Using a 5volt wall wart in lieu of a higher voltage and regulator

Comments

• pwillard Posts: 321

  2007-07-10 15:00 edited 2007-07-10 15:00

  The 5 Volt wal warts are usualy designed to be used with Cell Phones and the like. These do require a better supply voltage regulation, but be warned... I've seen a few of these for cell phones that claim 5 volts DC out that used capacitive coupling and a zener. (No smps or transformer).
• LoopyByteloose Posts: 12,537

  2007-07-14 14:56 edited 2007-07-14 14:56

  pwillard,
  I do realize that I took a risk. And yet....
  This particular 5volt wall wart has been running an SX on my desk for several weeks now without a glitch. I do realize that it is nearly impossible to determine what is inside without destroying one, at least some appear to be quite good. I did notice that this one mentions a potential shock hazard, so I suspect there is no isolating transformer.
  
  I have run the 5volts +/- 5% directly and I have also run it through the 7805. Seems to run fine either way. From what I understand, the 7805 needs 7 volts to properly regulate and under that it will pass voltage directly through. Since 5 volts is within safe limits, passing through works [noparse][[/noparse]though I imagine it is less efficient]
  
  My thinking is that more recent ones are likely to have better regulation. A scope is needed for absolute measurement.
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
  

  ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
• Mike Green Posts: 23,101

  2007-07-14 15:18 edited 2007-07-14 15:18

  Kramer,
  These tend to use a switching regulator which would have an isolating transformer and there is a shock hazard if you spill water on them or try to take them apart. In today's environment, I don't think you will find anything that isn't powered by a low voltage battery that doesn't have a claim of being a shock hazard.
  
  I like to use a 6V wall wart with a low dropout 5V regulator. I can always substitute a 4 cell alkaline or a 5 cell NiMH battery for portability (or even a 6V sealed lead-acid battery).
• LoopyByteloose Posts: 12,537

  2007-07-15 15:25 edited 2007-07-15 15:25

  My thinking is that I can use a 5v wall wart to safely supply directly to an SX or I can use the same to trickle charge 3AA NiCad with a 0.7 voltage drop. Since regulators generally use 20-30% of the batteries capacity, elimination of the regulator would effectively boost capacity by a similar margin. And there would be a little less weight and board real estate. Also.... Seems the battery would in some ways provide some form of added regulation.
  
  ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
  "Everything in the world is purchased by labour; and our passions are the only causes of labor." -- David·Hume (1711-76)········
  

  ···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan