Electronic 101: Diode N BJT Transistor

During our wiring on DC fan, there is a optional component mention – Diode. What is this diode use as? Why do we need diode parallel with DC fan. From diode, we will try to understand Bipolar Junction Transistor.

Credit: coutant.org

Diode PN Junction

• A diode is a semiconductor device that essentially acts as a one-way switch for current. It allows current to flow easily in one direction.
• Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc).
• Diodes have polarity, determined by an anode (positive lead) and cathode (negative lead). Most diodes allow current to flow only when positive voltage is applied to the anode.
• A PN-junction is formed when an N-type material is fused together with a P-type material creating a semiconductor diode.

Credit: Fluke

BJT Transistor

• BJT Transistor is form by joining together two individual signal diodes back-to-back, this will give us two PN-junctions connected together.
• The transistor’s ability to change between these two states enables it to have two basic functions: “switching” (digital electronics) or “amplification” (analogue electronics).
• Bipolar transistors have the ability to operate within three different regions:
  • Active Region   –   the transistor operates as an amplifier
  • Saturation   –   the transistor is “Fully-ON” operating as a switch
  • Cut-off   –   the transistor is “Fully-OFF” operating as a switch

• BJTs are much more suitable than MOSFETs for driving low-power LEDs and similar devices from MCUs.
• MOSFETs are better for high-power applications because they can switch faster than BJTs, enabling them to use smaller inductors in switch-mode supplies, which increases efficiency.
•  Intel, one of the largest chip makers in the world, uses practically only FET transistors to build its chips which power billions of devices in the world.
• BJTs are current-controlled. They require a biasing current to the base terminal for operation. Whereas, MOSFETs are voltage-controlled. They only require voltage applied to the gate to turn the MOSFET either on or off. They do not require a biasing current for operation.

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