Chapter 5 - Application of diodes

What is the I–V characteristic of a silicon diode?

No current flows below ~0.5V, sharp current increase above ~0.7V (forward biased)

What is meant by forward bias for a diode?

Anode at higher voltage than cathode; current flows through diode

What is meant by reverse bias for a diode?

Cathode at higher voltage than anode; diode blocks current

What does a diode do in a circuit?

Acts as a one-way valve: allows current in one direction, blocks in the other

What is the typical forward voltage drop across a silicon diode?

Approx. 0.7V

What happens if a diode is forward biased?

Current can flow (switch is ON)

What happens if a diode is reverse biased?

Current is blocked (switch is OFF)

What is the main use of a diode for component protection?

Prevents damage if supply is connected backwards, or protects against damaging voltages

How does a diode protect from incorrect battery connection?

Blocks current if battery inserted the wrong way

Why protect transistors/MOSFETs connected to motors/solenoids with a diode?

To stop high reverse voltages generated by the coil when switched OFF damaging the transistor/MOSFET

How do you connect a protection diode to a motor or solenoid circuit?

Cathode to +Vs, anode to collector/drain/output side

What is the effect of this “flyback” or “freewheel” diode?

Provides safe path for current, clamps voltage, prevents damage

What is a rectifier?

Circuit that converts AC to DC using diodes

What does a half-wave rectifier do?

Only allows one half of the AC waveform to reach the load; blocks the other half

What happens to the output of a half-wave rectifier?

Negative half-cycles are blocked, producing a pulsed DC voltage

How much voltage do you lose across the diode in a rectifier?

About 0.7V (diode’s forward voltage drop)

What is the main disadvantage of half-wave rectification?

Only uses half the input, wasteful, produces ‘bumpy’ DC output

What device is used together with a rectifier to smooth DC supply?

Capacitor (not covered in detail in this chapter)

What symbol is used for a transformer in rectification circuits?

Two coils side by side; it steps down AC mains

What does a zener diode do?

Zener diode allows current to flow in reverse once a set “breakdown” voltage is reached

How is a zener diode used in voltage regulation?

Connected in reverse bias; maintains a fixed voltage across a load

How can you recognize a zener diode symbol?

Similar to standard diode but with bent bar on cathode side

What is the “holding current” for a zener diode?

Minimum current needed (> 5-10 mA) to maintain set (zener) voltage

How do you make a regulated power supply with a zener diode?

Zener in reverse bias across the load, series resistor to drop excess supply voltage/carry extra current

If a zener diode breakdown voltage is 5.1V, what voltage is maintained across the load?

5.1V (as long as holding current is met)

What happens if load is disconnected from a zener regulated supply?

All current passes through the zener, voltage is unchanged if within safe limits

What happens if too much load is connected?

Holding current is lost; voltage regulation fails, output voltage drops

What calculation is needed for the resistor in a zener regulator?

Allow for total load current + zener holding current, make sure resistor can dissipate required power

Why does the output voltage remain stable in zener regulation even if supply voltage varies?

Zener conducts more/less current to absorb changes, keeping voltage constant across load (within limits)

What happens if zener diode is connected the wrong way around?

Acts as a normal diode; does not regulate voltage

What is a real-life use of zener diodes?

Battery powered device that needs a stable lower voltage supply (e.g., 9V battery to 5V regulated circuit)

Where do you see diodes commonly used in electronics?

Power supplies, motor driver protection, signal demodulation, voltage regulation, LED indicators