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Hi expert, All below question refer to the diode/ rectifier. As you know, we usually can find the average forward current IF(av) and Non-Repetitive Peak Surge Current IFSM on the datasheet of diode, but it don't define the allowable repeative maximum forward current, for example, MURA215T3G, so i have some question showed as below, pls help to confirm:

1. what is the allowable repeative maximum forward current and how to get/caculate it? whether this spec is important or not for a diode application?
2. what are the relationship between IF(av) and IFSM and the allowable repeative maximum forward current?
3. how to read /understand the datasheet of a diode? have you any document to help me to better understant it?
4. why the IF(av) always kept the same value, even during low lead temperature case? what is the limitation?
5. Is there SOA concept for a diode, just like Mosfet?
6. sometimes, we can find the maximum rms forward currend defined in the datasheet, how to understand this spec and it is relationship between others?

Answering the questions in order:

1) The peak repetitive forward current parameter is often misunderstood. Both IO and IFM come from the derating curve for the device. The IO parameter is based on the DC curve while the IFM parameter is based on the square wave curve. The average current is the same but the device derates slightly faster in the square wave case due to the non-linear relationship between VF and IF. If the IFM parameter was on the datasheet it would be list as 4A with a lead temperature reference of 130°C (guardbanded about the same as IO ). This is not an absolute limit for the device.
2) There is no defined relationship between these two parameters. IFSM is non-repetitive and can be significantly influenced by package design. A package with significant copper mass will produce higher IFSM results. This may not have a significant impact on steady state thermal performance which is a limiting factor for IFM in most cases.
3) I do not have a document for this.
4) The IO or IF(av) parameters are pegged to a lead reference temperature. Again, this relates to the current derating curve.
5) The most common type of SOA applied to rectifiers is forward current surge SOA. This type of graph has peak current on the Y axis and pulse on time on the X axis. This is typically done for single pulse events. There are some variations that have peak current versus number of pulses applied at a given frequency.
6) Generally speaking, the IO parameter and IRMS are equivalent. The real limitation is typically a thermal limitation. Most rectifiers can handle high form factor waveforms provided the overall application thermal environment can dissipate the heat generated. It is important that the maximum junction operating temperature of the device is not exceeded in normal operation. If a thermal analysis under worst case operating conditions shows acceptable results, the device is generally OK.

Let me know if this answers the question.
Answered by:
ON Semiconductor
2013-07-16 09:37:42.857