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# Diodes

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### Diodes

1. 1. Junction Diode N Type P Typeextra electrons holes (missing electrons) depletion zone
2. 2. What happens when a voltage source is applied to the 2 ends of thediode?
3. 3. • 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.
4. 4. What happens when a voltage source is applied to the 2 ends of thediode?
5. 5. As more and more charges build up, easier for charges to move across the depletion zoneCurrent flows as electrons flow from N typethrough holes of P type out to positive source
6. 6. 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.
7. 7. What happens if the voltage polarity is reversed?
8. 8. What happens if the voltage polarity is reversed? depletion zone widens
9. 9. 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
10. 10. 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).
11. 11. 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)
12. 12. Types of diodesRectifier diodes– convert AC to DC, handles higher power • 1N4001 to 1N4007 IF = 1A, PIV = 50V to 100VSignal diodes or switching diodes– faster response at high frequencies • 1N4148 IF = 200mA, PIV = 100VZener diode– holds voltage level steadySchottky diode– fast recovery time, low voltage, low noise