snubber design
DESCRIPTION
Snubber DesignTRANSCRIPT
4. Snubber design (RC snubber)
RC snubber Secondary side diode
3
4
C102220nF
275VAC
LF10123mH
C101 220nF
275VAC
RT15D-9
F1 FUSE
250V
2A
C103100uF
400V
R102
30kΩΩΩΩ
R105
40kΩΩΩΩ
R10356kΩΩΩΩ2W
C10410nF
1kVD101
UF 4007
C106
47nF50V
C10522uF
50V
D102
TVR10GR104
5ΩΩΩΩ
1
2
3
4
5
T1
EER3016
BD101
2KBP06M3N257
1
2
R101560kΩΩΩΩ
1W
IC1
FSDM07652R
Vstr
NC
Vfb
Vcc
Drain
GND
1
2
34
5
6
ZD10122V
8
10
D202MBRF10100
C201
1000uF
25V
C202
1000uF25V
L201
12V, 2.5A
6
7
D201MBRF1045
C2031000uF
10V
C204
1000uF
10V
L202
5V, 2A
R201
1kΩΩΩΩ
R202
1.2kΩΩΩΩ
R204
5.6kΩΩΩΩ
R2031.2kΩΩΩΩ
C205
47nF
R2055.6kΩΩΩΩ
C301
4.7nF
IC301
H11A817AIC201
KA431
+
-
4. Snubber design (RC snubber)
Why Diode voltage oscillates when turned off?
Oscillation between the leakage inductance and diode output capacitance
Need to be damped with additional resonant network
Cout
Llk
Cout
Llk
Cout
Llk
3Cout
outrout
outlk
out
lk
CfC
CL
C
LR
π2
1===
Z
R
4. Snubber design (RC snubber)
(1) Measure the original resonance period (Tr) of the diode voltage waveforms.
(2) Find a capacitor value that doubles the resonance period when connected in parallel with the diode.
Tr=46ns
8
10
D202MBRF10100
C2011000uF
25V
Csn
With 680pF capacitor, the resonance period is approximately doubled (46ns 96ns)
4. Snubber design (RC snubber)
(3) Calculate the snubber resistor with the following equation.
8
10
D202
MBRF10100
C201
1000uF
25V
680pF 30
4. Snubber design (RCD snubber)
RCD snubber Primary side
4. Snubber design (RCD snubber)
Experimental results (Csn=2.2nF, Rsn=56kΩΩΩΩ, fs=66kHz)
WkuVV
VfIL
WkR
V
ROsn
snspklk
sn
sn
256.065122
122661.1)3(
2
1
2
1
266.056
122
22
22
=−
×××=−
==
WkuVV
VfIL
WkR
V
ROsn
snspklk
sn
sn
360.065143
1436641.1)3(
2
1
2
1
365.056
143
22
22
=−
×××=−
==
4. Snubber design (RCD snubber)
Design Procedure
Measure the leakage inductance : measure the primary side inductance with all other windings shorted
– LCR meter is not always correct (Normally 50% error) especially the leakage inductance is small
Determine the snubber capacitor voltage (Vsn) considering voltage margin of BVdss
Calculate the snubber resistor using
Determine the snubber capacitor considering the snubber capacitor voltage ripple (1~10nF)
If the measured drain voltage is different from the designed value, leakage inductance should be calibrated using
2
)(2
pkslk
ROsnsnsn
IfL
VVVR
−=
2
)(2
pkssn
ROsnsnlk
IfR
VVVL
−=
4. Snubber design (RCD snubber)
Design Example (VRO=65V, Vin=265Vac(VDC=370V), Ipk=1.5A)
Measure the leakage inductance with LCR meter: 5uH @ 70kHz
Determine the snubber capacitor voltage considering voltage margin of BVdss : Vsn=182V (Vsn+VDC=182+370=552V :85% of 650V)
Calculate the snubber resistor
Ω=
××
−××=
−= k
kuIfL
VVVR
pkslk
ROsnsnsn 57
5.1665
)65182(1822)(2
22
4. Snubber design (RCD snubber)
Determine the snubber capacitor considering the snubber capacitor voltage ripple : Csn=2.2nF
Measured the peak drain voltage : 520V (Vsn=146V)
uHkkIfR
VVVL
pkssn
ROsnsnlk 3
5.16656
)65150(1502)(2
22=
××
−××=
−=
Rsn=56kΩΩΩΩ, Csn=2.2nF
Vsn=520-370=150V
# Vsn is different from the
designed value
Recalculate the leakage inductance with measured Vsn
4. Snubber design (RCD snubber)
Recalculate snubber resistor
Ω=
××
−××=
−= k
kuIfL
VVVR
pkslk
ROsnsnsn 95
5.1663
)65182(1822)(2
22
Rsn=96kΩΩΩΩ, Csn=2.2nF
Vsn=543-370=173V
The drain voltage is lower than the designed value by 9V due to the
stray resistance (Measured:543V, Designed:552)