5V, 12V and 14V EEPROM programming

[banedon]

Hi guys

I'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 : 16-18V
Connected 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 LM7815
Connect a LM805 to the output of the LM7812

This 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 > 5V

Am I right? 

[singapol]

You should know that 78xx regulators need 3 volts headroom. That is for a 7815 input voltage
should 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 have
multi-tapped transformer or a 9-0-9 and use the half for 7805.

[thunderbolt87]

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!

[thunderbolt87]

Silicon Chip magazine published an EPROM programmer Nov 2002. http://archive.siliconchip.com.au/cms/A_30475/article.html

Thanks 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 fetish 
I'd rather have a CPLD+FT245 two-chip solution. Or just a single USB microcontroller with LUFA/VUSB.

They used a voltage doubler and LM317 to generate the programming voltage.

It 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 vintage 
http://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/