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Old 1st February 2006, 08:54 AM   #1
jlm is offline jlm  France
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Default Lm317

Hello,

Would you have a schematic to use and protect one lm317 with 60 V in input and 40V to output (Vin-Vout = 20V) ?

Thank you

Regards

jlm
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Old 1st February 2006, 09:04 AM   #2
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If you check the datasheet, then the option for floating the regulator is well documented.
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Old 1st February 2006, 03:43 PM   #3
jlm is offline jlm  France
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Pinkmouse,

Would you have this datasheet?
None of mine makes reference to this.

Thank you

jlm
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Old 2nd February 2006, 03:52 PM   #4
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I believe he refers to the 'tracking regulator' which uses 2x LM317. However, you might find something like the 'high voltage difference regulated PSU' on my website www.readresearch.co.uk suits your needs nicely with the appropriate zener and feed resistor
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Old 2nd February 2006, 04:00 PM   #5
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Quote:
Originally posted by jlm
Pinkmouse,

Would you have this datasheet?
None of mine makes reference to this.

Thank you

jlm
The max condition is only the max voltage _across_ in and out.

You can have 135 volts in and 107.5 Volts out if you want to.
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Old 2nd February 2006, 04:08 PM   #6
Eva is offline Eva  Spain
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I don't know whether the LM317 has that feature, but its major cousin the LM338 just folds back as the current limit is reduced to almost zero when it's exposed to more than 37V. I've had several LM338 exposed to up to 56V without damage, they only enter some kind of latched-off state and power has to be removed in order for them to work again.

As far as I know, the datasheet doesn't mention this behaviour at all. Also, damage would probably happen as soon as the voltage across the shutted-down regulator exceeds the Vce rating of any of its internal transistors (that is likely to be between 60V and 100V), so this undocumented feature should be used with care.
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Old 2nd February 2006, 04:30 PM   #7
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Hi,

HV-Regulator from Maida with Lm317:
http://www.national.com/an/LB/LB-47.pdf
or
http://www.linear.com/pc/downloadDoc...C3,P1243,D4099

or like Morgan Jones:
http://www.diyaudio.com/forums/attac...amp=1078186659


Carsten
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Old 2nd February 2006, 05:44 PM   #8
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Quote:
Originally posted by Eva
I don't know whether the LM317 has that feature, but its major cousin the LM338 just folds back as the current limit is reduced to almost zero when it's exposed to more than 37V. I've had several LM338 exposed to up to 56V without damage, they only enter some kind of latched-off state and power has to be removed in order for them to work again.

As far as I know, the datasheet doesn't mention this behaviour at all. Also, damage would probably happen as soon as the voltage across the shutted-down regulator exceeds the Vce rating of any of its internal transistors (that is likely to be between 60V and 100V), so this undocumented feature should be used with care.
Indeed, and upon power up when the caps on the output of the device are short for a brief time, the full supply voltage can appear across the regulator. It might not like that very much.
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Old 2nd February 2006, 07:24 PM   #9
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Quote:
Originally posted by Eva
Also, damage would probably happen as soon as the voltage across the shutted-down regulator exceeds the Vce rating of any of its internal transistors (that is likely to be between 60V and 100V), so this undocumented feature should be used with care.
In normal use it will work but to really protect it I'll guess you must add more parts.
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Old 2nd February 2006, 07:31 PM   #10
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Quote:
Originally posted by carawu
Hi,

HV-Regulator from Maida with Lm317:
http://www.national.com/an/LB/LB-47.pdf
or
http://www.linear.com/pc/downloadDoc...C3,P1243,D4099

or like Morgan Jones:
http://www.diyaudio.com/forums/attac...amp=1078186659

Carsten
While that's good information, it's actually bad for this case. If the max input is 60V you can just buy an LM317HV and it is rated to withstand a dead short. Doesn't make sense to build those big circuits for a 60V input.
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