Sir,

please find the attached circuit, I connected this in bread board. The 120 ohm of 1Watt was fired two times. I cant find the reason for its breakdown. got frustrated after building this circuit.

The LM337 regulator is not wired correctly for it being an adjustable voltage regulator device. The connections are what would be used for a positive fixed voltage regulator device. THAT is the main problem with the circuit that is shown attached.
The circuit is not at all correct for the LM337 device .

 

why do you say that? the regulator part matches the datasheet and it is set to -26V output.
this is straight from the manufacturer website:



the schematics is missing bypass capacitors, values etc. but it is passable.


the problem i see is that we do not see actual construction. btw breadboard is ok for low voltage and current but it is unsuitable for circuits like this.

 

 

OK it did not look correct to me at the time.
Also, if the voltage out is 26 volts, consider that: P=VxV/R= 26v x 26v/ 122.5 ohms >>2 watts.

 

Sir,

please find the attached circuit, I connected this in bread board. The 120 ohm of 1Watt was fired two times. I cant find the reason for its breakdown. got frustrated after building this circuit.

Get rid of the components on the input and ground the ADJ pin (0 ohms at the 2.5k resistor). There should be -1.25V at the output. Now set this resistor to 500 ohms and report back the voltage at the output. Also, there should always be 1.25V across the 120ohm resistor regardless of what the output voltage is.

If you get that working, I can show you an alternative way to boost the current output. I suspect the parallel pass transistors on the input are giving you problems because they generate feedback.

 

Get rid of the components on the input and ground the ADJ pin (0 ohms at the 2.5k resistor). There should be -1.25V at the output. Now set this resistor to 500 ohms and report back the voltage at the output. Also, there should always be 1.25V across the 120ohm resistor regardless of what the output voltage is.

If you get that working, I can show you an alternative way to boost the current output. I suspect the parallel pass transistors on the input are giving you problems because they generate feedback.

Sir,

1)What is the alternative way to get current boosted output?

2) how much current can be obtained if I use 24v-0-24v , 10 ampere centre tapped transformer for positive and negative output each?

3)how feedback loop is created?

 

1) What is the alternative way to get current boosted output?

The circuit shown should be fine, but you only need one boost transistor for the current available form the transformer (LTspice sim below):

2) how much current can be obtained if I use 24v-0-24v , 10 ampere centre tapped transformer for positive and negative output each?

Due to the high peak RMS current drawn from the transformer by a capacitor rectifier filter, the maximum DC current should less than 60% of the transformer RMS ranting, so about 6Adc max. from your 10Arms transformer.

In case you don't know, a low parts count way to get plus and minus voltage from a center-tapped transformer is to ground the center-tap, and connect the other two output wires to a bridge rectifier module.
That will then give a full-wave rectifier output for both the positive and negative outputs.
The advantages of this are, only one diode drop to the DC output, and the currents from both loads are balanced in the transformer output windings.

 

The circuit shown should be fine, but you only need one boost transistor for the current available form the transformer (LTspice sim below):

View attachment 317885

Due to the high peak RMS current drawn from the transformer by a capacitor rectifier filter, the maximum DC current should less than 60% of the transformer RMS ranting, so about 6Adc max. from your 10Arms transformer.

In case you don't know, a low parts count way to get plus and minus voltage from a center-tapped transformer is to ground the center-tap, and connect the other two output wires to a bridge rectifier module.
That will then give a full-wave rectifier output for both the positive and negative outputs.
The advantages of this are, only one diode drop to the DC output, and the currents from both loads are balanced in the transformer output windings.

Sir,

It means we can obtain output 23v@6amps for positive regulator output and another 23v@6amps for negative output, at the maximum.

 

It means we can obtain output 23v@6amps for positive regulator output and another 23v@6amps for negative output, at the maximum.

You could also, in theory, draw 12A from one output, if the other has no load.

 

You could also, in theory, draw 12A from one output, if the other has no load.

Sir,

Rms power= 48*10=480va

Average power=(.9*Vac)(.6*Iac)
=(.9*24)(0.6*10)
=21.6*6
=129.6 watts
On end of coil I could take=129.6 watts

Overall I could take 260watt from 480va transformer.

 

Can you post a photo of your construction?
There must be something wrong with it if the 120R burns.
As has been pointed out, the LM337 and LM317 pinouts are not the same. And the heat sink tab MUST be insulated from the rest of the circuit as it is not electrically isolated.
Check both of these points.

 

Sir,

please find the attached circuit, I connected this in bread board. The 120 ohm of 1Watt was fired two times. I cant find the reason for its breakdown. got frustrated after building this circuit.

You'll have to hire a new 120 Ohm resistor

Ok, so where is your load resistor?
It may be that in this kind of circuit you NEED a load resistor because with the slightest current draw for the LM337 the external transistors will be turned on and that will force the output to go very high even through it shouldn't if everything worked right. It could even be leakage current causing the output to go too high with no load.

Try adding a reasonable load, and also you probably have to reduce the 22 Ohm resistor significantly.

You have to realize that there is a sort of current balance going on here in order for the 'feedback' to work right. If that balance weighs too heavily toward the transistors BE junction(s) the output may not reduce enough to get actual regulation, especially with no load.

I have a feeling you may be better off just going with a higher current version of the LM337 than trying to boost it with external transistor(s). That would be a different part number.

Here is a cleaned up version of your drawing...

 

The circuit shown should be fine, but you only need one boost transistor for the current available form the transformer (LTspice sim below):

View attachment 317885

Due to the high peak RMS current drawn from the transformer by a capacitor rectifier filter, the maximum DC current should less than 60% of the transformer RMS ranting, so about 6Adc max. from your 10Arms transformer.

In case you don't know, a low parts count way to get plus and minus voltage from a center-tapped transformer is to ground the center-tap, and connect the other two output wires to a bridge rectifier module.
That will then give a full-wave rectifier output for both the positive and negative outputs.
The advantages of this are, only one diode drop to the DC output, and the currents from both loads are balanced in the transformer output windings.

The last time Ilooked, the LM337 was a NEGATIVE voltage regulator.So I see a bit of a problem in the circuit shown.

 

The last time Ilooked, the LM337 was a NEGATIVE voltage regulator.So I see a bit of a problem in the circuit shown.

I think it's more helpful to assert what you actually think is wrong rather than suggest a mistake has been made.

Clearly TS is already having trouble understanding and this is often made worse with users undermining each other. And I'm not being flippant about this because it's a big problem on this site.

 

The last time I looked, the LM337 was a NEGATIVE voltage regulator. So I see a bit of a problem in the circuit shown.

Which circuit? I don't see the problem.

 

You could also, in theory, draw 12A from one output, if the other has no load.

Sir,

Rms power= 48*10=480va

Average power=(.9*Vac)(.6*Iac)
=(.9*24)(0.6*10)
=21.6*6
=129.6 watts
On end of coil I could take=129.6 watts

Overall I could take 260watt from 480va transformer.

 

Which circuit? I don't see the problem.

The circuit in post #47 is what I was responding to. Yes, I should have been more specific.

 

Overall I could take 260watt from 480va transformer.

That sounds about right.

 

The circuit in post #47 is what I was responding to. Yes, I should have been more specific.

Oh ok, I thought that might be it. However, I do not see a problem with that circuit either unless I am reading something wrong. What is it exactly that you see is wrong with it? I could take another look.

 

Sir,

1)What is the alternative way to get current boosted output?

2) how much current can be obtained if I use 24v-0-24v , 10 ampere centre tapped transformer for positive and negative output each?

3)how feedback loop is created?

I found that using the 1.5 amp current limited version of the LM317, the base emitter resistor had to be around 0.7 Ohms to get around 10 amps output current limit.
The external transistor I used was a single TIP36 PNP transistor. That's rated for 25 amps I think but you could check that.

I set the output for 12.0 volts and used smaller and smaller load resistors, and the lower values drew around 10 amps and up to 11 amps with a complete short circuit.

It's a little tricky because the transistor base emitter forward voltage has a lot to do with the current limit and thus the choice of that series resistor shown as 22 Ohms on some of the schematics. The Beta might too but I did not check that yet. The higher you go with that resistor value, the higher the output current limit goes. That means you have to check the current limit function carefully and if it starts to go too high then you have to reduce the value of that 22 Ohm resistor. As you continue to lower the output resistance, you may have to lower the value of that 22 Ohm resistor several times until you get the max current output set right.

This would be the same circuit as the LM337 except for the external transistor, which would have to be a NPN type, and of course the input voltage is negative not positive.
It does help to check the LM337 and the LM317 for current limit before you even use it in a circuit with an external transistor. Make sure it works OK all by itself.