Understanding Supercapacitor Discharge Into A Constant Power Load

Focus:

Supercapacitors are gaining popularity as power backup devices in diverse power supply applications where they are called on to deliver constant power to the load for some specified period of time. In order to design the supercap-based backup module correctly, designers need to understand how the supercapacitors discharge more quickly when feeding a constant power load (such as a boost regulator) than when feeding a purely resistive load. To address this subject, which has been neglected in the literature, this article derives the voltage and current equations that describe the discharge of a supercap into a constant power load, plots voltage and current curves for an example design, and compares discharge into a constant power load versus a resistive load. An example circuit is also simulated.

What you’ll learn:

• How to understand how supercapacitor discharge into a constant power load differs from discharge into a resistive load
• How to select a supercapacitor value to achieve a specified period of power backup for a specified, constant power load
• How to calculate the time period of power backup provided by a specified supercap value for a specfied constant power load

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Author & Publication:

Gregory Mirsky, Design Engineer, Deer Park, Ill., How2Power Today, Oct 15 2021

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