Using 5.1V Zener Diodes in Place of 5V for Serial Microwire EEPROM Programmer

So, I am trying to build a serial microwire EEPROM programmer following a schematic I found online, and it shows using 3x 5V Zener Diodes. Problem is, I cannot find any through-hole 5V Zener Diodes anywhere. So my question is then, can I replace them with 5.1V?

A picture of the schematic is here: "Your text to link here...(http://img294.imageshack.us/img294/728/programmer.jpg)":http://img294.imageshack.us/img294/728/programmer.jpg

Yes, almost all eeproms are rated up to 5.5v.

It is possible.
Chips with a power 5 V usually the power and voltage inputs max 5.5 V.
For example, for the SerialEEPROM 24C64 see into the screenshot from the datasheet.

It is a good idea to know how to locate information for yourself, check up the data sheet to determine the maximum input voltage to the pins. It is good practice to get into this routine. Other than that it will most likely work. I was considering the same function for a different application and it was going to work OK.

The schematic shows 5V1, which is 5.1V.
Even if it was specified as 5V, there is no problem in using 5.1V in this case. In fact as Boi has said most EEPROMs are rated up to 5.5V, you could use any Zener Diode from 5V up to 5.5V.

The function of the diodes are simply to short to ground anything greater than 5.1V. It's a safety mechanism to protect the EEPROM. The 5.1V is actually the reverse breakdown voltage, once the voltage is exceeded, the zener diode will behave as if it was forward biased and current will flow to ground.

One consideration, though. The purpose of the zeners is to convert any higher voltages (up to 12V) on the RS232 lines, to "5V".

Using 5.1V zeners may result in voltages that exceed the max input voltage of the eeprom. Typically, the maximum input voltage is speced as something like: VDD + 0.3V and zener voltages can vary quite a bit between parts (e.g. TZX5V1 has a max zener voltage of 5.3V)

If the LM2936Z-5 outputs 4.95V, and the CS, CLK, DI and/or DO lines are at 5.3V, then you've exceeded your input max! And even if not exceeded, there may be forward bias currents that may put too much of a load on the RS232 line (which is being used to power this device).

I suggest using 4.7V zeners [but pay attention the the EEPROMs minimimum input high voltage spec].

And do as Malcolm suggested. Check the data sheets for the following:

*EEPROM datasheet:*
* Max input voltage
* Min input high voltage

*Zener datasheet:*
* Max zener voltage
* Min zener voltage (if using a 4.7V zener--and compare to EEPROM min input high voltage))

*LM2936Z-5 datasheet:*
* Minimum output voltage [always design to the extremes]

Also, pay attention to temperature effects and compensate where needed.

And then do the math.

BTW: don't confuse the absolute maximum supply voltage spec (the "5.5V" that Boi is refering to) with the max input voltage spec, which is typically determined by the supply voltage.

If you really want to play ultra safe what you do is write your data to pic micro for example using a serial port implementing max232 for received Rs232 to convert data to ttl levels Push this into a 16/8 bit buffer and then write this out using I2C protocol to the memory device that way you protect both the serial port and the memory chip You can always do subsequent read back from the memory device if you need to verify your data

Why you ask the long way round ? Reason .... fault condition .... 5v1 goes short circuit and takes the serial port down on the mother board

Thats is why ( expensive if you make a mistake ) same as the power supply derivative I see on your diagram ( Not very clever ) When initiating small tasks like this bear in mind Yes its cheap and does the job but , what people don’t think about is what if this fails or that enters fault mode and subsequent damage to connecting or connected equipments ( Dte's or Dce's)

It can lead to far greater misery and suffering than expected example Imagine doing this to a business computer in a workshop environment In certain instances it could cost or lose an entire business especially these days I notice and cant help but notice that an awful lot of people are buying Pc’s from the likes of PC World with no backup or backed up to the same drive and no operating system disks you name it (Our so called professionals who are concerned about data integrity etc ) and you will laugh at this as well because this actually true

In fact they don’t even bother to tell the consumers this when they buy ( another disgusting little trick which of course the comsumer doesent notice untll.... they have to reformat the drive for what ever reason ... normally too late by then )

Its the legal implications of some of this "They sue you if you damage their machines its that simple now "

Facts are not to many people know an awfull lot about thier own pcs nevermind the sofwtare or hardware or for that matter backup

Rule of thumb you should always buffer a port especially on a PC if you intend to read write from that port That’s why we have dedicated interfaces to the outside world

Little slower perhaps but you would at least guarantee data integrity

But to all intensive purposes 5v1 is sufficient to do what you need but be warned "One mistake may not even be down to you and that’s the risk you take "

They are that clever as well and they will deliberatley try to set you up just like this

Old saying wheres theres blame theres a claim

Last but not least Its easy to transfer a virus , backdoor trojan via memory 8 bit 16 bit or otherwise

I cant tell you the number of bussinesses Ive seen go down the pan just like this On a network this becomes an even bigger problem

I can look up information myself; I just know so little about the function of each component in this circuit to know what to look up (I am ME still in school, so I've essentially only worked with 12V on my car). There is a lot of good info replied here.

So, again, I'm an ME so basically the entire first paragraph you have there doesn't make a lot of sense to me.
Also, I don't own a computer with a physical serial port anymore, I will be using a USB to Serial adapter. I don't know if that would fry if the faults you talk about happen.
Lastly, the only thing I am doing here is swapping a gauge cluster in my car, and I just need to reprogram the mileage so it is correct to my car. There is absolutely no impact if a virus somehow got onto the IC.

It is definitely useful information though, don't get me wrong.

This is really good information, I will look at this closer later tonight or this weekend.

Just one more consideration, it may not be avoidable but zeners essentially short and draw max current through the device. If at all possible make sure the majority of your logic level is zero, and at the same time find a zener that can supply minimal current and increase the resistor as much as possible.

Now-a-days it is essential to create as low a power logic as possible. Good practice that is all.

Hi Isaac,

Mark has a tendency to "rant" so take what he says with a grain of salt

Not sure how a shorted zener is going to "draw max current through the device" in this circuit. On the serial port side, there is a 4k7 resistor that will limit the current, and on the 93CX6 side, those are all inputs, so little or no current will be drawn there.

For some clarification: The instructions for building the circuit actual just say "5V," and I had no idea the 5V1 meant 5.1V lol. That is good to know.

Yes, you'll see that a lot. For instance, 4K7 means 4.7 kΩ

Okay, so I think I found the correct datasheet for my IC, which is actually a 93C56PI (there were some differences in the different model years). Anyways, so I want to make sure I am reading it correctly. I am having a hard time reading it, actually. I have found Absolute Maximums, but noting about minimum input voltage so far. For reference, it is a DIP Package Chip:
"http://www.ic-on-line.cn/view_online.php?id=1773610&file=0388cat93c57pi-18rev-e_3885861.pdf(http://www.ic-on-line.cn/view_online.php?id=1773610&file=0388cat93c57pi-18rev-e_3885861.pdf)":http://www.ic-on-line.cn/view_online.php?id=1773610&file=0388cat93c57pi-18rev-e_3885861.pdf

Also, the only *_THROUGH HOLE_* LM2936Z-5 available on Digikey has a several week lead time. I was wondering what a suitable replacement would be for this system?

Thanks.

"but noting about minimum input voltage so far."

It's the VIH1 and VIH2 rows. The input voltage (in your application) can go as low as 2V and still be interpreted as a "High". Also, the input voltage can go as high as 1V over VCC with no damage. It doesn't state, however, what input voltages above VCC do to the input leakage current.

Have no ideas on a through-hole replacement.

Sorry Malcolm, my mistake. After looking at the datasheet, I realized that DO is an output, so in that case, a shorted zener would probably destroy the chip if DO went high for more than a second.

Its not the device you worry about Steve Its the load on the serial port of the mother board The supply rails and finally the processor Steve which saves and writes the data to the chip your trying to write to in the first place

That’s what I’m on about , not angry, not trying to be insulting trying to show people how to do this the right way round Saves money at the end the day you know , creates better standards , yes have to take more time ,agree , yes slower Agree , yes also more expensive , agree but i tell you what it creates more jobs at the end of the day than cheap cheap cheap cheap cheap and better class of people

"I agree I do rant and rave only because i don’t want to see people make a mistakes , be taken advantage of , suffer unbelievable hardship, all through wanting to do something quickly " , not being taught how to do this the correct way ]

This happens all to often in the Uk eventually it costs people their lives also starts wars

Normally Its business in trouble or no funds available " I guess I’m ranting again " I cant keep quiet about this , " Then its staff under pressure , cheap labour , shoddy workmanship , more mistakes , more mistakes , more job losses and whose made any money "

No one !!!

All that’s has happened is job needs to be done twice, three times over when little more time , careful attention , planning could have saved all of this and peoples jobs , homes , businesses plus someone is actually taught how to do something the right way round for change leading to a far brighter far better, far more professional business , and someone who actually knows what they are talking about

What would rather have Choice is yours lies or someone who tells you the truth which one Steve ??

I guess I already know what my expectations are I’d tens times have someone who tells the truth may not like it ,but at least i know where I stand with that person and last but not least I can trust them


Thats where too money doesent count in my book its what you have up top that does meaning the brains and the skill to get a job done doesent matter if your slow at least i know you will do it properly and if you make a mistake no worries we sit down and we work it out we help each other to do better in life not lead them on

EG collin and his 555 timers and dont advertise that wont get you work niether will someone who tells you that this circuit is a ok when really its not !!

Up to you i guess depends what standards you want

Also depend on if you want cowboys If you want cowboys watch John Wayne and be as gun ho as you want unfortunately professionals take a little longer and they need paying professional wages on time then you get professional results and also professional jobs and finally professional economies with long standing businesses that don’t fold over night

PROVIDING YEARS OF EMPLOYMENT TURNING OUT MORE PROFFESIONAL PEOPLE with quality goods and professional attitudes unlike some of the other attitudes Ive seen and experienced to date Big difference !! Like chalk and cheese
The difference between quality, quantity and solitary

I think I’ve made my point Steve no offence pal I do actually think quite highly of your answers

This is what I call a growing proffesional steve

http://www.eeweb.com/project/dilshan_jayakody/usb-base-custom-hardware-interface-for-unity3d

Have a look and read it thats an up and comming pro thats what you look after and help to flourish

This is another pro
www.dreamsound.co.uk

His organsitation and methods are pro Thats what i admire nothing less nothing more Big mouths huge cars and money dont impress me at all never will seen to many of those types of people thankyou They dont last long never do

Like music Wrap rock soul and classics Some will go in for etrenity and be rembered for eternity some wont and never will

Wrap is bar far the worst, sorry Queen how ever will go on for years to come as to will elvis, heart , even Kates bush which ive never seen " just as well " Oh yes and Eltons John nearly forgot !! someone flush the chain quickly

Never mind not to worry

Its down to taste and maturity Like a good wine , fine wisky takes a few good years and lots of practice

Its what they have upstairs and the pride in themselves and thier jobs that impress me That all starts with getting it right from the start with proffesional atttidues top down approach

meaning steve if they cant get it right upstairs you cant expect downstairs to ever get it right

I was considering more about the current draw from the serial interface. a Zener on the output would be tragic if the output came higher than the 5.1V . Anyway a 4K7 is good enough to limit the serial data but reducing it further if possible would provide a better overall power performance. This is not critical though. The other factor would be any stray capacitance that might stuff up the data transitions so there would be a final resistor value to consider both areas.

Not sure what the rant was about below (shrug)

Precise 5V Zener.