SU1750046A1 - Transistor key with protection against current overload - Google Patents

Abstract

The invention relates to a pulse technique and can be used in electric drives. SUMMARY OF THE INVENTION - the key contains 4 transistors (1-4), 1 comparator 5, 1 measuring resistor 7, 1 diode 6 2 voltage sources 14, 15, 1 voltage source 13 1 or

Description

The invention relates to the field of pulse technology and can be used in electric drives.

A switching device is known, in the circuit of the key element of which 5 current sensors (resistors) are included, which together with the emitter junction of the key element is. This is shunted by a protective transistor, which ensures the locking of the first. The device also contains a driver of 10 start pulses and clock pulses, logic elements, a threshold integral element, a current stabilizing element.

A disadvantage of the device is its relative complexity and insufficient reliability of the switch due to passive locking of the power transistor, which is not enough for a high-voltage switch.

The closest in technical essence and the achieved result is a transistor switch containing control and output transistors, a resistor current sensor, a timing unit, a comparator. 25

The disadvantage of this device is the lack of reliability due to shunting of the protective channel at current overloads of the key by the control channel at the input of the control transistor, which limits the matching of control signals when the switching power of the key increases, as well as due to the absence of its active locking.

The purpose of the invention is to increase reliability.

The drawing shows a diagram of the device. '. ·

The device contains first and second transistors G and 2 of direct conductivity, 40 power transistor 3, output transistor 4, comparator 5, diode 6, measuring resistor, resistor 7, resistors 8-12, reference voltage source 13, plus and minus sources 14 and 15 voltage. 45

The emitter transistor 1 is connected to the plus of the source 14 ', and the collector through the diode 6 and the resistor 8 to the base of the transistor 3 _: the emitter of which includes a measuring 50 resistor 7 connected to the first input of the comparator 5, and its second input is connected to the source 13 reference voltage through, resistor-10. The output of the comparator (with an open collector) is connected to the base of transistor 1 through transistor 4 and resistor 12. In parallel to diode 6, a base-emitter junction of transistor 2 is connected, the collector of which is connected to the minus of source 15 and to its base through resistor 9.

The device operates as follows.

Until the moment of overcurrent, the output of the comparator 5 has a low potential and when the input signal is applied, transistor 4 opens and a circuit is switched on for the base current of transistor 1. to flow. In this case, the voltage drop across the diode 6 is blocking for the transistor 2. The reference voltage source 13 is a voltage divider of the source 15, including a zener diode or a stabilizer.

When overcurrent, the voltage drop across the resistor 7 is equal to and slightly higher than the voltage level of the source 13, the comparator is triggered, and a high level is set at its output, which prevents the base current of the transistor 1 from flowing and is locked. In this case, the base current of the transistor 3 is stopped, the blocking voltage on the diode 6 is reduced to zero and the transistor 2 is unlocked, since its base through the resistor 9 becomes at a lower voltage than its emitter. As a result, the current from the plus of the source 15 connected to the emitter of the transistor 3 flows through its emitter-base junction, and the transistor 3 is locked. Similarly, it is locked in the absence of an input signal and the transistor is locked

4. After reducing the load current through the resistor 7, the comparator 5 turns on .. but with a delay, which provides its hysteresis. Depending on the requirements, the hysteresis can be reduced (the value of resistor 11 is much larger than the value of resistor 10) or, conversely, it can be increased more often by decreasing the value of resistor 11 to reduce the frequency of periodic connection of transistor 3 to eliminate the causes of overcurrent

Thus, the reliability of the key is improved due to the serial connection of the control channels and protection against overcurrent .. Moreover, the restoration of the initial state of the key when overload is eliminated occurs automatically. Also, an active locking of the power transistor occurs automatically at any sequence of disconnecting the control and protection channels. At the same time, the intermediate mode of finding the power transistor in the active mode, when current overload occurs slowly, is eliminated, which also increases the reliability of the key.

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Claims (1)

Claim A transistor switch with overcurrent protection, containing a power transistor, two direct conductivity transistors, a diode and a comparator, the emitter of the first transistor is connected to a positive power source, and the collector through a resistor to the base of the power transistor, to the emitter of which the first output of the measuring resistor is connected, the second output of which is connected to the first input of the comparator, and its second input is connected to a reference voltage source, which is characterized in that, in order to increase the reliability of operation, an input trans a source and a negative power source, the collector-emitter junction of the input transistor is connected between the base of the first transistor and the output of the comparator, which ^is made with an open output, a diode is connected in series to the base circuit of the power transistor, in parallel with which is the base-emitter junction of the second transistor, the collector of which connected to a negative power source and through a resistor to its base.