2. Junction Diode
N Type P Type
extra electrons holes (missing electrons)
depletion zone
3. What happens when a voltage source
is applied to the 2 ends of the
diode?
4. • Electrons are pushed from the negative
supply into the N side of the diode.
• Holes are pushed (electrons are drained)
from the P side of the diode into the
positive side of the supply.
5. What happens when a voltage source
is applied to the 2 ends of the
diode?
6. As more and more charges build up,
easier for charges to move across the
depletion zone
Current flows as electrons flow from N type
through holes of P type out to positive source
7. Forward Biased
• To cross depletion zone, must apply
enough voltage (pressure or push) to get
electrons past negatively charged region
of depletion zone.
• Forward bias voltage about 0.7 V for
silicon diodes and 0.3 V for germanium
diodes.
9. What happens if the voltage
polarity is reversed?
depletion zone
widens
10. Reversed Bias
• When diodes are reverse biased, depletion
zone widens
• Harder for charges to cross depletion zone
• High enough voltage will force charges
across depletion zone
– Breakdown voltage = voltage level that causes
diodes to conduct when reverse biased
– Heat from large reverse current destroys diode
11.
12.
13. Diodes act as switches
• When forward biased, diode acts as a
short (very low resistance).
• When reverse biased, diode acts as an
open circuit (huge resistance).
14. Testing Diodes
• Multimeter with + lead to anode and
– lead to cathode should show low
resistance.
• Multimeter with + lead to cathode and
– lead to anode should show high
resistance.
anode cathode
(end current flows into) (end current flows out of)
15.
16.
17. Types of diodes
Rectifier diodes
– convert AC to DC, handles higher power
• 1N4001 to 1N4007 IF = 1A, PIV = 50V to 100V
Signal diodes or switching diodes
– faster response at high frequencies
• 1N4148 IF = 200mA, PIV = 100V
Zener diode
– holds voltage level steady
Schottky diode
– fast recovery time, low voltage, low noise
