# Input voltage range for voltage regulator

This regulator is used to obtain a 3V3 output voltage. http://datasheet.elcodis.com/pdf2/78/81/788153/ld1117axx.pdf

What is the acceptable input voltage range for this regulator? I cannot get a clear answer from the datasheet. Would using an DC input of 12V,1.5A be safe? Can someone advise?

If you supply it with 12V, it's going to run pretty hot. (12V - 3.3V) x current draw = watts of power dissipated as heat by the part.

Page 5 shows an Absolute Max of 15V and Power Dissipation 12W. 12W > 8.7V * 1A, so you 'could' run the part at full rated current of 1A IF you had one big-as* properly thermally connected heat sink attached to dissipate 8.7W.

Page 9 shows characteristics with various of Vin: 5.3V, 4.75V to 8V, <10V, Vi - Vo of 5V, and Vi - Vo of 3V.

If you do input 12V, you're outside of what's been characterized.

According to the datasheet you reference, section 5, Vi (input voltage) is spec'd at 10v max. and the dropout voltage (max) is 1.3v at 1A so for 3.3 volts output, the minimum input voltage would be 3.3 + 1.3 = 4.6 volts. Recognize that needs to take into account any dips in the supply due to ripple - if the low point of any ripple falls below 4.6, you are likely to see that start showing up on the output.

gpsmikey:
According to the datasheet you reference, section 5, Vi (input voltage) is spec'd at 10v max. and the dropout voltage (max) is 1.3v at 1A so for 3.3 volts output, the minimum input voltage would be 3.3 + 1.3 = 4.6 volts. Recognize that needs to take into account any dips in the supply due to ripple - if the low point of any ripple falls below 4.6, you are likely to see that start showing up on the output.

The maximum rating is at 15V. Does it mean it is ok to supply DC 12V? Most DC jacks are 12V today.