| Electronics > Beginners |
| All about Linear Power Supplies |
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| queennikki1972:
I have tons of questions about linear power supplies and the people over at Stack Exchange are rude as #$%^ to newbie's. I have built a small linear power supply with a LM7812 and LM7805 and a 12VCT Transformer with Smoothing Capacitor. Diagram was accurate and works well for small bench circuits. I am looking at building a 12v 5a constant power supply next using the LM338T. I have a diagram I think will work, but I have what I thought was a simple question. Is a 6 amp bridge rectifier sufficient for a 5 amp load? The rectifier in question I already have and is rated 6amp at 800volts. The other power supply is a variable 0-30vdc using the LM317T or the LM338T. First off, which would be a better choice for 0-30vdc variable at 1 amp max? I have circuit links to both if needed and I apologize if I have offended anyone or asked a dumb question. Nikki |
| digsys:
Welcome to forums :-) They can get narky and rude at times, but this one is pretty ok. Just ignore a**wipes For a 5A op at 12VDC, your filter cap is 1,000uF + 1,000uF per Amp = ~ 6,000uF, so app 8-10,000uF is the closest ie 2x 4,700uF At that your inrush / charge current is ~ 2X+ the max op current. Worst case is if you switch on at full load or short. Bridges are cheap, so use a MIN of 10A, 20A ones are not a lot dearer, and it gives you headroom if you want to go up a bit. For the variable 1A PS, since you are dropping up to the entire range at min OP, you would either use a BIG heatsink with cooling, or go for the LM338T. It still needs a heatsink though. Again, it gives you headroom. Welcome to the forum, you should be safe here :-) |
| queennikki1972:
Wow! Thats all I wanted.. A simple direct answer. Thank you. And Yes, I have a HUGE vented aluminum heatsink from a old CPU, cut in half and tapped out with a M3 screw for the variable power supply. |
| ArthurDent:
You might get more responses if you combine your 2 similar threads. One way to get more ideas on the LM338 would be to check the application note on that regulator at the link below. The makers have a lot of ideas on how to use their chips. Also there have been a number of threads on building 0-30VDC supplies. Many are probably more complicated than you need, maybe not. Do a search using the search box in the upper right on the main page, you'll get a lot of references and a lot of ideas you may be able to use. http://www.ti.com/lit/ds/snvs771c/snvs771c.pdf |
| MarkF:
Welcome. A couple circuits you might want to study. |
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