1. Diodes

2. DIODES – Scientific & Historical Background
The broadcast-radio and television eras were based…
… on vacuum technology.
The simplest vacuum tube was ….
…. a diode.

3. Vacuum Tube

4. DIODES – Scientific & Historical Background
These vacuum diodes only allowed current to flow in one direction.
They act as a check valve.
This was a useful way of converting Alternating Current (AC) into Direct Current (DC).
This process is called rectification.

5. DIODES – Scientific & Historical Background
What was the downside to vacuum diodes?
Produce a lot of heat – they effectively have to “boil off” a stream of electrons.
It also takes time for the vacuum diode to heat up to the required temperature – so quite slow.
They also prevent miniaturization – the key behind technology today.
The glass tubes were also fragile and could break easily or just burn out over time.

6. Russell Ohl

7. DIODES – Scientific & Historical Background
Vacuum technology was eventually replaced by …
… solid-state technology.

8. DIODES – Scientific & Historical Background
These silicon diodes are collectively known as …
… semiconductors.
Semiconductors act like conductors sometimes, and like insulators at others.
They have revolutionized the field of electronics.

9. DIODES Study the diode carefully. What do you notice?
Does the electricity flow through the diode from black-band end to plain end or from plain to black-band end?
A: plain end to black-band end.

10. DIODES What is the component symbol for a diode?
The line represents the black band on the diode.
The electricity flows in the direction of the arrow – towards the black band.

11. DIODES

12. DIODES We are now going to work with a new component – the DIODE.
All components so far can be safely used directly attached to a battery.
This is NOT the case with diodes.
NEVER attach diodes directly to a battery.
If you do – the diode will BURN OUT!
What can we do to protect a diode?

13. DIODES Draw a schematic including : Battery; Switch; 75-Ω resistor;
Diode; and
Lamp.
Label the positive and negative terminals.
Draw arrows showing direction of current flow.

14. DIODES What are two important things to remember about diodes?
A1. Diodes conduct electricity in one direction only.
A2. Diodes need to be protected by resistance in series.

15. Minimum Voltage
Diodes only work when a minimum amount of voltage is exceeded.
In other words, diodes act like a gate that will only open when a certain amount of pressure is applied.
This is called the threshold voltage.

16. Minimum Voltage
Once the threshold voltage is achieved, the diode starts to conduct and the internal resistance drops to a very low level.
When resistance in a circuit approaches zero, high current can flow and destroy the diode.
This is why we always protect diodes and LEDs with a guardian resistor.

17. LEDs = light-emitting diode
After the discovery of solid-state diodes, researchers searched for other solid-state materials.
They played around with other elements near silicon in the Periodic Table.
They discovered that gallium doped with arsenic, phosphorus, aluminum and indium produced light as it conducted!

18. LEDs LEDs produce light by electroluminescence.
which is kinetic excitation that fires out photons of light (a photon is an energy carrier).
Scientists are trying to discover LEDs that produce different colors of light.
LEDs have a longer life and are more energy efficient than incandescent lights.

19. LEDs