modified 4 years ago

Please Help - Zener diode Configuration

01:20:38

Somebody told me the top diagram is the correct way, by adding 150ohm resistor leading to LED. Zener should give 5.1V. He said this is how you design correctly using 'blocks', so previous stage doesn't get unwanted side effects. If current is limited by 300ohm resistor anyway, why cant I connect output of Zener direct to LED like in bottom diagram? Why is 150 ohm resistor required? Also, why in bottom diagram zener not working?

published 5 years ago

PrathikP

5 years ago

Now the reason why the zener diode is off (don't say "not working") in the bottom circuit is because the LED, which has a voltage drop of 2V, is in parallel with it. Now I'm sure you know that when two components are placed in parallel, the voltage across them is the same. Since two volts is not enough to turn on the 5.1V zener, it stays off. As for which of the two circuits is correct, if all you want to do is power an LED from a 12V voltage, you can do so with just a series resistor. A zener diode is unnecessary. I hope this helps .

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.