12V voltage converter supplied from a LiIo Cell - Page 1
Forum section: electronics / beginners

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 01, 2015, 09:51:33 pm
content: Hello Folks!I would like to generate a 12V output at 30mA from a 3V-4.2V input.This is what i would like to power with that:http://www.opengeiger.de/index_en.htmlIt is a pin diode based radiation detector, ever since i found that site i wanted to build one.There are quite a few DCDC converters ICs available but they are a bit out of my league.During my search i came across charge pumps but all the ones that have a 12V output require a input voltage above 4.5V.I guess the only option is a DCDC converter, but the routing, inductor and diode selection to get a stable and clean output is a bit out of my league i think.I could buy a pre made DCDC-Module but i would like to build/route the whole circuit myself.What would be your recommendation?Greetings,Peter

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: February 01, 2015, 10:07:00 pm
content: you need a boost for sure, check texas instrument webbench , it will generate a bom for you in 5 minute

author: Seekonk
author_rank: Super Contributor
timestamp: February 01, 2015, 11:09:12 pm
content: Why such a low input voltage? The UNO takes 5V. It is easy to take one of the PWM outputs and boost the voltage. I have a sensor that takes 20V @ 6ma and that is what I will be doing. If you are dead set on using a 3-4V battery, this discussion is ended.

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 02, 2015, 12:10:44 am
content: Thanks for your replyQuote from: hamdi.tn on February 01, 2015, 10:07:00 pmYea, that is not the problemThe thing is, i have to get the components. That is not that easy.I either pay through the nose for shipping and handling or i am stuck with what i am sold locally.

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 02, 2015, 12:13:15 am
content: Quote from: Seekonk on February 01, 2015, 11:09:12 pmSweetie... you better look up what "discussion" means.You clearly have no clue

author: Skimask
author_rank: Super Contributor
timestamp: February 02, 2015, 02:18:58 am
content: Sweetie?All right there honey bunches....

author: Rick Law
author_rank: Super Contributor
timestamp: February 02, 2015, 05:49:26 am
content: Quote from: PeterFW on February 01, 2015, 09:51:33 pmWhy not just buy one of the pre-made LM2577 booster from eBay, $1 to $2 dollars.If you insist on making one and found the LM2577 a bit too difficult, try the MC34063 based boost.If you have an old CLA (cigarette lighter Adapter plug for cars) phone charger that you don't need, chances are, you will find one of those 34063 running it in buck mode. It has all the parts you need to convert to boost - except a capacitor or two and a resistor or two or a trimpot. You may even be able to do it on the same PCB. Cut a few traces, rewire it a bit (see the 34063 datasheet), swap the fixed voltage divider feedback sense to use a trimpot, and you are off and running with an adjustable boost.Typically, the output capacitor will be too low since it likely bucks 12V down to 5V, so you would likely find a low (10V-ish) rated output capacitor. You need to change that to at least 16V. Swapping the input and output capacitor in your case would work. The original input capacitor should be at least 16V. You wont get the cleanest of power, and most efficient of boost, but it should work.Check the 34063 datasheet, you will see the traces to cut and modify is not that many. If all you need is just 30mA, 34063 works rather nicely.Good luck, and have fun. I made a few doing exactly that, and it was fun.

author: Seekonk
author_rank: Super Contributor
timestamp: February 02, 2015, 02:08:52 pm
content: Some people are just enamored with using a single low voltage battery. Then they have to jump through all kinds of hoops to just use that battery. A pwm output of a UNO can easily be used with an input choke of an old switching power supply to form a boost converter. No exotic parts needed, cheap and dirty. Guess it is a generational thing. If I was any older I would be clinging to tube voltages. For me Lipo batteries are free and two of them just give me more operating time.

author: Rick Law
author_rank: Super Contributor
timestamp: February 02, 2015, 07:27:51 pm
content: Quote from: Seekonk on February 02, 2015, 02:08:52 pmI think it may be a simple issue of convenience.Trouble with 2S for TTL is: voltage will run from 8V down to about 5V. I can either regulate the extra away and use it to warm up the circuit, or buck it down.Bucking from 8V to 5V is a lot more efficient than boosting from 3V to 5V, but I have to deal with balancing the charge. If I run it with 2P and boost, I can charge the 2P like a single cell... Well, now that I am boosting, in lower current draw situations, why not just single so I can charge one while using the other...Ah, this reminds me about the MC34063 based boost. Unlike the LM2577 that can go down to about 2.6V in, the MC34063 likes higher input voltage and will cut out a lot sooner than 2.6V. That is why I peronally do not use the MC34063 for single cell boosting.

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 03, 2015, 12:24:11 am
content: Quote from: Rick Law on February 02, 2015, 07:27:51 pmConvenience, maybe.All my logic runs at 3.3V for now, maybe i will lower that to 3V at some point.That means those chips will release the magic blue smoke at 5V.The microcontroller would use 50% more power if i run it at 5V.A LDO will perform just fine with a single LiIo cell.5V chargers are everywere in my house, cables too.A single MCP73833 costs under 1€ and will work just fine with a 5V cellphone charger.I do not need a extra charge plug on the unit, only the mini-usb plug that is annyway used to get the data from the unit.And so much more...

author: PeterFW
author_rank: Frequent Contributor
timestamp: February 03, 2015, 12:31:19 am
content: Thanks for your reply!Quote from: Rick Law on February 02, 2015, 05:49:26 amBoth of those are rather power hungry, id like to run the whole thing for extendet periods with a microcontroller to get long term readings.And id like everything on a single neat board ;^^After a days search i routed a small board with a TPS61041 with hopefully the right components after a long study of the datasheet.

author: lgbeno
author_rank: Frequent Contributor
timestamp: February 03, 2015, 03:03:54 am
content: Don't be scarred, you did the right thing and just went ahead and layed out the boost converter.It's really not that bad and I don't understand why everyone makes it sound impossible. Just get you hands dirty and try, what is the worst that could happen?I've also have good luck with Semtech SC4503. It's only 5pins, easy to route pretty fool proof.