The 10 Most Common Circuits

Electronic products are often complex masses of circuits. As you peel back the layers of any complex electronic product, common circuits, subsystems, and modules become visible. Common circuits are simple circuits that are easy to design, work with, and test. The circuits listed here are common circuits frequently used in electronics. 

Resistive Divider

One of the most common circuits used in electronics is the humble resistive divider. The resistive divider is a great way to drop the voltage of a signal to the desired range. Resistive dividers offer the benefits of low cost, ease of design, and few components, and they take up little space on a board. However, resistive dividers can significantly load down a signal, which changes the signal significantly. In many applications, this impact is minimal and acceptable, but designers should be aware of the effect a resistive divider can have on a circuit.

OpAmps

OpAmps are useful in buffering a signal while boosting or dividing the input signal, which comes in handy when a signal needs to monitored without being affected by the circuit doing the monitoring. Also, the boost and divider options allow for a better range of sensing or control.

Level Shifter

Modern electronics are full of chips that require different voltages to operate. Low-power processors often operate on 3.3 or 1.8v, while many sensors run on 5 volts. Interfacing these different voltages on the same system requires that signals either be dropped or boosted to the required voltage level for each chip. One solution is to use a FET-based level shifting circuit or a dedicated level shifting chip. Level shifting chips are the easiest to implement and require few external components, but they all have their quirks and compatibility issues with different communication methods.

Filter Capacitors

All electronics are susceptible to electronic noise that can cause unexpected, chaotic behavior or completely halt the operation of electronics. Adding a filter capacitor to the power inputs of a chip can help to eliminate noise in the system and is recommended on all microchips. Also, caps can be used to filter the input of signals to lower the noise on the signal line.

On/Off Switch

Controlling the power to systems and subsystems is a common need in electronics. Several methods achieve this effect including using a transistor or a relay. Optically isolated relays are the most effective and simplest ways to implement an on/off switch to a subcircuit.

Voltage References

When precision measurements are required, a known voltage reference is often needed. Voltage references come in a few form factors. For much less precise applications, even a resistive voltage divider can provide a suitable reference.

Voltage Supplies

Every circuit needs the right voltage to operate, but many circuits need multiple voltages for every chip to work. Stepping down a higher voltage to a lower voltage is a relatively simple matter using a voltage reference for very-low-power applications or a voltage regulator for more demanding applications. When higher voltages are needed from a low voltage source, a DC-DC step-up converter generates many common voltages and adjustable or programmable voltage levels.

Current Source

Voltages are relatively simple to work with within a circuit, but for some applications, a steady fixed current is required, such as for a thermistor-based temperature sensor or to control the output power of a laser diode or LED. Current sources are easily made from simple BJT or MOSFET transistors and a few additional low-cost components. High-power versions of current sources require additional components and demand a greater design complexity to accurately and reliably control the current.

Microcontroller

Nearly every modern electronic product has a microcontroller at its heart. While not a simple circuit module, microcontrollers provide a programmable platform to build any number of products. Low-power microcontrollers (typically 8-bit) run many items from your microwave to your electric toothbrush. More capable microcontrollers are used to balance the performance of your car's engine by managing the fuel-to-air ratio in the combustion chamber while handling other tasks simultaneously.

ESD Protection

An often forgotten aspect of an electronic product is the inclusion of electrostatic discharge and voltage protection. When devices are used in the real world, they can be subjected to incredibly high voltages, which causes operational errors and even damage the chips. Think of ESD as miniature lightning bolts attacking a microchip. While ESD and transient voltage protection microchips perform the job admirably, basic protection comes from simple Zener diodes placed at critical junctions in the electronics, typically on critical signal runs and where signals enter or exit a circuit to the outside world.