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Topic: Zener Diode Protection (Read 7977 times) previous topic - next topic

Paul__B

I would replace the zener/gate resistor for a 100ohm trimpot (gate to wiper).
In the context, that suggestion is an absolute scream!
     :smiley-lol:       :smiley-lol:       :smiley-lol:       :smiley-lol:       :smiley-lol:       :smiley-lol:       :smiley-lol:

Watcher

Paul__B: Do you have any specific part values to suggest for 5V MCU supply protection?

Lavan

Thanks all for your responses.  Good to know about crowbar circuit protection.  Also there was a recommendation to use 7805 instead of LM317, is that means 7805 is short circuit protected?  i.e., even if its failed, there are no chances of input = output?

raschemmel

If you don't exceed the Maximum electrcal specs and you use a heatsink , it will shutdown the output if there is a short on the 5V lines.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

raschemmel

Quote
would replace the zener/gate resistor for a 100ohm trimpot (gate to wiper). 
Quote
In the context, that suggestion is an absolute scream!
@Paul,
Forgive my ignorance but I'm not seeing the humor in this. What is your point ?
Is it that less than 100 ohms might not be enough current limiting for the zener ?
Or is it that there is no need for adjustment in this application ?

Please enlighten me .
 
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Paul__B

Forgive my ignorance but I'm not seeing the humor in this. What is your point?
Whilst regulators can fail of themselves, at least two people agreed with me that the trimpot is the weakest link in the use of a variable regulator, failure of contact of whose slider will necessarily cause over-voltage.

You then suggested a crowbar circuit using - a trimpot!

Just sayin'.

Wawa

Two completely different things.
While adjusting the pot of the voltage regulator, contact bounce can/will spike up the voltage.
While adjusting the crowbar pot, nothing bad will happen.

Zeners come in selected voltages only 3.9volt, 4.7volt, 5.1volt, etc.
Some finetuning could be needed when 5.5volt is ok and 6volt is not.

As suggested, ditch the LM317 use the 7805.
No crowbar circuit needed.
Leo..


raschemmel

Quote
You then suggested a crowbar circuit using - a trimpot!   
You are mistaken

A- The crowbar circuit I linked did NOT have a trimpot
B - I didn't suggest a trimpot

My only post was Reply#11. Read it. Look at the link. No trimpot.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Paul__B

Ah!  Sorry, my apologies - it was of course Wawa who suggested the trimpot, wasn't it?

But you were the one who then queried my derision - slight glitch (sic.) in my reply.

Watcher

Quote
As suggested, ditch the LM317 use the 7805
Why is  7805 preferable in this case instead of  LM317?
Is it just because it is not adjustable, or is there another reason?

raschemmel

#25
Dec 14, 2015, 07:31 am Last Edit: Dec 14, 2015, 07:36 am by raschemmel
I questioned your post because you quoted ME instead of Wawa.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

Wawa

#26
Dec 14, 2015, 08:01 am Last Edit: Dec 14, 2015, 08:11 am by Wawa
Why is  7805 preferable in this case instead of  LM317?
Is it just because it is not adjustable, or is there another reason?
Every Arduino uses a fixed regulator.
Easier to use, less parts that can go wrong.
A micro doesn't care if the voltage is 4.75 or 5.25volt.
Leo..

Lavan

Seems LTC4360 is the robust protector.  Not sure if any of you already used in your projects.  Any comments?

http://www.linear.com/product/LTC4360#overview

raschemmel

Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

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