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Topic: Zener Diode not Zenering at all ;-( ... (Read 2 times) previous topic - next topic

DROBNJAK

#5
Jan 05, 2013, 04:02 pm Last Edit: Jan 05, 2013, 04:04 pm by DROBNJAK Reason: 1
OK, but is there a way to just 100% solid limit the voltage to a desired value? So whenever a spike happens, the component just shaves it off clean.

I mean, all the tutorials on the web are talking about Zener diodes regulating voltage. When in reality they are quite loose. On this one that was rated 4.3V, it can go all the way to 5.0V and even higher.

dc42


OK, but is there a way to just 100% solid limit the voltage to a desired value? So whenever a spike happens, the component just shaves it off clean.


Yes, use a silicon diode or Schottky diode between the signal and a power supply with a voltage just below the desired limit voltage, with a capacitor across the supply to absorb the energy. That is how the pin protection diodes work.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

DROBNJAK


Yes, use a silicon diode or Schottky diode between the signal and a power supply with a voltage just below the desired limit voltage, with a capacitor across the supply to absorb the energy. That is how the pin protection diodes work.


Many thanks. I'll try that. I've just tried the above lamp trick on L78M09CV 9.0V Voltage Regulator and it didn't glitch at all. No spikes whatsoever. No wander one always see these things on all the Arduino breakout boards ;-). So that's the way to go. Maybe I'll use Zeners for something else.

What is really the real use for Zener diodes, if they are quite loose as voltage regulators?

Grumpy_Mike

Quote
I tried, just now, covering the cables with aluminum foil.

As you have discovered it is a wast of time doing that. Even proper shielded cable doesn't act like you expect.
What is wrong is your expectations and supposed requirements for protection.
There is a balance between low impedance and effective suppression. The better the suppression the higher is the input impedance.
The ultimate is to add a buffer on the front end, rather than just putting a signal into an expensive chip.

DROBNJAK


The ultimate is to add a buffer on the front end, rather than just putting a signal into an expensive chip.


@Grumpy_Mike
Yeah, that was what I thought Zener will do. Sorry for my newbie's ignorance, what would be a good buffer in this case?

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