How to use zener diode as a regulator

[catalyst]

Hi everyone,

I made a circuit as a classic Led strip. But the zener diode that i used it, if or not it regulates the circuit, i'm not sure. Do i need to use a resistor that between inductor and d3 ? Because when I increase the voltage to 24V, zener diode explodes. Normally does it need to feed the circuit with 18V?

[Vtile]

Zeners do need a current limiting resistor (or active circuit) to work as meant. They can be thought of an voltage generator in the nominal current region (zener current).

You can look basic examples ie. from here:
http://www.electronics-tutorials.ws/diode/diode_7.html

In attached picture you can see the Zener "created" voltage and current relation. I turned the electronics-tutorial picture 90degrees, so it might be more expressive.

[danadak]

These might be useful -


http://www.americanradiohistory.com/Archive-Bookshelf/Author-Groups/Rufus-Turner/Diode-Circuits-Handbook-Rufus-Turner.pdf


http://www.rsp-italy.it/Electronics/Databooks/Semicond/_contents/Motorola%20-%20TVS%20Zener%20device%20data%20-%20dl150rev1.pdf


Regards, Dana.

[rdl]

Zener diodes don't make the greatest of voltage regulators. If the input voltage and load current are fairly steady they are okay, but if not it's better to use a three terminal device.

[tszaboo]

If you drive LEDs, then dont make a voltage source, then current limit it with a resistor. Make a current source.

[bd139]

Exactly that.

here's the circuit I use for this stuff. It's not a great current source but it works for driving LEDs over a reasonable range of voltages.

As it's a current source, you can just stack any number of LEDs in series as long as the combined drop is less than VIN - 1v (ish). the 1.5K resistor should be changed for other voltage ranges to maintain about 10mA through the diodes at the lowest expected voltage. BD139 transistor or even smaller ones do the job most of the time



If you want to drive it from an AC source (read isolation transformer), add a rectifier diode and reasonable electrolytic capacitor. You can omit the capacitor if you like 50/60Hz flicker.

You can omit the 1.5K resistor, 2x 1n4148 diodes if you use a MOSFET but picking the resistor value is difficult because it depends on each individual device.

[Belrmar]

i would recommend o use the zener with a series current limiter resistor and feed the output to an unity gain negative feedback opamp , if you want to drive higher currents you will need to feed the output to a power transistor or even an darlignton if needed, there are a lot of exapmles around and i would recommend you to watch Daves series on power supplies

[Zero999]

I'd use the TL431.

https://electronics.stackexchange.com/questions/107699/tl431-constant-current-source

[bd139]

Good solution   

[catalyst]

Thanks a lot for everyone,

Zener diode in this circuit, what does it do? Should I delete this?

[Zero999]

Thanks a lot for everyone,

Zener diode in this circuit, what does it do? Should I delete this?

A zener diode acts as a shunt regulator, by reducing its resistance, as much as it can, to keep the voltage across it constant. If there's nothing to limit the current, as is the case with your circuit, the zener will short circuit the supply and destroy itself and/or the fuse.

[bd139]

In mathematical terms: P=IV. V=18v. I=Loads. P>>Pmax. Ergo kaboom!