The LM317 datasheet recommends a 100nF disc capacitor or a 1uF tantalum.
Let's ignore the tantalum. I have found the following comments:
Use any of the film ones and not the ceramics, as those you show there have a breakdown voltage of 25V, and at that are likely not going to be 100n any more but likely under 30n
Vs
C3 & C9 should be close to the reg leadouts. But do not use low ESR film capacitors.
So... what should I do? 🙂 Ceramic or film?
Let's ignore the tantalum. I have found the following comments:
Use any of the film ones and not the ceramics, as those you show there have a breakdown voltage of 25V, and at that are likely not going to be 100n any more but likely under 30n
Vs
C3 & C9 should be close to the reg leadouts. But do not use low ESR film capacitors.
So... what should I do? 🙂 Ceramic or film?
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I've always used the cheapest and physically smallest 47 microfarad electrolytic capacitor I could find, with a healthy excess DC voltage rating. I love margin-of-safety.
Doesn't matter really, it's a regular decoupling cap, just a bit more important on supporting transient current draw, distance matters more. that don't use low esr film capacitors is talking about Cout, which is a lot more tricky.
in my design I use 0.1uf film cap as part of CLC, and the distance is a bit far from power in about 1cm, so I put another 0805 cap under power pin, if the film decouple isn't good enough, I can just solder the backup C0G cap on it and save the day.
Just don't use X7R this type in Cin, if lm317 is used to regulate after smoothing cap...I heard piezoelectric effect is a thing, and I don't want the capacitance jump around with the voltage ripple. ja...maybe film + lytic is better.
in my design I use 0.1uf film cap as part of CLC, and the distance is a bit far from power in about 1cm, so I put another 0805 cap under power pin, if the film decouple isn't good enough, I can just solder the backup C0G cap on it and save the day.
Just don't use X7R this type in Cin, if lm317 is used to regulate after smoothing cap...I heard piezoelectric effect is a thing, and I don't want the capacitance jump around with the voltage ripple. ja...maybe film + lytic is better.
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If you go at the top of that page, you can find the schematic. C3 is the Ci capacitor and that's why it's a bit confusing to me.
I've built a few power supplies and up until now I've used 0.1uF polyester for Ci, but after reading these comments I'm not sure anymore 🙂
