Regarding the "Current Ratings of Diode", this article will explain the information below.

- Current Ratings of Diode
- Average Forward Current \(I_O\)
- Surge Forward Current \(I_{FSM}\)
- Repetitive Peak Forward Current \(I_{FRM}\)
- Rated Peak Pulse Current \(I_{SM}\)
- RMS Forward Current \(I_{F(RMS)}\)
- Peak Repetitive Reverse Surge Current \(I_{RRM}\)

## Current Ratings of Diode

The absolute maximum ratings in the datasheet of a diode show the current ratings.

The current ratings are listed in the following ways, although the information varies from datasheet to datasheet.

- Average Forward Current \(I_O\)
- Surge Forward Current \(I_{FSM}\)
- Repetitive Peak Forward Current \(I_{FRM}\)
- Rated Peak Pulse Current \(I_{SM}\)
- Peak Repetitive Reverse Surge Current \(I_{RRM}\)

Each current rating is explained in turn below.

## Average Forward Current I_{O}

"Average Forward Current \(I_O\)" listed in the absolute maximum ratings of the diode is the maximum value of the average value of the forward current under the specified conditions and resistive load.

For the specified conditions, waveform and temperature are listed. Each condition is shown below.

Specified Conditions

Waveform

Generally, it is specified as "sine wave of commercial frequency (50Hz, 60Hz) or square wave under specified conditions".

For example, "50Hz sine wave, Resistance load," is described in the data sheet.

Therefore, the average forward current \(I_O\) listed in the absolute maximum ratings in the datasheet is the maximum value of the average value of forward current when rectifying a sine wave of commercial frequency (50Hz, 60Hz) or a square wave under the specified conditions.

The "maximum value of the average value of forward current" is the same for both 50Hz and 60Hz.

Temperature

The case temperature is described.

For example, "\(T_C=115{\mathrm{{^{\circ}C}}}\)" is described in the data sheet.

### Another Notation for "Average Forward Current I_{O}"

"Average Forward Current \(I_O\)" has various designations on the datasheet as shown below.

Another Notation

- Average Rectified Forward Current
- Average Rectified Output Current
- Average Output Current
- Maximum Average Forward Rectified Current
- Maximum Average Forward Current

There are various symbols for the average forward current; sometimes \(I_{F(AV)}\) or \(I_{FAV}\) is used instead of \(I_O\). \(I_O\) are often used with compound diodes such as center-tapped types, while \(I_{F(AV)}\) and \(I_{FAV}\) are used with single diodes.

## Surge Forward Current I_{FSM}

"Surge Forward Current \(I_{FSM}\)" listed in the absolute maximum ratings of the diode is the peak value of the non-repeatable forward current for one half-sine wave cycle.

The sine half-wave pulse width \(t_p\) is \(t_p=10{\mathrm{ms}}\) at \(50{\mathrm{Hz}}\) and \(t_p=8.3{\mathrm{ms}}\) at \(60{\mathrm{Hz}}\).

In addition, \(I_{FSM(50{\mathrm{Hz}})}\) and \(I_{FSM(60{\mathrm{Hz}})}\) have the following relationship: \(I_{FSM(50{\mathrm{Hz}})}\) multiplied by approximately 1.1 yields \(I_{FSM(60{\mathrm{Hz}})}\).

\begin{eqnarray}

I_{FSM(50{\mathrm{Hz}})}×1.1=I_{FSM(60{\mathrm{Hz}})}

\end{eqnarray}

This surge forward current \(I_{FSM}\) is used for inrush currents flowing at power-on.

Note, however, that since it is non-repeating, it cannot be applied to inrush currents that flow after the power is turned back on before the temperature returns to the specified conditions (typically 25°C).

If the inrush current flows for more than one cycle, refer to the "Peak Surge Forward Current \(I_{FSM}\) - Number of Cycles Characteristics" in the datasheet. The following is the "Peak Surge Forward Current \(I_{FSM}\) - Number of Cycles Characteristics" ofs Shindengen's S3V80. You can see that the maximum value of \(I_{FSM}\) decreases as the number of cycles increases.

If the half-wave pulse width \(t_p\) differs, refer to the "Peak Surge Forward Current \(I_{FSM}\) - Pulse Width Characteristics" in the data sheet. The following is the "Peak Surge Forward Current \(I_{FSM}\) - Pulse Width Characteristics" of Shindengen's S3V80. It can be seen that the maximum value of \(I_{FSM}\) decreases as the pulse width \(t_p\) increases.

Supplement

- There is also \(I_{FSM}\) with "1": \(I_{FSM1}\) is "the peak value of the non-repeating forward current for one cycle of a sine half-wave with a specified pulse width \(t_p=1{\mathrm{ms}}\)".

### Another Notation for "Surge Forward Current I_{FSM}"

"Surge Forward Current \(I_{FSM}\)" has various designations on the datasheet as shown below.

Another Notation

- Surge Current Non-Repetitive Current
- Peak Forward Surge Current
- Peak Surge Forward Current
- Non-Repetitive Forward Surge Current
- Non-Repetitive Surge Current

## Repetitive Peak Forward Current I_{FRM}

"Repetitive Peak Forward Current \(I_{FRM}\)" listed in the absolute maximum ratings of the diode is the peak value of the repetitive forward current under the specified conditions.

For the specified conditions, waveform and temperature (25°C if not specified) are listed. Each condition is shown below.

Specified Conditions

Waveform

Generally, it is specified as "Sine or Square Wave at specified conditions".

For example, "Square Wave, \(20{\mathrm{kHz}}\)", "\(t_p=10{\mathrm{ms}}\), Half Sine Wave", "\(t_p=10{\mathrm{ms}}\), Pulse", "\(t_p=1{\mathrm{ms}}\)", etc. are described in the data sheet.

Temperature

The case temperature is described.

For example, "\(T_C=115{\mathrm{{^{\circ}C}}}\)" is described in the data sheet.

### Another Notation for "Repetitive Peak Forward Current I_{FRM}"

"Repetitive Peak Forward Current \(I_{FRM}\)" has various designations on the datasheet as shown below.

Another Notation

- Peak Repetitive Forward Current
- Repetitive Forward Surge Current

## Rated Peak Pulse Current I_{SM}

"Rated Peak Pulse Current \(I_{SM}\)" listed in the absolute maximum ratings of the diode is the peak value of the impulse forward current under specified conditions.

The specified conditions are described in the data sheet as "\(t_p=8/20{\mathrm{μs}}\)".

Supplement

- There are various symbols for the rated peak pulse current; sometimes \(I_{PPM}\) or \(I_{PP}\) is used instead of \(I_{SM}\).

## RMS Forward Current I_{F(RMS)}

"RMS Forward Current \(I_{F(RMS)}\)" listed in the absolute maximum ratings of the diode is the maximum value of the effective value of the forward current.

The RMS forward current \(I_{F(RMS)}\) is determined by the bonding wire limit of the diode (since the bonding wire heating is proportional to the square of the RMS value of the current).

Supplement

- There are various symbols for the RMS forward current; sometimes \(I_{RMS}\) is used instead of \(I_{F(RMS)}\).

## Peak Repetitive Reverse Surge Current I_{RRM}

"Peak Repetitive Reverse Surge Current \(I_{RRM}\)" listed in the absolute maximum ratings of the diode is the maximum value of the reverse direction current (leakage current) flowing through the diode.

#### Summary

In this article, the following information on the "Current Ratings of Diode" was explained.

- Current Ratings of Diode
- Average Forward Current \(I_O\)
- Surge Forward Current \(I_{FSM}\)
- Repetitive Peak Forward Current \(I_{FRM}\)
- Rated Peak Pulse Current \(I_{SM}\)
- RMS Forward Current \(I_{F(RMS)}\)
- Peak Repetitive Reverse Surge Current \(I_{RRM}\)

Thank you for reading.