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LM723C: current limiting is not happening in LM723???

Gurumurthy J
Prodigy 140 points

Part Number: LM723C

Hi!!!

I designed a Lab power supply with LM723(for 0-30V @ 5Ampere),Initially  I limited the current at .65 ampere(I limit=o.65V/1 ohm). But the problem is ,the IC is not performing the current limiting operation, even though it had potential difference(Current Sense ReLM723 Regulator .docxsistor) is 5V across its base to emitter transistor which does this current limiting function.

What could be the problem?
   1)is with current sense resistor precision?
   2) is it with Base emitter junction breakdown with transistor? Because of 5V across it?

I have attached the circuit.Totally confused . Help me in this regard...

  • 0
    TI__Guru 62930 points
    Gurumurthy,
    This device is supported by multiple groups within TI. Can you provide the full part number?
    Thanks,
    Wade
  • 0 in reply to Gurumurthy J
    TI__Mastermind 23361 points
    Hi Gurumurthy,

    Will you please attach your schematic? It's not showing up on your thread.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Prodigy 140 points

    Hi Jason,

     This was a circuit obtained by google image .

    1)the doubt is first circuit , how does the current control knob operates that is 1Kohm 10 turns potentiometer in the first circuit?

    2)the second circuit contain potentiometer of 500ohm which control the current in output of regulator Circuit?

    3)the third circuit contain potentiometer accross a Diode, How does it make Current variable regulator?

    4) how to calculate the potentiometer which determines output voltage? The table1 give value for P1 not the technique for calculating for my application.LM723_variable_current limiting.doc8686.LM723_variable_current limiting.doc


    Please help me in such way i could understand Variable current control circuit using LM723 Voltage regulator from above three circuit. How potententiometer is helping in varying the current?

    Particularly Variable current limiting with Potentiometer not constant current limiting.



    So i am totally confused with these circuit. Please make me to understand the Technique behind Current control transistor in LM723 for Variable current control in power supplies..

    Suggest me better technique to design Variable current Limiting power Supply using LM723..

    Help me in this regard.. I think i have conveyed my thoughts.if any thing is incomplete . Correct me if i am wrong..