Lt317 problems

• Lt317 problems
  Posted by House91320 on 29 May, 2011 23:09
• I have a power supply that i built recently before the lt317 is 8 after the lt317 its 4 any one got any ideas.
• #1 Reply
  Posted by alm on 29 May, 2011 23:15
• Your schematic appears to have disappeared in thin air, so it's somewhat hard to debug. Dropping voltage is exactly what a linear regulator is supposed to do, so depending on what you connected to the adjust pins, this could be within spec.
• #2 Reply
  Posted by House91320 on 29 May, 2011 23:21
• http://www.eleccircuit.com/lm317-lm338-lm350-current-regulator-calculator/ its this but the resistor is 1ohm
• #3 Reply
  Posted by EEVblog on 29 May, 2011 23:34
• Quote from: House91320 on 29 May, 2011 23:21

  http://www.eleccircuit.com/lm317-lm338-lm350-current-regulator-calculator/ its this but the resistor is 1ohm
  

  
  That's a constant current circuit, not a voltage regulator for a power supply.
  I think you have the wrong circuit.
  Try:
  http://www.electronics-lab.com/articles/LM317/
  
  Dave.
• #4 Reply
  Posted by House91320 on 29 May, 2011 23:38
• i know i am using another regulator for the variable out put voltage and that works fine. I am using the 317 as the current regulation
• #5 Reply
  Posted by Bored@Work on 30 May, 2011 05:13
• Quote from: House91320 on 29 May, 2011 23:38

  i know i am using another regulator for the variable out put voltage and that works fine. I am using the 317 as the current regulation
  

  
  And we are now supposed to beg you to give us the complete schematic? From my point of view, you either show us the real and full schematics, and you write a useful problem description, or you can stick it where the sun doesn't shine.
• #6 Reply
  Posted by Simon on 30 May, 2011 07:45
• Quote from: BoredAtWork on 30 May, 2011 05:13

  Quote from: House91320 on 29 May, 2011 23:38

  i know i am using another regulator for the variable out put voltage and that works fine. I am using the 317 as the current regulation
  

  
  And we are now supposed to beg you to give us the complete schematic? From my point of view, you either show us the real and full schematics, and you write a useful problem description, or you can stick it where the sun doesn't shine.
  

  
  hahaha couldn't have put it better myself 
  
  House: we need to see the full schematic to get an idea of what your up to. My guess is that you have a lower resistance load than the final current regulator can supply current to so there is a massive voltage drop
• #7 Reply
  Posted by Zero999 on 30 May, 2011 17:55
• It's not a very good way of doing it. The current limiter circuit drops around 4V just before the current limiting kicks in and the voltage regulator will drop around 2.5V so the input voltage needs to be a whopping 6.5V higher than the output voltage.
• #8 Reply
  Posted by House91320 on 30 May, 2011 19:54
• solved it i had the taps on my power supply wrong