12V REGULATOR - Page 1
Forum section: electronics / beginners

author: rodrigopires
author_rank: Regular Contributor
timestamp: September 14, 2015, 09:50:42 pm
content: Hi, for my ZVS driver i use a 12V fan, but with inputs as high as 60V i need some regulator. I used a simple LM7812 and it worked up to 30V, but when i put 60V it explodedIs the there an alternative to the LM78XX regulators? Thanks

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: September 14, 2015, 10:17:18 pm
content: Hi rodrigopires,if you look at the datasheet for the 78xx/79xx series (i attached it for you) you will find at page two the absolute maximum ratings for those ICs. they are rated for a maximum of 35 / 40 volts, so that is the reason why you let the magic smoke escapeI actually don't know any linear regulators that work up to 60 volts.To power your 12V fan you can use several ways. The most efficient would be a small switching regulator, but building one as a beginner is not realy the easiest thing. But you can buy them for a reasonable low price from i.e. china. Take a look at ebay and search for buck converter or step down converter.The other thing you could do, if you just want to have a really cheap quick and dirty way to power that fan from 60 volts, would be a voltage divider made out of two high power resistors.I guess you are familiar with ohms law and the voltage divider rules? If you are, you should be able to calculate the needed values for your resistors. You could even put your 7812 right behind that divider to get a better load regulation (respectively any load regulation at all).

author: DimitriP
author_rank: Super Contributor
timestamp: September 14, 2015, 11:13:59 pm
content: Quote from: rodrigopires on September 14, 2015, 09:50:42 pmThere is always the LM317, there are versions with a 60V max input like the LM317HVT/NOPBdigikeyP/N: LM317HVT/NOPB-NDAs for DC-DC converters the list is long and expensive:http://www.digikey.com/product-search/en?pv1525=324&pv1525=113&pv1525=44&FV=fff40042%2Cfff800df%2C8f40010%2C8f40011%2C8f40012%2C8f40021%2C8f40087&k=12V+DC+DC&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

author: Seekonk
author_rank: Super Contributor
timestamp: September 14, 2015, 11:22:59 pm
content: My solar system has a 52V DC bus Most of the 100-240V wall warts work fine at your voltage with reduced power, enough though to power a fan.

author: mariush
author_rank: Super Contributor
timestamp: September 15, 2015, 03:25:11 am
content: Just don't use linear regulators with such high input voltages.Let's say you have a fan rated for 12v @ 0.15A then with 40v input you're regulator will dissipate (40v - 12v ) x 0.15 = 4.2 watts as heat. You'll need a big heatsink which will be constantly hot just for the fan voltage regulator. With up to 52v or whatever, it would be even worse.When you have so high voltage differential, it's best to just go with switching, much higher efficiency, less heat. Buy existing dc-dc converters or build one yourself on a prototyping board, lots of cheap switching regulators available on the market :http://goo.gl/qq2gDd(or this for through hole parts for easy prototyping :http://goo.gl/feX7CC)

author: fivefish
author_rank: Frequent Contributor
timestamp: September 15, 2015, 03:42:26 am
content: or you can use a 24VDC fan, the LM317HVT as someone else mentioned. (60V - 24V = 36V, well within the deltaV of the LM317HVT regulator.) Of course, you'd still be dissipating a lot of heat. You can use (2) LM317HVT in series so you can gradually drop off the voltage and distribute dissipation between 2 regulators. Then might as well use the cooling fan to also cool your 317 heatsinks.