Overview
This lecture introduces the diode, a key electronic component that allows current to flow in only one direction, and demonstrates its use in circuits for controlling current and protecting components.
Diode Basics
- A diode is an electronic component that permits current to flow in only one direction.
- LEDs (Light Emitting Diodes) are a specific type of diode that emits light.
- Diodes have two terminals: the anode (positive side) and cathode (negative side).
- Diodes must be connected in the proper orientation; anode to positive, cathode to negative.
Current Flow and Circuit Symbols
- Conventional current flow is from positive (anode) to negative (cathode).
- The schematic symbol for a diode is a triangle pointing at a line; triangle base is the anode, line is the cathode.
- An LED symbol is similar but includes arrows indicating light emission.
Diode Operation Modes
- In forward bias, the diode allows current from anode to cathode.
- In reverse bias, the diode blocks current from cathode to anode, acting like an open switch.
- If too much reverse voltage is applied, diodes can enter breakdown mode, potentially damaging them.
Voltage Drop and Real-World Behavior
- All diodes have a forward voltage drop (e.g., 0.7V for typical diodes, ~3V for LEDs).
- If applied voltage is less than the forward voltage drop, current will not flow.
- Diodes have maximum voltage ratings that must not be exceeded.
Identifying Diode Leads
- The cathode is marked with a stripe on the diode body; the other end is the anode.
Circuit Demonstrations
- Inserting a diode in correct orientation allows current, lighting an LED.
- Reversing the diode blocks current, preventing the LED from lighting.
- Using a multimeter, voltage drop across the diode can be measured.
- Amperage (current) can be measured to confirm current flow (forward bias) or blockage (reverse bias).
Using Diodes with Capacitors
- Diodes can act as protection devices in circuits with capacitors, preventing damage from incorrect power polarity.
- Larger capacitor values allow an LED to remain lit longer after power is disconnected.
- Diodes ensure that reversing power connections does not harm the circuit.
Key Terms & Definitions
- Diode — component that allows current flow in only one direction.
- Anode — positive terminal of a diode.
- Cathode — negative terminal of a diode, usually marked with a stripe.
- Forward Bias — mode when diode allows current (anode to cathode).
- Reverse Bias — mode when diode blocks current (cathode to anode).
- Breakdown Mode — state when too much reverse voltage damages the diode.
- Voltage Drop — the voltage required to drive current through the diode.
Action Items / Next Steps
- Practice identifying anode and cathode on actual diodes.
- Build and test circuits with diodes in both forward and reverse bias.
- Measure voltage drops and currents using a multimeter in diode circuits.