Thank you
And the other questions please

Sir,

Under no load condition, these shorts were happening.

 

Sir,

Under no load condition, these shorts were happening.

And ...
I feel like your spoon feeding us small bits

Please review the posts , and answer all the questions so we can come up with a conclusion ..

 

And ...
I feel like your spoon feeding us small bits

Please review the posts , and answer all the questions so we can come up with a conclusion ..

Dear Sir,

Extremely sorry, here are the answer



1)Your output diode is in the wrong place,

Ans: correct me

2) What output voltage and current were you measuring before the last two broke?
Ans: full input voltage, no variation if I vary the potentiometer.

3) What were you doing at the time?
Ans: Just a spart came during unexpected short, Regulator which is mounted in heat sink got heated up.

4)What load was the PSU connected to ?

Ans: Under no load, due to unexpected short the regulator went to breakdown.

Thank you

 

Dear Sir,

Extremely sorry, here are the answer



1)Your output diode is in the wrong place,

Ans: correct me

2) What output voltage and current were you measuring before the last two broke?
Ans: full input voltage, no variation if I vary the potentiometer.

3) What were you doing at the time?
Ans: Just a spart came during unexpected short, Regulator which is mounted in heat sink got heated up.

4)What load was the PSU connected to ?

Ans: Under no load, due to unexpected short the regulator went to breakdown.

Thank you

where did you get the diode protection schematic from ?

https://forum.allaboutcircuits.com/threads/lm317-reverse-voltage-current.105878/

if it was just a short circuit , and you had a quick blow fuse designed for dc, not a mains fuse and you had the required heatsink , that chip would not have gone pop.

please review the questions as you are still missing a lot.

 

where did you get the diode protection schematic from ?

https://forum.allaboutcircuits.com/threads/lm317-reverse-voltage-current.105878/

if it was just a short circuit , and you had a quick blow fuse designed for dc, not a mains fuse and you had the required heatsink , that chip would not have gone pop.

please review the questions as you are still missing a lot.

where did you get the diode protection schematic from ?

https://forum.allaboutcircuits.com/threads/lm317-reverse-voltage-current.105878/

if it was just a short circuit , and you had a quick blow fuse designed for dc, not a mains fuse and you had the required heatsink , that chip would not have gone pop.

please review the questions as you are still missing a lot.

Sir,

Thank you.

Dear Sir,

Extremely sorry, here are the answer

• Vin ? AC or DC in ?
• Ans: DC
  
  
• Do you need to use a lm388, if so why ? Who's setting that requirement ?
• Ans: That fits my voltage range and Available in market.
• 
  
• Vout is 1v2 to 24v at 5 Amps
  Ans: output current will be fixed by Pd=(Vin-Vout)* I Load

Pd is taken 25W for protection

LT338(MAX CURRENT:5AMPS)​
Vin​	Vout​	Vd​	Pd​	Iload​
28.28​	1.2​	27.08​	50​	0.92​
28.28​	2​	26.28​	50​	0.95​
28.28​	3​	25.28​	50​	0.99​
28.28​	4​	24.28​	50​	1.03​
28.28​	5​	23.28​	50​	1.07​
28.28​	6​	22.28​	50​	1.12​
28.28​	7​	21.28​	50​	1.17​
28.28​	8​	20.28​	50​	1.23​
28.28​	9​	19.28​	50​	1.30​
28.28​	10​	18.28​	50​	1.37​
28.28​	11​	17.28​	50​	1.45​
28.28​	12​	16.28​	50​	1.54​
28.28​	13​	15.28​	50​	1.64​
28.28​	14​	14.28​	50​	1.75​
28.28​	15​	13.28​	50​	1.88​
28.28​	16​	12.28​	50​	2.04​
28.28​	17​	11.28​	50​	2.22​
28.28​	18​	10.28​	50​	2.43​
28.28​	19​	9.28​	50​	2.69​
28.28​	20​	8.28​	50​	3.02​
28.28​	21​	7.28​	50​	3.43​
28.28​	22​	6.28​	50​	3.98​
28.28​	23​	5.28​	50​	4.73​
28.28​	24​	4.28​	50​	5.00​
28.28​	25​	3.28​	50​	5.00​

• 
  
• 
  
• What do you want the output to do if you try to take more than 5A ?

Ans: internal protection should protect the regulator

• Turn off, lower voltage to keep a constant current of 5A ?
  If it's to turn off in over current , how is it to be turned on again ?
• Ans: I can’t understand the question. But regulator is configured in voltage mode.
• 
  
• 
  
• To use a linear regulator like a ldo , you would be looking at around 2V greater input than max output. Say 28V
  
  At your minimum out of 1v2 , and 5 A
  Your linear regulator is going to have to dissiate ( 28-1.2) * 5 = 134 watts of heat whilst keeping the ldo / transistors below around 70 degrees. That's around a 0.3 degree per watt heat sink you need. Do you have room for that ?

Ans. Sufficient heat sink is attached

• Your output diode is in the wrong place,

Ans: I copied from below circuit idea. What should be done.

8) What output voltage and current were you measuring before the last two broke?
Ans: full input voltage, no variation if I vary the potentiometer.

9) What were you doing at the time?
Ans: Just a spart came, Regulator which is mounted in heat sink got heated up.

10)What load was the PSU connected to ?

Ans: Under no load, due to unexpected short the regulator went to breakdown.

 

Under no load, due to unexpected short the regulator went to breakdown.

And has been repeatedly noted, the regulators should have self protected.
So where did you obtain those regulators?

 

And has been repeatedly noted, the regulators should have self protected.
So where did you obtain those regulators?

Sir,

Local electronics shop for 130inr(1.48 dollars).

 

Unless the circuit your regulator is supplying is providing reverse power, the LM338 should be nearly indestructible (and even then your reverse protection diodes should cover that).

Listed prices for LM338K are around 100 times greater than what you paid, so seems likely you have bought poor (counterfeit) stock.

 

Unless the circuit your regulator is supplying is providing reverse power, the LM338 should be nearly indestructible (and even then your reverse protection diodes should cover that).

Listed prices for LM338K are around 100 times greater than what you paid, so seems likely you have bought poor (counterfeit) stock.

Dear sir,

Ok sir

 

I have to ask, is the lm338 insulated from the heat sink, or is the heat sink isolated from the rest of the circuit? The case of the 338 is the output, which makes the heat sink the same if not insulated between the two.
Having no insulation and the heat sink touching some other part of circuit would produce a short.
Otherwise, you may have counterfeit device.

 

I have to ask, is the lm338 insulated from the heat sink, or is the heat sink isolated from the rest of the circuit? The case of the 338 is the output, which makes the heat sink the same if not insulated between the two.
Having no insulation and the heat sink touching some other part of circuit would produce a short.
Otherwise, you may have counterfeit device.

Sir,

With all the advices, Last time i will check with LM338K i have .

what are the correction i should make in this circuit.

 

Unless the circuit your regulator is supplying is providing reverse power, the LM338 should be nearly indestructible (and even then your reverse protection diodes should cover that).

Listed prices for LM338K are around 100 times greater than what you paid, so seems likely you have bought poor (counterfeit) stock.

Sir,

Yes, now I went through manufacturer sites and all stopped manufacturing TO-3 package.

 

As others have mentioned, the TO-3 package of the LM338 were discontinued many years ago. What remains are mostly used for hi-rel applications and cost a small fortune. The price you paid for it means that it is certainly a counterfeit, most likely a LM317 die.

 

also the current limiting circuit is not very good. Vbe of Si transistor is about 600-700mV. using 0.15 Ohm means current is about 4A. but that is when sensitivity is the greatest - with wiper on the right side (b-c). moving wiper to the left reduces sensitivity. for example if set in mid position, that limit will be about 8-9Amp. and fully on the right (a-b), will not work at all.

 

also the current limiting circuit is not very good. Vbe of Si transistor is about 600-700mV. using 0.15 Ohm means current is about 4A. but that is when sensitivity is the greatest - with wiper on the right side (b-c). moving wiper to the left reduces sensitivity. for example if set in mid position, that limit will be about 8-9Amp. and fully on the right (a-b), will not work at all.

View attachment 355233

Sir,

Yes. Then emitter connected to position a and base connected to position c will be ok.

Removing variable current limiting potentiometer will limit the current to 5 amp and this protect the regulator from accidental shorts.

Thank you

 

Sir,

Yes. Then emitter connected to position a and base connected to position c will be ok.

Removing variable current limiting potentiometer will limit the current to 5 amp and this protect the regulator from accidental shorts.

Thank you

your reverse diode, needs to be able to take the full current , depending on your output capacitance , then a 4001 might be on small side,

dont know why you have the extra output current limit, when the proper do is bullet proof, id remove it

you have the old problem of over temprature when you have a low output voltage . your relying on the ldo switching off,
you seem to not trust the ldo to switch off when over current, yet your trusting the ldo to switch off if over temoratured !

 

your reverse diode, needs to be able to take the full current , depending on your output capacitance , then a 4001 might be on small side,

dont know why you have the extra output current limit, when the proper do is bullet proof, id remove it

you have the old problem of over temprature when you have a low output voltage . your relying on the ldo switching off,
you seem to not trust the ldo to switch off when over current, yet your trusting the ldo to switch off if over temoratured !

Sir,
May be you can give circuit with current boosting with lm317 TO-220 ideas with sufficient protection.

Thanks a lot .

 

Sir,
May be you can give circuit with current boosting with lm317 TO-220 ideas with sufficient protection.
Thanks a lot .

The circuit you supplied in post #10 showed a current boosted LM317 with over-current protection. If the LM317 is mounted on the same heatsink and in close proximity to the power pass transistors, then there will be over-temp regulation as well.

 

Sir,
May be you can give circuit with current boosting with lm317 TO-220 ideas with sufficient protection.

Thanks a lot .

why have you dropped the requirement for the supermarket lm338 Of the post title?

BTW. you did not get back on that reverse diode, it needs to be a schokty, low Vforwaed

as you are now changing from the requirmentbto usevthe lm338, what about the earlier post #5, showing a lab psu with over current and over voltage ?

 

why have you dropped the requirement for the supermarket lm338 Of the post title?

BTW. you did not get back on that reverse diode, it needs to be a schokty, low Vforwaed

as you are now changing from the requirmentbto usevthe lm338, what about the earlier post #5, showing a lab psu with over current and over voltage ?

Sir,

I have already went through the web link. In which this is the circuit which suits my electrical specification. But I have to buy multi tapping Transformer which is again expensive. As well as we have to design custom PCB for these design.

I preferred LM317 Instead of this circuit which uses less number components and Point of making fault will be less.



I facing the reality now.

There is a cinema song which conveys this meaning , written by Poet Vali


Desire came to me,
and pushed me in to sin.

Why should I point out
others for my fault?

In the pouring rainy season,
I went out to sell salt.

In the time of heavy winds,
I went out to sell flour.

By making wrong calculations,
I suffered in life.

Thank you for the support through out, After all these conversation the songs says my answer.