SU1170583A2 - Amplifier with overload protection - Google Patents

Abstract

AMPLIFIER WITH OVERLOAD PROTECTION by author. St. 1 708491, characterized in that, in order to increase the gain while at the same time increasing its speed and reliability, an additional resistor is inserted in it connected between the point of connection of the diodes and the point of connection of the capacitor with the signal source. 9 0/3. § gt: D СП 00 from I to U g: I -0-b

Description

1 The invention relates to a pulsed technique and can be used in automation and computing devices. Closest to the proposed is an amplifier with protection against overload, containing two series-connected cascades on transistors of different types of conductivity connected according to a common emitter circuit, as well as two series-connected diodes connected opposite to each other between the input base and the collector an output transistor, a capacitor, one of the outputs of which is connected to the base of the input transistor, and the other to the signal source and the point of connection of the diodes. In order to ensure the normal operation of such an amplifier, at the moment of input of the input signal, the condition (t) must be met - the voltage drop at the base-emitter junction. input transistor; U (t) is the voltage across the capacitor; threshold voltage of the protective diode. In this case, it turns out that in order to fulfill such a condition in practice, several real diodes must be connected in series as a protective diode (two-three). Since for normal operation of the amplifier in k.z. its input must be accomplished by another condition of the direct fall, for example, on the protective diode when the input current of the amplifier is flowing through it; threshold voltage of the base diode; The threshold voltage of the transition. The base-emitter of the input transistor at which it begins to turn on. As a base diode, it is necessary to include in series also several (four to six) real diodes. A significant number of diodes7 included in the base circuit of the input transistor of the amplifier reduces the gain of the amplifier due to an increase in the threshold voltage 832 of its input circuit, and the total total number of diodes with which the amplifier and the protective diodes are implemented in the amplifier is six to ten pieces, which significantly increases the number of radio-radio elements (ERE) in the amplifier, which contains in addition to these diodes only an additional 7 ERE, and reduces its reliability. In addition, the capacitor of such an amplifier in the pause between the input signals must have time to discharge to a voltage almost close to zero. However, at the final stage, the discharge of the capacitor occurs through the base diode of the amplifier with a direct voltage across this diode of a lower threshold, i.e. through a large dp. resistance of the diode, increasing in the process of discharge of a condenser from ten kΩ to 10 ohms or more. This results in a significant amount of recovery time of the initial state of the amplifier, therefore, reduces the maximum frequency of the signal that can be rationally amplified, i.e. reduces amplifier performance. The disadvantage of such an amplifier is its low gain, low reliability and performance. The purpose of the invention is to increase the gain while enhancing the speed and reliability of the amplifier. FIG. 1 shows a circuit diagram of an amplifier; in fig. 2 - plots showing his work. The amplifier contains two series-connected cascades on transistors 1 and 2 of different types of conductivity connected according to a common emitter circuit, as well as two series-connected diodes 3 and 4. connected opposite to each other between the base of the input transistor 1 and the output of the device, a capacitor 5, one output which is connected to the base of the input transistor 1, and the other to the signal source, an additional resistor 6 connected between the diode connection point and the connection point of the capacitor to the signal source, resistors 7-11, turn on nye to provide Tpe6yeMofo mode, hydrochloric input and output terminals 12 and 13, the load 14.

31

The device works as follows.

With no input terminal 12, the transistors 1 and 2 are closed, the load 14 and the resistor 7 are de-energized. If a voltage Ug is applied to the input of a given value (FIG. 26), the transistors 1 and 2 are turned on and saturated, the voltage is applied to the load 14

and E-5dL. ..

off - R + R

where E is the supply voltage of the amplifier;

 - load resistance 14; R is the resistance of the resistor 7 (usually R is much less

R ,,).

At the same time, diode 4 is displaced in the opposite direction by the output voltage vb (x (Fig. 2d) of the amplifier and practically does not affect the operation of the circuit.

At the moment when the switching signal Ug is applied to terminal 12, a current is taken from the signal source (Fig. 2c).

Uix.I.y.,

R. "

their

and - voltage drop at the base-emitter junction of transistor 1;

R is the resistance of the resistor 10,

Ie load 14 through a resistor, the diode 4 branches part of the current (Fig. 2e) is equal to

i

  R ..

where and. (t) is the voltage across the capacitor 5;

and - direct voltage drop across the protective diode 4; Rg is the resistance of the resistor 6 By choosing the resistance of the resistor 6, it is not difficult to satisfy condition i "i. Then, regardless of the magnitude of the load 14, almost the entire input current

the amplifier enters the base

in

input transistor circuit 1. By choosing the time constant (Rg II R) Cg, where GS is the capacitance of capacitor 5, it is possible to turn on transistors 1 and 2 during the charging time of capacitor 5. After turning on transistor 2, diode 4 is shifted in the opposite direction and consumed current from the input circuit to the load 14 is completely stopped. After the end of the charge of the capacitor 5, the amplifier consumes

170583

from the control signal source current

and

- UA, - and,

L i iiii.

R. R, o

x

where and my fall voltage

on the base diode 3. By selecting the resistance of the resistor, 10, the value of i. is set at the pa level,

R

sufficient to hold the amplifier

in the on state.

When the control signal Ug is disconnected, the capacitor 5 is discharged across the circuit by a resistor 6 - diode 3 with a constant time f, Cg. At the same time for normal operation of the amplifier with its

reclosing is sufficient for the capacitor to discharge to the level of the direct threshold voltage of diode 3, j, i.e. recovery time

The initial state 0 of the amplifier can be estimated as 3RCj, where the resistance R is usually 10 to 10 ohms. This resistance is several orders of magnitude less than the direct resistance of diode 3 with a direct voltage across it less than U ,,. After

- POR

capacitor 5 discharge The amplifier is again ready to be switched on again. I

Since the inclusion of an additional resistor 6 in the circuit makes it possible to virtually eliminate the shunting of the input of the amplifier by the load 14 at the time the input signal is applied, it is sufficient to include one diode as diode 4.

When k.z. load 14 (R 0, Fig. 2a), the input current of the amplifier is closed through the protective diode 4 and, if 0, the value of the direct voltage drop across the diode 4 And satisfies the condition

and. tu., - + Ub,

 ....... OT.

And p then. . inoP

where and.

j is the threshold voltage of the base diode 3;

and

- threshold voltage

ve

the base-emitter junction of transistor 1, at which it starts to turn on,

Transistors 1 and 2 will be turned on for as long as the output of the amplifier is connected to a short-circuited load, and an input signal is present at the input. In order to fulfill the specified condition when one real diode is turned on as a protective diode 4, in practice it is sufficient to include two real diodes as diode 3 in series. Thus, the total number of real diodes carrying out the functions of the basic and protective diodes in such an amplifier does not exceed three, and only two diodes are connected in series in the basic circuit of the input transistor of the amplifier. When applying a switching signal to the input of the amplifier working for short-circuited load, the output transistor 2 operates in the mode of pulsed overload of the collector current (Fig. 2e) in the charge current of the capacitor 5; Such a pulse overload of the Transistor 2 does not cause it to fail or reduce its reliability In this case, if transistor 2 operates within its permissible modes, this ensures with the inclusion of an additional ballast resistor 7 in the collector circuit of transistor 2 (as in the example of the amplifier circuit) or selecting the type of transistor 2 and its baseline mode. Thus, due to the inclusion of an additional resistor 6, a sharp decrease in the shunt effect of the amplifier circuit on the input amplifier circuit is achieved at the time of the application of the input signal. This minimizes the number of diodes included as a protective diode 4 (one diode) and basic diode 3 (no more than two diodes), which not only increases the reliability of the amplifier due to a significant decrease in the total number of electrical radio elements contained in it, but also increases amplification of the amplifier due to a decrease in the threshold voltage of its input circuit. In addition, the inclusion of an additional resistor 6 changes the discharge and charge circuits of the capacitor 5 in such a way that the recovery time of the initial state of the amplifier after the input signal is reduced significantly (by several orders of magnitude). This increases the permissible frequency of the signal at the input of the amplifier, i.e. its speed increases.

/

with

Claims (1)

AMPLIFIER PROTECTED FROM OVERLOAD by ed. St. No. 708491, characterized in that, in order to increase the gain while improving speed and reliability, an additional resistor is inserted into it, connected between the diode connection point and the connection point of the capacitor with the signal source. Figure 1 P70583