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Topic: Zener diodes - Over voltage I/O circuit (Read 879 times) previous topic - next topic

Burntpizza

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
 :)




zoomkat

Quote
Also do zeners require a load like LEDs?
Zeners require a certain level of current to regulate properly at their design voltage.
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jremington

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html#c1

Burntpizza

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)

Grumpy_Mike

#4
Dec 06, 2014, 09:08 pm Last Edit: Dec 06, 2014, 09:10 pm by Grumpy_Mike
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.digikey.com/us/en/techzone/microcontroller/resources/articles/protecting-inputs-in-digital-electronics.html

Burntpizza


TomGeorge

#6
Dec 07, 2014, 08:46 am Last Edit: Dec 07, 2014, 08:48 am by TomGeorge
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...... :)
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