need 4.5 - 4.7v from 12v or 5v

[DrSpanky]

need it either from the 12v or the 5v from a molex connector that can be used in powering a gfx card.

[Xenocide]

ok?

id say get a pot and put it on your 5v line...take some measurements and see what you need.

[four4875]

could go with diodes, they have a set voltage drop per diode. could go with a series / parallel configuration till you get what you need.

[JamminPotato]

my powersupply's 5v line only puts out 4.7...want it? lol

[DrSpanky]

ok?

id say get a pot and put it on your 5v line...take some measurements and see what you need.

but arnt resistors only good for a certain amout of ampage? if i used a pot resistor and got my 5v down to 4.7v and then tryed running my gfx card wouldnt the resistor give out?

my powersupply's 5v line only puts out 4.7...want it? lol

lol i want to use my ocz thats why i have to do it, as i can boot with over 4.7v going into my gfx card with out it cutting out.

could go with diodes, they have a set voltage drop per diode. could go with a series / parallel configuration till you get what you need.

wuld that be able to provide the power my gfx card needs thou?

[four4875]

well.. if you use the big rectifier diodes, they would be able to handle the power of your whole system, especially in a parallel configuration, caus they ar usually a 1 to 1.2 V drop each, so paralleling them would get a lower drop.

[snvpa]

why not just adjust the 5v rail on the back of the powerstream to 4.7v? It should be sufficient for the rest of the system.

[3DFlyer]

OK, since no one esle has asked, I must...

What exactly are you attempting to do? That is alot of voltage going to a Grahpics Card. Please do tell! Inquiring minds want to know! :)

[ajrettke]

OK, since no one esle has asked, I must...

What exactly are you attempting to do? That is alot of voltage going to a Grahpics Card. Please do tell! Inquiring minds want to know! :)
^
What he said...

Why such a relatively small drop?

[DrSpanky]

ok ever since i got my OCZ psu ive had problems plug it is and, fans spin for less then a second then psu cuts out no matter what i did i got nothing, but if i replace my gfx card with a fx5200 no problem. end up rmaing the psu......some time later. i get it back still same problem so this time i lower all rails to the lowest and YAY it boots.

but damn the voltages are low i up them so there just in the green on the light on the back and it sometimes works other times it dont. and finally jsut before i did this post i tested each rail to see what rail was stoping my system from starting. test the 3.3 was ok and 12v was ok. test the 5v no boot. overvolt 12v and 3.3v lower 5v boot. get the multi meter out and tested the 5v line and kept turning the computer on and off while slowly uping the voltage back to it 5v managed to get to 4.6-4.7 above that i would get the same problem as before.

so this lead me to think that the 5v is the problem. BUT only on boot i can lower the 5v rail then get to bios then put it back up to 5v on multi meter or the voltage monitors in bios and the machine runs stable.

thus the only logical step for me is to use a Y spliter and jump something on one of them rails that will give me 4.6-4.7v from my 5v line or 12v to supply to my gfx card.

[DrSpanky]

i found an dead mobo. and i hooked 5v on one of the legs on a mosfet and measured the center pin and was getting around 4.72, if i used 2 or 3, 47k resistor i think i get get it to 4.65 ish, do u think thats worth a try (not i dont really understand what im doing) but want to see if i can make up what i need from parts i have in my deadware draw

[four4875]

when using resistors to drop voltage, its only accurate if the load doesnt change. o if you start to draw more power, the voltage will change. andim not sure abut using the mosfet as a source. could fix the problem (the vid card as it seems?)instead of trying to rig it up.

[DrSpanky]

what can i do to the video card thou? i had the same problem with my mates 9800 pro. so the chances are its a problem with the range cards. ive seen posts from other people on other forums with the same problems... so thought the best plan would be to do what i wanna do now but im open to suggestions.

[persivore]

This might sound a bit obvious, but are you using the dedicated Molex lead on the powerstream for the graphics card?

If you want to drop the 5v rail down by just a small amount, the easiest way would be to use diodes. Using resistors would give you an unstable voltage supply as the current flow changes.

You should be able to find rectifer diodes rated to at least 20A relitively cheaply, which should cope with the load (but they might drop 1v or more accross them)
I think that there might be some problems with running diodes in parallel (although I'm not sure), but I would expect one diode to conduct more than the other, and thus take more of the load. I don't think that running diodes in parallel will change the amount of voltage that is dropped accross the diodes tho (again, I'm not sure about that because I've never tried putting diodes in parallel)
If you can find some high current germanium diodes (if they are actually available), they will normally drop 0.2v each, so 2 germanium diodes in series will bring the voltage down to ~4.6v

[Dell_Axim]

You need a Schottky diode. You can take one from a broken/generic PSU.

[DrSpanky]

You need a Schottky diode. You can take one from a broken/generic PSU.


whats one look like? i have some old psu i dont mind cutting up
and would i just run them run them in series till i got the voltage i want?
do i run a few in parallel so im spreading the load across more then one diode?

[Pro*Banshee]

Google is your friend!
http://en.wikipedia.org/wiki/Schottky_diode

[four4875]

just look for the cylindrical things that are black with a silverish stripe at one end, they have leads from each end, the black part should be a few mm in diameter, near the AC plug on the board. hopefully it'll havethem instead of a one piece rectifier. or some cheap psus will have 2 of hem mounted to a heatsink instead of using a normal one thats in a normal transistor casing style.

http://www.herbach.com/Merchant2/graphics/00000001/q6134.jpg

[sangram]

No, dropping the voltage to the GFX card is not going to solve this.

If you think that that is the way out, then diodes wil not help as they drop .7 volts each.

Paralleling diodes will not reduce this drop. It will only increase current capacity but the drop will remain same.

The way I see is that there is some OVP kicking in when the voltage is hitting 5V. This is actually abnormal and replacing a defective component will be better in the long run than starving your GFX card. It points to a defective/flaky/failing mobo or graphics card. I would suspect the mobo much more readily in that it actually works OK with 5V but needs a lower voltage on cold boot.

[sangram]

Oh, sorry, I forget to tell you how to get the 4.6 volts.

4.6 = 12-7.4 Volts. You need to derive this voltage off the 12 V line.

You have to homebrew a small linear regulator using a pass transistor. An LED is a nice 1.65 V reference (Red LED) and a small variable pot will allow you a good control range from 12V to about 3V. Each junction drops about .7 volts. So a typical regulator with a Darlington junction will drop 1.4 volts inside itself.

If you don't know how to do this, I suggest taking it to a tech or try a mobo swap.

[DrSpanky]

No, dropping the voltage to the GFX card is not going to solve this.

If you think that that is the way out, then diodes wil not help as they drop .7 volts each.

Paralleling diodes will not reduce this drop. It will only increase current capacity but the drop will remain same.

The way I see is that there is some OVP kicking in when the voltage is hitting 5V. This is actually abnormal and replacing a defective component will be better in the long run than starving your GFX card. It points to a defective/flaky/failing mobo or graphics card. I would suspect the mobo much more readily in that it actually works OK with 5V but needs a lower voltage on cold boot.

well i can tell you its not the mobo ive had this booting issue with a epox 8rda and now a brand new abit nf7s.

i also got the same problem when using my mates 9800 pro on my epox...

[greenman100]

No, dropping the voltage to the GFX card is not going to solve this.

If you think that that is the way out, then diodes wil not help as they drop .7 volts each.

Paralleling diodes will not reduce this drop. It will only increase current capacity but the drop will remain same.

The way I see is that there is some OVP kicking in when the voltage is hitting 5V. This is actually abnormal and replacing a defective component will be better in the long run than starving your GFX card. It points to a defective/flaky/failing mobo or graphics card. I would suspect the mobo much more readily in that it actually works OK with 5V but needs a lower voltage on cold boot.



grrr, don't give the guy bad information


not all diodes drop .7v, there are many varieties.


.3v here for instance:
http://en.wikipedia.org/wiki/Schottky_diode

also he is better off pulling off the 5v rail, pulling off the 12v rail at 10A and 7v drop is a 70w heat dissipation. you'd need something like an SK7 sized heatsink to cool the pass transistor