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LM317/337 ripple/noise/oscillation
LM317/337 ripple/noise/oscillation
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Old 5th February 2018, 10:18 AM   #41
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by phase View Post
Great subjective results using 100uf 50v (370 milliohm ) electrolytic for the output, approx. .200A load...
please use the leading zero (0) for values less than 1.
It is very easy to not see the leading decimal point when the leading zero is omitted.
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Old 9th February 2018, 07:37 PM   #42
fabrice63 is offline fabrice63  France
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Sure , 200 A in an LM 317 / 337 looks so real , you'r so funny sometimes !!!!

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Old 12th April 2018, 08:26 PM   #43
asuslover is offline asuslover  Romania
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LM317/337 ripple/noise/oscillation
I do have some trouble understanding the lm317/337 datasheet. What is the V in max for them ?

http://www.ti.com/lit/ds/symlink/lm317.pdf

"1 Features
1• Output Voltage Range Adjustable
From 1.25 V to 37 V
• Output Current Greater Than 1.5 A
• Internal Short-Circuit Current Limiting
• Thermal Overload Protection
• Output Safe-Area Compensation"

"9 Power Supply Recommendations
The LM317 is designed to operate from an input voltage supply range between 1.25 V to 37 V greater than the
output voltage. If the device is more than six inches from the input filter capacitors, an input bypass capacitor, 0.1
μF or greater, of any type is needed for stability."

Am I wrong to think that the vin max is 37V max out +37max difference ?
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Old 12th April 2018, 08:35 PM   #44
fabrice63 is offline fabrice63  France
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Top of the page 4 , VI - VO : max 40 v , means that for 37 v out you give it 40 v in

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Old 12th April 2018, 08:52 PM   #45
asuslover is offline asuslover  Romania
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LM317/337 ripple/noise/oscillation
thanks,
Vin -Vout cannot be more than 40V. Great , but if I want to get 37V out why cant I use , lets say 60vIn ? 60v -37=23( less than 40 v)
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Old 12th April 2018, 09:09 PM   #46
FauxFrench is offline FauxFrench  France
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asuslover, you are right. It is the relative voltage on the LM317/LM337 that counts. Max. 40 volt between input and output (and 41.25V between input and the control pin).
Your input voltage may be 200V and your output voltage 170V. The LM317 will not notice the high potential to ground because it is not connected to ground.
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Old 12th April 2018, 09:18 PM   #47
asuslover is offline asuslover  Romania
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LM317/337 ripple/noise/oscillation
Aha!
I am very confused about these infos , but thank you! that's why I like the forum!
Now , I am looking to get 35v /10amps from lm317+ power transistors , is that doable?Ac will be 30v, so 40v dc after rectifiers.
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Old 12th April 2018, 09:31 PM   #48
FauxFrench is offline FauxFrench  France
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It is doable. I will draw you a schematic tomorrow, European time.
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Old 12th April 2018, 09:47 PM   #49
asuslover is offline asuslover  Romania
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LM317/337 ripple/noise/oscillation
thanks a lot!
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Old 13th April 2018, 10:01 AM   #50
FauxFrench is offline FauxFrench  France
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Here are my suggestions (appended).

First schematic: LM317 buffered with a TIP3055 (15A max). No fine regulation of the output so the output may sag about 0.4V from 2A to 10A loading. Simple circuit and no need to adjust a regulation loop.

Second schematic: LM317 buffered with a TIP3055 (15A max) and including a fine regulation loop. More complex and a need to adjust the regulation loop.

Third schematic: The traditional way to buffer a voltage regulator with a PNP-transistor (TIP2955/15A). The problem is to "ẗame" the loop if it oscillates.

Fourth schematic: LM317 for high voltage use with power zener diodes for start-up and shut-down protection.

Now to the more problematic part - your transformer:
When a transformer is loaded much below its capacity, the buffer capacitor(s) "rides" on top of the rectified sine-wave and we get the transformer RMS voltage multiplied with 1.4 (minus the diode voltage drops). The more we approach the nominal loading of the transformer, the more the transformer voltage drops (winding resistance) and the buffer capacitors start having important ripple. At the nominal loading of the transformer, the voltage at the buffer capacitors will be only little above the RMS voltage of the transformer and with important ripple.
The schematics I suggest will require around 3V (input-to-output) for regulation. If you want 35V output, the voltage at the buffer capacitors must not drop below 38V, including ripple.
I doubt a 30V transformer can maintain a rectified voltage above 38V (at any moment) when loaded with 10A. My guess is that you need a transformer with close to 40V RMS and quite some buffer capacitors.
Attached Files
File Type: pdf LM317Use.pdf (9.4 KB, 67 views)

Last edited by FauxFrench; 13th April 2018 at 10:23 AM.
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