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How do make a current limiting knob using LM723 for Linear Reg power supplies?
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Gurumurthy:
Dear oldway,

                  True sir, as you said i am a novoice to Practical Electronics. I want to learn power supply design by simple ICs like LM317 and 723 because they cost around 10 rupee, so i can afford to buy these Ics rather than LT308X series ICs. When some smoke comes from my breadboard, It is my money which is wasted. I have learnt certain basic things with LM317 and 723 and TIP142,2N3055,Mj4502 Transistors when things went wrong.This is my study for past 45 days.


                     Now i understand that i have to move to SMPS preregulator to save my Circuits. I am ready to learn things and apply that in practical circuit design. I am more inspired my the way you approach things . Hence please guide me. Give some reference book so that i am strong to handle big Circuit similar to Philips power supply circuits. Not based on university exam. Please help me!!!!!!!!

                         Forgive me if iam wrong...


oldway:
If you don't want to waste your money with "magic smoke", you should start with low voltage, low current power supply projects, not a 30V 5A power supply.

For exemple, you could make a very reliable double linear power supply 0 to +/-25V with a LM317 and LM327.

Current limit will not be ajustable but will be safely limited under 1A.

Now, a question for the people who are looking at this topic.... 

I said there was something horribly wrong with the project of the Philips power supplies with pre-regulator as pe-1642....

The problem is with the pre-regulator....

Somebody found what's wrong with it ?
MagicSmoker:

--- Quote from: oldway on May 19, 2017, 02:30:21 pm ---...
I said there was something horribly wrong with the project of the Philips power supplies with pre-regulator as pe-1642....

The problem is with the pre-regulator....

Somebody found what's wrong with it ?

--- End quote ---

No inductor in series with the output of the half-controlled bridge.
oldway:

--- Quote from: MagicSmoker on May 19, 2017, 03:02:15 pm ---
--- Quote from: oldway on May 19, 2017, 02:30:21 pm ---...
I said there was something horribly wrong with the project of the Philips power supplies with pre-regulator as pe-1642....

The problem is with the pre-regulator....

Somebody found what's wrong with it ?

--- End quote ---

No inductor in series with the output of the half-controlled bridge.

--- End quote ---
No, there is an inductor in the primary to limit the peak current....that's something more complicated....
Ian.M:
I've just put together a LTspice sim of the regulator section of the Philips PE 1535-00  0V - 40V, 0A - 0.5A. single output PSU.

Some of the models for the discrete semiconductors are a little rough (heavy use of ako:), but its good enough to see what's going on with the current limit circuit.   I didn't bother with the transformer + bridge or the meter circuit.

Part numbers are as per the Fig. 1000 circuit (page 20 of Philips PSU manual, from Oldway's Reply #7 link). Edit: Link Rot! :( As of 2020 it can be found [here].

Controls and Adjustments

* R1 - Set output voltage
* R2 - Set current limit
* R104 - Trim max current limit (500mA)
* R108 - Trim zero current limit
* R123 - Trim zero output
* R127 - Trim max output (40V)I've trimmed all the presets to sane values.  R108 is a little fussy, if you trim with the output unloaded it starts dropping the output voltage well before you reach zero current.  The practical lower limit for R2 will be a few tens of mA. 

I've parameterised the R1 and R2 pot positions as vset and iset respectively, for ease of sweeping them in the simulation.   All pots & presets take a parameter wiper which is the position as a number between 0 and 1.

Zipped LTspice simulation attached - Unpack it to a subfolder of your LTspice working folder and enjoy!  :popcorn:  I *think* I've packaged all the custom models it needs - if anything is missing ask.

N.B. The dp() function defined on the schematic wont be seen by the .op data labels unless you copy it to your plot.defs file.  See https://www.eevblog.com/forum/blog/eevblog-516-ltspice-tutorial-dc-operating-point-analysis/msg1383565/#msg1383565 for details (and a better function for limiting displayed data precision).

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