AN443 datasheet(3/14 Pages) STMICROELECTRONICS

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AN443 APPLICATION NOTE

Taking into account all these parameters, the voltage V1 across the diode D1 is given by the relation:

(1)

The resistance R must be chosen to limit the voltage V1 under the maximum value VRRM specified for this

rectifier. Thus:

(2)

For today’s fast rectifiers we can use k = 0.8.

IRM EVALUATION

IRM is the maximum leakage current at the maximum reverse voltage VRRM. This current depends on the

junction temperature (see Figure 4).

Generally, the manufacturer specifies a maximum value IRM at VRRM at Tj = 100°C, in the data sheet.

When we know the operating junction temperature (Tj), it is possible to calculate IRM by using the following

relation:

IRM(Tj) = IRM(100°C) exp[–0.054(100-Tj)]

Figure 4. Reverse leakage current versus junction temperature. BYT 261-1000 (typical value)

∆ IR estimation

In fact

∆ IR is the sum of ∆ IR1 and ∆ IR2 – ∆ IR1 is due to the leakage current dispersion of the rectifiers in

the same conditions of voltage and temperature.

For the fast rectifiers available today on the market the dispersion of the reverse current at VR = VRRM and

Tj = 100°C is about:

∆ IR1 = 0.6 IRM

This dispersion varies from one batch to another.

–

∆ IR2 is due to the difference between the junction temperatures of each device (∆Tj).

M 1a

() V

RRM

–

()I

RMR

() kn 1

–

() 1a

()∆I

RRVRRM

RMn1

–

() 1a

() V

RRM na

() R

–

∆I

R 1k

–

() 1a

() n1

–

()

---------------------------------------------------------------------------------------------------------------------------------------------------------------------

RRM VRRM na

() V

M 1a

()

–

()

∆I

RVRRM 1a

() n1

–

() I

–

() 1a

() nV

RRM

–

()

----------------------------------------------------------------------------------------------------------------------------------------------------

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