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#41
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isn't there a step down treansformer taking 110vAC down to 12vAC then
rectified to 12vDC???? Steve A&P and Computer Guru (and very interested in your Idea) John wrote: John wrote: Thanks for the continuing input. The LM79XX's will do you no good unless you have a source of negative voltage to feed them. This generally will mean a dc to dc converter which generally means switching regulators. Try putting your current powersupply in a case and attach it directly to the MB's case and use feedthrough capacitors in the common case bulkheads to feed the dc voltage in. Put fedtrough caps and ferite beads on the dc in to the powersuppply case. Cheep and will get you a good start to eliminating the noise. John About $1.00 a piece from a couple sources I checked. So about $7.00 for the PS voltages plus the dc input. (although some are sold only in 10 lots) if you have multiple projects to use them up in you can order 100 quantity for about $.50 each. John Just checked Newark Catalog They have an interesting item: A feed through teminal block with built-in filter capacitors part # 95F895X where x = number of terminals from 2 to 6. Just something interesting to look into. They have a lot of ideas for cap/ferite/filter ideas. John |
#42
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#43
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All kinds unfortunately this is for aircraft use, he's starting with 12v
DC (transformers don't work with DC) and needs to get +-12v +5 and +3.3v all DC. John John, I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). Evan Yes I did a little research on it and the only thing the negative is needed for is the rs232 serial ports. for this you can get a $1.50 ic to convert +12 to -12 V low current. That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220 regulator along with one of the TO-220 adjustable 1 amp regulators for the 3.3 v and run it all off the 12V (highly filtered) input. That said, (again) you might have problems with th 12V regulator if the input drops below 13.8V! So you might need to use a separate battery for it and diode isolate it from the aircrafts electrical systm and have it charged when it exceeds the 13.8 volt figure. John |
#44
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1 John wrote: wrote: isn't there a step down treansformer taking 110vAC down to 12vAC then rectified to 12vDC???? Steve A&P and Computer Guru (and very interested in your Idea) All kinds unfortunately this is for aircraft use, he's starting with 12v DC (transformers don't work with DC) and needs to get +-12v +5 and +3.3v all DC. John John, I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). Evan -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFCEgqopxCQXwV2bJARAvUpAJ9QJP/GjpzrhRBgI73a8UrVyWBD+QCgsgGj ONCHJdB56/BtoKbGC18OFS4= =Lq2H -----END PGP SIGNATURE----- |
#45
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-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1 John, I wonder if we are trying too hard on the +12V issue. Couldn't you simply let it float free with something like a MOV to keep it from getting too high? If the voltage goes too low, a simple current limiting sacrificial resistor (AKA fuse) would protect the equipment. You could even use one of those self healing plastic fuses. Looking at the design again, there won't be any hard drives or fans to suck juice from this voltage, so the only thing it will be powering is the PCI bus. John wrote: Yes I did a little research on it and the only thing the negative is needed for is the rs232 serial ports. for this you can get a $1.50 ic to convert +12 to -12 V low current. That said, what I'd do is get a 1.5 amp 5v TO-3 regulator and a 1 amp TO-220 regulator along with one of the TO-220 adjustable 1 amp regulators for the 3.3 v and run it all off the 12V (highly filtered) input. That said, (again) you might have problems with th 12V regulator if the input drops below 13.8V! So you might need to use a separate battery for it and diode isolate it from the aircrafts electrical systm and have it charged when it exceeds the 13.8 volt figure. John -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFCEmEhpxCQXwV2bJARAvYPAKC5/3ys03DwDrklsBMYLKhzbeeNtgCdFDb/ 7wukjwVF2NQz4kVSOqNayms= =ohFv -----END PGP SIGNATURE----- |
#46
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Evan Carew wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 John, I wonder if we are trying too hard on the +12V issue. Couldn't you simply let it float free with something like a MOV to keep it from getting too high? If the voltage goes too low, a simple current limiting sacrificial resistor (AKA fuse) would protect the equipment. You could even use one of those self healing plastic fuses. Looking at the design again, there won't be any hard drives or fans to suck juice from this voltage, so the only thing it will be powering is the PCI bus. Yes it probably wouldn't matter, an MOV wouldn't do much good but you could still feed a 12V regulator I guess and when the voltage started to go above that it would regulate and when below it would just slump. I don't think it would hurt the regulator to take the input too low. That being said you could build a low differential voltage regulator for the 12V line it's possible to do it with less than 1 volt drop you just can't do it with the simpler 3 terminal regulators. The main point is you get rid of the switching regulators and their inherent noise. It also makes it easier to filter the PC's noise out of the supply. John PS I checked out his site and found it quite interesting. I use to program with hex and then onto assembler when I started out with computers in 1976. I had a SWTPC 6800 with a whopping ~800KHZ clock! You had to build the whole thing from a kit soldering on the buss connectors (SS50 bus) ic's powersupplies etc. It did not have video you had to use an external terminal although I later build a video board for it and modified the boot rom's to use it. I started with a Mega memory of 4Kilobytes and eventually got up to 48Kilobytes. Those were the days! |
#47
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Blueskies wrote:
"Evan Carew" wrote in message ... John, I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). Evan What is the +12 vdc for? serial ports, fans and disk drives mainly |
#48
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Frank van der Hulst wrote:
John wrote: I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). What is the +12 vdc for? serial ports, fans and disk drives mainly And nowadays CPUs.... late last year I upgraded a PC motherboard from 800MHz to to 2.4GHz by replacing the motherboard. The new motherboard had an extra connector to provide 12V to the CPU 9Celeron, IIRC), so I had to replace the power supply as well. I'm guessing that the CPU had onchip regulators to provide the other voltages that it required. Frank Thats true. my athlon 64 bit has it too. it was originally for the P4 chip. Although the project that was the focus of this thread delt with a mini-atx case that does not have this. For that matter he was not using any disk drives instead he's using an USB thumbdrive. so he probably could get away with leaving out the 12v. I've never tried it so I don't know. Maybe this weekend I'll pull out one of my older atx boards and see if I can get it to boot without the other supplies. John PS Don't forget to emulate the pwr good signal! |
#49
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"Evan Carew" wrote in message ... John, I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). Evan What is the +12 vdc for? |
#50
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John wrote:
I think you'll find that the -12V is used only in "legacy" PC design for ISA busses, or serial ports (which he probably isn't using). What is the +12 vdc for? serial ports, fans and disk drives mainly And nowadays CPUs.... late last year I upgraded a PC motherboard from 800MHz to to 2.4GHz by replacing the motherboard. The new motherboard had an extra connector to provide 12V to the CPU 9Celeron, IIRC), so I had to replace the power supply as well. I'm guessing that the CPU had onchip regulators to provide the other voltages that it required. Frank |
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