Brief polarity indicator LEDs circuit

Connecting LEDs in parallel, but biased in opposite directions, allows you to visually see which direction (polarity) the power supply is attached to the circuit at any given time.

Brief circuit schematics with short video – List of pages
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Using different color LED can be used to color code which direction the voltage is being applied, and that current is flowing.

Simple polarity indicator circuit schematic diagram by electronzap electronzapdotcom
Simple polarity indicator circuit schematic diagram by electronzap electronzapdotcom


Quick power supply polarity indicator LEDs circuit schematic to breadboard build

Main points:

  • LEDs are a type of diode (Light Emitting Diode). – Diodes conduct relatively easily in one direction, called forward biased. They also light up while conducting forward biased. They do not conduct in the other direction, called reverse biased. They do have a breakdown voltage though, where a high enough voltage will start conducting current while reverse biased, but that amount of voltage must be avoided.
  • Forward biased (FB)- Anode more positive than cathode.
  • Reverse biased (RB)- Cathode more positive than Anode.
  • Protective resistor is needed. The value depends on the voltage that will be applied and the forward voltage drop of the LEDs. Use the lower Vdrop if they aren’t equal.
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