Cheap negative LDO regulator with enable pin.... - Page 1
Forum section: electronics / projects

author: Smokey
author_rank: Super Contributor
timestamp: April 08, 2015, 01:58:22 am
content: I'm looking for a cheap negative LDO regulator that has an enable pin. Preferably something second sourced. I need -15V output from around -22V input. Fixed -15V or adjustable down to that is fine. Something like the negative equivalent of the 2951 would be perfect. The 2951 is super cheap and multiple sourced but I can't find it's negative mate!http://www.digikey.com/product-detail/en/LP2951CMX/LP2951CMXFSCT-ND/1626231The cheapest one I found so far is the LT1964, but it's $3.15 in 1s. Unfortunately I need 4 of them per board.http://www.digikey.com/product-detail/en/LT1964ES5-SD%23TRPBF/LT1964ES5-SD%23TRPBFCT-ND/4694475Anyone know of something cheaper that meets the -15V output and has an enable pin (and second sourced would be nice)?

author: kjs
author_rank: Regular Contributor
timestamp: April 08, 2015, 03:18:50 am
content: That's a constant struggle! I have a similar issue as I need an adjustable one to generate -4V. Very few options and none are cheap....... Looks like negative voltages aren't popular any moreI am using an LM337 (SOT223) now. Not the perfect solution but better than no solution and half the price of the 1964. However, no enable pin....

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: April 08, 2015, 06:00:49 am
content: How much current?

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 08, 2015, 06:32:01 am
content: Time to design your own from an opamp, a N channel MOSFET, and some passives?

author: Marco
author_rank: Super Contributor
timestamp: April 08, 2015, 07:16:58 am
content: With the headroom he has he could use a shunt regulator like the TL431 to drive a PNP darlington ... the problem is you don't get protection circuitry that way.

author: wraper
author_rank: Unknown
timestamp: April 08, 2015, 11:24:00 am
content: As you need 4 of them, it could be feasible to use cheap 79L15 and just disconnect the power with a mosfet for all of them.

author: Smokey
author_rank: Super Contributor
timestamp: April 08, 2015, 04:44:55 pm
content: Thanks for the feedback. Good questions, and sorry for not including some of the details... It's always a struggle of how much detail to include in the first post. It's like a google search, start board and then narrow it down based on the results...Current is around 50mA actual draw, so a 100mA reg is probably needed.They all need to be isolated, so I can't group them.Also, like always, I'm space limited so making a discrete solution is probably out.Looks like I'm stuck with 10 dollars of negative voltage regulators. Sucks.

author: Marco
author_rank: Super Contributor
timestamp: April 08, 2015, 05:26:09 pm
content: Discrete needs 3 SC70s and 4 passives, it's not going to be huge.

author: Smokey
author_rank: Super Contributor
timestamp: April 08, 2015, 07:43:01 pm
content: Quote from: Marco on April 08, 2015, 05:26:09 pmBigger than an SOT23 and a cap?

author: Marco
author_rank: Super Contributor
timestamp: April 08, 2015, 08:04:05 pm
content: Sure, it's bigger ... unless you get dies

author: tszaboo
author_rank: Super Contributor
timestamp: April 08, 2015, 08:29:02 pm
content: TPS7A30, four bucks, no second source. Dont expect to have one with enable. Otherwise 7915 and a carefully selected digital BJT transistor.