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Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
that circut should work how big is your power transformer and your electrolytics. that should be big enough to power your unit. the tranformer should be able to put out at least 30v ac.for the power you want it should be about 500w or as big as a micro wave oven transformer
Registered Member #2567
Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11
really? dang! so THAT'S why it wasn't working then....well, now it doesn't matter too much anyways because i have finally gotten my powersupply designed from scratch. basically it is a normal regulator circuit with a 70 ohm resistor on the +output and connected to two 2n5885's in a darlington configuration. the collector goes directly back to the positive supply voltage/Vin on the LM317 and the emitter is the new +output. I would put a schematic on here but i'm not exactly sure how. i still have to add capacitors on the output but so far from testing, it works quite well! i can regulate 1.4-18.6vdc from 20vac and about 4 amps of current max...but this is only running from a transformer. i don't have one that's big enough yet that is in the voltage range of the LM317. when i'm running it from a 12v lead acid battery, i can regulate the voltage between 1.23-11.56vdc and can have around (guessing) a max current draw of 12 amps?? i haven't actually found anything yet that runs off of 12v and 12amps, lol. so yep! it finally works! so happy! thanks for all the help guys!
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
Just a warning, from my interpretation of your description; You are basically producing a regulated voltage with the LM317 Then using a darlington emitter-follower to get more current (and lose some regulation as Vbe changes a little with Ic = Iout)
What limits the output current?
I like that you tried a few ways and re-designed it yourself. You need to regulate or limit the output current. As I'm sure you've discovered, heatsinking is important, I quite like cpu heatsink/fan combinations IF powering the fan is convenient and the noise doesn't matter but I maily use oversized natural convection heatsinks for reliability and I've got plenty of them. For a linear power supply with basic current-limited protection, your heatsinks would have to dissipate more than (dc supply voltage) x (output current limit) e.g. 40V x 8A = 320 Watts ..........That's a lot of heatsink (And quite expensive transformer & capacitors) Estimate your budget, re-consider the approach... that's my advice. If you design your hobby stuff around "12V" supplies you can use battery or psu from ac. A 1.5 Amp variable supply is good enough for most general-purpose uses. Any other requirement would probably require a new/specific supply
Registered Member #2567
Joined: Wed Dec 23 2009, 11:56PM
Location:
Posts: 11
haha yeah i still have to add that to the output, i was just happy that i got it working. i guess the current limiting could be just a resistor right? and a fuse, can't forget the fuse! and yes i have both a heat sink, well two sinks that is, and a fan on there too! i have it hooked into the regulator so that when more current is drawn the fan will turn faster. my heat sink isn't all too big really...i don't have any big big ones :( but i have two heatsinks on my output transistor, one on each face of it. that has seemed to work really well before, especially with the fan. as for my transformer the farthest i've seen it supply is 3.8amps at 24volts but i do have a 12v lead acid battery to power it with too. so i guess that solves the current problem...sorta? i'm gonna be trying the whole system out with my zvs driver just to see how well my transistor handles it plus i'm just curious to see the change in output voltage on my flyback when i run the driver at different voltages.
well, so far so good! next thing i'm building is a 20watt amplifier with the TDA2005 that i am hopefully about to unwrap for christmas!! yay! :)
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LM317T 12v 8amp power supply help!!
