SU1410006A1 - Current source - Google Patents

Abstract

The invention relates to electrical engineering and can be used in secondary power supply sources. The purpose of the invention is to increase the output resistance. The current source consists of four bipolar transistors 1-4, a field-effect transistor 5 and two bias elements 6, 7. A negative feedback loop formed by transistors 1, 3, 5 and bias elements creates a certain potential of the base of transistor 3, the Transistor 4 is made in one technological cycle with a transistor 3 with an emitter area, a specified number of times the emitter area of the transistor 3, Transistor 4 generates a collector current also a specified number of times more. The output current I giiix is determined by "1" 3 "7 —the emitter current transfer coefficients of transistors 1-4; n is the ratio of the emitter areas of transistors 3, 4; Igx input current. 1 il. . I g ratio; lex § (L

Description

The invention relates to electrical engineering and can be used in the sources of secondary power supply of electronic equipment.

The aim of the invention is to increase the output impedance of the current source.

The drawing shows a circuit diagram of a current source.

The device contains the first 1, second 2, third 3 and fourth 4 bipolar transistors, feedback field-effect transistor 5, the first 6 and the second bore 7 bias elements made, for example, on direct diodes or zener diodes, input 8 and output bus 9, the first 10 and second 11 power supply buses. At the same time, the emitters of the first 1 and second 2 transistors are collectors of the third and third and fourth 4 transistors, respectively, the bases of transistors 1 and 2 are connected to the bases of transistors 3 and 4 and to the source of the field-effect transistor 3, respectively, through the first 6 and second 7 elements of the bias, collector transistor 1 is connected to the input bus 8 of the current mirror, and the collector of transistor 2 to the output bus 9, emitters of transistors 3 and 4 are connected to the first bus 10 of the power supply, the drain of the field-effect transistor 5 to the second bus II of the power supply

The current source works as follows.

External current supply circuits are diverted from the input bus 8 by a current set by an external generator. On the base of transistor 2 a potential is formed such that its collector current passing through transistor 2 is equal to the input. The corresponding base potential of transistor 2 arises due to negative feedback, the loop of which formed by transistors 1 and 3, field-effect transistor 5, elements 6 and 7 of the displacement. Transistor 4, made in one technological cycle with transistor 3, with an emitter area that is a specified number of times larger than the emitter area of a transistor.3, generates a collector current that is also a specified number of times larger, since the current density of emitter transitions of transistors 3 and 4 is determined by one the same

0

five

0

0

five

0

0

five

The basic currents of these transistors come from the source of the field-effect transistor 5 times the 6 and 7 displacement. If the area of the emitters of the transistors and 2, executed in the same technological cycle, is also in a given ratio, the densities of the currents flowing through them are equal, then the relative parts of the currents are also equal the collectors of transistors 3 and 4, discharged through the bases of transistors I and 2, and the magnitude of the input and output currents are in a given ratio. This switching on of the transistor 1 allows to compensate for the losses of the collector current, transistor 4, which are reduced through the base of transistor 2, the share of which can reach 17% for the lateral pnp transistor, made according to standard planar-epitaxial technology with base current transfer ratio | 5, The bias element 6, which can be executed on one or several series-connected direct diodes, provides an offset sufficient to lock the collector junction, transistors 3 and 4. The potential difference across the terminals of the 7 element bias, which can also be performed on one or several series-connected direct-shifted diodes or zener diodes, is chosen approximately equal to the maximum possible cut-off voltage of the field-effect transistor 5, which ensures the operation of transistor 1 and the active region for any technological and temperature changes in the parameters of the active elements of the current mirror. The minimum value of the initial drain current in this case should be chosen as the total value of the base currents of the transistors 1 4 with the worst base current ratio.

The output current I (, ("devices (with equal voltages on the collectors of transistors 1 and 2) is determined by

oil 4

where 0 / - emitter current transfer coefficients of transistors 1-4;

Ibhx

 -In

P

n is the ratio of the emitter areas of transistors 3 and 4; I P - input current

The proposed current source has a significantly greater (more than 6 times) output resistance.

Claims (1)

Invention Formula A current source containing two bipolar transistors, a field-effect transistor and a first bias element, the first bipolar collector and the field-effect transistors being connected to the control input of the source, the second bipolar transistor connecting to the output terminal, The bases of the first and second bipolar transistors are combined and connected to the first one of the first bias element, which is also distinguished by the fact that, in order to increase the output impedance, the third and fourth analogous bipolar trans: sources and the second bias element are introduced into it, the emitters The first and second transistors are connected to the power bus through the collector-emitter circuit of the third and fourth transistors. Accordingly, the bases of the third and fourth transistors are combined and connected to the second output of the first element. That bias, the bases of the first and second transistors are connected to the source of the field-effect transistor by the second bias element.