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Hello readers! Today we will discuss about charging of super-capacitors and using them in UPS applications. Especially for Arduino or Raspberry pi, these capacitors can provide excellent backup for few minutes. Now, first step for designing a super-capacitor based power supply system is to select a super-capacitor and know how they should be charged.The one supercapacitors that I can easily get were 2.7V, 500F capacitors. I connected two of them in series to get a combination of 5.4V, 250F of capacitance. You can connect another same combination in parallel with it to get a 500F capacitance. Supercapacitors for those who don't know are widely used in solar powered applications, battery back-up applications, etc. They are like normal capacitors but can store massive amount of energy.Charging of supercapacitors is similar to that of an electrochemical cell but they are not as energy dense as a battery. They can be charged quickly due to their low ESR (it's the internal resistance of capacitor) and due to low energy density, they can be quickly discharged. They don't leak or give off toxic gases like batteries but store almost same amount of energy.We will use an LM317 based power supply for charging our supercapacitor. LM317 is a very robust little 1.5A current capacity voltage regulator IC. For 5.4V to charge, we use a 10k and 33k resistors for adjusting the voltage of the IC. You might use lower resistance but these resistors sink the current and thus keeping large resistance reduces the power loss. Next, we are keeping a 1 ohm, 5W resistor in series to limit the current at 1A. One thing about supercaps, they will take as much current as they can and will look like a short connection and this may heat up LM317 and thus a current limiting resistor of high power rating is necessary. And in addition, some diodes are also required to keep LM317 from malfunctioning.You can charge the supercap combination with 5.4V but not higher than that. If you supply your combination with 5.4V and leave it unattended, no problems at all! But this is not the case in batteries, they lose their integrity if kept charged of long time.We are powering our board with the similar power supply and if these supply fails, the boards continue to get power from DC-DC boost converter connected with supercapacitors. Now, while charging of supercaps, the terminal voltage at the output increase slowly as the capacitors get charged. An led indication is kept at 5V regulator to know that terminal voltage is greater than 5V and that it can happily power our boards now. A 5V regulator is necessary because for boards like Raspberry pi when powering it with GPIO pins where no further voltage regulation is provided, it is necessary to charge it with stable 5V and not more than that voltage otherwise you may damage its silicon.Suprecapacitors discharges a ton and so it is absolutely not a good idea to directly connect supercapacitors to your board, a DC-DC converter is necessary. The converter ICs have all types of protection circuits and feedback to keep your output stable and get disconnected if heavy discharge, short circuit or any other problem is detected.So this is it for today, I am currently working on a circuit that can switch to UPS regime when power failure is detected. I will update here the progress and also will continue the logic level shifter series in the upcoming posts. If you like the post, please comment, share and follow this blog!Thanks for reading!