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Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => The Newcomer's Forum => Topic started by: Zappacat on August 27, 2009, 12:39:09 PM

Title: LM317 3 terminal adjustable regulator datasheet info question
Post by: Zappacat on August 27, 2009, 12:39:09 PM
The following is an excerpt of the LM317 datasheet:

Output Current    500, 1500, 1000 mA
Input Min Voltage    4.2 Volt
Input Max Voltage    40, 37 Volt
Adjustable Output    Yes
On/Off Pin    No
Error Flag    No
Temperature Min    -40, 0 deg C
Temperature Max    125 deg C
RegType    Linear Regulator

What do the 40, 37 volt input max voltage figures mean?  Why are there 2 figures?  Thanks in advance.
Title: Re: LM317 3 terminal adjustable regulator datasheet info question
Post by: teemuk on August 27, 2009, 01:41:24 PM
According to datasheet, 40V is the recommended maximum voltage potential that can exist between input and output pins of the regulator.

Since there's some voltage drop over the regulator ("dropout V") too the maximum output voltage is naturally limited by this voltage drop. Furthermore, there's always a certain voltage potential that must exist between output and reference pins. I think these two summed together make up about 3V.
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