Resistor value and circuit example sought for Zener diode voltage protection

Thread Starter

daveyrocket68

Joined Jul 11, 2016
2
Resistor value for Zener diode voltage protection question


New member and first time posting . Hello My name is Josh. I am new to the forum so I am not sure if I am posting this in the right place or if there is any problem with my content here.


I am trying to protect a 5v addressable led controller from over voltage in a device I am building. My fear is that someone in the house hooks up a 12 v power supply and destroys the controller. I built a box and put a switch on it. I bought a cheap Chinese dc-dc converter but I get erratic operation from the Leds through it. I did tune it to 5-5.15 and I have run up to 5.5v volts and it is regulating so I can use any wall wart up to 30 v on it and it won’t blow but I am not happy with the erratic behavior of the controller(sometimes it does not operate the leds correctly) . When I run the controller directly off the correct wall wart it behaves correctly. I am aware of the current requirements of Leds i.e. max 60ma per led and I am using differing lengths so led # is x. Here is where my question lies. The plug on the controller is a 2.1x5.5mm center positive (+) plug that attaches to the wall wart. I want to build a simple circuit between the wall wart and the controller and to use a Zener to blow a fuse if the voltage exceeds 5.1v incoming. I have seen PTC’s SCR’s Crowbars and other circuits online. My problem is in testing on my benchtop power supply the Zener does its job in the circuit but I blow it up. I understand the need to have a resister in line with the Zener but most of the internet content I have seen show this on the power side and also seen by the load. If I put this in series with the zener then I am changing the voltage level at which the zener conducts to protect right? I am uncertain what resistance to use because I don’t want to limit the incoming voltage to the controller or the Leds behind it. I am using 1N4733A Zener 1 watt dissipation. Can you give me any advice? I have not seen a solution that meets my application. I am also using a 3a quick blow fuse. But On longer strips I may use a larger fuse. I have a separate 5v8a supply. I am not an engineer more of a hobbyist.


I am using this led controller

http://www.ebay.com/itm/like/252321120115?lpid=82&chn=ps&ul_noapp=true

I am using a 5v5a wall wart

http://www.ebay.com/itm/Power-Supply-AC-to-DC-Adapter-5V-12V-24V-1A-2A-3A-5A-6A-8A-10A-15A-for-LED-Strip-/301697610927?var=&hash=item463e9434af:m:maMJQqqcIz8tdSN8LZJ3ClA


I am using this voltage controller( I would prefer a simpler solution because I am not happy with its output (maybe you can suggest an alternative (ie smoothing cap on the output)? I just don’t know I am using a cap to avoid spikes on the output of the controller see below

http://www.ebay.com/itm/DC-DC-4-38V-to-3-3V-6V-9V-12V-24V-5A-Buck-Step-down-Converter-Voltage-Regulator-/311552007557?hash=item4889f25d85:g:4fIAAOSw5VFWOdwr

The leds are the ws2812b neopixel type and I have a 1000uf 6v cap on the input to prevent damaging spikes

Any help would be greatly appreciated. If I have not included enough info I apologize. Not exactly sure how to create and upload a pdf.

Regards

Josh
 

#12

Joined Nov 30, 2010
18,190
Your current needs and zener wattage are out of proportion for a series resistor. I think you need a crowbar circuit and a fuse.
 
Top