Using LM317 With LED Lighting

gagoon

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Hi guys!

I'm designing a LED lighting with LM317(RF:http://www.kynix.com/Detail/799868/LM317.html),and I have a problem trying to adjust the LM317 voltage with a digital pot (MCP41050, 50K). I have placed the pot in parallel with a 3,3K(R2) resistor and this makes me adjust the resistance from 3095ohm to about 270ohm+- (measured). The R1 resistor is 220 ohm. After what i have calculated, this will give me a range from bout 20V to 2.80V.

The problem is that I'm just able to adjust it from 2.80V to bout 7.00V.

Can anyone give me some pointers on what I'm doing wrong here?
 

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