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Old 8th September 2005, 08:51 AM   (permalink (permalink))
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Originally Posted by hexibot43
Alright. In choosing the Caps to go with a 7805, and a 7809 where does one start? I've read a few peoples thoughts, and come to the conclusion I'd better get some more input. And the choice of Cap type? I've seen specs from 1000uF to 10uFs. Stating all electrolytic. Then someone else wrote that using strickly electrolytics could give rise to problems.
I am really trying to understand this, so any info would be helpful. Thanks, Marcello
They aren't particularly critical about values, either small electrolytics (1uF to 10uF) or 'large' non-electrolytics (0.1uF to 0.47uF) all appear to work well. Something like a 1000uF is far too big, you often have one on the input side (as a reservoir capacitor), as well as a smaller capacitor for stability.

If you really want "belt and braces", use a 10uF and a 0.1uF in parallel on both input and output.

Remember, the stability capacitors MUST be as close as possible to the pins - if you check the hardware for my PIC tutorials I place them right next to the chip. Notice that I use small electrolytics on those boards!.
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Old 8th September 2005, 02:35 PM   (permalink (permalink))
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Now may I ask because the topic of the transorb has come up again. The tranorb would be used instead of the caps? Or you use in conjunction with Caps? I'm just going to go with the caps for now, since I have them on my bench. I'm going to order a couple of these transorb things to play with along with some self resetting fuses. I like the idea of the self resetting fuse.
I had my project running in the car with no trouble, but the power supply I was using was too big to fit in the case I wanted to use. Now the car is barely able to to 2000 rpm. All for the change of my power supply. But it sure is nice to have it all in a nice case. It is finally looking like a finished product. Although it isn't working yet.
Thanks everyone for your input. I see the light at the end is near. I'll have this thing working yet.

Marcello
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