LM317 Output Voltage Drops When Input Is Lowered—R1=240Ω, R2=1800Ω, Why?

Respected sir:

It should be grateful that spending your time in my post. I’m so glad to be here to show my project to you and now I need your help.

The following circuit is designed to convert 15V into 10V by using LM317. When the circuit board didn’t be finished ,R1=240 while R2=1800 .It’s normal. However,when all of them was wielded. The input and output are wrong.In the beginning,it can input 15V by using adjustable direct current and the current arrived 700mA.

Next,I adjusted it again,but now the input can just be adjusted to 12V while the output is 7V.

I am confusing about that what's wrong? How to solve it?

Your help will be appreciated.

From the formula, the more the value of resistor R2 increases, the greater the voltage output. I don't know why your input has lowered to just 12 volts. That should be fixed since its DC.

Review LM317 voltage regulators "here('')":http://www.learningaboutelectronics.com/Articles/LM317-voltage-regulator

Hi ling ling,
lm 317 ic has an internal drop of 3v so 15-3=12v you are on the brim side since the variation in the line voltage can effect your in put voltage so for safer side you must
increase your in put voltage min 18 or 21v you have to provide a good heat sink
for Lm 317 T to my practical experience it is safer to draw not more than 900 ma current fr lm317 that to with heat sink .

pl check my attachment and modify your circuit as per my circuit and review my rating

Good Luck.