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Question About Resistors

Discussion in 'LEDs and Optoelectronics' started by H2814D, Jun 9, 2020.

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  1. H2814D


    Nov 4, 2017
    Hi all. I have a question about the placement of resistors in a circuit. In this application, the circuit involves LED's in an automotive turn signal. Newer vehicles, originally built with incandescent bulbs, flash normally with the original bulbs. When replacing the bulb with an LED bulb, and the circuit is activated, the LED's draw much less current/amperage (right?) and will cause what is called "hyper flash," which is just another way of saying the blinking of the light is much more rapid than it should be.

    So the fix is to install what is called a load resistor in the circuit. That part, and the reason why, is understood, but here is my question: Why are the resistors wired in to bridge the positive and negative leads and not simply placed in-line with either the positive or negative lead? Isn't the idea to simply add resistance to the circuit? Wouldn't placing the resistor in either lead accomplish the same thing as bridging the leads together with the resistor? I'd just like to understand why, and I know this is the best place to get those answers. :)

    Thanks in advance.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    In-line is a series connection which further reduces the current.
    The goal is, however, to increase the current to trick the blinking circuit into working at normal speed. This is done by adding additional current to the LED current by means of an additional load between '+' and '-'. This is called a parallel connection. Read more about series and parallel connection of resistors e.g. here.
    hevans1944 likes this.
  3. H2814D


    Nov 4, 2017
    Thank you, Mr. Kapp.
  4. Bluejets


    Oct 5, 2014
    There is available a standard pin for pin drop in flasher unit that operates as a timer as opposed to current draw for flash rate.
    You may need to search for one which suits your model of vehicle.
  5. Ylli


    Jun 19, 2018
    Bluejets, you thinking of the old thermal flasher? With those, if a bulb burned out, it wouldn't flash at all - the good bulb would just stay on. Modern vehicles don't use an old time flasher, and the computer controls the flashing. If it detects a burned out bulb, the flash rate increases.
  6. H2814D


    Nov 4, 2017
    That's not necessary. I have the resistors, and I understand what they do in a circuit, I was just curious as to the placement option in the circuit. With Mr. Kapp's explanation of the "tricking the circuit" with the increased current draw, instead of just adding resistance to the circuit, I now understand the reason for where they are placed. That was actually my only question. But thanks for the reply. You guys always help out quite a bit.
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