LT1083/84/85 linear regulator family: what's the output voltage range?
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 25th July 2007, 03:57 AM #1 jarthel   diyAudio Member   Join Date: Jan 2002 Location: somewhere in Australia LT1083/84/85 linear regulator family: what's the output voltage range? I have the datasheet in front of me. BUT I cannot find the output voltage range for these chips. All I see is input-output voltage differential which is 30V. I look at the net and no luck there. Thank you.
 25th July 2007, 04:11 AM #2 gootee   diyAudio Member   Join Date: Nov 2006 Location: Indiana So, as long as the i/o differential is <= 30v, and the i/o differential is > the max dropout voltage, which is around 1.5V IIRC, then they'll work. As it is with all three-terminal regulators that I am familiar with, strictly speaking, there is no other limitation of the absolute output voltage range. For example, if you wanted to float the whole circuit at around 2000 volts, then the input and output voltages could be at around 2000 volts, as long as V_in - V_out <= 30V, always. - Tom Gootee http://www.fullnet.com/~tomg/index.html
 25th July 2007, 10:39 AM #3 jarthel   diyAudio Member   Join Date: Jan 2002 Location: somewhere in Australia I somewhat believe that is wrong (i.e. no limit on output voltage). I have looked at the datasheet of lm317 and lt1086. LT1086 (also from linear) has a max input voltage of 30V. so output voltage range is definitely 30V - dropout voltage. LM317 is around 30+ V and the HV version I think goes up to 40+ (fairchild's equivalent is 50+ V)
 25th July 2007, 12:02 PM #4 jan.didden   diyAudio Member     Join Date: May 2002 Location: The great city of Turnhout, BE Tom is right. If you put in 100V and set it for output of 80V you're OK. But that means you either need an adjustable reg like the 317 series, or use a non-adjustable and then put the ref voltage on the "ground" pin (which then is no longer at ground, of course). Check the data sheet for the LM317 for applications examples for floating regs. If you use a non-adjustable with the ref pin grounded, yes then you are stuck within Vin max. Jan Didden __________________ Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
jarthel
diyAudio Member

Join Date: Jan 2002
Location: somewhere in Australia
Quote:
 Originally posted by janneman Tom is right. If you put in 100V and set it for output of 80V you're OK. But that means you either need an adjustable reg like the 317 series, or use a non-adjustable and then put the ref voltage on the "ground" pin (which then is no longer at ground, of course). Check the data sheet for the LM317 for applications examples for floating regs. If you use a non-adjustable with the ref pin grounded, yes then you are stuck within Vin max. Jan Didden
I'm just confused that the datasheet would specify an output voltage range and you're saying there's really no limit?

in this datasheet (http://cache.national.com/ds/LM/LM117.pdf - 1st sentence), it is clearly said the max output voltage is 37V.

sorry to be a pain but I'm really confused.

thank you.

 25th July 2007, 11:48 PM #6 BWRX   diyAudio Moderator Emeritus     Join Date: Jan 2005 Location: Pennsylvania It says "The LM117 series of adjustable 3-terminal positive voltage regulators is capable of supplying in excess of 1.5A over a 1.2V to 37V output range." That does not imply that the maximum output voltage is 37V. You can float the regulator at a much higher voltage as long as the input to output differential is under 40V and it can handle the power dissipation. __________________ Brian
 26th July 2007, 02:53 PM #7 jarthel   diyAudio Member   Join Date: Jan 2002 Location: somewhere in Australia thank you all for the help

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