how to select lower voltage?

8-no , i mean wasted power in output cap dis charger resistor

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Hi Ali
A question , why you want to use a capacitor in out put ? to guarantee that ripple is as low as you want ? but this is not the good way because it will make your supply response and loop , relax . and it won't be able to affect fast changes .
and when you want to use a high capacity capacitor in out put , it is not a good idea to use a resistor or something else to discharge it , so what will be the benefit f it ? you can prevent to using a cap in out put then after that you discharge it !!! it is not a good way as i've mentioned before .

7-becuase r5 is 10k and if we except q6 Veb and q5 Vce we have about 3.5 ma in q5 collector , it isn't right?

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I think i couldn't get your exact meaning . i think it is a good idea to explain your mean as clear as possible .
How you've calculated 3.5 ma for collector of q5 ? no that's not correct . did you get what i've told you before ? i told you try to read about principles that i've mentioned . if you don't do what i've told you , it is impossible that you understand how this circuit does work . and you will never be able to design a simple circuit like that . i've showed you the way .

11- can i use 0.250W resistors for r1 to r4?

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if you need 5 amperes at out put then current through each resistor will be around 5/4=1.25 amperes . loss power across the each resistor will be (1.25)^2*0.1= 0.15 watt ( approximately )
So it means you can use that .

12-what is best way to turn on an led when output current limited?

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When limiter is working it means Q7 is conducting so you can use another resistor and transistor exactly like that and use a red LED in it's collector . if you can't catch the idea i can draw it for you .

13-what is the best way to make accurate voltages for opamps inputs? zener or tl431 or ...?

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What do you mean by op amps inputs ? is your mean those five volts and 0.3 volts supply ?

Good Luck
Goldsmith

hi
13-yes
thanks a lot

Hi and good morning in time of IRAN !
about those voltages , for example for 5 volt you can easily use a zener diode and resistor and take it from the 15 volts of op amp or perhaps using a 78L05 which is so small .
about 0.3 or perhaps 0.5 volts you can easily use a voltage divider network and obtain it from 5 volt

Best Luck
Goldsmith

hi again!
14-pn2222 is good for cc led?
15-how to select its base resistor when i don't have u3a output voltage?
thanks a lot

Hi Ali

14-pn2222 is good for cc led?

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I prefer to say how to select a transistor for LED ! you need to know about wasted power across the transistor which it's duty is turning on the overload LED . so it should be able to tolerate the required current of LED ( and you need to consider a safety factor in your design , which can be around 30 or 40 percent ) . about the voltage it should be able to accept VLED-VS

15-how to select its base resistor when i don't have u3a output voltage?

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Why you think that we don't have out put of U3 ? of course we have it . that op amp works as a comparator so it's out put will be zero volts ( approximately ) or it's VCC . so you have it's out put voltage and then you can easily calculate the resistor .
Best Wishes
Goldsmith

please check final schematic
thanks

Hi Ali
It seems fine . you can build it . after you build it let me know about it's behavior ok ?
Good Luck
Goldsmith