Datasheet

PRIMARY SECONDARY
+
−
+
−
+
−
PRIMARY SECONDARY
+
−
+
−
+
−
(a)
(c)
0V
0V
(b)
0V
0V
(d)
V
D
V
D
V
D
V
D
V
G
V
G
V
G
V
G
L
M
L
M
L
LEAK
L
LEAK
V
BULK
V
BULK
C
BULK
C
BULK
V
IN
V
IN
V
R
V
R
∆V
SNUB
∆V
SNUB
C
SNUB
C
SNUB
R
SNUB2
R
SNUB1
R
SNUB1
C
D
C
D
R
CS
R
CS
M
1
M
1
D
S
D
S
Reduced L
LEAK
C
D
Resonance
L
LEAK
C
D
Resonance
UCC28600
SLUS646J –NOVEMBER 2005– REVISED JULY 2011 www.ti.com
Snubber Damping
Resonance between the leakage inductance and the MOSFET drain capacitance can cause false load-OVP
faults, in spite of the typical 2-μs delay in load-OVP detection. The bias winding is sensitive to the overshoot and
ringing because it is well coupled to the primary winding. A technique to eliminate the problem is to use an R
2
CD
snubber instead of an RCD snubber, shown in Figure 15. A damping resistor added to the RCD snubber reduces
ringing between the drain capacitor and the inductance when the snubber diode commutates OFF.
Figure 15. (a) RCD Snubber, (b) RCD Snubber Waveform, (c) R
2
CD Snubber, (d) R
2
CD Snubber
Waveform
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