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Old Jan 30, 2013, 12:14 PM
RC beginner
New York
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Originally Posted by phil_g View Post
Ok, arrogant and pretentious. And rude. Further, you seem to take a strange pride in that attitude. Maybe its a culture thing.
culture? i got sh!tloads 'a culture!

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Originally Posted by phil_g View Post
Did it occur to you that some of us teach the stuff you've been learning?
"Those who can do, do; those who can't, teach".

sorry that WAS rude. as part time ta (that dont stand for what some of you are thinking) i should show more respect. imagine having me as a student though. count your blessings.
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Old Jan 30, 2013, 12:20 PM
RC beginner
New York
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Originally Posted by jakestew View Post


So what is the logical dispute against Dave's theory that the load bearing reg heats faster causing the resistance to increase and thus decrease it's current load?
.
hi jake,

but thats not my theory. i never said anything like that and makes no sense. sound like something a guy who recommends homemeade copper tips for soldering and thinks resistive dividers make good regulators for high current. fortunately theres nobody around here like that.

want any milk duds with that popcorn?
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Old Jan 30, 2013, 03:04 PM
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Staffs, UK
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Originally Posted by dave1993 View Post
i should bring up another point that maybe hasnt been discussed much here. did you know that most escs actually have a row or two of linear regulators on the back? and they are ALL wired in parallel. rarely with any "equalizing" resistors. i kid you not.
Yep. Did you know that many modern voltage reg ICs now have what you call "equalizing" resistors built in ? Even some of those marketed as 78XX replacements ?

It's almost as though the manufacturers had noticed that people weren't bright enough to follow instructions and decided to save them from the results of their own foolishness .

Steve
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Old Jan 30, 2013, 03:25 PM
RC beginner
New York
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or maybe they are parametric rejects due to process failure and they decided to re-market with "built-in equalizing resistor". in my own experience any added resistance at all did little more than reduce current capability. and little benefit in reliability either.

one thing cheapo chinese controllers might have that help level things off at lower drain is the parts are from same batch and bandgap probably varies little.
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Old Jan 30, 2013, 05:47 PM
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United States, ID
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Sounds to me like nobody here really knows the answer and would rather continue the argument endlessly rather than risk a pair of regulators to find out and settle the issue once and for all.

Makes for some good drama at least.
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Old Jan 31, 2013, 01:37 AM
Stuart
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Originally Posted by jakestew View Post
Sounds to me like nobody here really knows the answer and would rather continue the argument endlessly rather than risk a pair of regulators to find out and settle the issue once and for all.
Probably because it would not prove a lot.

So one pair of regulators from a particular batch from a particular manufacturer do work in parallel. Can you then say the same applies to all regulators ?

Prudent design means following manufactures advice, if they advise against paralleling of regulators ...............

Linear changed the architecture\design of some of thier regulators specifically to allow paralleling, was that not necessary maybe ?
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Old Jan 31, 2013, 04:54 AM
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United Kingdom, Oxford
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Here's one that Linear says you can parallel providing you insert 15mOhm current sharing resistors in the outputs but it has a specification that goes up to 7.5A which means you probably wouldn't want to.

http://www.linear.com/docs/3741

I haven't read the entire datasheet so there may some "gotchas" in there, but isn't that what we've been discussing here.

A.
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Old Jan 31, 2013, 05:06 AM
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Originally Posted by AndyOne View Post
Here's one that Linear says you can parallel providing you insert 15mOhm current sharing resistors in the outputs but it has a specification that goes up to 7.5A which means you probably wouldn't want to.

http://www.linear.com/docs/3741

I haven't read the entire datasheet so there may some "gotchas" in there, but isn't that what we've been discussing here.

A.
I used ic linear AMS1084, It is very vey hot
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Old Jan 31, 2013, 11:26 AM
Oxford Panic
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There's no getting away from heat dissipation with a linear regulator (or any number in parallel), that's why it's best to use a switching regulator for high current.

A.
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Old Jan 31, 2013, 12:16 PM
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there are some applications where a linear can be far more efficient than switching. also switchers are noisy and usually cost more so i only consider them as a last resort..

please note my tests were done with venerable 7805/lm340 5v. however i suspect the same principles apply to other types and its safe to parallel any of them. imo mfg spec sheets, even if they did recommend against (which, apparently, they dont), might only be a consideration in mission critical or life support apps where liability is an issue. not the case here anyway.
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Old Jan 31, 2013, 01:45 PM
Stuart
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Originally Posted by dave1993 View Post
might only be a consideration in mission critical or life support apps where liability is an issue
If its perfectly safe it obviously would not be a concern in mission critical or life support apps or where liability is an issue.

Its safe and or recommended or its not, which is it ?
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Old Jan 31, 2013, 02:56 PM
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New York
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Originally Posted by srnet View Post
Its safe and or recommended or its not, which is it ?
yes. its safe and or recommended or its not.
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Old Feb 03, 2013, 04:46 AM
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Polska, Zachodniopomorskie, Szczecin
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Little different question:
I'm about to build kind of Zagi mainboard (connections between rx, vid tx, servos, camera, 2 dividers for frsky & bec for servos).

As I don't want regular radiator on the vreg I came to conclusion to use LM2940 together pass transistor (tip42C).
Additionally 200ohm transistor with jumper in paraller to switch between 5/6v.
Up to 0.6A power wasted is about 2W per IC - should be fine without radiator, and little aluminium plate should make 1A safe.

Can you find anything wrong with this solution? (except caps - as I need to adjust them..)
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Old Feb 03, 2013, 05:40 AM
Stuart
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UK, Cardiff
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[QUOTE=xader;24018421Can you find anything wrong with this solution?[/QUOTE]

The circuit diagram does not relate to your description, different pass transistor, different regulator.
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Old Feb 03, 2013, 07:35 AM
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Originally Posted by srnet View Post
The circuit diagram does not relate to your description, different pass transistor, different regulator.
Yes - I cannot find LTSPICE models for LM2940 or TIP42C, thus I've used somehow similiar models - I'll try it next week on breadboard if i'll get ic's. But preffer get opinions earlier especially that I'm just starting having fun with electronics.

Attached schema without correct caps yet. (need to find ones with appropriate esr and adjust position)
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