5 Ampere Regulator using LM 317 or LM723

[Gurumurthy]

Hi to all..

I want to design lab power supply with the transformer rating of 30V , 5 ampere using LM317 or LM723. Because after rectification it would give around 42V  Pulsating DC, So both these IC could Handle voltage around 40V. Hence this is the reason for adapting to these ICs.

At the initial stage started with LT1084 and LM338. Both went to break down condition and they are much costly then LM317 and LM723. I went outboard transistor for current boosting(for LM317) but my MJ4502 got hot and burned and also used TIP142/147,2N3055 etc. but all these circuit failed and I have used old 1ohm/25watt resistor for loading. I have taken output of secondary of transformer and connected 6A bridge and connected my regulator ICs(317 or723) but every thing failed.

I want design power supply which should have control over voltage and current ,should be reliable in delivering power to load.Please help me in this regard.

I have seen Video of Dave jones for constructing power supply. The problem is LT3080 is a current reference based regulator which is costly and not available in shops in chennai.Thanks Jones.

[Paul Price]

To get some help, please show a schematic with component values and your output load.
Your description suggests you have made design and connection errors.

[Kalvin]

As a quick hack, you could use a linear pre-regulator or a simple transistor voltage regulator which will take the higher input voltage and output 30V feeding the L317 or LM723. In power efficiency-wise the result will be the same anyway, but in thermal management wise the situation will be easier to handle as there are two regulators sharing the thermal load.

[Kleinstein]

If the transformer is rated for 5 A (AC current) this would allow about an 3 A DC current without overloading the transformer, if no power factor correction is used.

For a linear power supply it is normal the the transistor of other power element (like LM338) will get hot. A worst case 40 V times 3 A load is too much for a single TIP141 / 2N3055 / MJ4502 or similar. So one would need at least 2 of these, maybe even 3.

The LM723 based circuit is good for voltage regulation, but not for a precise variable current regulation. Also the sometimes slightly more than 40 V can be a problem to the chips.

So the circuit of choice is more like one based on OPs and power transistors. With 30 V this is just about at the upper limit where the emitter follower output stage can work with more normal OPs. The more flexible version is that with a floating regulator powered by a small second transformer. Many cheap Chinese supplies (and old HP supplies too) are build like these. Something like the HY1803 might be an inspiration. Plans for this supply are available in the net.

[BravoV]

..At the initial stage started with LT1084 and LM338. Both went to break down condition  ...

.... my MJ4502 got hot and burned and also used TIP142/147,2N3055 etc. but all these circuit failed

....... shops in chennai ....

Went there once long time ago, basically the market is filled with counterfeit stuffs.

Assuming you're using the right transformer to do the job, the right schematic and properly heat sunk ..... are you sure you're using the genuine stuffs ?

[Zero999]

The LM338 will not be able to work up to 5A when the input-output differential is high.

The LM317 is a floating regulator which means there's no upper voltage limit, just the voltage difference between the input and output. It's possible to add a couple of transistors and a zener diode to allow the LM317 to work at higher voltages. The main disadvantages are: more components, higher drop-out and you need to watch out for the current through D1 increasing the output voltage under light loads.

[Zero999]

For completeness here it is again with a PNP pass transistor for higher currents.

I want to design lab power supply with the transformer rating of 30V , 5 ampere using LM317 or LM723. Because after rectification it would give around 42V  Pulsating DC, So both these IC could Handle voltage around 40V.

Why not use a transformer with two 15V secondary windings? When higher output voltages are required, use both secondary windings but for lower voltages use a single 15V winding. The selection could be performed using a relay or transistor.

[Gurumurthy]

Thanks a lot for all. I want to design Lab power supply which is variabble from 0V to 30V . I found a circuit which is variable from old data sheet of LM317. I cant understand the operation of opamp with passive devices.Give clear functioning of circuit with good scenario. thank you all. i am attaching the circuit for your reference.

[IanB]

If you look at commercial linear power supplies that go from 0 to 30 V, they typically are limited to 1 or 2 A. Regulated linear power supplies that can go from 0 to 30 V and 0 to 5 A are very, very expensive. This might suggest to you that you are reaching beyond practical limits, especially if trying to make one from an LM 317.

Maybe you should set your sights a little lower?

[DBecker]

Who would design a straight linear power supply in the modern era?  The thermal challenge is just too much of a problem.

For a quiet power supply you use a switching first stage with good output filtering, and use a quiet LDO final stage to remove switching noise and improve the transient response.

[Gurumurthy]

Please find attachment.I can't understand the function of opamp which is acting as comparator with many passive devices. It would give insight ,if explained with some assumptions at circuit nodes.

[Kleinstein]

Especially for a beginner, a linear supply is much easier than switched mode. It is also usually lower noise - especially common mode noise is difficult (or expensive) to avoid in switched mode supply. For a commercial product, the combination of switched mode and linear is definitely a good option, alone from saving on the heavy transformer and allowing for PFC.

To save on the power loss one would tend to use at least 2 transformer taps, maybe even 4. This is at least what the cheap Chinese do. For the beginning 2 taps are a good start and that does not need a special transformer, but can use a more normal one with a split output winding (e.g. 2 times 15 V). With a fan, a power loss of 100 W is not that bad.

In a linear regulator the OPs in the regulation loop are usually not working as comparators, but as linear amplifiers. Starting with voltage regulator chips looks easy at first, however it does not really help for a lab supply. These chips are made for a fixed current limit and a well behaved load - whereas a lab supply should be stable with any realistic load. So a voltage regulator is not a first step towards a simple lab supply. The LM317 would be used as a kind of transistor (small and relatively slow) with internal thermal protection.

For the beginning, I would start at lower power to learn. Much of the design is the same, but much less magic smoke escaping if things go bad. I attached a PDF file for a simple lab supply design with a floating regulator. This is about as simple as it can get, if you leave out the optional transformer tap switching. It is probably good for about 1-1.5 A and sold by the Chinese as a 2 A supply.

[Zero999]

Please find attachment.I can't understand the function of opamp which is acting as comparator with many passive devices. It would give insight ,if explained with some assumptions at circuit nodes.

Just posting it again won't help. You should post a PNG or GIF file and a link to the original source, rather than an M$ Turd document which hardly anyone will read.


http://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS009063.PDF

The op-amp is not just acting as a comparator. It's a linear amplifier. Why not try building/simulating it?

[Gurumurthy]

Sure Sir. I will simulate.

[technix]

Hi to all..

I want to design lab power supply with the transformer rating of 30V , 5 ampere using LM317 or LM723. Because after rectification it would give around 42V  Pulsating DC, So both these IC could Handle voltage around 40V. Hence this is the reason for adapting to these ICs.

At the initial stage started with LT1084 and LM338. Both went to break down condition and they are much costly then LM317 and LM723. I went outboard transistor for current boosting(for LM317) but my MJ4502 got hot and burned and also used TIP142/147,2N3055 etc. but all these circuit failed and I have used old 1ohm/25watt resistor for loading. I have taken output of secondary of transformer and connected 6A bridge and connected my regulator ICs(317 or723) but every thing failed.

I want design power supply which should have control over voltage and current ,should be reliable in delivering power to load.Please help me in this regard.

I have seen Video of Dave jones for constructing power supply. The problem is LT3080 is a current reference based regulator which is costly and not available in shops in chennai.Thanks Jones.

At this level of current it may be a better idea to use a switch-mode design so the heat output is manageable.

42V/5A means 210W of total power. For a linear regulator this number is the sum of the power dissipation of your load the regulator itself. Assuming a short circuit at the output (e.g. when charging up supercaps at CC mode) your regulator need to dissipate this full 210W and it will fry the power elements very quickly.

If you need the low ripple performance of linear regulators, You can add a 5A-capable switch-mode pre-regulator that tracks the actual output voltage, to cut the input voltage to the linear stage to somewhere slightly above the actual output, for example 2V above output, so the linear stage dissipates no more than 10W power.

[Gurumurthy]

Dear Sir, you suggest me some pregulator circuits..Thank you sir..

[Kalvin]

In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

[technix]

In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

I personally would like a mains-direct approach instead, using adjustable isolated mains switching regulator chained to the linear regulator. This allows the mains-side optimizations like power factor correction to be used.

[Kalvin]

In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

I personally would like a mains-direct approach instead, using adjustable isolated mains switching regulator chained to the linear regulator. This allows the mains-side optimizations like power factor correction to be used.

Typically the mains switching power supplies have a Y-capacitor between the mains and the secondary causing sufficient leakage current which can damage sensitive electronics. The mains transformer can have multiple, isolated secondaries with adjustable regulators so one can get multiple isolated and independent outputs in addition to the better mains insulation. Also, using the mains smps one cannot achieve the low noise benefits of the linear power supply on lighter loads.

[technix]

In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

I personally would like a mains-direct approach instead, using adjustable isolated mains switching regulator chained to the linear regulator. This allows the mains-side optimizations like power factor correction to be used.

Typically the mains switching power supplies have a Y-capacitor between the mains and the secondary causing sufficient leakage current which can damage sensitive electronics. The mains transformer can have multiple, isolated secondaries with adjustable regulators so one can get multiple isolated and independent outputs in addition to the better mains insulation. Also, using the mains smps one cannot achieve the low noise benefits of the linear power supply on lighter loads.

That Y capacitor isn't necessarily required. I am designing not aiming at minimum ripple, but a compromise between ripple and efficiency. Maybe I cannot guarantee the 20uV ripple, but I can shoot for a 80 Plus Gold rating.

[Kalvin]

In order to achieve the best qualities of the linear power supply and the switched mode power supply, one could use a tracking switched mode pre-regulator which can be bypassed on light loads. In that way one can get a decent high current performance with reduced switching noise and good low current performance without switching noise, while minimizing the thermal problems.

I personally would like a mains-direct approach instead, using adjustable isolated mains switching regulator chained to the linear regulator. This allows the mains-side optimizations like power factor correction to be used.

Typically the mains switching power supplies have a Y-capacitor between the mains and the secondary causing sufficient leakage current which can damage sensitive electronics. The mains transformer can have multiple, isolated secondaries with adjustable regulators so one can get multiple isolated and independent outputs in addition to the better mains insulation. Also, using the mains smps one cannot achieve the low noise benefits of the linear power supply on lighter loads.

That Y capacitor isn't necessarily required. I am designing not aiming at minimum ripple, but a compromise between ripple and efficiency. Maybe I cannot guarantee the 20uV ripple, but I can shoot for a 80 Plus Gold rating.

Agreed. Typically a design is a compromise between many different requirements.

[Kleinstein]

If the mains input includes PE, the Y-class capacitor is not a problem. It is only a problem it the input is only 2 wires, as than the capacitor is effectively at half the mains voltage. The Class Y capacitor has nothing to do with ripple, but it is about common mode voltage. With the capacitor there might be several 10s of volt of common mode voltage at the switching frequency.

Still for a beginner, the SMPS part is way to complicated, especially starting from mains.

With tap switching one can also reduce the worst case power dissipation. With 4 taps one might cut is to about 1/3.

[Gurumurthy]

Dear all,
           please give me some reference to study the Study of Regulated power Supply and Various Pre regulator circuit using SMPS Techniques.

[Zero999]

Dear all,
           please give me some reference to study the Study of Regulated power Supply and Various Pre regulator circuit using SMPS Techniques.

http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Noty%20aplikacyjne/Linear%20Technology/AN140fa.pdf
http://www.ti.com/lit/an/snva559a/snva559a.pdf
http://www.ti.com/lit/an/slva001e/slva001e.pdf

[coromonadalix]

You have some good variable smps circuits on ebay going down to zero with decent protection,  just add main transformer rectifier and capacitor