 # Series and Parallel Circuits 5: More About Circuits

1. Series and Parallel Circuits 1: The Basics
2. Series and Parallel Circuits 2: Resistors
3. Series and Parallel Circuits 3: Capacitors
4. AC Series and Parallel Circuits 4: Inductors and Capacitors

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An almost unlimited number of useful circuits and associated variants are available to the circuit designer.  Electronic Design Automation (EDA) software, such as those available from Altium, or EEsof (Keysight), and the like, include databases of circuits and circuit modules, as well as automated circuit design and modeling capabilities, etc.  The capabilities of EDA software systems are amazing and are ever improving!

Analog and digital circuits are available to serve myriad functions.  Websites such as “All About Circuits,” “Electronics Notes,” “Circuit Lab,” “Electronics Tutorials,” and numerous others provide a plethora of circuit types and examples, as well as valuable related information.  Additionally, numerous books, such as Graf’s, et al. Encyclopedia of Electronic Circuits (Vols. 1-7) and others, disclose and describe an abundance of electronic circuits, as well as their uses and how to “fine tune” them for your application.  While there are simply too many to cover in a post, let’s review a few.  Voltage divider circuits are useful in that they produce different voltage levels from a common voltage source.  As shown below, a basic voltage divider is a series circuit, where the output current is the same through each component.

In the above voltage divider circuit:

where:

VS is the voltage drop across the entire circuit (V)

VRi is the voltage drop across resistor i (V)

RT is the total circuit resistance (Ω)

Ri is the resistance of resistor i (Ω)

Voltage divider circuits may have voltage sources or “taps” that are both positive and negative in the same circuit as shown below for a 60W, 2.5A multiple voltage power supply voltage divider circuit, which is useful for computer applications, and other DC circuits, etc.

In the above case, the zero-voltage point is placed between R3 and R4 (i.e., at tap node 4) so as to enable three different positive DC voltages and one negative DC voltage (i.e., +12V between tap nodes 1 and 4, +5V between tap nodes 2 and 4, +3.3V between tap nodes 3 and 4 and -12V between tap nodes 4 and 5) from the 24V DC source.

Additionally, capacitive and inductive voltage divider circuits are useful in enabling multiple voltage AC power sources as shown below.

Capacitive Voltage Divider:

Inductive Voltage Divider:

Current divider circuits are useful in situations requiring two or more parallel circuit branches having different currents, but the same voltage; such as in the case of parallel LEDs having the same forward voltage (Vf) but different power ratings (currents).  Again, “All about Circuits” does an excellent job of explaining current divider circuits.

Filtering circuits are another useful category of circuits.  Filters may be active or passive.  Active filters are typically analog circuits that utilize active components (such as amplifiers (Op-Amp or the like)) to actively filter signals. Active digital filter circuits are also a major category of circuits.

Passive filters are analog circuits that are comprised of passive electronic components (capacitors, inductors, resistors).  Different passive filter circuit topologies, such as L-filters, C-filters, π-filters, multi-element filters, etc., are available to pass signal (e.g., DC-block) in your circuit, or to remove noise from your circuit, whether the signal or noise be relatively low or high frequency, or a band of frequency.[11,12,13,14]

Many other types of circuits exist to meet the needs of designers and their customers.  With proper circuit choice and design, almost any electronic need can be solved.

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