{"id":2209,"date":"2015-03-08T18:44:58","date_gmt":"2015-03-08T18:44:58","guid":{"rendered":"http:\/\/www.richardmudhar.com\/?p=2209"},"modified":"2015-03-09T00:40:16","modified_gmt":"2015-03-09T00:40:16","slug":"the-texas-lp2950-oscillates-as-an-adjustable-regulator","status":"publish","type":"post","link":"https:\/\/www.richardmudhar.com\/blog\/2015\/03\/the-texas-lp2950-oscillates-as-an-adjustable-regulator\/","title":{"rendered":"The Texas LP2950 oscillates as an adjustable regulator"},"content":{"rendered":"

Nowhere in the datasheet <\/a>does Texas tell you “hey use this fixed regulator as an adjustable”. However, I’m used to being being able to do that with the venerable 78XX series – indeed Texas tell you that you can do that with the 78L05 datasheet<\/a> in Fig 14.<\/p>\n

\"Adjustable<\/a>
Adjustable 78l05. Bear in mind the shocking Iq of 3mA that’ll stand you up an extra 3V if resistor R2 is 1k, keep ’em low…<\/figcaption><\/figure>\n

Given that there’s an adjustable variant of the LP2950 that appears on the same datasheet (the LP2951) I laid out a PCB and being the lazy sort I am I assumed that since I was using a load of these parts in their 3.3V KY5033 variant, where I wanted an 8V stabilised voltage for an audio mic amp sourced off a 12V supply I can simply do the LM317 trick, drop in a couple of resistors from the output to ground and the ground pin to real ground, job done.<\/p>\n

\"what<\/a>
what I planned…<\/figcaption><\/figure>\n

For this I made R1 6k8 and R2 10k.I expected an output voltage of 3.3+3.3\/6800*10,000=8.2V or near enough. I screwed up labelling the o\/p 10V, mistakes happen…<\/p>\n

What does that look like then?<\/p>\n