LED’s do have a fairly low breakdown voltage, though I’ve never tried using one as a zener.
How would you use a diode as a zener?
Diodes go POOF when the PIV is exceeded… I’m not getting how you would use one as a zener which has completely different characteristics.
Please explain.
Greg
Nope. You need to limit the current.
As you increase the voltage, current begins to flow when you’re above the PIV. If you increase the battery voltage now, the current will increase, but the voltage across the diode will stay about the same. As long as you don’t overheat the diode, all will be happy. A Zener diode is one designed to be used this way and will have a tight curve at a specific voltage. A non zener diode behaves the same, but the exact voltage will vary from part to part.
You can use a diode this way as a primitive voltage regulator, but only with small and steady loads. Of course, with a capacitor and an opamp, you get a simple but effective linear regulator. Add an output transistor and you have a more powerful linear regulator.
(http://barefootelectronics.com/graphic/zener.gif)
(http://www.electrotechservices.com/electronics/images/diode_graph.jpg)
So how do you know what to limit the current to when you go into piv breakdown?
I’m not looking at a data sheet, is this normally specified?
Greg
Usually not for an LED, since you don’t usually operate LED’s that way. If you want to try it, start with a couple ma and slowly increase till the LED starts getting warm to touch. I’ve always wondered if it would light. Should try it some day.
Tom, not much of an answer… so what you were stating was you could use an ordinary diode as a voltage reference… but no idea how much current… no way to figure it out. (rather than a Zener designed and rated for this)
Wait until you get the LED warm? That cannot be very reliable either.
If you research this, you will see that the doping of the PN junction in a zener is different from a regular diode to handle the current from reverse voltage.
OK, so honestly what was the point? You can use a garbage disposal to grind coffee also, although it won’t work very well. :-p
Any diode will work as a zener. The difference is a zener diode is calibrated and designed that way. I didn’t say an led would make a good zener diode, just that it would have a breakdown voltage.
What would kill it would be watts. Keep it down to a couple ma at whatever breakdown the diode turns out to have, and it would likely work. If you want a voltage reference, buy a zener.
So in this remark, where do you decide you have to argue against using LED’s as zener diodes? You just try to pick fights?
Nope, was asking why you brought it up? “OK, so honestly what was the point?” very clear question in English.
By the way, I’ve endured several snide personal comments from you on this forum, completely unrelated to the topic, so let’s not start about who is picking fights.
Greg
Civility, Gentlemen…