AN4544 datasheet(31/35 Pages) STMICROELECTRONICS

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AN4544

Datasheet explanation

2.7.8

Diode switching characteristics (inductive load)

A typical reverse recovery waveform is shown in Figure 30. The reverse recovery time trr is

defined as the time from diode current zero-crossing to where the current returns within 25%

of the peak recovery current IRM(rec). A better way to characterize the rectifier reverse

recovery is to divide the reverse recovery time into two different regions, ta and tb, where ta

time is a function of the forward current and the applied di/dt. A charge Qa can be assigned

to this region, the area under the curve. tb portion of the reverse recovery current is not well-

fixed, in fact measured tb times vary according to the switch characteristic, circuit parasitic,

load inductance and the applied reverse voltage. A relative softness can be defined as the

ratio of tb to ta. General purpose rectifiers are very soft (softness factor about 1.0), fast

recovery diodes are fairly soft (softness factor about 0.5) and ultrafast rectifiers are not soft

(softness factor about 0.2).

Table 12. Diode switching characteristics (inductive load)

Symbol

Parameter

Test conditions

Min.

Typ.

Max.

Unit

trr

Reverse recovery time

IF = 40 A, VR = 400 V,

VGE = 15 V, di/dt=1000 A/µs

-41

Qrr

Reverse recovery charge

440

Irrm

Reverse recovery current

21.6

dIrr/ /dt

Peak rate of fall of reverse

recovery current during tb

-1363

A/µs

Err

Reverse recovery energy

151

µJ

trr

Reverse recovery time

IF = 40 A, VR = 400 V,

VGE = 15 V, di/dt=1000 A/µs

TJ = 175 °C

109

Qrr

Reverse recovery charge

2400

Irrm

Reverse recovery current

44.4

dIrr/ /dt

Peak rate of fall of reverse

recovery current during tb

670

A/µs

Err

Reverse recovery energy

718

µJ

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