Author Topic: Zener voltage clamping  (Read 267 times)

0 Members and 1 Guest are viewing this topic.

Offline tester43

  • Regular Contributor
  • *
  • Posts: 67
  • Country: lu
Zener voltage clamping
« on: July 03, 2018, 07:42:01 am »
Hi again,

So ... here I am adding zener diode 1n4728 as overvoltage protection.
Voltage is AC rectified unfiltered.
To my terrror and shock I found that near zero zener stops at very special value around 0,7-0,8V. I was expecting 0.
Looks like typical p-n diode voltage.
It's very typical circuit: AC transformer output + load (8ohm).
From one end of load goes 680ohm resistor + zener and to GND on rectifier.
Probe is between resistor 680 and zener.
High end is as expected around 3V.
But why low is not ground?
Is it because of minimal required current?

But here is my "poor man scope" picture attached.
« Last Edit: July 03, 2018, 07:44:23 am by tester43 »

Offline tester43

  • Regular Contributor
  • *
  • Posts: 67
  • Country: lu
Re: Zener voltage clamping
« Reply #1 on: July 03, 2018, 07:51:04 am »
I will reply to myself because I am stupid.
Once voltage drops below 3,3 it's not this diode any more.
It's coming form totally different place.
Please feel free to ignore my message.

Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo