor time constant in the saturation region, expressed through its parameters in the forward and inverse modes; IB - locking current base;

IK is the collector current;

B is the current transfer coefficient in saturation mode.

The neglect for the IB scheme under consideration compared to (B and, input designation

(.GR Kn.

where 1c, gr is the minimum necessary (boundary) base current for introducing the transistor into saturation mode;

Knm is the saturation coefficient of the transistor (the ratio of the actual base current to the minimum necessary to ensure saturation); expression (1) can be rewritten as

tp Tsln Knas; (2)

It has been found by applicants that the resorption time of low-frequency transistors is commensurate with the times between collisions and bounces of some types of reed switches during their bounce.

In addition, it is known that the time interval between the first and second collisions of the reed contacts ti2 is the longest compared to the others (see the upper fragment of Fig. 2). Therefore, if, by increasing Knas (for example, by decreasing the resistance of resistor 3), provide

tp t12, (3)

then, due to the inertia of resorption, the current in the load will also flow during the time intervals between the collisions of the contacts of the reed switch until they are completely closed (see the lower fragment of Fig. 2).

Obviously, to fulfill (3), the saturation coefficient must be chosen from the condition

t19

Knas, and the value of the base current has the value:

tl2

SB - te.rp exp.

It should be noted that increasing the base current above the limit value decreases the rise time, practically does not affect the collector (load) current, and improves the stabilization of the saturation mode.

In FIG. Figure 3 shows the oscillograms of the operation of a reed relay, performed on a magnetically controlled contact of the KEM - 2 type, without using the claimed method (a) and when using it (6): 5 introducing the KG 816G transistor into the relay circuit and providing.

Analysis of the waveform shows that the implementation of the proposed method eliminates the penetration of vibrations

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5

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5

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current caused by the bounce of the contacts of the reed switch to the load circuit of the relay.

Thus, the claimed method is much simpler than the known ones.

Claims (1)

SUMMARY OF THE INVENTION A method of bounce-free load switching of a reed switch, including applying a signal to operate a reed switch, switching a control circuit of a transistor switch, providing a time delay between the moment of operation of the reed switch and the moment of operation of the transistor switch, and subsequent operation of the transistor switch switching the load current, characterized in that, with to simplify implementation 0 load switching method, the specified time delay between the moment of operation of the reed switch and the moment of operation of the transistor switch is provided by increasing the current of the control transition of the transistor switch to a value defined by the expression .rpexp (ti2 / TS), where 1c. gr is the boundary current of the control transition of the transistor switch; ti2 is the value of the time delay determined by the duration of the bounce of the contacts of the reed switch; Ts is the time constant of the transistor switch in the saturation region. + (lr) l FIG. 2 fts. 1 twenty ISS fig.Z