Diode Basics 1

[Banner showing selection of different Diode types]

Diodes act like one way valves. They let current flow through them but only in one directon, blocking the current if it tries to flow the other way. We can see this in these two circuits.

Forward Biased Diode in circuit Reversed Biased Diode in circuit
This circuit allows conventional current
to flow from positive to negative,
so the bulb will be lit
With the diode the other way around,
the conventional current is blocked,
and the light is off.

Conversly, if we connected the battery the opposite way around, we would have the opposite effect. The first circuit would fail, but the second would work under the same principal that conventional current is being allowed through only in one direction (forward biased) , and not the other (Reversed Biased).

Schematic Symbol Description Circuit Schematic Reference
Standard Diode Symbol Diode - Standard Symbol N/A
Alternative Diode Symbol Diode - In alternative representations, the triangle is often filled in. N/A

The arrow in the symbol points in the direction that the current can flow. The line is like a wall, blocking the current were to flow from the other direction.

Diodes take a toll on the circuit needing a minimum voltage of around 0.7V to conduct. This is known as the forward voltage.

Diodes also make a voltage drop of around 0.7V, so a circuit that is 3V will have its voltage dropped to around 2.3V by the diode.

The 0.7V for both voltage drop and forward voltage are typical for standard diodes, however, diodes can vary so data sheets should be checked for each diode model.

When the amount of voltage that the diode is blocking rises past the breakdown voltage limit, the diode will start to conduct power in the opposite direction. For standard diodes, this will usually result in permanent failure (often accompanied with smoke and perhaps a flame). Some diodes are designed to continue operating at past the breakdown voltage limit as a normal part of their operation.

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