AN443 datasheet(8/14 Pages) STMICROELECTRONICS

8 / 14 page

AN443 APPLICATION NOTE

8/14

n order to limit the voltage across D1 under the specified value VRRM we calculate C by solving thus:

QRR and ∆QRR consideration

For a given diode the reverse recovery charge QRR is a function of the circuit commutation conditions such

as the magnitude of forward current (IF), the rate of decay of this current (dIF/dt) and the junction temper-

ature.

Typical values of QRR are given in the data sheet of each part number (see Figure 9).

Figure 9. Example of reverse recovery charge specification. (case of BYW 51)

For fast rectifiers coming from the same lot the dispersion of this parameter is low and we can use, with a

good safety margin:

∆QRR = .30 QRR

Is it possible to remove the equalizing capacitor?

In the blocking state, diodes have a junction capacitance. For a given diode this capacitance decreases

with an increase in the applied reverse voltage according to Figure 10.

–

()∆Q

()V

RRM

M 1a

()

–

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