7805 Voltage source .Should I use a backup Zener?

[april]

Without a good connection to ground, how can the regulator know what the input voltage is? It would be like trying to measure a voltage with your multimeter, with only one probe.

It should be looking at voltage on the input and voltage on the output and ensuring the difference (In minus Out) never goes above its rating... if it does ,cut supply .

Put one probe on one point and the other probe on the other ?
Then build in a resetable cut-off fuse that cuts the supply ?
I'm not an engineer but it seems possible to me

 

[april]

It appears this device is my answer .
DE-SWADJ3 Voltage regulator

Official from the manufacturer , if it looses ground it outputs 0 (zero) Volts

Now why didn't someone tell me that ?
https://www.dimensionengineering.com

 

[picbits]

Now why didn't someone tell me that ?

It's a module - not an off the shelf component. There is no schematic for it so we wouldn't know the exact components inside. If you open it up it will have a circuit board with inductors, capacitors and a switching regulator onboard.

 

[Mike odom]

It appears this device is my answer .
DE-SWADJ3 Voltage regulator

Official from the manufacturer , if it looses ground it outputs 0 (zero) Volts

Now why didn't someone tell me that ?
https://www.dimensionengineering.com

Seems like the 'manufacturer' did... we don't know about this part, er, because in my 30 years of engineering using microprocessors and microcontrollers I have never, never lost a micro to a bad regulator ground... maybe a lightning hit, but never a faulty layout. Of course, I also use 5V snubbers (transient voltage suppressors) at the micro power supply, not for this reason, to eliminate spikes, but it'll do the same thing.

 

[april]

It's a module - not an off the shelf component. There is no schematic for it so we wouldn't know the exact components inside. If you open it up it will have a circuit board with inductors, capacitors and a switching regulator onboard.

So ? Its only slightly larger with the same pinout and will not blow up more expensive components down the line .
The 78L05 is also a circuit board when you look at the datasheet so what , they are all black box components and the 78L05 should be redesigned to give out nothing if it looses ground . They can do it !

$10 each but well worth it if you have a micro further on .

These "I have never blown up a component " posts are just egotistical rubbish . Bet you have but you would not admit it .
And the Manufacturer did not. I emailed them and asked them specifically smartarse.

 

[Frank Nash]

Byte magazine's Steve Ciarcia discusses over voltage protection in his book 'Build your own Z80 computer', chapter 1 pages 17,18&19. It can be read for free at Google Books. I used his OVP crowbar on all my uPC projects.

https://books.google.com/books?id=mVQnFgWzX0AC&printsec=frontcover

 

[april]

Byte magazine's Steve Ciarcia discusses over voltage protection in his book 'Build your own Z80 computer', chapter 1 pages 17,18&19. It can be read for free at Google Books. I used his OVP crowbar on all my uPC projects.

https://books.google.com/books?id=mVQnFgWzX0AC&printsec=frontcover

Thats good stuff . Thank You Didn't know Google let you read anything for free
OVP is simple when you know how isn't it!

I have learned a bit about google books too. How to add to books to read so again thanks you so much Mr Nash .

 

[Mike odom]

oh, I never said I've never blown up a component... quite the opposite, I've smoked my share... they don't call me 'Sparky' for no reason. I had one ic looked like a volcano on top, and so much of the plastic had vaporized you could plainly see the die (no pun intended)... I've left my fingerprints in a few others testing to see if they were getting hot (they were)... I said I never blew up a micro due to poor layout... and never had to buy a $10 module to keep a 25 cent part from blowing up a circuit... a 25 cent part that has so much built in protection I used one one time to keep users from plugging 12V into our 5v output and blowing up our board... I remember when the 7805s first came out... they were a godsend.. they reduced a large power supply/protection circuit down to the size of a single transistor (TO220), now people take them for granted...

and why buy a $10 switcher module when you can build one for less than $2... I have a design that will give a rock solid 5V output with a 3v to 24V input... my old boss designed it... it's a buck/boost design that he came up with before they sold buck/boost converters... I've used it in designs to output 5V, 8V, 12V, and 15V (with a few mods, mostly change the feedback resistors). I don't even know it's rating (I guess I could figure it out if I had the fancy), but I've never overpowered it, and it surely never blew up any of the micros I was using it to power up.... (there he goes saying never again)...

 

[april]

An Additional note here

The L4949 voltage regulator does the same thing
Remarkably using one on a controller for a 72 watt solar panel which out puts up to 80 Volts I was feeding the chip through a 50 volt zenner diode.
This dropped the supply voltage to around the 28 Volts upper limit on its data sheet .
The zenner blew and 70 odd volts hit the supply pin and fried it . The output pin at that time showed the full 70 volts and that fried TTL chips down the line. Ridiculous design in this day and age.

Also a side note ,before this I had wired in the chip separately just playing with it and it was quite stable at 70 Volts on the power pin in continuous and 4.78 out . The data sheet gives a max of 40 V for 2 secs, so it far exceeded that.

Don't get me wrong . I am just noting this behavior here in the likelihood of one of our designers browsing this forum for ideas on what to design and sell next.!

 

[panic mode]

it fried TTL chips? how many?

 

[JoeJester]

it seems this is not a simple 7805 problem. It would be nice to layout the whole idea ... from the solar panels model number to the end plan. That would get you the maximum help.

You could post a block diagram of your project and then discuss and finish each block to do what you intended.

GIGO ... Garbage In = Garbage Out. From what I've read, there was incomplete information being passed so conclusions' were clouded by the communication failure.

 

[crutschow]

The usual (and most reliable) way to protect a load from a failure in a power supply is to use an OVP SCR crowbar circuit at the output with a series fuse between the power supply and the crowbar and load.

 

[april]

it fried TTL chips? how many?

And this is important because? 2 and a bit serves

it seems this is not a simple 7805 problem. It would be nice to layout the whole idea ... from the solar panels model number to the end plan. That would get you the maximum help.
You could post a block diagram of your project and then discuss and finish each block to do what you intended.
GIGO ... Garbage In = Garbage Out. From what I've read, there was incomplete information being passed so conclusions' were clouded by the communication failure.

Can I get some of what u r on?

The usual (and most reliable) way to protect a load from a failure in a power supply is to use an OVP SCR crowbar circuit at the output with a series fuse between the power supply and the crowbar and load.

I'll have a look at that thanks

 

[panic mode]

hello April,

i typed a nice long reply with explanation and example of what you should do, why your last circuit failed and what to pay attention to when selecting or sizing voltage regulators. but after looking at your reply i checked a bit closer on this entire tread and i decided not to post it (at least not yet). if you need help, you need to change your attitude and try to cooperate with people willing to contribute.

wish you luck