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Internet Message Format  |  1992-11-09  |  1.9 KB
  1. Path: sparky!uunet!dtix!darwin.sura.net!zaphod.mps.ohio-state.edu!sdd.hp.com!ux1.cso.uiuc.edu!news.iastate.edu!class1.iastate.edu!sehari
  2. From: sehari@iastate.edu (Babak Sehari)
  3. Newsgroups: sci.electronics
  4. Subject: Re: 12 V -> 3V, 0.6 A
  5. Message-ID: <sehari.721280522@class1.iastate.edu>
  6. Date: 9 Nov 92 03:42:02 GMT
  7. References: <1992Nov7.141550.538@ludd.luth.se>
  8. Sender: news@news.iastate.edu (USENET News System)
  9. Organization: Iowa State University of Science and Technology, Ames, Iowa.
  10. Lines: 43
  11. Originator: sehari@class1.iastate.edu
  12.  
  13. In <1992Nov7.141550.538@ludd.luth.se> d89-ahg@ludd.luth.se (Anders Hedberg) writes:
  14.  
  15. >A friend wants to listen to his CD player powered from the car.
  16.  
  17. >The CD-player wanna have 3Volts at max 600 mA, and the car has a battery
  18. >of 12 volts.
  19.  
  20. >I thought of a LM317 or something similar, but I've never designed something
  21. >alike, and I need to know how to calculate the resistor values.
  22.  
  23. >/Anders Hedberg
  24.  
  25. There are many ways to do this the cheapest way is to put:
  26.  
  27.   12-3
  28. --------- = 13 diodes in series with the input voltage of your CD player,
  29.     0.7
  30.  
  31. Like this:
  32.  
  33. +12V -|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|- +3V
  34. GRD  --------------------------------------------------
  35.  
  36. The problem might be generated if the input voltage swings.  To avoid
  37. this problem try putting a 2N3055 transistor as follows:
  38.  
  39. +12V |>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-|>|-    ---+3V
  40.                                         | \_/ Emitter
  41.                                         R  |
  42.                                         |--|
  43.                                         |
  44.                                         ||>|-|>|-|>|-|>|-|>|-|
  45.                                                              |
  46. GRD ---------------------------------------------------------+-----
  47.                                     
  48.  
  49. R=1000 ohm
  50. Trans=2n3055
  51. Diodes= 1N4001 or 1N4005
  52.  
  53.                          With highest regards,
  54.                               Babak   Sehari.
  55. -- 
  56.