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Power Supply Circuit Explained

Key Takeaways

  • Rectification and smoothing is responsible for converting AC to DC and smoothing out the waveform. Provides a stable voltage output, with rectifiers adjusting the waveform and smoothing circuits reducing fluctuations.

  • Voltage regulators maintain a stable output voltage, crucial for the reliability and performance of electronic devices, offering either fixed or variable levels based on specific requirements

  • Over-voltage protection ensures device safety from potential damage by blocking or limiting excess voltage.

Power supply circuit blocks explained below

Power supply circuit blocks explained below

Power supply operation is crucial for enabling a vast array of our modern-day devices. Understanding the role each sub-circuit plays is critical in designing electronics. From the initial filtering of power inputs to protect against line spikes and noise through the transformation and rectification processes that convert and smooth electrical currents, to the vital regulation and over-voltage protection mechanisms that ensure stability and safety, each element of a power supply circuit is important. This “Power Supply Circuit Explained” guide will discuss the role of each within modern-day power supplies.

Building Blocks of Power Supply Circuits Explained

Power supply circuits can encompass different operating principles but all consist of the same basic elements.

Power Supply Element


Power Input Filtering

Necessary to prevent power line spikes from entering the power supply and to mitigate noise generated by the power supply itself. Circuitry at the input filters out noise and limits the impact of spikes. Growing demand for high levels of electromagnetic compatibility (EMC) prompts many power supplies to incorporate filtering and other EMC best practices to mitigate interference and prevent the spread of unwanted emissions.

Input Transformer

Utilized to adjust incoming line voltage (110 or 240 volts AC) to the required level for the power supply design.


Converts incoming AC waveform to a DC waveform via an AC rectifier circuit.

Rectifier Smoothing

Output from the AC rectifier circuit consists of a waveform ranging from zero volts to 1.414 times the RMS input voltage, adjusted for any losses introduced by the rectifier.


Voltage regulator circuit is essential to maintain stable voltage output with minimal hum and noise, even after rectification and smoothing. Regulators can provide stable voltage at fixed or variable levels based on requirements.

Over Voltage Protection

Crucial to protect against over-voltage situations. Over-voltage protection circuitry detects and trips when the output voltage exceeds acceptable limits, disconnecting the supply from the regulator and typically clamping the output to zero volts.

Over Voltage Protection

Over-voltage protection ensures the supply either shuts off or limits its output once the voltage surpasses a predetermined threshold. Power supplies typically incorporate a circuit designed for over-voltage protection to shield electronic parts from harm. Over-voltage scenarios can range from the destruction of components to their gradual deterioration and even to the malfunctioning of circuits or the ignition of fires. Generally, power supply over-voltage protection circuits have the following features:

  • Block surplus voltage from reaching the components.

  • Quick enough to act against transient phenomena that pose a risk to the power supply and the components connected downstream. 

  • Operate without disrupting the usual activities of the system or circuit, avoiding any additional load on the power 

  • Avoid false activations or overlook actual over-voltage events, as false alarms can be bothersome, and missing genuine over-voltage conditions can be hazardous.

  • Differentiate between normal voltage swings and dangerous over-voltage incidents.

Power Supply Regulation Toplogies 

The regulation component of the power supply circuit, is where different technologies shine. Whether they are linear regulated or switch-mode, each with distinct electronic circuit design topologies. Below, we’ve summarized the three major technologies for power supply circuits.

Power Supply Type



Simplest type of power supply circuit, and simnply consist of a transformer, rectifier, and low pass filter. As there are no regulating elements, the load regulation is very low. They are rarely used in modern-day consumer electronics.

Linear Regulated

Offers high performance but employs a series regulator element, leading to comparatively high inefficiency and significant heat dissipation. Gradually becoming less prevalent due to inefficiency and added cost, although still essential in applications requiring exceptionally clean supplies.

Switch Mode

Utilizes switching technology to regulate output, despite the presence of spikes. Utilizes a PWM square wave duty cycle, with the transistor operating as an on/off switch. Regulation occurs through altering the duty cycle of the DC-to-AC inversion. Boasts exceptional efficiency, allowing for smaller packaging compared to linear counterparts. Reduced heat dissipation leads to lower heat removal costs, impacting both power supply and overall equipment costs. Commons variations are buck (DC-DC step down) and boost (DC-DC step up) converters.

Switching Power Supply Circuit Topologies 

One of the most significant benefits of SMPS is their ability to operate independently of the input voltage, making them “universal” power supplies. This makes them ideal for a broad range of electronic power systems. Depending on the DC level needed, they come into main topologies, with an additional buck/boost topology that combines both. 

  • Buck converters (step-down converters), reduce the voltage from the input to the output while increasing current capability. By adjusting the duty cycle of the switching element, buck converters efficiently control the amount of energy transferred to the output, ensuring a stable and lower voltage level. For this reason, buck converters are useful for high-efficiency applications across a wide range of input voltages.

  • Boost converters (step-up converters) store energy in the inductor during the "on" phase and release it to the load during the "off" phase, and thus supply a continuous higher voltage output from a lower voltage source. This is useful in energy harvesting systems, portable electronics, solar and solar panels.

After this power supply circuit explained guide, if you’re ready to elevate your power supply circuit designs look no further than OrCAD X.  OrCAD X is the premier PCB design solution tailored for engineers who demand precision and efficiency. With OrCAD X, you can seamlessly integrate power input filtering, rectification, regulation, and over-voltage protection into your designs, leveraging advanced simulation tools to predict performance and identify potential issues early in the design process. 

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