LP2951 with 1A output - Page 1
Forum section: electronics / beginners

author: lk
author_rank: Regular Contributor
timestamp: April 01, 2012, 10:44:49 pm
content: Greetings,I am battling to find a voltage regulator, that can take around 14-15volts on the input, and then drive a PIC microcontroller and its external components(leds,relays,displays), i currently have the LP2950-3.3 for this purpose and that is good and well, but that only handles 100mA, but its does this with less than 100uA quiescent power consumption. Every time i look at a different VR they have a quiescent of 5-10mA (LM317, LM1117 and so on). Then i found the LP2951 that seems to be able to do what i want with only 400uA quiescent current, this would work for me.there is always a but, I'm somewhat price conscious and i cannot find the LP2951-33 for a reasonable price, but the adjustable ones are readily available. So i was wondering if anyone has had any experience with this part.I'm wondering if adjustable part can somehow be made to work, as shown with the 5 volt in this picture? I need 3.3 volt.I'm guessing a resistor between Pin 6 and pin 7 to set the feedback voltage, in relation to the 1Mohm resistor, but i really don't know.and the P-channel fet seems to be of older design, i have not been able to find it anywhere, and i don't really know if it would work, in my setup.If there is a generic part with a quiescent Iq of 1mA that would work as well.Thanks in advanceLK

author: amspire
author_rank: Super Contributor
timestamp: April 02, 2012, 12:01:07 am
content: Use the adjustable circuit from the application notes in the data sheet. Pin 2 is left open, and the feedback pin is used instead.The MOSFET drain connects to the output as in your current diagram.Alternatively the Linear Technology LT3080 would be ideal for you (as long as you have a big enough heatsink), but I don't know if it is too expensive for you.In general, the cost of the heatsink to get rid of 11W can be much more then you might save on device selection.You might want to look at some of the new buck converter switching regulator IC's that switch to a micropower mode at low currents. They are not hard to use and they run cool - no heatsink and no wastage of 11 W of useful power.Richard.

author: lk
author_rank: Regular Contributor
timestamp: April 02, 2012, 08:52:15 am
content: Thank you Richard,sometimes I need someone to pull me out of the one track that i have ended up in, i found these two, and currently the AP34063 looks like the right option for me, i need to study it further, but the icc looks promising, its at least half of what the linear regulators, and heat if less of a problem. And i can get it in a dip-8 package which makes breadboarding much easier.I did notice that regulators quickly get expensive, when you can not get by with the classic ones.ap34063 icc 3.5 ma max 0.76$l4971 icc 3.5 mA max ~4$You mention new buck converters, everything is new to meI found the 555 last year, and was impressed with its possibilities, then to realize that its 1-2 years older than meupdate : Currently i have settled for this digikey part number "497-4280-5-ND" the MC34063E from STmicroelectronics update to the update, i now realize that this is the switchmode regulator dave explains in eevblog #110-lk