Current Source

It is an active circuit element developed across terminals that can provide a constant current flow to a voltage circuit, regardless of a current source

As the name suggests, a current source is a circuit element that maintains a constant current flow regardless of the voltage that develops throughout its terminals, since this voltage is determined by other circuit elements.In other words, an ideal constant current source continuously provides a certain amount of current, regardless of the impedance it drives, and therefore an ideal current source can theoretically provide an infinite amount of energy.Therefore, a voltage source can be rated as 5 volts or 10 volts, for example, and a current source will have a current rating of 3 amps or 15 amps, for example.

Ideal constant current sources are represented in a similar way to voltage sources, but this time the current source symbol is a circle with an arrow inside to indicate the flow direction of the current.The direction of the current will correspond to the polarity of the corresponding voltage flowing through the positive terminal.The letter "i" is used to indicate that it is a current source as shown.

Ideal Current Source

Current Source

Then an ideal current source is called a "constant current source", since it provides a constant stable state current that produces an IV characteristic represented by a straight line, regardless of the load attached to it.As with voltage sources, the current source can be either independent (ideal) or fixed elsewhere in the circuit, or dependent (controlled) by a voltage or current that changes over time.

Ideal independent current sources are typically used for circuit analysis techniques to solve circuit theorems and circuits containing real active elements.The simplest form of a current source is a serial resistance with a voltage source that creates currents ranging from several shafts of amps to hundreds of amps.Note that a zero-value current source is open circuit as R = 0.

The concept of current welding is a two-pronged element concept that allows the flow of the current indicated by the arrow direction.A current source then has a value in amperage unit (A) and is typically shortened as an amperage.The physical relationship between the current source and voltage variables around a network is given by the Ohm law, as these voltage and current variables will have certain values.

It can be difficult to specify the size and polarity of the voltage of an ideal current source as a function of the current, especially if there are other voltage or current sources in the connected circuit.Then, unless the power supplied by the current source is given as P = V*I, we can know the current provided by the current source, but not the voltage on it.

However, if the current source is the only source in the circuit, it will be easier to establish the polarity of the voltage along the source.However, if there is more than one resource, the terminal voltage will depend on the network to which the source is connected.

Connecting Current Sources

Ideal current sources, such as voltage sources, can also be connected to increase (or decrease) existing current.However, there are rules on how two or more independent current sources with different values can be connected serially or in parallel.

Parallel Current Source

Current Source

Connecting two or more current sources in parallel is equivalent to a current source given as the algebraic sum of separate current outputs.In this example, two 5-amp current sources are combined to produce 10 amps as I T = I 1 + I 2.

Current sources of different values can be connected in parallel.For example, one in 5 amps and one of the 3 amps are combined to give a single current source of 8 amps, since both the arrows representing the current source point in the same direction.Then, when the two currents are added together, their connection is said to be as follows: parallel help.

Although not best practice for circuit analysis, parallel opposing connections use current sources that connect in opposite directions to create a single current source whose value is algebraical extraction of individual sources.

Parallel Contrast Current Sources

Current Source

Here, the two currents come out of each other, as the two current sources are connected in opposite directions (indicated by their arrows), the two of them provide a closed loop pathway for a circulation current that complies with Kirchoff's Current Law, KCL.For example, two current sources of 5 amps each will result in zero output in 5A -5A = 0A.Similarly, if the two currents are of different values, 5A and 3A, then the output will be the value extracted by removing the smaller current from the larger current.5 – 3 = 2A results in I T.

We found that the ideal current sources are connected to each other in parallel, creating parallel auxiliary or parallel contrasting current sources.What is not allowed for circuit analysis or is not best practice is to connect the ideal current sources in serial combinations.

Current Sources in Series

Current Source

Current sources cannot be serially connected to each other at the same value or different values.In this example, in this example, two current sources of 5 amps each are serially connected, but does the resulting current value equal to a 5 amp source or the addition of two sources, that is, a resource of 10 amps?Serial connected current sources add an unknown factor to circuit analysis, which is not desirable.

In addition, another reason why serially connected resources are not allowed for circuit analysis techniques is that they cannot provide the same current in the same direction.No serial auxiliary or serial opposite currents are available for ideal current sources.

Current Source Question Sample 1

Two current sources of 250 milli-amps and 150 milli-amps respectively are connected in a parallel aid configuration to provide current to a connected load of 20 ohms.Calculate the voltage drop and the power spent on the load.Draw the circuit.

Current Source

Then, I T = 0.4A or 400mA, V R = 8V and P R = 3.2W

Practical Current Welding

We found that an ideal constant current source can provide the same amount of current indefinitely, regardless of the voltage in its terminals, thus making it an independent source.Therefore, this means that the current source has an infinite internal resistance, (R = ∞).This idea works well for circuit analysis techniques, but in the real world current sources behave a little differently, since no matter how large the practical current sources (usually in the mega-ohm range), they always have an internal resistance, which causes the produced source to change during load.

A current source that is not practical or ideal can be represented as an ideal source with an internal resistance attached to it.Internal resistance (RP) produces the same effect as a resistance that connects parallel (shunt) to the current source as shown.Keep in mind that parallel connected circuit elements have exactly the same voltage drop between them.

Ideal and Practical Current Welding

Current Source

A practical current source can also be closely replaced by an equivalent circuit consisting of any linear current network constant current source", you may have noticed the similarity of norton theorem rules to a Norton equivalent circuit IS, in parallel with a resistance R, P".If this parallel resistance is too low, if R P = 0, notice that there is a short circuit in the current source.When parallel resistance is too high or infinite, the current source can ideally be modeled ≈ ∞ R P.

An ideal current source draws a horizontal line on the IV characteristic, as shown above.However, since practical current sources have an internal welding resistance, this takes some of the current, so the characteristics of this practical source are not flat and horizontal, but since the current is now divided into two parts, it decreases when a part of the current flows in.

Ohm law tells us that when a current (i) passes through a resistance, (R) a voltage drop occurs along the same resistance.The value of this voltage drop will be given as i*R P.Then V OUT will equal the voltage drop on the resistance when the load is not connected.

The sum of the current around the loop given by Kirchoff's current law KCL: I OUT = I S – V S /R P .This equation can be drawn to give the IV properties of the output current.When ideal as shown in the source, –R P is given as a straight line with a slope that cuts the vertical voltage axis at the same point as the I S.

Practical Current Welding Properties

Current Source

Therefore, all non-ideal current sources exhibit IV characteristics by opening slightly with an amount equal to V.

Current Source Question Sample 2

A practical current source consists of a 3A ideal current source with an internal resistance of 500 Ohms.Calculate the open-circuit terminal voltage of existing sources and the load-free power absorbed by internal resistance when the load is not plugged in.

1. Unloaded values:

Current Source

Then the internal welding resistance and open circuit voltage in terminals A and B (V AB) are calculated at 1500 volts.

Part 2: If a load resistance of 250 Ohm is connected to the terminals of the same practical current source, calculate the current passing through each resistance, the power absorbed by each resistance, and the voltage drop along the load resistance.Draw the circuit.

2. Data supplied when load-dependent: I S = 3A, R P = 500Ω and R L = 250Ω

Current Source

2a.We can use the current-splitting rule to find currents in each resistant branch.

Current Source

2d.The power absorbed by each resistance is given as follows:

Current Source

2c.Then the voltage drop along the load resistance, R L is given as follows:

Current Source

We can see that the terminal voltage of a practical open circuit current source can be very high, in this example it will produce the voltage required to provide the specified current 1500 volts.In theory, this terminal voltage may be infinite because the source is trying to transmit the nominal current.

Connecting a load to its terminals will reduce the voltage from 500 volts in this example, since the current has a place to go and the terminal voltage for a constant current source is directly proportional to the load resistance.

In the case of non-ideal current sources, each with an internal resistance, total internal resistance (or impedance) will be the result of combining them in parallel, exactly the same as resistances.

Dependent Current Source

We now know that an ideal current source provides a certain amount of current, completely independent of the voltage on it, and therefore will produce the voltage necessary to maintain the required current.This then makes it completely independent of the circuit to which it is connected and causes it to be called the ideal independent current source.

If it is a controlled or dependent current source, it changes its current depending on the voltage or passing current opposite another element connected to the circuit.In other words, the output of a dependent current source is controlled by another voltage or current.

Dependent current sources behave in a similar way to the current sources that we have examined so far, both ideally (independently) and practically.The difference this time is that a dependent current source can be controlled by an input voltage or current.A current source connected to a voltage input is often called a Voltage Controlled Current Source or VCCS.A current source connected to a current input is often called the Current Controlled Current Source or CCCS.

In general, the source connected to an ideal current with voltage or current control is indicated by a diamond-shaped symbol, in which an arrow shows the direction of the current, as shown.

Dependent Current Source Symbols

Current Source

An ideal dependent voltage controlled current source, VCCS, provides an output current proportional to the control input voltage, I OUT , V IN.In other words, the output current "depends" on the value of the input voltage, which makes it a dependent current source.

The VCCS output current is then defined by the following equation: I OUT = αV IN.This multiplication constant has si units α (alpha), mho, ℧ (an inverse Ohm sign), because α = I OUT /V IN , and therefore their units will be amperage/volt.

CcCS, an ideal dependent current controlled current source, maintains an output current proportional to a controlling input current.Then the output current "depends" on the value of the input current, which again makes it a dependent current source.

As a control current, I IN determines the size of the output current, I OUT multiply magnification constant β (beta), the output current for a CCCS element is determined by the following equation: I OUT = βI IN.Note that the multiplication constant β is a dimensionless scaling factor in β = I OUT /I IN, so its units will be amps/amps.

Current Source Summary

In this tutorial on Current Sources, we found that an ideal current source (R = ∞) is an active element that provides a constant current that is completely independent of the voltage on it as a result of the load attached to it producing a current.IV characteristic represented by a straight line.

Ideal independent current sources can be connected in parallel as parallel auxiliary or parallel opposing configurations for circuit analysis techniques, but they cannot be connected serially.In addition, current sources become open circuit sources to equalize their currents to zero to solve circuit analysis and theorems.Also note that current sources are capable of powering or absorbing.

In the case of non-ideal or practical current sources, they can be modeled as an equivalent ideal current source and an internal parallel (shunt) dependent resistance that is not infinite but produces R ≈ ∞ IV. It is characteristic, which is not flat but tilts down as the load decreases.

Here we also found that existing resources can be dependent or independent.A dependent resource is a resource whose value depends on another circuit variable.Voltage controlled current welding, VCCS and current controlled current source CCCS are the types of dependent current sources.

Very high internally resistant constant current sources find numerous applications in electronic circuits and analysis and can be created using a combination of bipolar transistors, diodes,zeners and FET's,as well as these solid state devices.