Can someone explain what the 220uF capacitor at the input of the LM317 is for? I dont think this is for filtering am i wrong?
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I thought thats what the .1uf capacitor was for.Yes it is filtering. If the LM317 is more that 6 inches away from the normal powersupply filter the capacitor is recommended.
I did some more research and from what i can infer the 220uf cap is serving as a "reservoir" cap, while the .1uf is the filter cap. I think the reservoir cap is there to provide extra energy to keep the input voltage from drooping when a current surge occurs at the regulators output. The reservoir cap will recharge the filter cap when it becomes depleted. This would make sense as to why the "reservoir" cap is large-so it can store a lot of additional energy. Again i dont know if this is right but it kinda makes sense.I looked a three data sheets and two had an electrolytic capacitor on the input. Both wrote it is for transcient protection. Only one mentioned the
6" rule.
I mostly use the 317T with AC/DC wall warts and the cable from the wart to the box where the 317T is is about 4 feet, so I insert a 100uF right at the input pins and don't use a 0.1uF.
Yes, i think the 220uf cap is serving a dual purpose as a filter cap and reservoir cap.Both the 220uF and the 0.1uF capacitors are for filtering. The 0.1uF cap is generally a ceramic capacitor and has a faster response than the electrolytic. At least this is my understanding of them.
by Jake Hertz
by Jake Hertz
by Jake Hertz
by Aaron Carman