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Kai Klaas
02/15/06 09:27
Read: 670 times

#110076 - Floating regulator
Responding to: Suresh R's previous message
Sursh said:
It is said that R7 is fixed and holds the voltage accross the o/p and adj terminal (1.24V). So by putting R7 = 120V/.25W will dissipate all power in it.
If this is the case, how could Q4 (emitter pin) receive voltage to drive the major part of the 10mA current through it.

LM338 isn't a standard voltage regulator like LM7815 or similar. It does not produce a constant voltage at output referening to ground, but produces a constant voltage between output and adjust pin. This type of regulator is called 'floating regulator', because all it does is to produce a constant voltage between output pin and adjust pin, which can, shall and must float refering to ground. Correct output voltage is provided by letting the current (1.24V dropping across 120R resistor) running through an additional resistor, here Pot R6.

Suresh said:
i would like to know how the diode nature helps to avoid this current flow.

It shunts the current arround the regulator, at the same time limiting the voltage to one forward voltage drop of a diode.

Suresh said:
How does a diode help in overcoming these problems.

See above.


List of 21 messages in thread
3A constant current source      Suresh R      02/11/06 04:41      
   Where did you find it?      Andy Neil      02/11/06 05:56      
   Ripple      Andy Neil      02/11/06 06:00      
      plating purpose      Suresh R      02/11/06 09:45      
         I got it from a person known to me      Andy Neil      02/11/06 15:04      
            replies      Suresh R      02/12/06 09:24      
               plating circuit      Terry Lingle      02/12/06 11:40      
                  Compliance of source      Steve M. Taylor      02/12/06 13:51      
                     yes      Terry Lingle      02/12/06 16:21      
         Think about that      Neil Kurzman      02/11/06 16:08      
   Component Purposes      Bruce Bailey      02/11/06 12:58      
   This circuit will never work!      Kai Klaas      02/11/06 19:46      
      Could it be?      Neil Kurzman      02/11/06 23:55      
         Function      Kai Klaas      02/12/06 20:08      
            issues      Suresh R      02/13/06 02:42      
                plating quality control.      Terry Lingle      02/13/06 07:29      
               Answers      Kai Klaas      02/13/06 11:36      
                  followups      Suresh R      02/14/06 02:20      
                     Answers II      Kai Klaas      02/14/06 07:01      
                        followups & Back EMF's?      Suresh R      02/15/06 03:59      
                           Floating regulator      Kai Klaas      02/15/06 09:27      

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