## Introduction

Circuit diagram refers to a diagram showing electrical connections with either basic images of parts or industry standard symbols. That is to say, it is a kind of principle for layout diagram that shows the relationship between components drawn by physical and electrical standardized symbols for research and engineering planning of of people. A diagram meant to depict the physical arrangement of the wires and the components. From the circuit diagram, you can know the working principle of the components, and it provides solutions for analyzing performance, installing electronic and electrical products.

**Catalog**

Ⅱ Common Characteristics and Calculation of Series and Parallel Circuits |

Ⅲ Six Circuit Design Software Tools Introduction 3.1 Protel PCB Design Platform |

## Ⅰ Series and Parallel Circuits

Series vs Parallel Circuits

Series connection is one of the basic ways to connect circuit elements. The circuit formed by connecting various electrical parts in series. In the series circuit, the current through each part is equal.

Parallel connection is another connection method between electrical components. Components connected in parallel are connected in multiple paths so that the current can split up, and the same voltage is applied to each component.

## Ⅱ Common Characteristics and Calculation of Series and Parallel Circuits

### 2.1 Resistors

- Resistors in Series

As shown in the figure, n resistors connect in series. Now connect the power supply to both ends of this series circuit. According to Kirchhoff’s current law, the current given from the power supply is equal to the current through each resistor, so .

According to Ohm’s law, the voltage across the k-th resistor is equal to the current through multiplied by its resistance .

According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all resistors.

Therefore, the equivalent resistance Req of n resistors in series is .

According to Ohm’s law, the voltage across the power source is equal to the given current times the equivalent resistance .

Pay attention to the voltage shared by the resistors of the series circuit is proportional.

Conductance G is the reciprocal of resistance R, so the equivalent conductance of n resistors in series is

Among them, Gn is the conductance of the n-th resistor.

For the simple case of two resistors in series, the equivalent conductance is .

- Resistors in Parallel

When linear resistors connect in parallel, the conductance (the reciprocal of resistance) is equal to the sum of the conductances of the parallel resistors, which is called the equivalent conductance, and the reciprocal is called the equivalent resistance. For example, the resistances of R1, R2, and R3, their conductances are G1, G2, and G3, respectively. The total resistance R and total conductance G of the parallel circuit are calculated according to the formula .

Note: Calculate the total series and parallel resistance of a circuit using Apogeeweb's * Parallel and Series Resistor Calculator*.

### 2.2 Capacitors

- Capacitors in Series

As shown in the figure, n capacitors are connected in series. From the definition of capacitor, it can be obtained that the current passing through the k-th capacitor is equal to its capacitance multiplied by the voltage change rate across it:

According to Kirchhoff’s current law, the current i given from the power source (ac or dc) is equal to the current passing through each capacitor, so

According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the algebraic sum of the voltage across all capacitors:

The voltage change rate of the power supply end is .

Therefore, the equivalent capacitance Ceq of n capacitors in series is

Each capacitor has a “voltage rating” set by its manufacturer. Assuming that the working voltage exceeds the voltage rating of the capacitor, it may cause capacitor failure. In order to avoid it, several similar capacitors can be connected in series to make the algebraic sum of the voltage rating greater than the operating voltage. However, this will also reduce the equivalent capacitance of the circuit.

- Capacitors in Parallel

As shown in the figure, n capacitors are connected in parallel. From the definition of capacitor, it can be obtained that the current ik through the k-th capacitor is equal to its capacitance Ck multiplied by the voltage change rate across it:

According to Kirchhoff’s voltage law, the voltage across the power supply is equal to the voltage across each capacitor:

According to Kirchhoff’s current law, the current given from the power source (dc or ac) is equal to the algebraic sum of the current through each capacitor:

Therefore, the equivalent capacitance Ceq of n capacitors in parallel is .

Note: Calculate the total series and parallel capacitance of a circuit using Apogeeweb's * Series and Parallel Capacitance Calculator*.

### 2.3 Inductor

- Inductor in Series

As shown in the figure, n inductors are connected in series. According to the method described above, the equivalent inductance can be calculated as .

Among them, Ln is the inductance of the n-th inductor.

The magnetic field generated by the inductor will be coupled with the winding coil of the adjacent inductor. So it is difficult to avoid the mutual influence of the adjacent inductors. The mutual inductance M of physical quantities can give a measure of this influence.

A series circuit composed of two inductors L1 and L2, and the mutual inductance Ms.

1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation:

2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:

For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated. The equivalent inductance is the algebraic sum of all self-inductance and mutual inductance.

For example, a series circuit composed of three inductors will involve three self-inductances and six mutual inductances. The self-inductances of the three inductors are M11, M22, and M33, and the mutual inductances are M12, M13, M21, M23, M31, and M32.

Equivalent inductance is .

Since the mutual inductance between any two inductors is equal to each other, the latter two sets of mutual inductance can be combined:

- Inductors in Parallel

N ideal inductors without mutual inductance are connected in parallel. Similar to the method described above, the equivalent inductance Leq can be calculated as .

Among them, Li is the inductance of the i-th inductor.

The above equation describes an ideal case where n inductors are connected in parallel without mutual inductance.

A parallel circuit composed of two inductors with inductances L1 and L2 and mutual inductance M:

1) Assuming that the magnetic fields or fluxes generated by two inductors are in the same direction, the equivalent mutual inductance Leq is expressed by the equation:

2) Assuming that the magnetic fields or fluxes generated by two inductors are in opposite directions, Leq is expressed by the equation:

For a parallel circuit with three or more inductors, it is necessary to consider the self-inductance of each inductor and the mutual inductance among the inductors, which makes the calculation more complicated.

### 2.4 Switch

- Switch in Series

Two or more switches are connected in series to form an or gate circuit. Assuming a power supply is connected to both ends of the circuit, current will only flow when all switches are closed.

- Switch in Parallel

Two or more switches are connected in parallel to form an or gate circuit. Assuming that a power supply is connected to both ends of this circuit, even though any one of the switches is closed, current will flow.

### 2.5 Power Supply

- Power Supply in Series

For example, assuming that several cells in the battery pack are connected in series to form a power source, the voltage across the power source is the algebraic sum of the voltages across all cells.

- Power Supply in Parallel

For example, assuming that a battery pack uses several single batteries with the same voltage connected in parallel as a power source, the voltage across the power source is equal to the voltage across the single battery.

Note: Get more info from * Switching Power Supply Circuit Diagram with Explanation*.

### 2.6 Rules for Series and Parallel Circuits

How to judge whether the electrical circuits are connected in series or in parallel? Series and parallel are the two most basic forms of circuit connection, and there are certain differences between them. So get to know their basic characteristics well according to the following specific methods.

(1) Visual Check

Look at the connection form of electrical parts in the circuit. The one by one in sequence is series; the one paralleled between two points of the circuit is parallel.

(2) Current Flow

When the current flowing from the positive pole of the power supply to each element in turn shows that the circuit is in series; when the current flows to two branches and get together at a certain place finally, it indicates that the circuit is in parallel.

(3) Removing Components

Remove one electrical part at will to see whether other electrical components are working normally. If the circuit can continue to work, then the connection relationship of this circuit is in parallel, otherwise, it is in series.

## Ⅲ Six Circuit Design Software Tools Introduction

### 3.1 Protel PCB Design Platform

Protel PCB is a CAD software for the circuit industry launched by Protel Systems Pty Ltd in 1985, and has rebranded to Altium Designer. It has many advantages compared with many EDA software for circuit designers. Almost all circuit companies use it. The early Protel PCB was mainly used as a printed board automatic wiring tool. It ran in DOS and had fewer hardware requirements. It can run under the 1M memory of a 286 machine without a hard disk. However, it’s less functional, only electrical schematic drawing and printed board design functions, and the PCB layout rate of automatic wiring is also low.

It is a professional circuit board drawing tool. It includes electrical schematic drawing, analog circuit and digital circuit mixed signal simulation, multilayer PCB design, programmable logic device design, chart generation, circuit table generation, and supports macro operations, etc. And it has a client/server architecture. PROTEL is also compatible with some other design software file formats, such as ORCAD, PSPICE, EXCEL, etc. Using automatic routing of multi-layer can achieve 100% layout rate of high-density PCBs.

### 3.2 Altium Designer

Altium Designer is one of the most popular of the high end PCB design software packages on the market today. It provides a single, unified application that incorporates all the technologies and capabilities necessary for complete electronic products, which mainly runs on the Windows operating system. This software provides designers with brand-new design solutions through the perfect integration of schematic design, circuit simulation, PCB drawing editing, topology logic automatic routing, signal integrity analysis and design output, etc. When using this software, the quality and efficiency of circuit design can be greatly improved.

Fully inheriting the functions and advantages of the previous series of versions of Protel 99SE and Protel DXP, Altium Designer has many improvements and many high-end features. The platform broadens the traditional interface of board-level design and fully integrates FPGA design functions and SOPC design implementation functions, allowing engineers to integrate FPGA in system design with PCB design and embedded design. With these advantages, Altium Designer requires higher computer system performance than the previous version.

### 3.3 Quartus II

The Altera Quartus II design software is a multiplatform design environment that easily adapts to your specific needs in all phases of FPGA and CPLD design. In other words, Quartus II software delivers the highest productivity and performance for Altera FPGAs, CPLDs, and HardCopy ASICs. It is a comprehensive CPLD/FPGA development software, and supports schematics, VHDL, VerilogHDL and AHDL (Altera Hardware supports Description Language) and other design input forms. Quartus II embedded with its own synthesizer and simulator, can complete the process of design input to the hardware configuration. It can run in Windows, Linux and Unix. Use Tcl scripts to complete the design process, and it also provides a complete user graphical interface design method. Quartus II has the characteristics of fast running speed, unified interface, centralized function, easy to learn and easy to use.

Quartus II provides a fully integrated development which independent of circuit structure, with all the features of digital logic design, including:

1. You can use the schematic diagram, structural block diagram, VerilogHDL, AHDL and VHDL to complete the circuit description, and save it as a design entity file.

2. Chip (circuit) plane layout wiring editing

3. With LogicLock region, users can build and optimize the system, and add subsequent modules that have little or no impact on the performance of the original system.

4. Powerful logic synthesis tool

5. Complete circuit function simulation and sequential logic simulation

6. Timing analysis and critical path delay analysis

7. Signaltap ii logic analyzer can be used for embedded logic analysis.

8. Support the addition and creation of software source files, and link them to generate programming files.

9. Use the combined compilation method to complete the overall design process at one time.

10. Automatically locate compilation errors.

11. Efficient period programming and verification

12. Read into standard EDIF, VHDL and Verilog netlist files.

13. It can generate VHDL and Verilog netlist files used by third-party EDA software.

### 3.4 Electronics Workbench (EWB)

EWB is is a mixed-mode SPICE-based electronics design and simulation tool, launched by Interactive Image Technology Co., Ltd. in the early 1990s. It is used for mixed simulation of analog circuits and digital circuits. With this powerful software, you can directly see the output of various circuits on the screen.

Compared with other EDA software, EWB is a smaller software, and its function is relatively single. However. its simulation function is very powerful, almost 100% simulation results of real circuits. It provides parts such as multimeters, oscilloscopes, signal generators, frequency sweepers, logic analyzers, digital signal generators, logic converters, etc., and its device library contains many transistor components, integrated circuits and digital gate circuit chips from large companies.

In addition, components that are not in the device library can also be imported externally. Among many circuit simulation software, EWB is the easiest to use. Its working interface is very intuitive. The schematic diagram and various tools are in the same window. People who have never touched it can use the software proficiently with a short-time learning. For electronic designers, it is an excellent EDA tool. For many circuits, you can know its results without using a soldering iron. If you want to change components or change parameters, you only need to click the mouse. It can also be used as an auxiliary teaching software for electrical knowledge.

### 3.5 NI Multisim

Multisim is a Windows-based simulation tool launched by National Instruments (NI) Co., Ltd.. It is industry standard SPICE simulation and circuit design software for analog, digital, and power electronics in education and research. It includes graphical input of circuit schematics, circuit hardware description language input, and has rich simulation analysis capabilities. Engineers can use it to interactively build circuit schematics and simulate the circuit.

With SPICE simulation, designers can quickly capture, simulate and analyze new designs without knowing SPICE deeply, which also makes it more suitable for electronics education. Through Multisim and virtual instrument technology, PCB designers and electronics educators can complete a complete integrated design process from theory to schematic capture and simulation to prototype design and testing.

NI Multisim software is an EDA tool software specially used for electronic circuit simulation and design. As a personal desktop electronic design tool running in Windows, NI Multisim is a complete integrated design environment. Its computer simulation and virtual instrument technology can solve the problem of disconnection between theoretical teaching and actual reality experiment. Students can easily reproduce the theoretical knowledge they have learned through computer simulation, and can use virtual instrument technology to create their own instruments. It has an intuitive graphical interface, abundant components, powerful simulation capabilities, abundant testing instruments and complete analysis methods. NI Multisim software is a not bad teaching tool.

### 3.6 Allegro PCB

Allegro PCB is an advanced PCB design routing tool introduced by Cadence. It provides a good and interactive working interface, and powerful and complete functions. Provide the most perfect solution for the current high-speed, high-density, multi-layer complex PCB design and wiring, with the combination of its front-end products Cadence, OrCAD, and Capture. Allegro has a complete constraint setting. Users only need to set the wiring rules as required. The wiring design requirements can be met without violating DRC, thus saving tedious manual inspection time and improving work efficiency. It can also define parameters such as minimum line width or line length to meet the various requirements of today's high-speed circuit board wiring. Allegro PCB enables you to do high-speed design, RF antenna, flex-circuitry, and design for manufacturing (DFM) technology.

For the drawing and modification functions of copper foil that the industry attaches great importance to, Allegro provides a simple and convenient inner layer division function, as well as the ability to review the inner layer of the positive and negative film. For copper paving, it can also be divided into dynamic copper or static copper, which can be used for different applications. Dynamic copper parameters can be divided into different levels of settings for all copper, single copper or single object, so as to meet the requirements of different connection effects or spacing values to match the special settings due to design requirements.

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