WESTCODE An IXYS Company
Soft Recovery Diode Types M0358WC120 to M0358WC180
5.0 Reverse Recovery Loss
The following procedure is recommended for use where it is necessary to include reverse recovery loss.
From waveforms of recovery current obtained from a high frequency shunt (see Note 1) and reverse
voltage present during recovery, an instantaneous reverse recovery loss waveform must be constructed.
Let the area under this waveform be E joules per pulse. A new sink temperature can then be evaluated
[ ]TSINK = TJ (MAX ) − E ⋅ k + f ⋅ RthJK
Where k = 0.2314 (°C/W)/s
E = Area under reverse loss waveform per pulse in joules (W.s.)
f = Rated frequency in Hz at the original sink temperature.
RthJK = d.c. thermal resistance (°C/W)
The total dissipation is now given by:
W(tot ) = W(original ) + E ⋅ f
NOTE 1 - Reverse Recovery Loss by Measurement
This device has a low reverse recovered charge and peak reverse recovery current. When measuring the
charge, care must be taken to ensure that:
(a) AC coupled devices such as current transformers are not affected by prior passage of high
amplitude forward current.
(b) A suitable, polarised, clipping circuit must be connected to the input of the measuring oscilloscope
to avoid overloading the internal amplifiers by the relatively high amplitude forward current signal.
(c) Measurement of reverse recovery waveform should be carried out with an appropriate critically
damped snubber, connected across diode anode to cathode. The formula used for the calculation of this
snubber is shown below:
R2 = 4 ⋅ Vr
Where: Vr = Commutating source voltage
CS = Snubber capacitance
R = Snubber resistance
6.0 Snubber Components
When selecting snubber components, care must be taken not to use excessively large values of snubber
capacitor or excessively small values of snubber resistor. Such excessive component values may lead to
device damage due to the large resultant values of snubber discharge current. If required, please consult
the factory for assistance.
Data Sheet. Types M0358WC120 to M0358WC180 Issue 1
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