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Kai Klaas
02/13/06 11:36
Modified:
  02/13/06 11:39

Read: 576 times
Germany


 
#109877 - Answers
Responding to: Suresh R's previous message


Suresh said:
I think its due to the RC network connected to the base of Q4. Hence the impedence of the adj terminal towards ground decreases with increase in cap charge. Is it so?

Between output pin and adjust pin of LM338 internal circuitry of regulator produces a very stable reference voltage of 1.24V. This voltage drops across R7, so that a current of about 10mA is flowing. At turn-on this current flows via emitter collector path of Q4 to ground. The base current, which is needed to allow this current to flow charges up C9. This current is much greater than the current that flows through R8 driven by the Ube of Q4. R8 is needed to fully charge C9, when Ube of Q4 becomes smaller than 0.7V

Suresh said:
Is this power dissipation in R12 needed or can i remove it.

Without this resistor the constant current source will not work at all! R12 can be reduced a bit, but not too much. Otherwise regulation performance will suffer.

Suresh said:

The adj current is equal to the current flowing through the current set resistor - R7(120E). How the power rating could be calculated for this resistor.
The presently running one has a R7=120E/.25W and is working well.

1.24V is dropping across R7, yielding a heat dissipation of 1.24V^2 / 120Ohm = 13mW. So, 0.25W type is sufficient.

Suresh said:
For instance let me assume that the regulator delivers 2A at 6V to the load. for this voltage value, how the power rating of R7 will be calculated.

Heat dissipation of R7 is constant and does not depend on current of constant current source.

Suresh said:
The temperature of the plating bath will be at 65 degree celsius.
Will this need to be taken into account for setting the current. will the load experience any additional current due to this temperature effect.

I neither know how your plating machine looks like nor how it works. So, I cannot answer this question.

Suresh said:
Is the buck regulator proving main cause of power dissipation?
I would like to know how, more power is being dissipated in the regulators and mje3055 referring to my circuit.

Don't know what you mean. What do you mean by 'buck regulator' by the way?

Kai

List of 21 messages in thread
TopicAuthorDate
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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