5V, 12V and 14V EEPROM programming - Page 1
Forum section: electronics / beginners

author: banedon
author_rank: Regular Contributor
timestamp: September 21, 2015, 06:07:38 pm
content: Hi guysI'm thinking of making an EEPROM programmer using and AVR. In particular I want to write Winbond W27C512-45Z ICs.Looking at the data sheet, it mentions the voltages for nominal operation (the usual 5V), programming (12V) and erase (14V) voltages.I've only created a few projects so far and all of them rely on 5V. As such I have no real experience with obtaining different voltages and the choosing ideal sources.Here's my take:As I don't plan to run this from battery, I assume that the best option for this project is a mains transformer which steps down to 16-18V and then voltage regulators in series.So...Mains transformer output : 16-18VConnected to LM7815 and two diodes to drop that to 13.8V (a little low, but within the EEPROM tolerance) - I cannot seem to find a LM7814.Connect a LM7812 to the output of the LM7815Connect a LM805 to the output of the LM7812This way I should be able limit the amount of wasted power and also limit heat because the regulators are in series and stepping down 16-18 > 15V > 12V > 5VAm I right?

author: singapol
author_rank: Frequent Contributor
timestamp: September 21, 2015, 06:33:57 pm
content: You should know that 78xx regulators need 3 volts headroom. That is for a 7815 input voltageshould be 3V more or 18V. I would prefer to use an adjustable regulator like LM317 to get 14V rather than use 2 diode drop. Then feed all 3 regualtors from 18V sure lots of wasted power unless you havemulti-tapped transformer or a 9-0-9 and use the half for 7805.

author: thunderbolt87
author_rank: Contributor
timestamp: September 22, 2015, 07:57:40 am
content: Hi. I would not worry about heat that much. We're talking 30 mA max. Even if you used a single linear regulator 20V->5V it would dissipate 0.03*15V=0.45 W max.Having multiple regulators spreads the dissipation, so individual devices run even cooler.However, I would encourage you to use a MC34063 or equivalent switching regulator. It is much easier to use than you might think. Especially using an online calculator.Search the net for 34063 online calculator. One result:http://www.nomad.ee/micros/mc34063a/Using this part in step-up mode you can easily convert 5 -> 12/14V as done in several programmers I've seen.Isn't that a nice little project for a beginner?You might be interested in using the ATMEGA32u4 (or Arduino Micro) to build a USB-powered programmer.Have fun!

author: thunderbolt87
author_rank: Contributor
timestamp: September 22, 2015, 01:39:10 pm
content: Quote from: wilfred on September 22, 2015, 10:24:26 amThanks for the link. There are couple interesting design decisions.Personally, I am a fan of compact solutions and this one is for those hwo have a 74xx descrete gate fetishI'd rather have a CPLD+FT245 two-chip solution. Or just a single USB microcontroller with LUFA/VUSB.Quote from: wilfred on September 22, 2015, 10:24:26 amIt does the business if you only have to double the voltage. Wouldn't probably use it to up the voltage x6 for 5V -> 30V.Having one transistor to adjust the regulator between programming/erasing voltages (12V or 14V) is elegant.Would even look exactly the same for the DC-DC step-up case.Thanks, Dave for these two episodes on the topic. Smells like 2010 vintagehttp://www.eevblog.com/2010/05/29/eevblog-90-linear-and-ldo-regulators-and-switch-mode-power-supply-tutorial/http://www.eevblog.com/2010/09/10/eevblog-110-lets-design-a-dc-to-dc-switchmode-converter/