DC Circuit

Direct Current Circuit or DC Circuit is a closed electrical circuit in which the flow of electricity is in one direction. DC Circuit has a DC Power Supply which produces Direct Current in the circuit. As opposed to alternating current, Direct Current has a fixed magnitude and flows in one direction only. Direct Current Circuit forms a major backbone of the electronics industry.

In this article, we will learn what is Direct Current Circuit, its types, the derivation of voltage and current in different types of DC Circuits, application of DC Circuits, and how to convert AC to DC Circuits.

Direct Current Meaning

Direct Current is the current that has a unidirectional flow of electric charge. In this current, the direction and magnitude of the current remain constant throughout. DC is a scalar quantity. This is because direct current represents the value of current and flows in one direction only. Direct current finds its use in many household devices and in all devices that use batteries.

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Direct Current Symbol

The symbol of DC is a straight horizontal line above a dashed line. The horizontal line is straight to denote that the amplitude of current remains same at all the time.

DC Symbol

Direct Current Circuit

Direct Current circuit is an electrical circuit in which Electric Current flows through in one direction. In a DC Circuit there are components like DC battery, switch, connecting wires, resistors and ammeter and voltmeter.

There are various other types of circuit like series, parallel and some complex circuits which are combination of both the types.

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Direct Current Circuit

Types of DC Circuit

Based on circuit combination DC circuits can be classified into three types:

• Series DC Circuit
• Parallel DC Circuit
• Series-Parallel DC Circuit

Series DC Circuit

When the components of a DC circuit are connected end-to-end, they form a Series DC Circuit. This kind of circuit has the components lined up together to create a linear path for current to flow. The current flowing is same across all the elements in a series ciruit.

Series DC Circuit

Here three resistors R₁, R₂, R₃ are in series with voltage V. Let’s learn to calculate the total resistance in a series DC Circuit.

Consider V₁, V₂ and V₃ as the voltage drops over the resistors R₁, R₂ and R₃.

Then,

V = V₁ + V₂ + V₃

From Ohm’s Law we know that V = IR

IR = IR₁ + IR₂ + IR₃

IR = I(R₁ + R₂ + R₃)

Cancelling out I on both sides, we get

R = R₁ + R₂ + R₃

Hence, in Series DC Circuit total effective resistance is equal to the sum of all individual resistances.

Parallel DC Circuit

A Parallel DC Circuit is the one in which there is multiple path for a current to flow from one juction to another junction. Both the ends of each component are connected by a common point then it results in a parallel DC circuit.

Parallel DC Circuit

In case of Parallel DC Circuit, all elements will have same voltage which will be equal to voltage drop across the two end points. Lets learn to calculate the total resistance in a Parallel DC Circuit.

In the above circuit diagram, resistors R₁, R₂ and R₃ are joined in parallel over a V voltage supply. I₁, I₂, and I₃ are the currents flowing through them.

The total current flowing through the circuit is,

I = I₁ + I₂ + I₃

I = V/R₁ + V/R₂ + V/R₃

Then total electrical resistance R,

V/R = V/R₁ + V/R₂ + V/R₃

1/R = 1/R₁ + 1/R₂ + 1/R₃

Series-Parallel DC Circuit

When we talk about practical circuits, they are usually a combination of series as well as parallel circuits. These circuits can be solved by series an parallel circuit laws

Series-Parallel DC Circuit

In the above circuit diagram, resistors R₂ and R₃ are joined in parallel and their equivalent is on series with resistor R₁

The parallel combination of resistors 2 and 3 is

1/R₂₃ = 1/R₂ + 1/R₃

R₂₃ = R₂R₃/R₂+R₃

Now, the series combination with total voltage V

R_eq = R₁ + R₂₃

R_eq = R₁ + R₂R₃/R₂+R₃

DC Circuit Power Formula

In DC Circuit, the power is calculated as follows

Power = Voltage × Current

From Ohm’s Law we know that

V = IR

Using ohm’s law in power formula

Power = (IR) × I = I²R

Hence, Power can be calculated in DC circuit as follows:

• P = VI
• P = I²R

Direct Current Circuit Breaker

DC Circuit Breaker is a device used in DC power distributed system to prevent circuit from overcurrent and any other potential hazards.

DC Circuit Breaker

Principle of DC Circuit Breaker

DC Circuit Breaker works on the following principle

• When the current exceeds a rated value, thermal protection trips the breaker and the circuit breaks.
• There is a bimetallic strip heats up and then expands.
• With increase in current, the metallic strip expands.
• This can assist current overload situation. Magnetic protection in DC circuit breakers trips the breaker when many fault current is present.
• This helps to prevent short circuits and other failures.

How to Convert AC to DC Circuit

AC to DC convertors are electrical circuits that are used to convert AC voltage to DC voltage. AC to DC Converter are also called ‘Rectifiers’. Hence, Rectifiers are the devices which convrerts AC to DC. Many devices require the use of AC and DC voltages both, thereby it becomes necessary to develop such technologies that can convert AC voltage supplied at homes to DC voltage. This conversion is optimally suitable according to user’s requirement. Let’s understand how Rectifier works.

How does Rectifier Work?

Rectifiers are devices which converts AC to DC by blocking the flow of current in reverse direction and allowing the flow in only one direction. The working step of Rectifier is mentioned below:

• Intially, transformers are used as power supplies in homes to change voltage of AC .
• When converting AC to DC, voltage is rectified using diodes( they allow current to pass in one direction only) which transform sinusoidal AC wave into positive peaks.
• After this there are still fluctuations in the voltage that need to be removed. This is because fluctuations can damage the load if they pass to the output side.
• The filter applied at the end performs the task of removing AC ripples in output voltage, leading to smooth DC output voltage. This will generate a stable DC voltage matching peaks of AC voltage input.

Learn More, How to Convert AC to DC

AC and DC Circuit

There are two types of electrical cicruit namely AC and DC Circuit based on the power source used. In AC Circuit, current continously change its direction while in DC Circuit, current follows unidrectional. There is significant difference between AC and DC Cicruit which is tabulated below:

Difference between AC and DC Circuit

The difference between Alternating Current and Direct Current is tabulated below:

AC vs DC Circuit
AC Circuit	DC Circuit
The direction of current changes periodically with varying magnitude.	The flow of direct current does not change periodically and has constant magnitude
AC has around 50-60 Hz frequency in households.	DC has no frequency or 0 frequency.
In AC Circuit, current can be transferred over larger distances with minimum energy loss.	DC can’t be transferred over large distances since it looses power over time.
Voltage varies in a sinusoidal pattern.	Constant Voltage is maintained.
AC current is a vector quantity	DC circuit generates scalar quantities like scalar current

Applications Of DC Circuit

DC circuit finds its applications in day-to-day activities like:

• Many electronic devices such as smartphones, laptops, digital cameras use DC circuits for constant power supply. They are fundamental units in integrated circuits.
• DC circuits are often used in transportation where electric vehicles are involved. Electronic vehicles use dc circuits to supply power from batteries to electric motors.
• Modern telecommunication is largely dependant on DC circuits for amplification, signal processing. These circuits are used in both wired and wireless communication.
• Many medical equipments like pacemaker and electronic monitoring equipments use DC Power supply. These circuits are also used in various diagnostic devices making them of great medical use.
• DC circuits are also used in industrial equipment in processes like electroplating which require a constant power source as well as in some automotive devices.

Solved Examples on Direct Current Circuit

Here are some solved examples based on DC circuit.

Example 1: Three light bulbs of 40W, 60W and 100W are connected in series with 220 volt source. Which of the three bulbs will glow the brightest?

Solution:

It is obvious that the bulb with most power will glow the brightest.

Now current across each resistance will be same due to series circuit so we calculate the resistance of each bulb.

P=V²/R …….(1)

For the first bulb, substituting the values we get,

⇒ R₁ = (220)²/40

On calculating we get,

⇒R₁ = 1210 Ω

Similarly for the second bulb, we get the resistance by substituting the values as,

⇒R₂ = (220)²/60

On calculating we get,

⇒R₂ = 806.67Ω

For the third bulb on substituting we get,

⇒R₃ = (220)²/100

On calculating we get,

⇒R₃ = 484Ω

Now we calculate power across each bulb using by P = I²R

Bulb 1: P₁= 1210 × I²

Bulb 2: P₂= 806.67 × I²

Bulb 3: P₃= 484 × I²

Since P₁ is the largest bulb 1 glows the brightest.

Example 2: Find values of current I₁ and I₂ in the circuit given below:

Direct Current Solved Example 2

Using Kirchoff’s Law in loop 1:

V₁ – I₁R₁ – (I₁+I₂)R₃ = 0

V₁ = I₁(R₁ + R₃) + I₂R₃ ……..(1)

Using Kirchoff’s Law in loop 2:

V₂ – I₂R₂ – (I₂ + I₁)R₃=0

V₂ = I₁R₃ + I₂(R₂ + R₃) ……..(2)

On solving 1 and 2,

I₁ = (V₁ – I₂R₃)/R₁ + R₃

I₂ = (V₂ – (V₁ – V₂) × R₃/R₁₎/(R₂ + (R₁ + R₂) × R3/R1)

Direct Current Practice Problems

Try on Practice Problems given below based on Direct Current Concept.

Q1: For the circuit given below find current across R₇ resistor.

Direct Current Practice Question 1

Q2: What is the voltage in the middle branch(with resistor R₂) given that total current I flows through circuit.

Direct Current Practice Question 2

DC Circuit Frequently Asked Questions

What is DC Circuit?

DC Circuit is a closed electrical path in which the power supply produces direct current

What are 3 Basic Types of DC Circuit?

The three basic types of DC Circuit are Series DC Circuit, Parallel DC Circuit and Series-Parallel DC Circuit

What does Direct Current Mean?

Direct Current means that the current is flowing in one direction only and there is no phase change in the current with time

Who developed Direct Current?

Direct current was developed by Thomas Edison in US during the war of currents with Thomas Tesla.

What is DC Circuit Analysis?

DC Circuit Analysis is the method of Finding unknown values of quantities such as voltage, current and resistance

What are the two methods of DC Circuit Analysis?

The two different methods of DC Circuit Analysis is Node Volatge Method and Mesh Current Method

What advantage do AC Circuits have over DC Circuits?

AC circuits can be used to step down or step up by fluctuating the current values. This helps to induce current in secondary coil of transformer whereas DC circuits have constant values and can’t be used for inducing currents.

What is DC Circuit Beaker?

DC Circuit breaker is a device that operate on direct current and interrupt the flow of current in the circuit in case of oversupply of current