3 Key parameters of damper diodes
TA0319 - TECHNICAL ARTICLE
Figure 3.
Current, voltage and switching energy in DAMPER diode at turn on
(DTV1500HDFP)
V
FP
= 20V
W
ON
= 16.4
µ
J
For high switching frequencies, P
on
is high and V
FP
becomes a critical parameter. V
FP
increases with (dI/dt)ON. In this application, this parameter is mainly fixed and is generally
lower than 100A/µs.
3.2.3
Leakage current and reverse losses
The new family of DAMPER diodes uses new technology allowing a very low leakage current
and negligible reverse losses in comparison with the other losses.
3.2.4
Reverse recovery time (t
rr
) and turn off switching losses (P
off
)
At t=t0, when the diode turns off, the reapplied voltage is low (V
CEsat
of the transistor), and the
corresponding switching energy W
off
is also very low (between t0 and t1). Due to this low
reapplied voltage, the DAMPER diode takes time to evacuate all these reverse recovery
charges.
For a given frequency, if t
rr
is too high, there are still charges when the transistor turns off (at
t1). In this situation the reverse recovery charge is evacuated over a high voltage inducing high
switching energy W
off
(Figure
2).
We can consider this as a critical frequency F
C
. Below F
C
, W
off
is negligible (the DAMPER
diode has evacuated all the reverse recovery charges at t0).
Above F
C
, the switching energy increases very rapidly and can lead to a thermal runaway
problem. This critical frequency depends not only on the reverse recovery time, but also on the
operating junction temperature of the diode and V
CEsat
of the transistor.
This is the reason why STMicroelectronics has developed two DAMPER diode families with t
rr
optimized for the CRT TV deflection frequencies and optimized for CRT monitor frequencies.
Figure 4
summarizes the main features of the different losses as follows:
P
on
are proportional to V
FP
and F
P
cond
depend on V
F
(Vt
0
,R
d
), I
P
and
δ
P
rev
are negligible
P
off
are negligible for F<F
C
and increase very quickly for F>F
C
F
C
depends on t
rr
, T
j
, V
CEsat
4/10
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