Engineering Reference
Diode Types and Electrical Parameters Reference
Quick-reference diode types, forward-voltage behavior, current and reverse-voltage ratings, leakage, recovery time, capacitance, Zener parameters, and thermal terms.
- Reading Time
- 12 min
- Format
- Lookup tables
- Updated
- September 24, 2026
Diode Type Comparison
Technology labels identify a starting point, not a complete selection. Compare the actual datasheet conditions and curves.
| Type | Technology | Forward-voltage behavior | Recovery behavior | Common use | Parameters to compare |
|---|---|---|---|---|---|
| Silicon rectifier | Silicon PN | Current- and temperature-dependent; often higher than Schottky at a comparable operating point | Stored-charge recovery may matter; compare trr and Qrr | Power rectification | VRRM, IF(AV), IFSM, VF, trr, thermal limits |
| Small-signal switching | Silicon PN | Specified as VF at a stated IF | Often optimized for switching, but labels are not universal speed classes | Signal switching, clamping | VR, IF, VF, trr, leakage, capacitance |
| Fast / ultrafast | Silicon PN | Tradeoff with recovery, leakage, and voltage rating | Compare measured trr/Qrr and test conditions, not the marketing name alone | Switch-mode power paths | VRRM, IF, VF, trr, Qrr, thermal limits |
| Schottky | Metal-semiconductor | Generally lower VF, strongly dependent on IF and temperature | No PN minority-carrier recovery in the usual sense; capacitance and charge transients remain | Low-voltage rectification, fast switching | VRRM, VF, leakage at temperature, capacitance, thermal limits |
| Zener | Reverse-operated PN | Forward operation resembles a diode; reverse regulation is specified separately as VZ at IZT | Not selected primarily by forward recovery | Shunt regulation, references, limiting | VZ at IZT, tolerance, dynamic impedance, power, temperature coefficient |
| TVS | Avalanche suppression device | Forward drop is usually not the primary selection quantity | Transient waveform and dynamic behavior dominate | Transient and ESD suppression | VRWM, VBR, VC, pulse current/power, waveform |
| SiC Schottky | Wide-bandgap Schottky | Different VF/leakage/temperature tradeoffs from silicon devices | Low reverse-recovery charge, but capacitive switching effects remain | High-voltage, high-frequency power conversion | VRRM, VF, leakage, capacitance/charge, package, cost |
Approximate Forward-Voltage Behavior
| Technology | Broad behavior | Required check |
|---|---|---|
| Silicon PN | Moderate forward drop; the familiar 0.7 V is only a rough teaching estimate | Read VF at the intended IF and temperature |
| Schottky | Usually lower than silicon PN at a comparable operating point | Leakage and reverse-voltage tradeoffs can dominate, especially hot |
| Germanium | Often low at small signal currents | Leakage, availability, ratings, and temperature behavior vary widely |
| SiC Schottky | Can be higher than low-voltage silicon Schottky while supporting different voltage/temperature regimes | Do not infer suitability from technology name alone |
| LED boundary | Strongly material, color, current, and temperature dependent | Use the dedicated LED references and datasheet curves for LED design |
Key Datasheet Parameter Reference
Symbols are common notation, not guaranteed universal labels. Always use the definition and conditions in the specific datasheet.
| Symbol | Parameter | How to interpret it | Common mistake |
|---|---|---|---|
| VF | Forward voltage | Voltage at a specified forward current and temperature | Treating it as a fixed device constant |
| IF / IF(AV) | Forward / average forward current | Continuous or waveform-averaged rating under stated thermal conditions | Ignoring package and thermal assumptions |
| IFSM | Non-repetitive surge current | Specified pulse waveform, duration, and starting temperature | Using it as a continuous-current rating |
| VRRM | Repetitive peak reverse voltage | Maximum repetitive reverse-stress rating | Confusing it with working, breakdown, or clamp voltage |
| IR | Reverse leakage current | Measured at stated reverse voltage and temperature | Ignoring strong temperature dependence |
| trr | Reverse recovery time | Recovery test circuit, IF, di/dt, and reverse current criteria | Comparing values without matching test conditions |
| Qrr | Reverse recovery charge | Stored charge removed during commutation | Assuming trr alone describes switching loss and EMI |
| CJ / CT | Junction / terminal capacitance | Usually measured at stated reverse bias and frequency | Treating one pF value as bias-independent |
| PD | Power dissipation | Package- and temperature-dependent maximum | Assuming the headline maximum applies on any PCB |
| TJ(max) | Maximum junction temperature | Device junction limit | Using ambient temperature as junction temperature |
| RθJA / RθJC | Thermal resistance | Junction-to-ambient or junction-to-case test configuration | Ignoring board copper, airflow, mounting, or interface conditions |
| VZ / IZT | Zener voltage / test current | Nominal reverse voltage defined near a stated test current | Assuming VZ is exact at every operating current |
| ZZT | Zener dynamic impedance | Incremental voltage-current slope near the test point | Treating the Zener as an ideal voltage source |
Engineering Interpretation Notes
Forward, average, and surge current
Reverse voltage terms
Leakage and temperature
Recovery and capacitance
Zener operating point
Power and thermal path
Worked Reference Examples
Forward conduction estimate
Two operating points
Surge versus continuous
Zener test current
Datasheet Lookup Workflow
- 1Identify the diode function and technology.
- 2Check required working and transient reverse voltage.
- 3Check continuous or average forward current.
- 4Check the defined surge-current requirement.
- 5Read VF at the actual current and temperature.
- 6Read leakage at reverse voltage and hot temperature.
- 7Check trr/Qrr for commutating PN applications.
- 8Check capacitance for high-frequency operation.
- 9Verify package, TJ, and thermal-path limits.
- 10Confirm curves, margins, and all test conditions.
Common Interpretation Mistakes
- Treating 0.7 V as universal silicon-diode VF.
- Ignoring the VF current and temperature conditions.
- Using IFSM as a continuous-current rating.
- Confusing VRRM, breakdown, working, and clamp voltage.
- Ignoring reverse leakage at hot temperature.
- Comparing trr or Qrr under unlike test conditions.
- Claiming Schottky devices have zero switching effects.
- Ignoring bias-dependent junction capacitance.
- Treating nominal Zener voltage as exact at every current.
- Using headline PD without the specified thermal setup.
- Selecting from the diode type name alone.
- Using LED approximations in place of dedicated LED data.
Support reference
FAQ
Is a silicon diode always 0.7 V?
No. About 0.7 V is a rough estimate for some silicon PN operating points. Actual VF depends on current, junction temperature, construction, die size, and product family.
Why does diode forward voltage change with current?
Junction current and voltage are nonlinear. Datasheets therefore specify VF at a particular IF and often provide curves rather than one universal value.
How does temperature affect forward voltage?
For typical silicon PN operation, VF commonly decreases as junction temperature rises, but the magnitude depends on device and operating current. Use the device curves for design.
What is the difference between Schottky and silicon PN diodes?
Schottky diodes generally offer lower forward drop and avoid conventional PN minority-carrier recovery, but often have higher temperature-sensitive leakage and different reverse-voltage and capacitance tradeoffs.
What does VRRM mean?
VRRM commonly means repetitive peak reverse voltage. It is not automatically identical to working reverse voltage, breakdown voltage, or transient clamp voltage.
What is IFSM?
IFSM is commonly a non-repetitive forward surge-current rating defined for a specific pulse waveform, duration, and thermal condition. It is not a continuous-current rating.
What is reverse recovery time?
trr characterizes part of the transition from forward conduction to reverse blocking in PN diodes. It must be interpreted with the test current, di/dt, reverse conditions, and recovery criterion.
Does a Schottky diode have zero reverse recovery?
It does not have PN minority-carrier recovery in the usual sense, but junction capacitance, displacement current, parasitic inductance, and switching transients still produce dynamic effects.
What is diode junction capacitance?
CJ or CT describes junction or terminal capacitance under stated bias and frequency conditions. It can materially affect RF and fast-switching circuits.
Why does Zener voltage depend on current?
A Zener has a nonzero dynamic impedance. Nominal VZ is specified near a test current IZT, so voltage changes away from that operating point and with temperature.
Is surge current the same as continuous current?
No. Surge ratings apply to defined short events. Continuous or average current must satisfy steady thermal and electrical ratings.
What should I check besides forward voltage?
Check reverse-voltage behavior, continuous and surge current, leakage at temperature, recovery or capacitance, package, junction temperature, thermal path, transient stress, and datasheet test conditions.
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