AC Peak Voltage vs. Peak-to-Peak Voltage vs. RMS Voltage

November 20, 2020 Cadence PCB Solutions

Key Takeaways

  • Learn how to calculate AC peak voltage.

  • Gain a greater understanding of the importance of AC peak voltage to overall circuit design.

  • Learn how to differentiate between AC peak voltage, peak-to-peak voltage, and RMS voltage.

 Man checking AC peak voltage in an electrical energy distribution substation

Checking the AC peak voltage at a distribution substation.

The credit for discovering the electrical charge goes to the Greeks, and this discovery dates back to 2600 years ago. An electrical charge is also called static electricity or inert electricity. For several millennia, humans have possessed an unquenchable fascination with lightning and electricity. From Benjamin Franklin's kite experiment in 1752 to Volta's invention of the battery in 1800 to the electric light bulb invention in 1879 by Thomas Edison, this fascination is undeniable.

Fast-forward to present day and there is still a desire to understand, harness, and efficiently use electricity. This is understandable since nearly every device we utilize relies on some form of power or electrical charge. However, not all sources of electrical energy are compatible with every device design. As our knowledge and understanding of electricity has increased, so have our power requirements. With this in mind, our designs rely on our ability to assess both electrical limits and power requirements accurately. This includes being able to calculate parameters like AC peak voltage.

What Is Voltage?

Voltage is the electric potential within a circuit that provides the potential for current to flow. But, the mere presence of voltage within a circuit does not indicate that there is current present in the circuit. For current to flow within a circuit, the circuit must be complete (closed path).

Therefore, voltage provides the potential for current to be present in a circuit, but current only flows if there is a completed or closed path. This is because voltage provides the force which pushes or moves electrons within the circuit when the path is completed.

For example, an electrical outlet does not have current flow if there is no device plugged in. However, the electric potential or voltage is still present. Once we plug in a device and complete the circuit by turning it on, the voltage is active and there is current flow in the device.

AC Peak Voltage

Every electronic device requires a power source that is fully compatible with its design. Some devices utilize DC, whereas other devices use AC. There are also devices, such as personal computers, that utilize DC converted from AC electrical outlets. In every case, there are parameters to which this electrical power source must adhere to for the device to function.

The need to differentiate between maximum or peak voltage and RMS (root-mean-squared) or average voltage is paramount to both design and functionality. One such parameter is the AC peak voltage. As you might imagine, utilizing a voltage that exceeds a device's design will undoubtedly lead to catastrophic failure and possibly injury or death. So, what is AC peak voltage?

As the name implies, AC peak voltage is the maximum or peak voltage the source can or will achieve. Peak voltage, which we designate as VP, is measured from the horizontal axis (at 0 reference height) to the top of the waveform or crest. 

AC Peak Voltage vs. AC Peak-to-Peak Voltage

Keep in mind that AC stands for alternating current, and this also means that the voltage alternates (changes polarity) a set number of times in a given period. Take, for example, a 60Hz, 120 volt AC signal:

The 60Hz designation indicates that the signal will alternate from negative (peak) to positive (peak) voltage 60 times within one second. This particular voltage parameter is called peak-to-peak or VPP, and it is not interchangeable with peak voltage.

Understandably, these parameters affect the application that a particular voltage is compatible with and, thus, affect overall functionality. Calculating the AC peak voltage, peak-to-peak voltage, and RMS voltage is critical.

A graph showing a peak-to-peak voltage waveform

Calculating AC Peak Voltage

We can calculate peak voltage (VP) by using the peak-to-peak voltage (VPP), RMS voltage, or the average voltage. The formulas for calculating the VP for sinusoidal AC signals are as follows:

If you acquire the peak-to-peak voltage (VPP) value, you can calculate the peak voltage (VP) by using the following formula:

VP = VPP x 0.5

If you acquire the RMS voltage value, you can calculate the peak voltage (VP) by using the following formula:

 If you acquire the average voltage value, you can calculate the peak voltage by using the following formula:

VP = average voltage x (π ÷ 2)


VP = average voltage x 1.57

AC peak voltage, like a myriad of other parameters we find in the field of electronics, is beneficial to overall design and functionality. The understanding of an electrical source's maximum, average, and minimum potential greatly enhances your design accuracy, functionality, and device performance.

An isolated AC power strip

An AC peak voltage that exceeds the power strips capacity will lead to catastrophic failure.

As the image above illustrates, when designing electronic circuits, it is important to be able to accurately determine the parameters of your AC signals to ensure adequate protection is included. This allows you to prevent contingencies that may damage equipment or threaten users. 

Cadence’s PCB Design and Analysis software leads the industry by providing comprehensive and integrated schematic capture, board layout and simulation and analysis capabilities. For simulation, which includes the ability to view various representations of AC waveforms, PSpice is the standard. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.


About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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