Feasability of Adding a Second Parallel Darlington?

If you do that, you will change it from being a current amplifier (Keeping the voltage regulated based on the two adjustments on the LM linear regulator, im assuming a course and fine adjustment)

After the change the transistor would be working as a voltage amplifier and very dependent on temp and other factors

The circuit John posted is a classic circuit to boost the capacity of a regulator, I have been using variations of it for over 30 years with no issues

Look at any linear regulator circuit and you will see this, think of the LM as a voltage reference with a higher then normal output ability, the pattern is also the same as almost every single linear bench power supply out there just without current limiting so I don’t think John needs to change the topology of the design

The rising and turning off in this case is supposed to happen and is the negative feedback, the voltage gain is ideally 1. With a massive current gain, look at the WIKI on common collector BJT for more details and a fuller description

Peter

Hi John,

Today, driving the car, I found back the way to include the load correctly in the calculation of the output current. I updated the calculation above.

John Wiltrout wrote:

 

One thing that has me concerned is that the rectified voltage 36V * 1.4 = 49.7V should be too high for the LM317. Is this possible because the adjust and output are not at 0V?

Probably it is saved by a slowly rising supply in combination with the voltage at the adjust terminal.

important question:

Do you know what the calibration procedure is? Is the output voltage tuned to a certain value, or is it tuned per load device?

more important question:

you have a problem with overload. Do you know what the requirements are for the load? Do you need a constant voltage, or a constant current limit or both? Without this, it's hard to know what the 'right' solution for your problem is. Adding a thermal fuse (polyfuse) might protect the darlington, but cut down the motor power too much.

If you know what current / voltage limit you need, you could design for that purpose. Linear has some nice constant current / constant voltage solutions, actually meant for LEDs, but maybe also for this application.

The LM317 is good for 0 - 37V out according to https://www.fairchildsemi.com/datasheets/LM/LM317.pdf

and it can have a Vin to Vout of up to 40V so as long as the output is never taken to less than about 10V on the LM317 it should be good

regards

John

Is this a custom design you created or a commercial unit your repairing ?, just curious

Thanks

Peter

Peter your videos are well on the way to been the same length as Dave Jones's.

I think that they could easily be split in to two although how you do it is a different matter.

Either way as you know very well making the video is the easy bit all the prep and post work is the hard bit!

wouldn't having a larger darlington rather than several smaller ones serve better as you wouldn't need to mach them up, probably fit the same mountings and probably cheaper than several smaller transistors.

I think Mark may of alluded to that or similar?

I did allude to that for sure way up there somewhere, and as it is working in common collector mode, the differences in parameters will have minimal if any impact to the performance

Still smaller if that is an issue but yeah I suppose it doesn't really matter

For sure, I start out intending to keep it to 30 mins or less, then start filming, then oops, 1 hr. elapsed and I’m only half way through… Yes that’s what I said, I already broke it into two

Second half is rendering as we speak, dealing with MOSFETs N and P channel and it too is an hour I’m afraid

I guess a logical split would be 30Mins for NPN, 30 for PNP, 30 for N Channel… you get the idea

Problem was there was no easy break in the middle to split it

In future I will try to deliberately pretend there is an end every 20-30 mins and if I don’t want it I can always delete the ending statements and concatenate

I just hope I don’t ramble on too much, I can sometimes get kinda carried away and I’m always conscious of trimming too much and losing the less experienced viewers that may not get the concepts with the abridged versions so I ere on the side of longer

I know this does not help the poor souls who have to sit and watch, but then that’s what pause and fast forward are for no ?

problem with pause and fast forward is that you need to know where to fast forward. I may not be our target audience either in as far as I can remember at least some of my transistor theory and  watch your videos the way through when I start

The attention span for the average youtuber is less than 2 mins... to go much longer than that you need either boobs, explosions, lol cats, or BS .... preferably several of each in every video.

That said I bet you generally get much better than that I would imagine since electrogeeks have already found you and are generally willing to watch.

Even so 4 x 15 min videos may be better ?