Diodes, Rectification, and Protection
One-Way Conduction in Practice
How diodes work
A diode is a - junction that conducts significantly when forward biased and blocks current when reverse biased, up to breakdown. In circuits, diodes are used for rectification, voltage protection, signal steering, and wave shaping.
Common diode roles
| Application | Purpose | Typical example |
|---|---|---|
| Rectifier | Convert AC to pulsating DC | Bridge rectifier |
| Flyback protection | Protect switching devices from inductive kick | Diode across relay coil |
| Reverse polarity protection | Prevent damage from reversed supply | Series or shunt diode |
| Clamping | Limit waveform peaks | Signal clamps |
Inductive kickback
When current through an inductor is interrupted, the voltage can rise sharply. A flyback diode provides a safe path for the current and protects switches and transistors.
What is the main purpose of a bridge rectifier?
A bridge rectifier flips the negative half-cycles so the load sees pulsating DC.
Correct answer: Convert AC to DC
What happens to a diode when it is reverse biased, ideally?
An ideal diode blocks current in reverse bias until breakdown conditions are reached.
Correct answer: it blocks current
Why is a flyback diode used across a relay coil?
The diode provides a path for current when the coil is switched off, reducing voltage spikes.
Correct answer: To absorb inductive voltage spikes
What is the approximate forward voltage of a silicon diode in many simple circuits?
A silicon diode often has a forward drop near , though actual values depend on current and temperature.
Correct answer: 0.7 V
Using a diode in a design
-
1
Step 1: Identify the required direction of current flow.
-
2
Step 2: Choose a diode with adequate current and reverse-voltage ratings.
-
3
Step 3: Check the forward voltage drop and power loss.
-
4
Step 4: Add protection for inductive or surge conditions if needed.