DC Circuit Analysis

DC circuit analysis is to understand and analyze DC circuits with ohm law, Kirchoff laws and similar methods. The basic relationship between voltage, current and resistance in an electrical or electronic circuit is called the Ohm Act.

All materials are made up of atoms, and all atoms are protons, neutrons and electrons.Protons have a positive electrical charge.Neutrons have no electric charge (i.e. neutral), while electrons have negative electrical charge.Atoms are interconnected by the powerful gravitational forces that exist between the atomic nucleus and the electrons in its outer shell.

These protons, neutrons and electrons are happy and stable when they coexist inside the atom.But if we separate them, they want to reform and start to implement the potential for attraction, called a potential difference.

Now, if we create a closed circuit, these loose electrons will start to move and drift back to the protons, creating an electron flow due to their shots.This electron flow is called an electric current.Electrons do not flow freely because the material they pass through creates a restriction on the flow of electrons.This restriction is called resistance.

Then all basic electrical or electronic circuits consist of three separate but very interrelated electrical quantities called Voltage, ( v ), Current, ( i ) and Resistance, ( Ω ).

Electrical Voltage

Voltage (V) is the potential energy of an electrical source stored in the form of an electric charge.Voltage can be considered the force that pushes electrons along a conductor, and the higher the voltage, the greater the ability to "push" electrons through a given circuit.Since energy is capable of doing business, this potential energy can be defined as the necessary work in joule to move electrons around a circuit in the form of electric current from one point or node to another.

Then, the voltage difference between any two points or connections (called nodes) in a circuit is known as The Potential Difference (pd) and is often called Voltage Drop.

The potential difference between the two points is measured in Volts, the circuit symbol V or lowercase letter " v ", but Energy , E lowercase " e " is sometimes used to indicate an emk (electromotor force) produced.Then the larger the voltage, the greater the pressure (or thrust force), and the greater the capacity to do business.

A constant voltage source is called DC Voltage and is called a voltage AC voltage, the voltage of which changes periodically over time.Voltage is measured in volts; a volt is defined as the electrical pressure required to force an electric current of one amp through an Ohm resistance.Voltages are usually expressed in Volts with prefixes used to indicate the lower multiples of voltage, such as microvolt ( μV = 10 -6 V ), millivolt ( mV = 10 -3 V ) or kilovolt ( kV = 10 3 V ). The voltage can be positive or negative.

Batteries or power supplies are mostly used in electronic circuits and systems to produce a fixed DC (direct current) voltage source of 5v, 12v, 24v, etc.AC (alternating current) voltage sources are available for domestic and industrial power and lighting and power transmission.

General electronic circuits operate with low voltage DC battery sources from 1.5V to 24V DC. The circuit symbol for the constant voltage source is usually given as a battery symbol with the plus, + and minus, – sign indicating the polar direction.The circuit symbolof the alternative voltage source is a circle with a sine wave inside.

Voltage Symbols

A simple relationship can be established between a water tank and a voltage source.The higher the water tank above the output, the higher the pressure of the water when releasing more energy, the higher the voltage, the higher the potential energy when releasing more electrons.

Voltage is always measured as the difference between any two points in a circuit, and the voltage between these two points is often referred to as " Voltage drop ".Keep in mind that voltage can exist in a circuit without current, but the current cannot exist without any voltage source, as it hates any short-circuit conditions, even if the DC or AC likes the open or semi-open circuit state.

Electric Current

Electric Current ( ( I ) is the movement or flow of the electric charge and is measured mainly in Amps, which is the symbol of i.It is the continuous and smooth flow of electrons (negative particles of an atom) around a circuit that is "pushed" by the voltage source (called drift).In reality, electrons flow from the negative (–and) terminal of the source to the positive (+and) terminal, assuming that the traditional current flows from the positive terminal to the negative terminal to facilitate the understanding of the circuit.

In circuit diagrams in general, the flow of the circuitd current usually includes an arrow associated with the I symbol or lowercase i to indicate the actual direction of the current.However, this arrow usually indicates the direction of the traditional current flow, not the direction of the actual flow.

Conventional Current Flow

Traditionally, this is the flow of positive load around a circuit, and from positive to negative.The diagram on the left shows the positive charge (holes) flowing from the positive pole of the power supply andindicates the movement of the power supply around a closed circuit that rotates to its negative pole.This current flow from positive to negative is often known as traditional current flow.

This was the tradition chosen during the discovery of electricity, which is thought to flow in a circuit of the direction of the electric current.To continue this line of thought, the arrows shown in all circuit diagrams and diagrams, symbols of components such as diodes and transistors, indicate the direction of the traditional current flow.

Then the Conventional Current Flow gives the flow of the electric current from positive to negative and in the opposite direction of the actual electron flow.

Electron Flow

The flow of electrons around the circuit is inverse of the direction of the traditional current flow from negative to positive. The actual current flowing in an electrical circuit consists of electrons flowing and returning from the negative pole (cathode) of the battery.

This is due to the fact that the load on an electron is negative by definition and therefore drawn to the positive terminal.This electron flow is called electron current flow.Therefore, electrons actually flow from negative terminal to positive around a circuit.

Both traditional current flow and electron flow are used by many textbooks.In fact, as long as the direction is used consistently, it does not matter which direction the current flows around the circuit.The flow direction of the current does not affect what the current does in the circuit.In general, it is much easier to understand the flow of traditional current. Positive to negative.

In electronic circuits, the current source is supplied as a circle with an arrow pointing in its direction.

The current is measured in amps and the amperage is defined as the number of electrons or charges (Q in Coulomb) ( t in seconds ) that pass through a certain point in the circuit in a second.

Electric current is usually expressed in Amps with prefixes used to indicate micro amps ( μA = 10 -6 A ) or milliamper ( mA = 10 -3 A ).Note that electric current can be positive or negative in value depending on the direction of flow around the circuit.

The current flowing in a single direction is called Direct Current or DC,the current that changes back and forth in the circuit is called Alternating Current or AC.Whether the AC or DC current flows through a circuit only when a voltage source is connected to it, its "flow" is limited to both the resistance of the circuit and the voltage source that pushes it.

In addition, since alternating currents (and voltages) are periodic and change over time, the value of "active" or "RMS", (Root Mean Square) given as I rms, produces the same average power loss equivalent to DC current Iortalama.Current sources are the opposite of voltage sources in that they like short or closed circuit conditions, but do not like open circuit conditions because the current will not flow.

Using the water tank relationship, the current is equivalent to the flow of water through the pipe through the flow, which is the same along the pipe.The faster the flow of water, the greater the current.Keep in mind that the current cannot exist without voltage, so DC or AC likes any current source short or semi-short circuit state, but hates any open circuit conditions as it prevents it from flowing.


Resistance (R) is the capacity to resist or block the current flow of a material or, more specifically, the flow of electrical charge within a circuit.The circuit element that does this perfectly is called "Resistance".

Resistance is a circuit element measured in Ohm, represented by the Greek symbol (Ω , Omega), along with prefixes used to indicate Kilo-ohm ( kΩ = 10 3 Ω) and Mega-ohm (MΩ = 10 6 Ω). Keep in mind that resistance can not only be positive and negative.

Resistance Symbols

The amount of resistance that a resistance has is determined by the relationship of the current passing through it with the voltage, which determines whether the circuit element is "good conductor" – low resistance or "bad conductor" – high resistance.Low resistance means that, for example, 1Ω or less, the circuit is a good conductor made of materials such as copper, aluminum or carbon, while resistance of 1MΩ or higher means that the circuit is a bad conductor made of insulating materials such as glass, porcelain.

On the other hand, a "semiconductor", such as silicon or germanyum, is a material whose resistance is halfway between a good conductor and a good insulator.Therefore, the name "semiconductor".Semiconductors are used to make Diode and Transistor etc.

Resistance may not be linear in nature, but it can never be negative.Linear resistance complies with the Ohm Act because the voltage on the resistance is linearly proportional to the current passing through it.Nonlinear resistance does not comply with the Ohm Act, but on it there is a voltage drop proportional to some power of the current.

Resistance is pure and cannot be affected by frequency and, as a result, negative, as the AC impedance of a resistance is equal to DC resistance.Remember that resistance is always positive and never negative.

Resistance is classified as a passive circuit element and therefore cannot provide power or store energy.Instead, resistors absorb what appears to be heat and light.The power in a resistance is always positive, regardless of voltage polarity and current direction.

For very low resistance values, for example, milli-ohm, ( mΩ ) sometimes it is much easier to use the opposite of resistance ( 1/R ) rather than the resistance itself ( R ).The response to resistance is called conductivity and represents the ability of a conductor or device to transmit electricity.

High conductivity values mean a good conductor, such as copper, while low conductivity values mean a bad conductor, such as wood.The standard unit of measure for conductivity is the Siemens symbol (S).

The unit used for conductivity is mho (ohm is written backward), symbolized by an inverted Ohm sign ℧.Power can also be expressed using conductivity as follows: P = i 2 /G = v 2 G .


If we increase the voltage in a constant-resistant linear circuit, the current rises, and similarly, if we lower the voltage, the current decreases.This means that if the voltage is high, the current is high, and if the voltage is low, the current is low.

Likewise, if we increase the resistance, the current decreases for a certain voltage, and if we reduce the resistance, the current rises.This means that if the resistance is high, the current is low, and if the resistance is low, the current is high.

Then we can see that the current flow around a circuit is directly proportional to the voltage (∝), (V) causes I, but is inversely proportional to the resistance (1/∝), (R) causes I↓ ( R).

A basic summary of the three topics is given below.

  • The voltage or potential difference is the measure of potential energy between two points in a circuit and is often referred to as " voltage drop ".
  • When a voltage source is connected to a closed loop circuit, the voltage will produce a current that flows around the circuit.
  • In DC voltage sources, the +and (positive) and -and (negative) symbols are used to indicate the polarity of the voltage source.
  • Voltage is measured in Volts and has the symbol V for voltage or E for electrical energy.
  • Current flow is a combination of electron flow and hole flow through a circuit.
  • The current is a continuous and smooth load flow around the circuit and is measured in Amperage or Amps and has the symbol I.
  • The current is directly proportional to the voltage ( I ∝ V )
  • The effective (rms) value of the alternating current has an average power loss equivalent to the direct current flowing from a resistant element.
  • Resistance is resistance to current flowing around a circuit.
  • Low resistance values mean a conductor, and high resistance values mean an insulator.
  • Inversely Proportional to Current Resistance ( I 1/∝ R )
  • Resistance is measured in Ohm and has the Greek symbol Ω or R.
VoltageV or EVoltV

In the next content related to DC Circuits, we will look at the Ohm Act, a mathematical equation that describes the relationship between Voltage, Current and Resistance in electrical circuits and is the basis of electronic and electrical engineering. The Ohm Act is defined as: V = I*R .