Diodes 101: Rectifier, Schottky, Zener, and TVS (When to Use Which)

Diodes 101: Rectifier, Schottky, Zener, and TVS (When to Use Which)

Diodes are one of the most common components on any PCB, but “a diode is a diode” is a fast way to get problems like heat, voltage drop, unstable power, or blown ports. Different diode types solve different problems.

This guide explains the most common diode types—rectifier, Schottky, Zener, and TVS—and how to pick the right one using practical specs.

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What does a diode do?

A diode mainly lets current flow in one direction and blocks it in the other direction. Depending on the diode type, it can also:
• clamp voltage spikes
• protect against reverse polarity
• reduce switching losses
• protect ports from ESD (static)

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1) Rectifier diodes (standard diodes)

What they’re for

Rectifier diodes are used for basic one-way current control and power conversion.

Common uses:
• AC to DC rectification (bridge rectifiers)
• Reverse polarity protection (simple but inefficient)
• Freewheeling / flyback protection (basic versions)

Pros
• Cheap
• Strong and widely available

Cons
• Higher forward voltage drop than Schottky (more heat)
• Slower than Schottky in high-speed switching applications (depends on type)

Key specs to check
• VRRM (reverse voltage rating): choose higher than your max voltage (with margin)
• IF (average forward current): current handling
• Forward voltage (Vf): affects heat and efficiency
• Recovery time (trr): important in switching power supplies

When to choose a rectifier diode:
• For general power input protection where efficiency is not critical
• For mains rectification (proper rated parts)
• For basic polarity/flyback uses where speed is not important

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2) Schottky diodes (low drop, fast)

What they’re for

Schottky diodes are known for low forward voltage drop and fast switching.

Common uses:
• High-efficiency power OR-ing (two supplies)
• DC-DC converter output/input paths
• Preventing reverse current in power paths
• Fast clamping in switching circuits

Pros
• Low Vf (less heat, better efficiency)
• Fast response

Cons
• Usually higher leakage current (especially at high temperature)
• Reverse voltage ratings are often lower than standard rectifiers (varies by part)

Key specs to check
• Vf at your actual current
• Reverse voltage rating
• Leakage current (important in battery devices)
• Current rating and thermal performance

When to choose Schottky:
• You care about efficiency and heat
• You’re in a switching power application
• You need fast diode behavior

Common mistake:
• Picking a Schottky with too low reverse voltage rating and it fails under spikes.

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3) Zener diodes (voltage clamp/reference)

What they’re for

Zener diodes are designed to “break down” at a specific voltage and clamp the voltage at that level (within limits).

Common uses:
• Simple voltage reference (basic circuits)
• Overvoltage protection for low-power signals
• Clamp circuits for inputs (with a resistor)

Pros
• Cheap and simple
• Useful for low-power voltage clamping

Cons
• Not as accurate as a proper reference IC
• Must be used with correct current limiting (usually a resistor)
• Not ideal for absorbing large surges (TVS is better)

Key specs to check
• Zener voltage (Vz) (example: 3.3V, 5.1V, 12V)
• Power rating (how much it can dissipate)
• Test current (Izt) (Vz is specified at this current)
• Dynamic resistance (affects clamp stability)

When to choose Zener:
• Simple clamping/reference in low-power circuits
• Protecting a GPIO input from mild overvoltage (with series resistor)

Common mistake:
• Using a Zener where you need surge/ESD protection → it won’t survive.

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4) TVS diodes (the real protection for ESD and surges)

What they’re for

TVS (Transient Voltage Suppressor) diodes are made to absorb fast spikes like:
• ESD from human touch
• cable plug/unplug surges
• inductive spikes on long wires

Common uses:
• USB, HDMI, Ethernet protection
• Power input surge protection
• Automotive and industrial input protection
• Protecting sensitive IC pins from spikes

Pros
• Designed for fast, high-energy transient events
• Much better than Zener for ESD/surge

Cons
• Must be placed correctly in layout (close to the connector)
• Wrong selection can add capacitance to high-speed data lines

Key specs to check
• VRWM (working standoff voltage): should be above normal voltage
• VCL (clamping voltage): the voltage during a surge event
• Peak pulse power (PPP): how much surge energy it can absorb
• Capacitance: critical for high-speed data lines (choose low-cap TVS for USB 2.0/3.0)

When to choose TVS:
• Any external port that humans touch or cables connect to
• Products needing EMI/ESD robustness
• Industrial/automotive environments

Common mistake:
• Putting TVS too far from the connector. The spike enters your board first—protection becomes useless.

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How to choose the right diode (quick decision rules)

Use a rectifier diode when:
• basic one-way current is needed
• cost is key
• switching speed/efficiency isn’t critical

Use a Schottky diode when:
• you need low loss / low heat
• fast switching matters
• you’re dealing with DC-DC power circuits

Use a Zener diode when:
• you need a simple voltage clamp or reference at low power
• you can limit current properly

Use a TVS diode when:
• you need real ESD/surge protection on connectors or power inputs

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Practical selection tips (avoid the most common failures)

1) Always derate reverse voltage

If your rail is 12V, don’t choose a 12V diode. Spikes exist.

Rule of thumb:
• 5V rail → choose 20V+ reverse rating
• 12V rail → choose 30V–60V reverse rating (depends on environment)
• 24V rail → choose 60V+ reverse rating (industrial often higher)

2) Check heat at real current (Vf matters)

Heat ≈ Vf × I

Example:
If Vf = 0.6V at 2A → heat = 1.2W (that’s big on a small package)

Schottky helps because Vf may be 0.3–0.4V instead.

3) For inductive loads, pick the right flyback diode

For relays, motors, solenoids:
• fast switching: consider fast recovery or Schottky (depends on design)
• basic protection: rectifier diode may work

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Common diode mistakes (real-world)
• Using a normal diode instead of a Schottky in a high-current path → overheating
• Using a Zener as a “surge protector” → it fails
• Choosing a TVS with wrong working voltage → it clamps during normal operation
• Ignoring diode package thermal limits → the diode survives on paper but cooks on PCB
• Placing TVS far away from connector → protection is ineffective

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FAQ

Can I use a Zener diode instead of a TVS diode?

For real ESD/surge protection on external connectors: usually no. TVS diodes are designed for it.

Why do Schottky diodes leak current?

It’s a property of their structure. Leakage increases with temperature—important for battery devices.

What diode should I use for reverse polarity protection?

A diode works but wastes power. For higher current designs, a “reverse polarity MOSFET” circuit is usually better.