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Old 16th September 2013, 04:44 PM   #51
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+ some nice and simple current limit and soft start circuits can be found from the LM317 data sheets...
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Old 16th September 2013, 05:43 PM   #52
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Originally Posted by sextaafondo View Post
I guess only at start up Osvaldo. There would be no threat if a soft start circuit is implemented or high current pass transistors are used.
I agree 100 %.

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Originally Posted by sextaafondo View Post
IMO if you don't implement a high capacitor value after the regulator, this (the reg) will be handling the amplifier load at signal frequency level, meaning that there might be sonic worsening if the regulator stage can not cope with transients, and certainly won't. Check out the regulator freq. response to demand transients.
A high value capacitor (bank) after the regulator will both handle the load transients and smooth out the demand to the regulator stage.

So I have to agree with palstanturhin regarding big capacitor banks (before and after the regulator stage).
Capacitor bank before the regulator is a must as you mentioned and per the datasheet recommendation but the capacitance after the regulator is usually implemented on the amp board closest to the chip supply pins did i get that right?
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Old 16th September 2013, 05:47 PM   #53
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Originally Posted by sextaafondo View Post
Each regulator has a minimum stated output current to run stable. If the chipamp at idle is not draining enough as to reach this value additional means have to be implemented to ensure this minimum current requirement is fulfilled.

Regarding the LM337 that would be used here I could not find the minimum output current requirement in the spec sheet, so might be no special one, but I assume wise to implement some current draw per rail in the order of 50mA, again, if the chip amp does not already have a significant drain at idle (which I don't know).
The idle regulator output current draw is already there in the schematic above (the resistor at the output) but thank you very much for your input.
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Old 16th September 2013, 06:03 PM   #54
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I never used a linear regulator for a power stage in amplifiers, I did using switching regulators (Fly Bach one), but in normal applications, I never use more than 47F or 100F at the output of the regulator.
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Old 16th September 2013, 07:16 PM   #55
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I agree 100 %.



Capacitor bank before the regulator is a must as you mentioned and per the datasheet recommendation but the capacitance after the regulator is usually implemented on the amp board closest to the chip supply pins did i get that right?
My suggestion is you add something in the order of 10000uf/rail after the regulator, on the board, or closest as posible to it will be OK.
The logic behind this is that the amplifier will feed from this capacitor bank instead of doing it straight from the regulator's output. This will efectively lower its output impedance quite a lot as you don't need to rely solely in the regulator/pass transistor freq. response lowering this requirement, thus improving the power supply transient available power. The sound will be amaizing.
If you notice any ill effect by implementing this capacitance value after the regulator please report back.
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Old 16th September 2013, 07:24 PM   #56
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The idle regulator output current draw is already there in the schematic above (the resistor at the output) but thank you very much for your input.
If you don't drain enough current through R1/R2 then add another resistor from Vout to gnd for a total 50ma drain to prevent any unstable behaviour.
You may install this resistor/s at the amplifier rail/s input to gnd
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Old 25th September 2013, 12:48 AM   #57
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hi guys,
i am thinking of using two lm317 regulators instead of the lm317/lm337 combination something like "Carlosfm regulated power supply", now if the input from the transformer is 48 VAC after the bridge it'll be 48*1.41-1.41= 66 VDC, can the regulator handle that amount? i know that input/output differential is 40v but if that so what is the recommended value of R2 (the variable resistor at the adjust pin)? and is it possible to use this one "Bourns 3296" or is it too small regarding wattage?

Also do you think a fixed resistor in series (or parallel) with the variable resistor is better?

Thanks for your help.
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Old 25th September 2013, 01:19 AM   #58
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If you may or may not use a bourns 3296 will depend on the value you choose for R1. Given you select a value that prevents R2 overloading then you shouldn't have any trouble using it.
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Old 25th September 2013, 01:35 AM   #59
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If you may or may not use a bourns 3296 will depend on the value you choose for R1. Given you select a value that prevents R2 overloading then you shouldn't have any trouble using it.
R1 is 120 Ohm 1/2 Watt resistor.

something to add to the miss ...Where does a zener diode comes into play? before the regulator to step down the input voltage a little or as reference to the regulator itself?
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Old 25th September 2013, 02:28 AM   #60
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You don't need to implement a zener but you need to keep the input/output difference below 40V.
If you can't do this you may want to switch to another regulator like the 723 and make it float.
I guess you may float the 317 as well but there are already positive and negative floating circuits for the 723 from TI that will make your life easier.

Check out the LM317 application hints. That will help a lot.

http://www.ti.com/lit/ds/symlink/lm117.pdf

LM723

http://www.ti.com/lit/ds/symlink/lm723.pdf
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