SU1734205A1 - Field transistor switch - Google Patents

Abstract

Usage: the invention relates to a pulse technique and is intended for switching various types of loads, including electromagnetic ones, at a constant supply voltage. The essence of the invention: the device contains two transistors 1, 4, three resistors 7, 8, 9, zener diode (5), load 2, power supply bus 3, two control buses 6, 10. 1 Cp. f-ly, 3 ill. The disadvantage of this circuit solution is the absence of electrical isolation of the control circuit from the power circuit; in addition, its energy efficiency is insufficient. Improving the performance of the field key leads to even more complication of the circuit, since this requires the formation of a process of shunting the input circuit of the field-effect transistor when it is locked. At the same time, the pulse duration required for controlling the power field-effect transistor is long, which leads to unsatisfactory overall dimensions of the control isolating transformer, which performs the function of electrical isolation of the control circuit from the input. It is more effective to control the power field-effect transistor using short pulses, the duration of which is substantially less than the duration w Ј N c; GO o SL

Description

open or closed state of the power transistor. Such a device makes it possible to significantly improve the overall dimensions of the control isolating transformer by reducing the duration of the transmitted pulses. This technical solution is the closest to that proposed by the technical nature.

A disadvantage of this device is the limited field of application, which is due to the presence of additional elements in the charge-source capacitance charge circuit, the lack of a sufficiently effective gate-source capacitance at the stage of its discharge. In addition, the Miller effect has a significant effect when the field-effect transistor is turned on. These factors cause a low recharge rate of the input capacitance of the field-effect transistor and, as a result, cause a low speed of the key. The desire to get more speed leads to an increase in power dissipated by the control circuit. Therefore, the application of the known technical solution is possible either with a low key speed or with increased power dissipated by the control circuit. Thus, its field of application is limited by these factors and it cannot be used in modern high-performance systems of electronics, automation, and converter technology.

The purpose of the invention is to eliminate this disadvantage, namely the expansion of the field of application of the field-effect transistor switch by increasing the speed and reducing the power dissipated by the control circuit.

This goal is achieved in that the proposed device, using the known control principle using short pulses, the gate of the field-effect transistor is shunted by a bipolar shunt transistor and is the control input for the unlocking signal, and the base of the shunt transistor is the control input for the locking signal and through one of the resistors connected to the collector of the field-effect transistor, and the gate of the field-effect transistor, in addition, through another resistor is connected to the potential pole of the source ka supply. To further increase the speed of the transistor field switch, an additional bipolar transistor was introduced into it, a collector-emitter junction connected in parallel with the base-emitter junction of the shunt transistor

and activated from the unlocking control signal.

In FIG. 1 and 2 are diagrams of a field-effect transistor switch according to claim 1 and 2

claims, and fig. 3 shows the timing diagram of the scheme.

The field-effect transistor switch according to the drawing of FIG. 1 contains a field-effect transistor 1, the load circuit of which is included in the drain circuit

0 2 and positive power supply bus 3. Parallel to the gate and the source of the field-effect transistor 1, a collector and an emitter are connected, respectively, of the shunt bipolar transistor 4, as well as a protective

5 zener diode 5. The gate of the field-effect transistor 1 is connected to the unlocking signal bus 6 and through the first resistor 7 to the positive bus 3 of the power supply. The base of the bipolar transistor 4 is connected through the second resistor 8 to the drain of the field-effect transistor 1, and through the third resistor 9 to the blocking signal bus 10.

The field-effect transistor switch according to the drawing of FIG. 2 contains, in addition to these elements, an additional bipolar transistor 11, the collector and emitter of which are connected to the base and the emitter of the shunt transistor 4, respectively, and the base of transistor 11 through the fourth resistor

0 12 is connected to the gate of the field-effect transistor 1.

Timing diagrams for FIG. 3 correspond: plot 13 to the unlocking signal at the input of 6 key circuits; plot 14 5 the locking signal at the input 10 of the key circuit; plot 15-voltage across the gate of field-effect transistor 1; plot 16 - current drain field-effect transistor 1; plot 17 — drain-source voltage of a field-to-transistor 1.

The field effect transistor switch of FIG. 1 works as follows. Suppose that at the initial considered instant of time the field effect transistor 1 is locked.

5 The locked state of transistor 1 is characterized by a high level of voltage across its drain. As a consequence, the current flowing through the resistor 8 goes to the base of the shunt transistor 4 and opens it, providing a zero voltage at the input of the field-effect transistor 1 and confirming its locked state.

At time point to (see plot 13 of Fig. 3), an impulse is unlocked. He charges

5, the input capacitance of the field-effect transistor 1 and the voltage across the gate begin to increase in accordance with the diagram 15 of the diagram of FIG. 3. When this voltage reaches the voltage Unop (time ti), the drain current (plot 16) of transistor 1 appears. Simultaneously, the drain-source voltage of the same transistor decreases and at time t2 it opens fully (plot 17 ). In this case, since the voltage of the drain to the source of transistor 1 is sufficiently small, the shunt transistor 4 is closed due to the termination of the previously existing base current. Since the transistor 4 is locked, the open state of the field-effect transistor 1 is maintained by the flow of current through the resistor 7 and the zener diode 5, the pulse of the unlocking signal at input 6 can be removed, and at the gate of transistor 1 the voltage will be equal to the stabilization voltage Zener diode 5 (DCT on the plot 15 of Fig. 3). Thus, a short unlocking pulse is required to open the field-effect transistor switch, then it is in the open state due to the internal feedback of the control circuit.

With the arrival of a blocking pulse at the input 10 (plot 14 of Fig. 3), a shunt transistor 4 opens during T3. The charge of the input capacitance of field-effect transistor 1 decreases rapidly. The voltage across the gate of the transistor 1 decreases and at time T4 reaches the value ipor (plot 15, fig. 3). The drain current of the transistor 1 begins to terminate, which terminates with at the moment of time ts (plot 16). An increase in the drain-source voltage of transistor 1 (plot 17) begins. The transistor 1 is completely locked. This leads to the appearance of the base current of the shunt transistor 4 through the resistor 8, which is then constantly in the open state. Thus, a short pulse is also needed to lock the key.

Further, the processes are repeated and the circuit operates in a similar manner.

Key scheme according to the drawing of FIG. 2 contains an additional transistor 11, which opens with the arrival of a trigger pulse at input 6. This prevents the signal current from unlocking through the open collector-emitter junction of the shunt transistor 4, which increases the switching speed of the switch by reducing the input charging time

capacitance of the field-effect transistor 1 with equal power input from the control circuit.

Thus, regardless of the presence or absence of control pulses after the end of switching switching processes, the field-effect transistor 1 is in one of two states, On or Off. This simplifies the control circuit, reduces its power consumption, and can reduce the weight and dimensions of the control isolating transformer, if required for electrical isolation of the control circuit from the power circuit. Shunting the input of the field-effect transistor provides an increase in the speed of the key, and also eliminates the negative effect of the Miller effect of the power field-effect transistor. Such positive qualities extend the field of application of the field key in modern automation systems and converter equipment.

Claims (2)

1. Field-effect transistor switch containing a key MOS transistor connected between a power and common pins of a key, a shunt bipolar transistor whose collector and emitter are connected respectively to a gate and a source of a MOS transistor, characterized in that, in order to expand the field of application, a zener diode is inserted, with the gate of the MOS transistor connected to the gate of the unlocking signal and connected via the first resistor to the connection point of the load and the power output of the switch, the base of the bipolar transistor through the second resistor with at MISFET and the drain of the third transistor through - with a bus latch signal, the zener diode is connected between the gate and source of the MIS transistor. 2.Transistor switch according to claim 1, which is based on the fact that, in order to increase speed, an additional bipolar transistor is introduced, the collector and emitter of which are connected respectively to the base and emitter of the shunt bipolar transistor, and the base through the fourth resistor - to the bus unlocking signal. about--- --- Q | -In u 3 o-lx L eight W 3 eleven 1.1 1 1 2 D 7  to and. st and, / 7Op t Fig 3