Diodes

Active component capable of controlling the current flow

How it works

• Can either create a depletion region or a conduction region in the center depending on the voltages on either end
  • Forward bias → allows flow
  • Reverse bias → prevents flow
• Forward bias
  • Anode: Positive
  • Cathode: Negative

Behavior

Ideal

• Non linear over large scale
  • Reverse bias → open
  • Forward bias → short

Real World

$$I_d=I_s\left(\exp \left(\frac{v_D}{n{V}_t}\right)-1\right)$$

• $I_S$ = saturation current
• $V_t=\frac{k_{B}T}{q}$ = thermal voltage

Constant voltage drop model:

Types

• Light Emitting Diode
• Photodiode (conducts when light hits the component)

Applications

Rectifier

• A diode after a voltage source will prevent a waveform from going negative
• A key component in regulated power supplies
• Half wave
  • Replaces negative values with 0
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• Full Wave
  • Replaces negative values with their absolute value
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• Peak
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  • Diode turns off at peak then C discharges through R
  • Signal hovers approximately around the peak of the signal

Voltage Regulator

• Uses Zener Diodes
  • Define $V_Z$ and $I_Z$ with opposite polarity
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