Arduino Forum

Using Arduino => General Electronics => Topic started by: Burntpizza on Dec 06, 2014, 08:28 pm

Title: Zener diodes - Over voltage I/O circuit
Post by: Burntpizza on Dec 06, 2014, 08:28 pm
Hi,

I'm a self taught enthusiast and am trying to ensure that 5v always occurs  as an output of a circuit.
 

If I built the attached circuit would applying say 6v on v1 or v2 result in 5v on the opposite end?

Also do zeners require a load like LEDs?

Thanks
 :)



Title: Re: Zener diodes - Over voltage I/O circuit
Post by: zoomkat on Dec 06, 2014, 08:35 pm
Quote
Also do zeners require a load like LEDs?
Zeners require a certain level of current to regulate properly at their design voltage.
Title: Re: Zener diodes - Over voltage I/O circuit
Post by: jremington on Dec 06, 2014, 08:37 pm
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c1
Title: Re: Zener diodes - Over voltage I/O circuit
Post by: Burntpizza on Dec 06, 2014, 08:52 pm
I'll rephrase...do zeners burn out or  short out without a load?

The circuit posted has a resistor to provide a load for 1 diode depending on what side the voltage is applied. (in my interpretation)
Title: Re: Zener diodes - Over voltage I/O circuit
Post by: Grumpy_Mike on Dec 06, 2014, 09:08 pm
You need a resistor to prevent too much current being drawn by a zener yes.
That circuit is bad because the zener at the end you apply the voltage will burn out. You only need the one diode not both. These two links review protection.

http://www.thebox.myzen.co.uk/Tutorial/Protection.html (http://www.thebox.myzen.co.uk/Tutorial/Protection.html)

http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html (http://www.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html)
Title: Re: Zener diodes - Over voltage I/O circuit
Post by: Burntpizza on Dec 06, 2014, 09:14 pm
Awesome Thank You!
Title: Re: Zener diodes - Over voltage I/O circuit
Post by: TomGeorge on Dec 07, 2014, 08:46 am
Hi, if you just want to clamp the input signal, then remove the left hand zener.
Also check what the current will be through the 220R resisitor when you have your over volt condition.
Then calculate the power dissipation in the resistor to make sure you fit one that will not fail due to overload.

Tom...... :)