Process required to design a dc converter(8A, 0.5V -> 500mA, 5V) - Page 1
Forum section: electronics / beginners

author: ninjastrike
author_rank: Contributor
timestamp: August 06, 2014, 09:20:42 pm
content: Hello,I'm currently building a 60 cell solar panel, and I've got a few cells left over.I'm thinking of building a portable solar charger for my phone/tablet, such that I'll be able to always have a reliable charging option when I'm camping...etc.What kind of circuitry do I need to be looking up ?Each solar cell produces about 4.4W @ 0.5V, 8.8AI need to convert this energy to either 500mA o r 1A @5V DCI'm quite new to electronic/electrical systems so please help.Cheers!

author: filip_cro
author_rank: Regular Contributor
timestamp: August 07, 2014, 01:33:48 pm
content: Can you connect them in series? You should get bigger voltage than that.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2014, 02:11:33 pm
content: If you have enough cells left over to make more than 5 volts, then a simple buck converter or linear regulator should be sufficient.

author: ninjastrike
author_rank: Contributor
timestamp: August 07, 2014, 08:49:37 pm
content: I probably might have to break them up into smaller pieces and connect them in series. I'm not sure if it would bring about an increase in voltage ? Need to do some tests.

author: ninjastrike
author_rank: Contributor
timestamp: August 07, 2014, 09:22:29 pm
content: I've done a bit of research, and have found some sort of IC that would be able to carry out such a task.http://www.linear.com/product/LTC3105Does anyone have any experience with similar devices?

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2014, 04:30:14 am
content: If you can even get the voltage a little bit higher, it will work much better. For that kind of of current level with a step up, look for one that uses an external transistor switch:http://www.linear.com/product/LT1619A discrete startup stage using germanium transistors could be used with any boost converter that will run on 5 volts to start from 0.6 volts.

author: mij59
author_rank: Frequent Contributor
timestamp: August 08, 2014, 05:37:08 am
content: Quote from: ninjastrike on August 07, 2014, 09:22:29 pmYes this is the kind of functionality you want.But as always something is getting in the way of success.The LTC3105 can't handle the high input current, although it could be used as a auxiliary power supply for a high current boost converter .

author: mzzj
author_rank: Super Contributor
timestamp: August 08, 2014, 11:39:50 am
content: Quote from: David Hess on August 08, 2014, 04:30:14 amor use depletion mode mosfets to start practically from zero input. ie LTC3108 starts at 20mV8 amps and 0,5 volts is doable but its not your easiest project. My guess is that it would need auxillary power supply to start a heavy duty transformer coupled half-bridge or push-pull. And not to forget that you would probably also need MPT

author: ninjastrike
author_rank: Contributor
timestamp: August 08, 2014, 03:09:56 pm
content: "The DC2042A is a versatile energy harvesting demo boardthat is capable of accepting piezoelectric, solar, 4mA to20mAloops, thermal-powered energy sources or any highimpedance AC or DC source. The board contains fourindependent circuits consisting of the following EH ICs:"Can anyone explain what "capable of accepting piezoelectric, solar, 4mA to20mAloops" means? Does it mean that the Imax is 40mA?

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2014, 03:17:37 pm
content: Quote from: mzzj on August 08, 2014, 11:39:50 amDepletion mode MOSFETs would be the obvious thing to use but oddly enough I have never seen this done with JFETs which makes me suspect there is an obscure issue with it.

author: ninjastrike
author_rank: Contributor
timestamp: August 08, 2014, 10:35:49 pm
content: Quote from: David Hess on August 08, 2014, 03:17:37 pm|Does this qualify ?http://www.ti.com/lit/ds/symlink/tps61202.pdf

author: David Hess
author_rank: Super Contributor
timestamp: August 08, 2014, 11:37:35 pm
content: Quote from: ninjastrike on August 08, 2014, 10:35:49 pmNo, because it does not include any details about how it works. I assume it uses enhancement mode MOSFETs in some type of sub-threshold charge pump instead of depletion mode devices but that is not going to be possible to replicate in a discrete circuit.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2014, 12:50:39 am
content: I was not even looking for it but found an example using a JFET which works exactly how I was thinking on page 1 of Linear Technology application note 113. It uses a transformer coupled JFET oscillator to start and run from 300 millivolts. A depletion mode MOSFET would work also.

author: ninjastrike
author_rank: Contributor
timestamp: August 11, 2014, 08:26:20 pm
content: Quote from: David Hess on August 11, 2014, 12:50:39 amThanks Dave! I've been looking into it.

author: David Hess
author_rank: Super Contributor
timestamp: August 11, 2014, 08:59:19 pm
content: The idea, which I believe the application note mentions, is to use the low voltage startup circuit to power a more powerful and efficient boost converter which then uses its own output to power itself.

author: ninjastrike
author_rank: Contributor
timestamp: August 15, 2014, 01:27:56 pm
content: I've decided that using just 2 Cells connected in series is much too much work and it would be difficult to source parts for the circuit.What I'm going to do is use a carbite or diamond tipped glass cutter to slice the cells into equal area strips and connect them in series.I've done some tests with some of the broken cells that I have; cells connected in series, even though they are not as large will produce a higher voltage than the 0.5V a 6" x 6" cell produces.I could possibly get around 5V under sunlight.On a side noteI've tabbed 60 cells, waiting on my glass panel and aluminium frame to arrive before i start connecting them into a string to get my 260W solar panel.