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Zener Diode and resistor help

Discussion in 'General Electronics Chat' started by beeson76, Mar 22, 2012.

  1. beeson76

    Thread Starter Senior Member

    Apr 19, 2010
    In my learning about Zener Diodes, I took apart a hand control. Looks like it may have been on a chair, or bed of some kind. Here is the schematic.

    I don't have voltages etc. for this control.

    Could anyone tell me what the resistor and zener diode would be used for. I know this is a vague question, Im just grasping for answers:)

  2. panic mode

    AAC Fanatic!

    Oct 10, 2011
    looks like you have multiplexer at work. since rest of the circuit is not shown one can only guess. zener is probably used to trim the voltage down, probably to protect the LED from high reverse bias.

    without resistor, LED could never turn on because it would be in parallel with zener and zener has much lower forward bias voltage. this can work if resistor is sufficiently small (so zener characteristic is not completely smeared).

    if this was the case, zener and resistor can be removed provided that LED has another diode in antiparallel for example (standard rectifier or small signal diode such as 1N4148 for example)
  3. jtrent

    New Member

    Mar 11, 2012
    A zener diode operates in the reverse bias mode. Notice that the LED and the zener diode have their anodes connected together. This means that when the circuit is operating such that the LED is turned on there would be about 1.8 volts across the LED in a forward bias manner. Now look at the zener diode...read more
  4. Wendy


    Mar 24, 2008
    A zener diode is a primitive voltage regulator. In many circuits they work surprisingly well, and can quieten a very noisy power supply with lots of ripple (done that). They are also excellent voltage references for more powerful voltage regulators.