Diode I FSM parameters, forward current, surge peak

小太阳yy

Diode I FSM parameters, forward current, surge peak [Copy link]

 

Diode I FSM parameters, forward current, surge peak,

IFSM is the maximum non-repetitive, single surge current of the diode. Its value is at a specific test pulse time and ambient temperature.

It is defined at TA = 25°C. In 60Hz AC rectification applications, it is used as a rectifier. The rectifier usually specifies the IFSM specification.

The surge time for a single half-sine wave is 8.3ms, for customer reference.

The above is the description of the diode surge peak in the specification. I would like to ask, what does this single sine wave surge time of 8.3MS look like?

maychang

[What does this single sine wave with a surge time of 8.3MS look like? ]

It is the waveform of half a 60Hz sine wave. The frequency of the US industrial power grid is 60Hz, and half a cycle is 8.3ms.

小太阳yy

maychang posted on 2024-5-25 20:24 [What does this single sine wave surge time of 8.3MS look like? ] It is the waveform of half a 60Hz sine wave. The frequency of the US industrial power grid...

Is that right, teacher? I also want to ask him that the single, non-repetitive, does it mean that it can only withstand this one waveform? Or can it withstand repeated waveforms?

maychang

小太阳yy posted on 2024-5-25 20:41 Is that right, teacher? And I want to ask him, when it says single time, non-repetitive, does it mean that it can only withstand this one waveform? ...

This picture is a bit too ugly.

[I want to ask him if the single-shot, non-repetitive part mentioned here means that it can only withstand this one waveform? ]

The definition is that it can only be used once. In fact, it can be repeated after a few dozen seconds. However, don't use the tube so hard.

maychang

小太阳yy posted on 2024-5-25 20:41 Is that right, teacher? And I want to ask him, when it says single time, non-repetitive, does it mean that it can only withstand this one waveform? ...

Remember that I FSM current refers to the half-wave effective value, not the peak value. So your diagram is wrongly marked, it is the peak value.

小太阳yy

maychang posted on 2024-5-25 21:23 Remember that IFSM current refers to the half-wave effective value, not the peak value. So your diagram is wrongly marked, it has become the peak value.

I see, teacher. I have another question. Does the reverse recovery time of a diode have anything to do with the junction capacitance indicated in the specification? Why does a large reverse current appear in the reverse direction?

maychang

Xiaoyangyy posted on 2024-5-25 21:29 I see, teacher. Then I have another question. Does the reverse recovery time of the diode have anything to do with the junction capacitance size marked in the specification? Why is it so...

This is because when a large forward current passes through the diode, a certain amount of charge will be stored in its PN junction. When the diode is suddenly subjected to a reverse voltage, these charges will not disappear immediately, but will flow in the reverse direction, forming a large reverse current, as if the diode is almost short-circuited. After a period of time, these charges disappear due to recombination, and only reverse leakage current remains in the diode in the reverse direction, reaching a stable state. To describe the reverse recovery phenomenon of the diode, the parameter "reverse recovery time" is usually used. Pay attention to the test conditions when using it. It can also be described by the parameter "reverse recovery charge". Pay attention to the test conditions when using it.

Junction capacitance is generally tested under very low current conditions and cannot fully reflect the reverse recovery time.

小太阳yy

maychang posted on 2024-5-25 21:58 This is because when a diode passes a large forward current, a certain amount of charge will be stored in its PN junction. When the diode is suddenly subjected to a reverse voltage, these...

Is this the capacitor?

小太阳yy

maychang posted on 2024-5-25 21:58 This is because when a diode passes a large forward current, a certain amount of charge will be stored in its PN junction. When the diode is suddenly subjected to a reverse voltage, these...

This is the explanation of reverse recovery I saw on the Internet. I would like to ask, what determines the maximum reverse current IR?

The formula in the figure is IR=VR/RL. Does that mean that the larger the reverse voltage, the smaller the equivalent resistance in the circuit, and the larger the maximum reverse current IR? Is this correct? Or does it mean that the larger the junction capacitance, the more charge stored, and the larger the maximum reverse current? I am a little confused.

maychang

小太阳yy posted on 2024-5-25 22:16 This is the explanation of reverse recovery I saw on the Internet. I would like to ask, what determines the maximum reverse current IR? ...

[The formula in the figure is IR=VR/RL. Can it be understood that the larger the reverse voltage, the smaller the equivalent resistance in the circuit, and the larger the maximum reverse current IR will be? Is this understanding correct? ]

That is exactly the understanding.

maychang

小太阳yy posted on 2024-5-25 22:16 This is the explanation of reverse recovery I saw on the Internet. I would like to ask, what determines the maximum reverse current IR? ...

However, it should also be noted that the times ts and tt are related to the maximum reverse current and the forward current IF before the voltage mutation , which cannot be explained by the junction capacitance.

小太阳yy

maychang posted on 2024-5-26 07:18 However, it should also be noted that the time ts and tt are related to the maximum reverse current and the forward current IF before the voltage mutation, which is not something that the junction capacitor can...

I am a little confused. There are still 4 questions about this that I am not very clear about. My current understanding is as follows:

Is this correct? Please correct me, teacher.

1) What parameters are related to the maximum current during diode reverse recovery?

First of all, it is related to the voltage VR at the reverse cutoff time. The larger the VR, the greater the maximum reverse current.

Secondly, it is related to the current during forward conduction. The more charge stored during forward conduction, the greater the maximum current during reverse conduction (I don’t know if this statement is correct).

The shorter the trr time, the greater the maximum reverse current (is this correct? Why?)

Are there other factors?

2) What parameters are related to the Trr time?

The smaller the reverse power supply voltage, the smaller the reverse recovery current, the slower the charge depletion, and the longer the reverse recovery time.

The larger the forward current, the more charge is stored, the longer the depletion time is, and the longer the reverse recovery time is.

The lower the carrier recombination efficiency of the semiconductor material, the longer the lifetime, the longer the charge depletion time, and the longer the reverse recovery time.

3) If the trr time is very short, will oscillation easily occur where the reverse current is close to 0?

Yes, if the trr time is very short, oscillation is likely to occur, causing EMI problems.

4) Is there any relationship between the length of trr and the junction capacitance in the diode specification?

The junction capacitance in the specification sheet is generally the capacity of the diffusion capacitance, which has little to do with the reverse recovery time. The barrier capacitance is strongly related to the reverse recovery time and is generally not marked in the specification sheet.

I don't know if there is any problem with my understanding above? Please correct me.

maychang

小太阳yy posted on 2024-5-26 11:28 I am a little confused. There are still 4 questions that I am not very clear about. My current understanding is as follows: But I don’t know if it is correct, ...

[The shorter the trr time, the greater the maximum reverse current]

There is no causal relationship between the two.

maychang

小太阳yy posted on 2024-5-26 11:28 I am a little confused. There are still 4 questions that I am not very clear about. My current understanding is as follows: But I don’t know if it is correct, ...

[The lower the carrier recombination efficiency of semiconductor materials, the longer the lifetime, the longer the charge depletion time, and the longer the reverse recovery time]

That's right. Early fast recovery diodes tried to speed up carrier recombination to achieve fast recovery.