Texas Instruments TPS92311A19230VEVM Evaluation Module TPS92311A19230VEVM TPS92311A19230VEVM Datenbogen
Produktcode
TPS92311A19230VEVM
R2
R3
D2
C
ZCD
PGND
PGND
PGND
L3
VCC
ZCD
D
ZCD
TPS92311
R
ISNS
SW
SW
GND
ZCD
VIN
SW
ISNS
SW
GND
COMP
MODE1
DLY
MODE2
NC
NC
NC
SNVS811B – MAY 2012 – REVISED MAY 2013
Calculate The Current Sensing Resistor
After the primary inductance and transformer turn ratio is determined, the current sensing resistor, R
ISNS
can be
calculated.
The resistance for R
ISNS
is governed by the output current and transformer turn ratio, the equation in below can
be used.
where
•
V
REF
is fixed to 0.14V internally.
(14)
Transformer turn ratio, N
P
: N
S
is 3.8 : 1 and I
LED
= 0.35A
(15)
Figure 21. R
ISNS
Resistor Interface
Figure 22. Auxiliary Winding Interface to ZCD
Auxiliary Winding Interface To ZCD
In
, R2 and R3 forms a resistor divider which sets the thresholds for over voltage protection of V
LED,
V
ZCD-OVP
, and V
ZCD-PEAK
. Before the calculation, we need to set the voltage of the auxiliary winding, V
LAUX
at open
circuit.
For example :
Assume the nominal forward voltage of LED stack (V
LED
) is 21V.
To avoid false triggering ZCD
OVP
voltage threshold at normal operation, select ZCD
OVP
voltage at 1.3 times of the
V
LED
is typical in most applications. In case the transformer leakage is higher, the ZCD
OVP
threshold can be set
to 1.5 times of the V
LED
.
Copyright © 2012–2013, Texas Instruments Incorporated
17
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