The simplest power supply circuits for various equipment

15 591
Burykin Valery Ivanovich

Current generator

and
a voltage generator
. What is the difference? What is a Current Generator and what are its areas of application.

***

For work, it was necessary to find some clear description of what a current generator is (current stabilizer, current source)

, its areas of application and calculation examples. We couldn't find anything acceptable.

I had to start writing an article answering these questions myself.

And yet, we had to replace the generally accepted designations “delta” and “infinity” with words. Unfortunately, instead of them, when you try to read the text, question marks are displayed.

02/28/2012

***

The first thing we need to understand is what the differences are between a current generator and a voltage stabilizer.

What are current sources

Current sources are elements of an electrical circuit that support energy with given parameters. At the same time, the energy supply of the circuit does not depend on the characteristics of the elements included in its composition, in particular, resistance.

Device for generating current

There are ideal and real devices for generating current:

• Ideal ones are determined only thanks to hypotheses and theoretical calculations. Thus, scientists often determine a number of conditions under which the current has maximum values ​​close to ideal. That is, an imitation of an ideal source is carried out.
• Real-life conditions support the specified output current and voltage parameters. Any device ensures its operation, provided that its technical characteristics allow it to do so.

Important! Thus, the maximum value of current and voltage make it possible to determine which version of the source will be used in the circuit - ideal or real.

Voltage regulator.

Other names:

— voltage source;

— voltage generator;

— reference voltage source (in circuits it is usually designated as ION).

Basic requirement:

Uout. = const.

Load current

connected to the output of the voltage stabilizer
changes
depending on the value of Rload.

The ideal operating mode of the voltage stabilizer corresponds to Rload. = infinity.

Ideal voltage generator

creates

stable voltage In this case, its internal resistance is zero (Ru = 0). The load current is determined by the formula:

Iload = U / Rload.

From this we can conclude:

- since the voltage is stable, then when Rload changes. the current flowing through the load will change, Fig. 1.

Rice. 1 Diagram of an ideal voltage source.

Ideal voltage source when reducing Rload. to zero is capable of creating a current of infinitely large magnitude.

But nothing ideal exists in life; all voltage sources have some internal resistance - Ru.

This leads to the fact that the source voltage is divided between the internal resistance Ru and the load resistance Rload, Fig. 2

Rice. 2 Functional diagram of a real voltage source.

Therefore, the load current is calculated using the formula:

Iload = U / (Ru + Rload)

The maximum current occurs at Rload. = 0.

It is clear from the formula that the current in the load depends on the voltage developed by the source, as well as on the value of the sum of resistances Rload. and Ru.

As a rule, the internal resistance of the voltage source (Ru) is selected at least 100 times less than the minimum possible

load resistance values ​​(Rload min). In this case, the voltage at the source output when the load resistance changes from infinity to Rload. min will change by no more than 1%.

Those. It is desirable that the following condition be met:

Rload min => 100*Ru

In this case, we do not consider the issue of the power of the voltage source. The power depends on the principle of construction of the source, the implemented circuit and the components used.

Now let's see what a current generator is

Types of sources

There are several types of devices for generating current, each of which has its own main indicators, characteristics and features, listed in the following table:

You might be interested in how electric current affects the human body.
Important! Each type has its own advantages and disadvantages, which are determined by the principle of use, as well as the initial indicators of the generated energy.

Mechanical sources

Mechanical units are the simplest in terms of their use and arrangement. The characteristics of such generators are very easy to understand. Special devices generate energy, which is subsequently converted into electricity. Such devices are used in thermal power plants and hydroelectric power plants.

Mechanical

Heat sources

Thermal source options provide a unique operating principle. Energy is generated through the formation of a thermocouple, which... This means that a calculated temperature difference is provided at the ends of the conductors, the elements interact with each other, creating an electric field.

Thermal

Note ! Radioactive thermocouples are used in the space industry. The effectiveness of such use is possible due to the long service life and efficient power output.

As a result of this movement of charged particles from the hot part of the conductor to the cold part, an electric current arises. Moreover, the greater the temperature difference, the higher the effective energy indicator. In practice, thermocouples are often included in measuring instruments.

Light sources

Lighting devices for generating electricity are considered the most environmentally friendly, efficient and relatively cheap. A special panel of semiconductors absorbs light particles, which during such interaction produce a certain voltage.

Light

At the same time, light panels have a low efficiency rate of 15%. Panels of this type have found wide application - from household appliances to innovative developments in the space industry.

Important! Light sources began to be used instead of lithium batteries due to the high cost of the latter. Despite the fact that many industrial facilities require significant re-equipment to switch to light sources, the final savings occur already in the initial stages of operation.

Chemical sources

This group includes 3 main devices that differ in structure and operating principle:

• A voltaic cell is an option for generating electricity that can be used once. That is, after complete discharge, re-accumulation of charge on the internal substance is impossible. Such devices include salt, lithium or alkaline batteries.
• Batteries are divided into several types: lead-acid, lithium-ion, nickel-cadmium.
• Thermal elements - used in the space and innovation industries to produce short-term current with high performance. The practical application of the units is based on the need for backup power sources.

You might be interested in this: Features of SMD markings

Important! Chemical-thermal devices require initial heating to 500–600 °C to activate the solid electrolyte.

Chemical

Each industry uses its own version with specific parameters. In domestic conditions, batteries are mainly used; in production - batteries.

Analog DC Source Circuit

Since this is a direct current source, that is, a kind of electronic load, it is adapted to work with a low-current independent 12 V power supply. The power part of the circuit is an available high-power MOSFET IRF3205, treated as a variable resistor. Note that a power FET can also be used in linear (rather than switching) mode, in which case it is usually treated as a variable resistor.

The next key element in this circuit is the TL431A three-pin programmable shunt regulator diode. There is also a low-power dual operational amplifier chip - LM358.

Designation of current sources

So that when choosing there is no question as to what type of current source is presented, special designations are used. In physics, there are precise graphical representations that allow you to identify the type of source used:

Designations

On each symbol chart you can see the following parameters:

• General designation of the current source and the driving force of the EMF;
• Graphic image without EMF;
• Chemical type;
• Battery;
• Constant pressure;
• AC voltage;
• Generator.

Thanks to graphic identifiers on an electrical circuit diagram, you can always determine which type is used in a particular situation and how to correctly designate it. There are also international designations, which are found a little less frequently, usually when implementing international projects.

Chemical voltage sources.

The next most important method of generating electrical energy is the use of chemical batteries. A battery consists of two electrodes made of dissimilar metals (for example, copper and zinc) and immersed in an electrolyte (acid, alkali or salt solution). They create contact between the circuit and the electrolyte. Free electrons are extracted from the copper electrode using an electrolyte, and the zinc electrode attracts these electrons. Thus, the copper electrode has a positive charge, and the zinc electrode has a negative charge. Several of these elements combine together to form a battery. Some examples of chemical voltage sources are presented in Figure 3.4.

Figure 3.4. Chemical voltage sources

Figure 3.5 shows the graphical symbols of a chemical element and a battery of chemical elements.

Figure 3.5. UGO a) chemical element; b) bateria.

Operating principle

Each marking of current sources determines the principle of its operation. In a standard situation, energy is generated through the interaction of component parts, namely:

• Mechanical type. As a result of the interaction of mechanism parts, friction occurs. Due to this phenomenon, static electricity arises and is converted into current.
• Mechanical structures work by producing sequentially moving charged particles. The phenomenon occurs due to the interaction of a chemical element with an electrolyte. Charged particles leave the structure of the metal crystal lattice, becoming part of the conducting liquid.
• Solar batteries (light sources) work by knocking out charged particles from a dielectric (silicon) base under the influence of a light flux. This creates constant tension.
• Thermal. As a rule, these are 2 metal bases connected in series. One part heats up, while the other remains cooled. When the temperature regime changes, a temperature difference occurs, resulting in the movement of charged particles.

You might be interested in Features of calculating power by current and voltage

Important! Any change in the structure of a substance can lead to irreversible consequences that will manifest themselves during the operation of the device.

Design

The design of the element affects the principle of its operation. Each source that produces electric current has a specific design:

• The simplest household battery includes a metal case, inside of which an alkaline environment is used. Additional elements are lead plates on which cathodes and anodes are accumulated.

Battery

• An ordinary household battery with a dry cell included in its composition has a metal case in which a cathode storage rod is placed. All other space is filled with salt electrolyte.

Battery

• An alternator is a device consisting of ratchets or a metal frame.

Mechanical principle of the device

• A thermal current source that is already included in the circuit. This is a regular frame mounted on a dielectric stand. Typically, the structure is connected to a measuring device, such as an ammeter. The heat source is a flame or an external electrical impulse.

Thermal device
Important! This design helps to understand exactly how energy is generated, which is subsequently converted into current. Each design option is usually enclosed in a special housing made of dielectric material.

Designations in graphic diagrams. Part 2

For convenience, use the search, this is the key combination Ctr+F

Table 6(d):

Table 6 (d)

Table 6(e)

Table 6 (g)

Table 6 (h)

Table 6(i)

Table 6 (k)

Table 6 (k)

Table 6 (m)

Table 6 (n)

Table 7

APPENDIX 1: Terms used in the standard and their explanations

APPENDIX 2: Dimensions (in a modular grid) of the main graphic symbols

Operating conditions of current sources

Any current source operates under certain conditions. In the absence of a chemical reaction, charged particles cannot form within the elements. If there is no anode and cathode, then particle movement will not occur even in the presence of a reaction.

A similar process occurs in batteries, but the impetus for the occurrence of a chemical reaction is a short circuit in the external electrical circuit. Charged elements begin to move from the anode to the cathode and vice versa, creating a constant flow.

Ideal and real

Light types cannot work without a light source. The efficiency depends on the type of dielectric element used. Additionally, it is necessary to have a device available for converting the received energy.

The thermal option will not work if it is based on 1 type of metal. If there is no source of heat, then the emergence of moving particles is out of the question.

Sources

To generate electrical energy, you need to select a current source that meets the needs of your specific application. There are several options for such devices, each of which has a specific structure, operating principle and individual technical indicators.

Stable current source from 5 µA to 20 mA

The author needed a source of stable current to debug circuits based on bipolar transistors, which, as is known, are controlled by current.
An important requirement for it is the isolation of the common wire of the device from the common wire of the device being debugged, so the power source had to be taken independently. A built-in four-digit microammeter with automatic switching of limits allows you to slightly reduce the amount of equipment simultaneously placed on the experimenter’s table. The idea for the diagram is taken from here. The actual source of stable current is designed like this:

The resistance of resistor R1 is not critical; it is only necessary that the base current of transistor T1 completely opens it. The current transfer coefficient of the BC559C transistor is about 500, the upper limit of current regulation at the source is 20 mA, which means 200 μA through the base is more than enough. A 10 kOhm resistor will provide about 1 mA at 10 V, in principle, you can increase it even to 50 kOhm.

Transistors T1 and T2 should be the same, but at high currents the parameters of T1 will still “float” a little due to slight heating.

The current supplied by the device to the external circuit is determined by the total resistance of resistors R3 - R5. Their functions: R3 - current limitation if both variable resistors are turned to zero, R4 - fine current regulation, R5 - coarse. The current is calculated by the formula I=0.7/(R3+R4+R5), therefore, for example, if resistor R3 is taken with a resistance of 27 Ohms, the upper limit of current adjustment will be 0.7/27=25.9 mA. In practice, it turned out to be 21.6 mA, since the voltage drop across transistor T2 turned out to be less - about 0.6 V.

Full device diagram:

“Krona” powers a stable current source, two AAA elements - a four-digit microammeter. Therefore, the power switch is taken with two normally open groups of contacts. Switch S1 allows you to disconnect the upper terminal and short-circuit the current source in order to configure it in advance, before connecting it to the circuit being debugged.

The parameters in practice turned out to be as follows: maximum current - 21.6 mA, maximum current with a “rough” regulator turned “to zero” - 0.3 mA, minimum - 4.7 µA. True, the built-in microammeter does not show less than 10 µA, so an external one may sometimes be required. The set current remains practically unchanged when the voltage on the external circuit changes from 0 to 8 V.

The microammeter is made from a multimeter with automatic limit switching JT-033A from SHENZHEN JINGTENGWEI INDUSTRY CO.,LTD: the mode switch is removed, instead jumpers are soldered in, forcing it to always work in current measurement mode.

The arrangement of components in the housing is as follows:

Jim made a simulation of the circuit in Falstad, the author slightly reworked it to display more parameters, it turned out:
$ 1 0.000005 7.619785657297057 65 5 50 t 224 240 176 240 0 -1 0.6771607865907852 -0.5873050244463638 500 t 256 272 304 272 0 -1 1.8738439949380101 -0.6771607865907852 500 r 176 304 176 400 0 10000 v 80 288 80 192 0 0 40 9 0 0 0.5 w 176 304 176 272 3 w 176 272 176 256 0 w 176 224 176 32 1 w 0 w 80 32 80 192 0 w 80 288 80 400 0 w 80 400 176 400 3 w 176 400 304 400 0 w 304 336 304 288 3 w 304 240 224 240 1 174 304 128 352 48 0 5000 0.995000000000001 tance w 176 32 304 32 2 w 304 256 304 240 0 w 304 240 304 Result simulation: And here is the result of the simulation with the resistance of resistor R1 at 100 kOhm: