How to use zener diode as a regulator - Page 1
Forum section: electronics / beginners

author: catalyst
author_rank: Contributor
timestamp: October 27, 2017, 12:17:11 pm
content: 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?

author: Vtile
author_rank: Super Contributor
timestamp: October 27, 2017, 12:28:59 pm
content: 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.htmlIn 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.

author: danadak
author_rank: Super Contributor
timestamp: October 27, 2017, 01:18:49 pm
content: These might be useful -http://www.americanradiohistory.com/Archive-Bookshelf/Author-Groups/Rufus-Turner/Diode-Circuits-Handbook-Rufus-Turner.pdfhttp://www.rsp-italy.it/Electronics/Databooks/Semicond/_contents/Motorola%20-%20TVS%20Zener%20device%20data%20-%20dl150rev1.pdfRegards, Dana.

author: rdl
author_rank: Super Contributor
timestamp: October 27, 2017, 01:51:56 pm
content: 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.

author: tszaboo
author_rank: Super Contributor
timestamp: October 27, 2017, 01:54:21 pm
content: If you drive LEDs, then dont make a voltage source, then current limit it with a resistor. Make a current source.

author: bd139
author_rank: Super Contributor
timestamp: October 27, 2017, 02:12:17 pm
content: 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 timeIf 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.

author: Belrmar
author_rank: Regular Contributor
timestamp: October 27, 2017, 04:15:06 pm
content: 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

author: Zero999
author_rank: Super Contributor
timestamp: October 28, 2017, 06:38:15 pm
content: I'd use the TL431.https://electronics.stackexchange.com/questions/107699/tl431-constant-current-source

author: bd139
author_rank: Super Contributor
timestamp: October 28, 2017, 06:40:46 pm
content: Good solution

author: catalyst
author_rank: Contributor
timestamp: October 29, 2017, 08:42:51 am
content: Thanks a lot for everyone,Zener diode in this circuit, what does it do? Should I delete this?

author: Zero999
author_rank: Super Contributor
timestamp: October 29, 2017, 09:23:11 am
content: Quote from: catalyst on October 29, 2017, 08:42:51 amA 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.

author: bd139
author_rank: Super Contributor
timestamp: October 29, 2017, 09:25:40 am
content: In mathematical terms: P=IV. V=18v. I=Loads. P>>Pmax. Ergo kaboom!