these sypplys are nothing to mess with...the designs i have seen have had large input caps with one large mosfet doing the switching on the primary of the transformer. This means high voltages! can kill you. And if everything is not perfect in these devices the high voltage tends to conduct where you wouldnt think it would and bang! 
anywho...Although it is possible. If youre going with a higher voltage you may need to replace the output caps to support that higher voltage. Also if you double the voltage output the current output in theory will be halfed.
The negative 12volt output and negative 5 volt on power supplys tend to be of the low current variety. Often just using a 7912 as a voltage regulator.
anywho...Although it is possible. If youre going with a higher voltage you may need to replace the output caps to support that higher voltage. Also if you double the voltage output the current output in theory will be halfed.
The negative 12volt output and negative 5 volt on power supplys tend to be of the low current variety. Often just using a 7912 as a voltage regulator.
Danger, Will Robinson!
/Circlotron - plays with audio stuff for fun, but is SMPS professional.
Not immune to electric shock either, BTW.
Agreed. If you don't know the definitions of "basic insulation" and "reinforced insulation" then do yourself a favour and give it a big miss. This NOT meant to sound condescending, but it is not something you should feel your way through. One flash and you're ash.Benjlv said:This means high voltages! can kill you. And if everything is not perfect in these devices the high voltage tends to conduct where you wouldnt think it would and bang!
/Circlotron - plays with audio stuff for fun, but is SMPS professional.
Not immune to electric shock either, BTW.
ok...doing this is probably not recommended and I'll get into the sinbin...but I'll tell u guys anyway...first find the %V output...there will probably a jumper connecteing that to a protection circuit..cutt off or desolder the jumper...look for another feedback resistor back to the controller chip..cut that one out as well...there will be another resistor from the 12V line to the same feedback pin...replace it with a 100K pot...then u'll find that u are now able to vary the output voltage by increasing the resistance...I'm not sure what the upper limit is though...but u'll need to upgrade the capacitors as they are good up to 25V only...
li_gangyi said:
wow.. isn't it FUN to repeat what someone has just said? and.. if you had looked at a powersupply in detail (which fairly obviously you haven't going by this post, and the following one) you would see, that the 12volts isn't provided by a 7912, because that doesn't even make sense... 7912 will only regulate a NEGITIVE voltage down to -12 volts.. and this doesn't exist... what you would find is that all powersupplies use a second pair of diodes on the 12volt winding, but in reverse, to obtain -12volts... and then, some powersupplies use a 7905 on the -12 volt rail for the -5volts, while others use the same reverse diode method on the 5volt transformer winding to obtain the -5volts.... now that thats cleared up, I request once again, that you stop posting the exact same thing as someone else, especially if its wrong..
li_gangyi said:
Depending on the amount of power you need you can make a single-ended "boost inverter" -- see the National Semiconductor website -- any of their "Simple Switcher" chips should have it. Thus you can take utilize any of the positive outputs. (or you could use one of the negative outputs and boost, same difference).
Jack
Re: Danger, Will Robinson!
Yes, I thought about trying to fix a compaq server SMPS once, when I stuck the multimeter in and found almost 700V between two points I turned it off and vowed never to play with a SMPS again! I don't know if its standard with SMPS's but it rectified the 240V directly into +- 338V (approx).
I've had a few shocks (literally) from when I was young and stupid. The 240V ones didn't scare me too much (I'm rather blessed with somewhat of an imunity to electricity, otherwise I may not have been here now).... but the one I got off a 12V car radio (Valve) scared the s*** out of me. I wasn't expecting 600V from a 12V car battery, didn't know enough about valves back then to know what sort of voltages they ran on, and naively thought it was safe because it worked off 12V!
The science teacher at school thought I was a freak, I had to get within about 5 mm of the vandergraph generator before It would throw a spark (everyone else about 30cm, and we all had the same type of school shoes), and I could just stand there with a continuous arc to my finger saying what's the big deal. When the teacher brought out the spark throwing coil He said lets see you stick your finger in that one, so I did, stood there for about a minute and said yeah what's the big deal. anyone else who tryed recoiled instantly and vilolently.
Tony.
BTW my comments about 240V are not meant to imply its safe or won't hurt you. I'm just lucky, I've had 240V up one arm and down the other twice, with no other effect than a hole in my thumb and a weird pulsing sensation in my arms (took a few seconds to realise what was happening). This would probably kill most people.
Circlotron said:
Yes, I thought about trying to fix a compaq server SMPS once, when I stuck the multimeter in and found almost 700V between two points I turned it off and vowed never to play with a SMPS again! I don't know if its standard with SMPS's but it rectified the 240V directly into +- 338V (approx).
I've had a few shocks (literally) from when I was young and stupid. The 240V ones didn't scare me too much (I'm rather blessed with somewhat of an imunity to electricity, otherwise I may not have been here now).... but the one I got off a 12V car radio (Valve) scared the s*** out of me. I wasn't expecting 600V from a 12V car battery, didn't know enough about valves back then to know what sort of voltages they ran on, and naively thought it was safe because it worked off 12V!
The science teacher at school thought I was a freak, I had to get within about 5 mm of the vandergraph generator before It would throw a spark (everyone else about 30cm, and we all had the same type of school shoes), and I could just stand there with a continuous arc to my finger saying what's the big deal. When the teacher brought out the spark throwing coil He said lets see you stick your finger in that one, so I did, stood there for about a minute and said yeah what's the big deal. anyone else who tryed recoiled instantly and vilolently.
Tony.
BTW my comments about 240V are not meant to imply its safe or won't hurt you. I'm just lucky, I've had 240V up one arm and down the other twice, with no other effect than a hole in my thumb and a weird pulsing sensation in my arms (took a few seconds to realise what was happening). This would probably kill most people.
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