Simplest DC/DC converter ? - Page 1
Forum section: electronics / beginners

author: netdudeuk
author_rank: Frequent Contributor
timestamp: December 06, 2013, 08:19:29 am
content: HiWhat's the simplest/cheapest way to get 12.5 volts from 5 volts for an EPROM programmer ? My own-design ATMEGA-based solution been working fine for EEPROMs but now I'd like to program 2764s and 27128s so need the relevant VPP.I've seen some chips that do it but they're pretty expensive. I may as well just buy a new programmer off eBay.I've read up and it seems that an inductor-based solution could be what I need but I've not found the ideal schematic.Any ideas please ?Thanks

author: johansen
author_rank: Super Contributor
timestamp: December 06, 2013, 08:41:32 am
content: http://www.romanblack.com/smps/smps.htm

author: mtdoc
author_rank: Super Contributor
timestamp: December 06, 2013, 08:44:59 am
content: From 5 to 12.5 V? Perhapsthis?

author: FrankBuss
author_rank: Unknown
timestamp: December 06, 2013, 09:22:12 am
content: Looks like the programming voltage needs only 100 uA for EPROMs, which means you could use just a simple voltage multiplier.Maybe with 4 steps to make something below 20 V and then a LM317 to regulate it down to 12.5 V (three steps would not work, because it would not result it 15 V because of the diodes, and the LM317 needs some headroom). Cost for four steps: a handful of diodes (5 cent for one 1N4148), capacitors (1 cent for one 100 nF), resistors (0.8 cent each) and a LM317 (40 cent). If the microcontroller can't provide sufficient power, you might need to add a transistor as well.

author: sync
author_rank: Frequent Contributor
timestamp: December 06, 2013, 01:03:46 pm
content: Quote from: netdudeuk on December 06, 2013, 08:19:29 amAre there any reasons not to use 28Cxxx EEPROMs instead?Quote from: FrankBuss on December 06, 2013, 09:22:12 amThis 27C64 need 30mAhttp://pdf.datasheetcatalog.com/datasheets/105/489501_DS.pdf.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 06, 2013, 01:27:48 pm
content: There are some very cheap white LED drivers that can be used to make simple step-ups e.g. AP5724

author: FrankBuss
author_rank: Unknown
timestamp: December 06, 2013, 01:31:36 pm
content: QuoteYou are right. I read a similar datasheet, but misinterpreted table 6, Ipp program current 100 uA, but the condition for this is Vpp=Vcc=5 V. The right value is in table 8, Ipp 30 mA for Vpp=12.5 V and Vcc=6 V. But this means an additional 6 V voltage source is required, too.I would use a boost converter for it. TI has a nice web application which designs the schematic for you:http://www.ti.com/lsds/ti/analog/webench/power.pagePlaying with it results in the LMR62014 as a cheap solution for the 12.5 V (1.46 EUR at Digikey). If you don't need high efficiency, you could use an additional LM317 to create the 6 V from the 12.5 V.

author: fcb
author_rank: Super Contributor
timestamp: December 06, 2013, 03:00:41 pm
content: Assuming you aren't doing 1000's of EPROMS and need it quick/dirty, why not a 9v alkaline battery or wall-wart ontop of the 5V rail and a voltage regulator like a LM1117 or LP2951. Perhaps even an LDO 12v regulator with a diode in the 0V bit.

author: sync
author_rank: Frequent Contributor
timestamp: December 06, 2013, 03:08:38 pm
content: Quote from: FrankBuss on December 06, 2013, 01:31:36 pmYes, programming EPROMs is cumbersome. I would simply use a 28Cxxx EEPROM. Needs only 5V. Problem solved.

author: netdudeuk
author_rank: Frequent Contributor
timestamp: December 07, 2013, 12:15:03 am
content: Thanks for all the replies guys. Some interesting ideas and links.I'm actually using a AT28C64B-15PU at this moment. This is what I'm programming with my DIY programmer. It works ok but when it's in the host system, it sometimes gets corrupted. I guess that this is due to default states on some of the pins. I've also got several more on their way to me.I was going to use the EPROMs because one, I've got them and two, because I've ordered an eraserInteresting about needing 6 volts as I didn't need that when I originally programmed them about twenty years ago. Back then, I loaded the hand assembled code into the chips using three 8 way DIP switches, some 12.5 volt source that I forget and a lot of patience. It can't have been too bad with only 5 volts VCC given that I'm still able to dump out the ROMs.Not having an eraser back them and a limited number of chips, I took advantage of the fact that erased EPROMS start with 0xFFs and that the Z80 NOP instruction is 0x00. Every time that I needed to update the code, I just inserted an even bigger block of NOPs at the start of the code and recalculated all the addresses.I've seen those TL866 and TOP853 programmers on eBay but it would have been ok, for my more limited needs, just to program the EPROMs using more or less what I've got already. I suppose I could also work out what's causing the EEPROMs to get corrupted.

author: sync
author_rank: Frequent Contributor
timestamp: December 07, 2013, 01:37:35 pm
content: Quote from: netdudeuk on December 07, 2013, 12:15:03 amYou can lock the AT28C64B against unwanted writes. See the datasheet.QuoteDifferent EPROMs use different programming settings. Even the same model from different manufactures. You must look at the datasheet of the exactly model and manufacture.

author: SeanB
author_rank: Super Contributor
timestamp: December 07, 2013, 01:58:28 pm
content: Programming with switches means your write cycle time was long enough to guarantee a write. The higher voltage step is for fast programming, otherwise you just program with a standard 200ms pulse for each byte. Means a 1M unit will take a hour or three instead of under 3 minutes.

author: c4757p
author_rank: Super Contributor
timestamp: December 07, 2013, 02:00:44 pm
content: Quote from: johansen on December 06, 2013, 08:41:32 amThat's a clever little circuit. It's basically a CFP/Sziklai pair with a buck converter inserted between the two transistors.Hmm... he has buck, boost and inverting. I may have to see if I can adapt it to an isolated flyback and complete the collection...(Sorry for the somewhat OT)