Resistor value and circuit example sought for Zener diode voltage protection

Discussion in 'The Projects Forum' started by daveyrocket68, Jul 11, 2016.

  1. daveyrocket68

    Thread Starter New Member

    Jul 11, 2016
    2
    0
    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-Suppl...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...007557?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
     
  2. #12

    Expert

    Nov 30, 2010
    16,261
    6,770
    Your current needs and zener wattage are out of proportion for a series resistor. I think you need a crowbar circuit and a fuse.
     
  3. daveyrocket68

    Thread Starter New Member

    Jul 11, 2016
    2
    0
    Thanks for the quick reply I will do more research on the crowbar circuit
     
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