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How do make a current limiting knob using LM723 for Linear Reg power supplies?

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Gurumurthy:
 Hi bravo,
            Yes bravo , I want to  build power supply with integrated circuits than discrete devices. But I know that power handling capability will be small.

        I want the circuit which will give understanding , so that I can trouble shoot the circuit when problem arises.


         I need the simple circuit which will control the current. The circuit should teach me how to control current. I don't want exact circuit with lm317 or lm723. So that I will be knowing what is happening and what I am doing.

       Mr. Old way has referred nice manual. Sure I will go through it.

      When the problem is small, we can find the solution easily rather than blinking with huge chunk. Hope u will understand sir. Correct me if I am wrong...


     Lot of thanks to mr.bravo , mr old ways and all those good heart who replied to my post.

     

oldway:
I think that Gurumurthy tries to do the squaring of the circle!  |O

Already, a linear supply of 0 to 30V with a max current of 5A, this represents a dissipation of 35V x 5a, that is 175W, it is totally unrealistic.   :palm:

You will have to use a way to reduce dissipation as a pre-regulator or switchover of transformer taps.

And in addition, he wants a simple circuit ....:-DD

I think he should open a topic in the "beginner" section and start by studying a little bit of electronics first.

It is clear that he does not know what he wants, nor if what he wants is possible or not ...   :scared:

There is no shame in being a beginner, we are here to help them, but at a minimum, the person should realize that he is a beginner and to have enough modesty to recognize it.

Kleinstein:
Adding current limiting to a regulator like LM317 or LM350, that is not made for it is usually not a good idea. So explaining the function of those circuits does not make much sense as they don't work well anyway. Dave's video about building a supply around an LT3081 (or similar) has the same problem to start with. So if you want to build a lab supply, forget about LM317 and similar chips with integrated power stage.

The advantage with the 723 circuit is that understanding of the circuit is relatively easy, as there is no magic black box with not so well defined properties. The Phillips circuit is still relatively simple (not too many parts), though it has quite a lot of background behind it - so a good example to learn from. So it is really worth trying to understand that circuit.

A supply circuit to learn from should be more like 1 A - the parts a cheaper and less smoke to escape. For learning, the small one is just as good as a larger one.

David Hess:

--- Quote from: Gurumurthy on May 19, 2017, 12:16:08 am ---Can you please explain me this circuit. I cant understant Current Limiting Circuit.
--- End quote ---

The LM317/LM338/LM350 wants to maintain 1.25 volts between its output and adjustment terminals.  R1 could be made to be adjustable however potentiometers which will support 1.5 amps and more through their wiper connection and with the necessary power rating are very rare.  So instead, R2 is used to add a voltage to the voltage across R1 and the LM350 acts to keep the sum of the voltages equal to 1.25 volts.

The 2N5640 operates as a constant current sink holding the voltage across R2 at 1.25 volts.  As the potentiometer is adjusted downwards, the voltage across R2 replaces the voltage across R1 and the output current decreases.

oldway:
It is not possible to use a LM317/LM338/LM350 for a 0-30V 0-5A labo power supply because it exceed the absolute max ratings of the device.
input-output differential voltage: +35V max.
Dropout voltage: 2.5V at 3A (-25°C)
Min input voltage at max current and min mains voltage: 32.5V
Mains voltage variation: +/-10%
At max mains voltage (+10%) full load: 32.5 +20% = 39V
At max mains voltage no load: above 40V....exceed the absolute max ratings of 35V

Max power dissipation at full load and max mains voltage with output in short circuit : 39V x 5A = 195W  :palm:

It far too high, you have to use a tap switching by relays or a preregulator.....

The Philips power supply is only 0-20V 0-1A.....

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