Linear voltage regulator datasheet question

[boylesg]

I can deduce what Vbeq1 refers to in the data sheet for BD536.
Ireg is 5mA
I know what BetaQ1 is.
But what are the terms Ireq and Iq1?

No idea.....and with a few guesses as to what they refer to I am getting no where near the value 3R as in this example.

 

[FvM]

The formulas near the schematic have several typos (e.g. + Q1 in the last line should be + ßQ1). Ireq means probably Ireg.

R1 of 3 ohm means that the power transistor starts to conduct at Io of about 0.2 A and keeps Ireg constant around 0.2 to 0.25 A for higher Io.

 

[boylesg]

The formulas near the schematic have several typos (e.g. + Q1 in the last line should be + ßQ1). Ireq means probably Ireg.

R1 of 3 ohm means that the power transistor starts to conduct at Io of about 0.2 A and keeps Ireg constant around 0.2 to 0.25 A for higher Io.

Well apparently there is more wrong with these formulas than just a few minor typos. If I calculate out the second one for BD536 I get 0.06mA.

Can you tell me how you arrived at 0.2A.....presumably not by using these formulas in this datasheet.

 

[FvM]

Start with Vbe,Q1 of 0.6V.

 

[boylesg]

Start with Vbe,Q1 of 0.6V.

Stiill don't get any where near 0.2A

Could you show me step by step how you calculated this value - clearly I am doing something fundamentally wrong.

 

[CataM]

stiill don't get any where near 0.2A

0.6 V/3 ohm = 0.2 Amps

Start with Vbe,Q1 of 0.6V.

FvM wanted to say Veb.

 

[d123]

Hi,

Ireq is the required current through the regulator, IQ1 is the current desired to pass through the pass transistor.

Without knowing the datasheet current expectations, let's suppose about 2A, with stated 0.2A for regulator and say Beta of 100...

R1 = 0.6V/(0.2A - (2A/100))
R1 = 0.6V/(0.2A - 0.02)
R1 = 0.6V/0.18
R1 = 3.333 Ohms.

I give up on the second formula as I get nothing sensible, no matter how I calculate it...

Who cares, the main one is the first one, to know how much you want to pass through the regulator, and how much through the transistor. I believe with this circuit it is good to know the maximum current that will be needed, as the pass transistor:regulator current is a ratio, not a limit.

 

[CataM]

Up to 0.6 V the transistor is not conducting so IQ1 = 0.

 

[boylesg]

Hi,

Ireq is the required current through the regulator, IQ1 is the current desired to pass through the pass transistor.

Without knowing the datasheet current expectations, let's suppose about 2A, with stated 0.2A for regulator and say Beta of 100...

R1 = 0.6V/(0.2A - (2A/100))
R1 = 0.6V/(0.2A - 0.02)
R1 = 0.6V/0.18
R1 = 3.333 Ohms.

I give up on the second formula as I get nothing sensible, no matter how I calculate it...

Who cares, the main one is the first one, to know how much you want to pass through the regulator, and how much through the transistor. I believe with this circuit it is good to know the maximum current that will be needed, as the pass transistor:regulator current is a ratio, not a limit.

OK so Ireq is the 'required current' to be provided entirely by the regulator and after that the transistor starts conducting.

I had assumed that Ireq in the first formula was also a typo and used the value for Ireg or 0.005mA

This is another classic case of technical people making for poor manual writers - it would have been really nice of the authors of this document to have taken the trouble to clearly define all the terms in their equations to make it easier for novices like me!

Anyway thanks for taking the trouble to show your workings out - I feel a great deal more confident in using other transistors and knowing how to do it properly.

 

[d123]

Hi,

It took me ages to understand that formula (because I'm not gifted with these things), also asking on a forum, and besides that, this was the only other explanation I found at the time: Understanding 78XX high current voltage regulator

If you ever have to get round to the bypass and short-circuit transistor version (figure 14), that is also easy to understand (takes a bit of trial and error to implement satisfactorily) once you get your head around it.

After having another go at formula 2...

Io = 0.2A + (100 * (0.2 - (0.6/3.333)))
Io = 0.2A + (100 * (0.2 - 0.18))
Io = 0.2A + (100 * 0.02)
Io = 0.2A + 2 (A)
Io = 2.2A

...phew, formula 1 and formula 2 give the same result! (give or take a few mA if done with a calculator)

I agree with your point about manual writing, but this happens with everything - software manuals or planting peppermint seeds to DIY furniture manuals, steps are skipped a beginner/newbie will not know, but nor is it the writer's fault - they can't be clairvoyant and have to assume a mimimum of knowledge in a given area. What's "bad" is when the basic formula includes somewhat more complicated terms in them that need to be discovered then calculated first and you can't proceed before doing so

If this is also for the Tesla thing circuit, it would be great to see it finished when you get there, looks interesting.

 

[boylesg]

Hi,

It took me ages to understand that formula (because I'm not gifted with these things), also asking on a forum, and besides that, this was the only other explanation I found at the time: Understanding 78XX high current voltage regulator

If you ever have to get round to the bypass and short-circuit transistor version (figure 14), that is also easy to understand (takes a bit of trial and error to implement satisfactorily) once you get your head around it.

After having another go at formula 2...

Io = 0.2A + (100 * (0.2 - (0.6/3.333)))
Io = 0.2A + (100 * (0.2 - 0.18))
Io = 0.2A + (100 * 0.02)
Io = 0.2A + 2 (A)
Io = 2.2A

...phew, formula 1 and formula 2 give the same result! (give or take a few mA if done with a calculator)

I agree with your point about manual writing, but this happens with everything - software manuals or planting peppermint seeds to DIY furniture manuals, steps are skipped a beginner/newbie will not know, but nor is it the writer's fault - they can't be clairvoyant and have to assume a mimimum of knowledge in a given area. What's "bad" is when the basic formula includes somewhat more complicated terms in them that need to be discovered then calculated first and you can't proceed before doing so

If this is also for the Tesla thing circuit, it would be great to see it finished when you get there, looks interesting.

I did have it working until I tried to run my TC4422s at 20V assuming this was the safe limit.....until FvM pointed out that the safe limit is actually 18V.

This is another confusing aspect of datasheets - the main tables of absolute maximums does not always correspond to what the voltage you can run the device at.

To my way of thinking the max voltage that should appear in the table of maximums for TC4422 should be 18V not 20V.

I have made a high current LM317 based power source set at 17.5V to run my GDT at rather than 12V.....to make sure the FET gates turn on an off as quickly and completely as possible.

Theoretically it should give my Tesla coil a bit more power.

Here is a video of a discharge I got from it before I fried my TC4422s:

https://www.facebook.com/video.php?v=1385525361508160

Just waiting on some replacement TC4422s

- - - Updated - - -

I agree with your point about manual writing, but this happens with everything - software manuals or planting peppermint seeds to DIY furniture manuals, steps are skipped a beginner/newbie will not know, but nor is it the writer's fault - they can't be clairvoyant and have to assume a minimum of knowledge in a given area. What's "bad" is when the basic formula includes somewhat more complicated terms in them that need to be discovered then calculated first and you can't proceed before doing so

Especially many Asians who also can't write good English on top of not being able to write a good manual! Very frustrating at times.

I don't really agree with the bit about minimum knowledge. If you are going to write a manual for a product that can be used by a wide range of people, beyond engineers etc, then surely you have to assume that the user has no knowledge at all. It requires you to put yourself in the shoes of a non-engineers.

I have had some experience here. My first attempt at a particular manual was dismal, but then I tried to put myself in the shoes of the non-programming testers. With abundant screen shots for nearly every step in a particular procedure the testers were rather impressed with my efforts and were able to carry out the procedure with relative ease.

 

[boylesg]

I reckon technical people tend to think of manual writing as a chore to get over with as soon as possible rather than looking at it as an important part of the total job!

 

[marce]

No technical people are often terrible at writing manuals, there used to be technical authors who could do the job properly but as with everything cut backs etc. mean that they expect engineers to do everything and it does not work, technical authoring, PCB layout and CAD library management are three main areas where the correctly trained people should be doing the job, not engineers doing it as a part time supplement to their primary role.

 

[boylesg]

No technical people are often terrible at writing manuals, there used to be technical authors who could do the job properly but as with everything cut backs etc. mean that they expect engineers to do everything and it does not work, technical authoring, PCB layout and CAD library management are three main areas where the correctly trained people should be doing the job, not engineers doing it as a part time supplement to their primary role.

Well when I was asked to write a manual for loading software onto and Easybet terminal I was employed as a programmer.

But after a s--- first attempt I decided to commit to the task, and I mean really commit, and I managed to do a pretty good job judging by the feedback.
This is another manual I have written and I have received some good feedback on that too:

**broken link removed**

Technical people are capable of writing good manuals but, was with most things in life, the question is really do they want to write a good technical manual.

If the answer is genuinely 'yes' then a good manual will be written.

If the answer is 'no' (it's not my job) then the technical manual will be flawed and incomplete.

 

[d123]

Hi,

Here is a video of a discharge I got from it

Great, thanks for sharing it, that's been fun to watch.

 

[boylesg]

I found this excellent high current linear voltage regulator circuit:

Very simple and allows you to use NPN transistors only - 3A plus NPNs are far more common on tv circuit boards etc so I have a heap of them to choose from.

I also learned something new about large cap in rush current the hard way - that the in rush current can exceed 1.5A and kill a small linear voltage regulator. I smoked two of my LM317s before I finally realised what was killing them. I should have put the large cap on the transistor output of the above circuit anyway, after I added the transistors, rather than on the LM317 output.

With a Gate Drive Transformer running at between 200 and 300kHz and the only thing consuming current from my laptop power supply through my LM317 circuit, am I likely to need a large cap on the transistor output of the LM317 circuit?

 

[c_mitra]

I found this excellent high current linear voltage regulator circuit:

It is very difficult to ensure that the three pass transistors will share their loads equally. Like in real life, one will decide sometime that it is not my job!

It is better to use one bigger one but load sharing can be improved by putting small resistors...

 

[boylesg]

If all have base current flowing into them then how is it that one won't conduct?

- - - Updated - - -

If all have base current flowing into them then how is it that one won't conduct?

Never mind....I read this: https://electronics.stackexchange.com/questions/77045/transistors-in-parallel

What value resistor would you suggest? I found this also: https://www.homemade-circuits.com/2011/11/transistor-facts.html- good enough rule of thumb in your view?

[h=4]How to Calculate the Emitter Current Limiting Resistor[/h]
It is actually very simple, and could be calculated using Ohm's Law:

R = V/I,

Where V is the supply voltage used in the circuit, and "I" could be 70% of the transistor's maximum current handling capacity.

For example let's say if you used 2N3055 for the BJT, since the max current handling capacity of the device is around 15 amps, 70% of this would be around 10.5V.

Therefore, assuming the V= 12V, then

R = 12/10.5 = 1.14 Ohmshttps://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/bjt-quirks/

 

[c_mitra]

Never mind....I read this:["https://www.allaboutcircuits.com/textbook/semiconductors/chpt-4/bjt-quirks/"]

Right. You just need to lift the emitter leg by about 0.3-0.5V.

 

[boylesg]

Right. You just need to lift the emitter leg by about 0.3-0.5V.

I put the value at 6.8 -> 8.2 ohms for a 3A max transistor. Does that sound about right before I go and solder them in?