Is my 5V to 16V Boost Conveter Schemactic alright?  - Page 1
Forum section: electronics / projects

author: EdimarDigital
author_rank: Contributor
timestamp: January 27, 2017, 03:21:29 pm
content: Hello EEVblog, the best electronics hobbyists community there is. I'm designing and building a replica of the ChronodeVFDhttp://www.johngineer.com/blog/?p=1595so i can impress the girls at my school. I'm only 17 years old and i have pretty good experience with electronics but i have never built a circuit from scratch with SMD parts and custom PCB's so I'm learning left and right. In this forum i have posted several of my schematics so professionals can take a look at it and give me a green light so i can go ahead and order the parts. Anyways, the VFD display that my clock is gonna use is the IVL2-7/5 which requires at least 14 volts on it's segment and grid pins to light up bright, i myself already ordered a pair to play with and now i know how to use them. Picture of my success below:I already have a 1.5V to 5V boost converter in work to power the micro-controller and my 5V to 16V boost converter will power the (MAX6920) VFD Driverhttps://datasheets.maximintegrated.com/en/ds/MAX6920.pdfthat will control and feed the IVL2-7/5. I selected a Texas Instruments TPS61080http://www.ti.com/lit/ds/symlink/tps61080.pdfand followed the datasheet to create a schematic. Before i go ahead and waste my mom's money on ordering, i wanna make sure my circuit is alright, wired correctly, has the right components and is ready to go. Help will be vastly appreciated!

author: Zero999
author_rank: Super Contributor
timestamp: January 27, 2017, 08:38:14 pm
content: Are you planning to cascade the boost converters i.e. power the 5V:16V converter from the 1.5V:5V converter?

author: EdimarDigital
author_rank: Contributor
timestamp: January 27, 2017, 09:22:02 pm
content: Yes indeed!

author: georges80
author_rank: Frequent Contributor
timestamp: January 28, 2017, 12:08:12 am
content: Layout of a high speed DC:DC switcher can be quite critical to success, so I'd suggest you post up your proposed layout.cheers,george.

author: Buriedcode
author_rank: Super Contributor
timestamp: January 28, 2017, 01:42:20 am
content: I suspect the reason Hero999 asked if you were cascading them was because, 5v boost converters powered by 1.5V generally do not have much output current. If you're drawing say 40mA from the 16V, thats 16V x 0.04A = 640mW. If the converter has 80% eff. (typical, could be higher), then it will draw.. 640mW/0.8 = 800mW. At 5V that is 0.8W/5V = 160mA.Say the same efficiency for the first boost, then that will draw.... 800mW/0.8 = 1Watt. From the 1.5V battery thats 1W/1.5V = 666mA - quite a lot of current.A microcontroller can draw anywhere from microamps to~10mA, so I'm sure any 1.5 - 5V boost would be fine with that, but add in the current draw from the other boost converter, possibly any LED's etc.. and it can add up to the point where the first boost just cannot output that current.Not to say it won't work! Just that it is always good to get an idea of the current draw of the system and making sure things cope with it. Whilst rough calculations are handy, best to measure the current draw on the 16V line, and the 5V going into the boost so you have real numbers to work with.I'll also second the request for a layout. That's an SMD IC so I'm sure you're making a PCB for this (wise) because even with low power switching converters, you want to keep paths short, and the whole circuit in a small area to minimize current loops.

author: EdimarDigital
author_rank: Contributor
timestamp: January 28, 2017, 02:25:10 am
content: Your arguments made me look this from a whole new perspective, sadly i still haven't gotten around designing the PCB but i will keep in mind your points. Thanks!

author: DaJMasta
author_rank: Super Contributor
timestamp: January 28, 2017, 03:38:49 am
content: In that same vein, since the layout is so critical to performance, there is very often a sample layout or some considerations given in the datasheet and you can often get at least reasonable success by just doing what it says. In the case of the TPS61080, there indeed is one.It's worth noting that there are boost converters that will get you 16V directly from your 1.5V input. It's a way around taxing the 5V converter too much if there aren't other design concerns that demand it boosting from the 5V rail.

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2017, 11:43:03 pm
content: Quote from: Buriedcode on January 28, 2017, 01:42:20 amYes, that's it. I was also implying that it would be better to use a separate 1.5V to 16V converter because it's more efficient than cascading two DC:DC converters.