| 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 | 125oC |
| Reverse Voltage | 0.75 | ||
| Forward Current | 0.75 | ||
| Voltage Regulator | Power | 0.50 | 125oC |
| Zener Current | 0.50 (Imax+ Inom) | ||
| Voltage Reference | Zener Current | N/A |
|
| Zener Voltage Suppressor | Power Dissipation | 0.05 | 125oC |
| Bidirectional Voltage Suppressor | Power Dissipation | 0.5 | 125oC |
| FET Current Regulator | Peak Operating Voltage | 0.80 | 125oC |
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 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.
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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.
How to Derate Components; Guideline for Derating Electronic Devices
Temperature derating is a common design practice for electronic engineers.
