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Old 6th February 2003, 10:07 PM   #21
sam9 is offline sam9  United States
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Sud's comments about a low value resistor and a cap accross the feedback/adj resistors makes sense.
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Old 7th February 2003, 03:14 AM   #22
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Default Re: the resistor before the regulator

Quote:
Originally posted by Christer
I agree with jackinnij, if you need to go near or above the limits
of what a 317 can handle, don't use it, but do you own regulator.

You might find the following handbook from On Semi helpful,
even though it is about IC regulators, it will teach you some
of the basic theory of voltage regulators.
http://www.onsemi.com/pub/Collateral/HB206-D.PDF

Quote:
Originally posted by jackinnj
is current sense for the regulator and pass transistor combo -- as the current drawn increases (and the voltage drop across the transistor increases) it reduces the amount of work which the regulator has to perform and shifts this function to the transistor.

if you tie two LM317's together as described you can get some nice oscillations -- in fact, getting an LM317 to oscillate isn't difficult at all. At any rate, it's using a more expnesive part to do a less expensive job.

well, idont ve that much experience working with discrete components so ican build my own regulator , thats why i started
to use the common LM317 reg. , ican substitute it with a more
current handling one like the LM150 ,LM138...etc. when they are
available in here..

can u explain more the oscillation prob.?! anyway to eleminate it ? i find it gonna be more easy if ican find away to parallel em than to do build the regs. from scratch...

and what about the thermal resistor i asked about before, anyone
has any ideas what it really does..?

sorry for my many ques. but we are almost near the end!!
thanks..
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Old 7th February 2003, 03:59 AM   #23
Sud is offline Sud
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Default Right you are!

Bobken,

Right you are - the bypass cap improves ripple rejection, not line regulation.

deepanger:
The 0.1 Ohm resistor at the output is only needed if you are paralleling the 317's. It is to stop the paralleled regulators from 'fighting' for control of the output voltage.
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Old 7th February 2003, 12:28 PM   #24
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Default Re: Right you are!

Quote:
Originally posted by Sud
Bobken,

Right you are - the bypass cap improves ripple rejection, not line regulation.

deepanger:
The 0.1 Ohm resistor at the output is only needed if you are paralleling the 317's. It is to stop the paralleled regulators from 'fighting' for control of the output voltage.
well, if i paralled the LM3x7 for both + and - rails and placing those 0.1 ohm resis. the schematic will be like this:
am i right??
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Old 8th February 2003, 12:39 AM   #25
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hey good guys..dont leave me in the middle of it!!
ineed someone just to check the previous diagram plz..
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Old 8th February 2003, 09:24 AM   #26
Bobken is offline Bobken  United Kingdom
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Quote:
Originally posted by deepanger
hey good guys..dont leave me in the middle of it!!
ineed someone just to check the previous diagram plz..

Hi,

Unfortunately, it is not clear from your diagram which lead is which, and at a quick look it doesn't seem to be very consistent.

Whatever you intend here, each similar lead from the same polarity device must be attached in an 'identical' way for the two devices to be truly in parallel.

Conventionally, when using a 'box' to indicate a 3 terminal reg,
it is shown with the input at the left side, the output at the right side, and the adjust (or ground for fixed regs) lead at the bottom and in the middle.

If you have used this conventional arrangement in your diagram, it will not be correct, but you show no labels to indicate which is which.

Regards,
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Old 8th February 2003, 12:43 PM   #27
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ithink its more clear now..
what do u think?
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Old 8th February 2003, 01:04 PM   #28
Bobken is offline Bobken  United Kingdom
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Hi,

As I suspected, this is not quite correct.

Bear in mind that the 'adjust' resistor needs to run between the adjust pins and ground.

If the unmarked horizontal line is ground, it looks like with the LM317 that this upper 'adjust' resistor goes between the adjust pin of the upper 317 and the adjust pin of the lower 317, and then the connection goes via ground (if this a *connection* where it crosses the horizontal line?), and/or then on to the 337's adjust pin.

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Old 8th February 2003, 01:29 PM   #29
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Default bench

Bob is right, the top and bottom regulators don't do anything. You need to connect ALL regs as he said: all need to be set up for the correct output voltage independently. Then, for say the pos pair, each output must go via a separate 0.1 Ohm to the final pos output. Same for the neg pair. It really is much simpler than you seem to think.

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Old 8th February 2003, 01:58 PM   #30
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i think its right now!!
"this s for the pos. side only of course"
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