Diode Derating Guide Lines

Recommended maximum power ratings

Diode Temperature Correction
Diode Type Critical Stress Parameter Derating Factor Maximum Junction Temperature
General Purpose,
Rectifier, Switching,
PIN/Schottky, Thyristors
PIV 0.70 125oC
Surge Current 0.50
Forward Current 0.50
Varactor Power 0.50
Reverse Voltage 0.75
Forward Current 0.75
Voltage Regulator Power 0.50
Zener Current 0.50 (Imax+ Inom)
Voltage Reference Zener Current N/A
Zener Voltage Suppressor Power Dissipation 0.05
Bidirectional Voltage Suppressor Power Dissipation 0.5
FET Current Regulator Peak Operating Voltage 0.80

Diode Temperature Derating Curves
Diode Manufacturers, and Zener Diodes Manufacturers

Use the figures in the table to determine how much to derate each parameter.
The figures [Derating Factor] should be taken as general guidelines and not hard and fast rules.
The amount of current a diode can handles depends on many factors;
package size and application being two. The terminals of an axial leaded package may be used to conduct heat away from the diode and into the printed wiring board, using the copper pads as a heat dissipator, while the body of the diode will lose heat by convection and radiation into the surrounding air.

The point is to never exceed the maximum junction temperature of the device. The link [above] to derating curves should be taken as a ruled as those pages provide precise Current-Temperature curves over ambient temperature, or in some cases give the derating equation from the data sheet.
Note that regardless of the device or application the tables shows that some amount of percent derating is used, which happens to be a good design practice.
Keep in mind that a higher amplitude pulse of a given amount of energy will produce a higher rise in junction temperature than will a lower amplitude pulse of longer duration pulse having the same energy.

The Derating Factor is a recommendation and can change from company to company depending on their design processes. While engineering departments may not have a design derating recommendation at all and just leave it up to the engineer. This particular table was derived from NASA recommendations for circuit design.
Some engineers use the term Stress Ratio instead of Dearting Factor, but they both mean about the same thing.
Here are four different examples of Diode Stress Ratio's.
Power Diode Stress Ratio = Operating PIV / Rated PIV = 50%
Power Diode Stress Ratio = Operating If / Rated If = 70%
Small Signal Diode Stress Ratio = Operating PIV / Rated PIV = 85%
Small Signal Stress Ratio = Operating If / Rated If = 85%
Remember because these figures are Rules-of-Thumb numbers, they may not agree with the table above, or some other recommendation.

Diode Acronyms;
IF: Forward Current
PIN Diode: --
PIV: Peak Inverse Voltage

Related Diode Topics:
Diode Types
Zener Diode Terms
Diode Array Types
Diode Package Styles
Diode Vendor Part Numbers off-site
LED Manufacturers

Guideline to Derating Components

Design Hint;
When using SMD diodes use larger pads
on the PWB to act as a heat sink,
Taking advantage of the
copper thermal conductivity.

PC motherboard

Distributor rolodex Electronic Components Electronic Equipment EDA CDROM Software Engineering Standards, BOB card Cabled Computer Bus Electronic Engineering Design Table Conversion DB9-to-DB25.
DistributorsComponents Equipment Software Standards Buses Design Reference

Modified 3/07/12
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