Yeah, in general, searches are pretty useless, ebay is one of the worst.I tried on Google using words like high voltage regulator, etc. The problem is when you don't know what to call the thing you are looking but you know there must be one it ends up as a 'thod it'.
Another one for the goody section of my notes.
I started out to build a 36V 4.4A power supply. Due to absolute stupidity (1.4141) I ended up way out of my comfort zone. 52V at 3.3A. The Amps don't matter but 52V for a linear supply suddenly became quite a challenge. Maybe that was not a bad thing though. It's more fun doing something that can be put two ways - 'Pushing the envelope' and '****ing Idiot'. I am tending towards the latter. At times there has been some controversy between people who know far more than me. That's not bad for the first thread ever. It does cause the 'if they can't make their minds up I don't stand a chance syndrome though'.A resistor power rating is a minimum requirement and any resistor that meets the minimum power requirement, or over will be suitable. For example the 500W resistor would be suitable (but it would be inconveniently big and a touch pricey). This is the same with most parameters for most devices. For example, suppose a circuit needs a 30V transistor, any transistor of 36V or over would do, even a 600V transistor.
The absolute value of emitter resistor is not that critical as long as they are all reasonably the same value.
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It is painful to see the angst of the inexperienced specifying components and equipment. One OP got into a right tangle about a replacement power supply. He searched all the net to find a 12V power supply that matched the current shown on the label of the equipment. The value was something like 1.255 Amps. Of course, he would never find a power supply with that exact current rating, neither would it be adequate. He had a slightly wider choice when I managed to convince him that any 12V power supply from about 1.5A to infinity amps would be suitable.I am glad you wrote that. If not an awful lot would have gone right out the window of my tiny brain.
Data sheets give the parameters of a particular device, but they don't necessarily explain the interaction between the parameters. It is the same with most devices. For example, a car (automobile) may do 40 MPG and have a top speed of 130MPH, but it will not do 40MPG at 130MPH, probably more like 15MPG.I do appreciate that the data sheet on the 2N3055 is almost a fairy story from any practical point of view.
I initially went down the LM317 route and read the data sheet, then found the LM338 at 5A data sheet and then realised they would both melt. It was then the 2N got added. Then that's not what the data sheet says it is (in the real world) and I got to 4 x 2N. I then needed a 60V regulator as neither the LM317 or LM338 were any good at 60V. Then I found the LM317AHVT.Hi John,
Now that i know that you are going for an LM317H as the control element in your PSU, I have knocked out the skeleton schematic below to illustrate the classic current boost circuit for an LM317. Also shown is automatic input voltage switching, which you asked about.
The LM317 has both over-current and over temperature protection, so the overall PSU would have these features.
The bad news is that the circuit needs PNP power transistors rather than NPN which you have.
By the way, if you plan to buy some PNP power transistors please let me know and I will give you the part number for an optimum device.
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There is no problem with time and patience, unless my missus starts being unreasonable an expects me to do other things: shopping, eating out, talking, fixing the house etc.If you are sure you have the time and patience I'll certainly have a go at the circuit of yours.
This is a major problem, especially with the internet. A lot of the information is either confusing or simply wrong.Much of what I read was very misleading, all one can do is find other peoples solutions, find the majority and hope it's right.
This is very good news. The #1 reason for failure to complete a home-built electronics project is the mechanics, so if you have mechanical skills and tools, that is a major bonus, persistence too.I have 3 spare cases and the tools to do most things.
One further point. I am VERY patient. If major mods need to be done for any reason - good. I shall be like a pig in..........
This is also very good news. You obviously know about heatsinks and fans - the bigger the better.The 4 heat sinks have a 0.86 C/W each. They were not overly expensive but it would be nice to use them. They are about the biggest I can fit in a PC power supply case with a 6W external fan. I could improve on that figure by removing most of the bottom of the case and raise it on legs. This would mean a straight pass for the air flow down the fins or even up them. The heat sinks are mounted with their fins vertical. I have almost no rear to the case, it's 90% vent. However after leaving the heat sink fins it only has a 25 mm gap to bend 90 Deg and go out the back. Not exactly a good idea.
At 12V the fan is supposed to produce a flow of 3.2M/s. I could drive it up to 14.4V. It was an automotive fan and 14.4V is considered the maximum a '12V' system runs at. It's not exactly quiet, it looks just like any ordinary PC fan but will helicopter. It would be better at the bottom underneath, less shrapnel if anything gets dropped in it. It's the only one I have. Incidentally if you put 2 fans together the output goes up by about 37%. Most PC fans will run at 20V+ - reduced life of course. I have done a bit on engine cooling systems, it was quite an eye opener. I would love a nice 125mm mixed flow fan.
[1] RL1 is a single-pole, two-way relay: a 12V automotive type would suit- they are cheap and freely available.What's :
[1] RL1
[2] Q5 Is the schottky near 39V used as a Volt limiter ?
[3] And as you say Q1 through Q4. (Nasty American things - LOL)
[4] I take it that's a 1.2V to 4a (3 + A) output
[5] Why 2 schottky diodes 'snogging' under R9
[6] I see they still need the emitter resistor, same reason no doubt.
I still miss the glow of an El34. Would I build another one - of course I would.Hi John,
Your power supply adventures, almost exactly match mine, except there were no chips then.
I came up with this wonderful power supply design with high accuracy, high current and high voltage. It also had precision current control.
One of the experienced engineers at work told me that I would have one hell of a job getting it stable in the frequency domain, and he said that getting rid of the heat would also be a big problem too. Of course, I knew better.
I never did get my perfect power supply working, although I did make a lesser version, which I used for years. But, although the perfect power supply was a failure, it taught me a lot about practical engineering, and that was invaluable.
spec
I'm glad you have the same problems I have. I have one more. Please God make me the person my dog thinks I am. That was very kind of you to use the word 'discussion', especially as I know nuffinc.There is no problem with time and patience, unless my missus starts being unreasonable an expects me to do other things: shopping, eating out, talking, fixing the house etc.
The circuit is not mine; it is straight out of one of the National Semiconductor (now Texas Instruments) three terminal regulator (TTR) application notes, and is pretty standard anyway. The only bit that is my design is the automatic switching of the transformer tap, but that is not exactly anything new. By the way, the sketch of post #40 is only an outline for discussion. It has not been analyzed in detail, so it is not necessarily a circuit you could build, at the moment.
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Once you start to use fans the orientation of the thing you are trying to cool isn't anywhere near as important as it is with just convection - until you switch off. I expect the same applies to transistors to some extent. I didn't know it was a monster PSU. Now, if we were to use this 40V - 80A old welder I have or the 15v 60A battery charger / starter .............. I jest.This is very good news. The #1 reason for failure to complete a home-built electronics project is the mechanics, so if you have mechanical skills and tools, that is a major bonus, persistence too.
This is also very good news. You obviously know about heatsinks and fans - the bigger the better.
No doubt you know that the optimum orientation for a heatsink is for the fins to run vertically, so that convection air currents can flow freely from the bottom of the heatsink and through the fins.
From what you say, there is little doubt that you will succeed with your monster PSU, in spite of your modesty.
spec
I just saw a tiny light at the end of the tunnel, only very tiny mind you. May I use the word 'trying' here - good. Basically you are just trying to make one BIG LM317.[1] RL1 is a single-pole, two-way relay: a 12V automotive type would suit- they are cheap and freely available.
[2] No, it is a 39V Zener diode, and is the voltage reference that tells Q5 when to energize the relay to reduce the voltage drop across the power transistors and TTR.
[3] The US nomenclature is much better because it is shorter (VT= Q, IC= N etc). You are talking to an Americanophile here- if it wasn't for the Yanks, the UK would be in a sorry state, in my opinion that is.
[4] I was a bit sloppy and just wrote 4A as opposed to 3A+. The output voltage will be 1.25V to whatever maximum voltage the circuit will do, probably about 42V. I have not worked it out. Without a bit of extra circuitry the LM317 family of TTRs cannot go any lower than their internal voltage reference, which is nominally 1.25V.
[5] They are Zener diodes (just one bent end on the symbol). Along with the resistor, they form a snubber to absorb the back EMF (voltage) from the relay coil (inductor) when the relay turns off. This not only protects the relay coil but also the transistor controlling the relay coil.
[6] Yes, the emitter resistors are for current sharing between the power transistors, as previously discussed. But the emitter resistors also have another function in the circuit of post #40. Consider the four parallel power transistors as just one big power transistor (which functionally is what they are). It is important to get the current ratio between the TTR and the power transitors right, so that the TTR, current limiting and over-temperature protection works for the power supply supply as a whole. That is why the emitter resistors are a higher resistance than would be needed just for current sharing alone. I expect the emitter resistor value to increase even more when the detailed analysis is done.
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Correct.I just saw a tiny light at the end of the tunnel, only very tiny mind you. May I use the word 'trying' here - good. Basically you are just trying to make one BIG LM317.
I can guess what a TTR is (I think it's the LM317) but if you could possibly use the full title just once it might save me thinking it's short for - Through The Rhubarb.
Not correct. A true low impedance 0V output for a bench power supply is absolutely essential.I have read that if you want 0V just add a couple of diodes on the end. Probably wrong of course. The minimum I will need will probably be the 2V for a red LED. That sounds silly I know but it's a fact.
I have heard of 'wiggly amps' but never 'wiggly bits'.Sorry but I think I had better find out what these circuit symbols mean. I was OK for resistors, plain diodes and simple stuff like that but once you start adding 'wiggly bits' I'm lost.
I have been collecting various bits. I have about 2000 0.25W resistors but only a few caps mainly ceramics. I have just about enough to make a couple of little LM317 regulators with variable pots.Yet another post. This time about the overall project and way forward.
The mechanical construction and layout of your power supply is essentially independent of the power supply architecture and detailed electronic design.
The overriding mechanical factor is the cooling of the pass elements (power transistors and TTR). So what I suggest is for you to design and make the mechanical side which will form a good foundation for the development of the power supply circuit. It will also be a good test-bed for any future experiments that you may undertake.
Just one piece of advise: make sure that you minimize wire lengths as much as possible and allow for massive conductors for the high current paths, especially 0V.
Also design for full accessibility, so that you can get at all the power supply components easily. Lack of accessibility is the second most common cause for project failure. For example, if you were housing some electronics in a box, always mount the electronics on the lid and not buried in the box. And always have the connections to any printed circuit board along one edge only, so that the PCB can hinge up for access to both sides of the PCB.
I expect you will be using panel-mount terminals (plus, minus, and earth) on the front panel for connection to the power supply. Panel-mount terminals are shown @ https://www.electro-tech-online.com/articles/core-components.782/
In parallel with the mechanical design and construction, we can thrash out a suitable circuit to do the job.
spec
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