SU377966A1 - NON-CONTACT KEY - Google Patents

Description

one

The proposed contactless key can be used in multichannel switches of weak signals, in particular, to create contactless input switches for universal control computers and various types of analog information cyclic processing systems, as well as for building high-precision high-speed converters of the type al-log-code.

Known contactless keys containing two of the same type of transistor, two diodes and two resistors :, in which the transistors form a bridge circuit. One short circuit, the source of the control signal source through the corresponding series-connected resistor and diode is connected to the point; m connection of emitters and collectors of the transistor, c.

The disadvantage of contactless switches of this type is that they do not have full compensation of the residual voltage, have significant zero-level drift, need careful adjustment of the operating mode over the entire temperature range and individual selection of thermocompressing elements, require prior rejection of transistors across a number of parameters, which reduces the reliability of work, especially when switching weak signals.

BIBLIO: The purpose of the invention is to eliminate these drawbacks.

To this end, the proposed key is equipped with a potentiometer, the extreme conclusions of which

connected to the bases of transistors, and the middle pin is connected to another terminal of the signal source :.

The drawing shows schematic diagrams: and the proposed contactless transistor switch.

The key is made on two transistors / and 2, connected in parallel and antiphasing along a switched circuit and forming a symmetrical bridge, with two opposite

the shoulders of which are the emitter transitions of transistors 1 and 2, and the other two are the collector transitions of these same transistors. A balancing potentiometer 5 is connected to one bridge diagonal, and 4 w resistors to another. 5 to diodes 5 and 7. A control voltage is applied between the bridge diagonals, i.e., between the moving contact of potentiometer 3 and the common point of resistors 4 and 5.

The key works as follows.

In the absence of a control voltage f / ynp, the transistors 7 and 2 are closed and provide a sufficiently large resistance for voltage-switched. With

supplying a control voltage in the specified polarity, the transistors / and 2 open, their resistance drops sharply.

The control currents flowing along the opposite shoulders of the bridge are close in magnitude, and the balancing potentiometer 3 can be used to establish the full balance of the bridge. At the same time, on the diagonal of the bridge in which the switched circuit is connected, the voltage drop from the control signal is absent with any necessary accuracy, i.e., there is full compensation for residual n: key strength.

This relays of the circuit is stable, the same as to changes in the control voltage or ambient temperature cause the current to increase in the opposite arms of the bridge according to the same law, which does not lead to the imbalance of the bridge.

Resistors 4 to 5 set the amount of control currents iB of the arm: X bridge, and the diodes and 7 eliminate the bypass of the key transistors

these resistors in the closed state of the key.

The proposed contactless transistor switch circuit does not require the selection of elements and the preliminary screening of transistors.

Subject invention

A contactless switch containing two transistors connected in a bridge circuit, one of the terminals of the control signal source is connected via a corresponding series-connected resistor and diode to the junction points of emitters and collectors of transistors, characterized in that Equipped with a potentiometer, the extreme terminals of which are connected to the bases of transistors, and the middle lead is connected to another terminal of the control signal source.