Texas Instruments TPS92310-12 Evaluation Module TPS92310-12FB/NOPB TPS92310-12FB/NOPB Ficha De Dados
Códigos do produto
TPS92310-12FB/NOPB
SNVS792 – FEBRUARY 2012
Design Example
The following design example illustrates the procedures to calculate the external component values for the
TPS92310 isolated single stage fly-back LED driver with PFC.
TPS92310 isolated single stage fly-back LED driver with PFC.
Design Specifications:
Input voltage range, V
AC_RMS
= 85VAC – 132VAC
Nominal input voltage, V
AC_RMS(NOM)
= 110VAC
Number of LED in serial =7
LED current, I
LED
= 350mA
Forward voltage drop of single LED = 3.0V
Forward voltage of LED stack, V
LED
= 21V
Key operating Parameters:
Converter minimum switching frequency, f
SW
= 75kHz
Output rectifier maximum reverse voltage, V
D3(MAX)
= 100V
Power MOSFET rating, V
Q1(MAX)
= 800V (2.5A/3.8
Ω
)
Power MOSFET Output Capacitance, C
DS
= 37pF (estimated)
Nominal output power, P
OUT
= 8W
Start Up Bias resistor
During start up, the V
CC
will be powered by the rectified line voltage through external resistor, R
1
. The V
CC
start
up current, I
VCC(SU)
must set in the range I
VCC(MIN)
>I
VCC(SU)
>I
STARTUP(MAX)
to ensure proper restart operation during
OVP fault. In this example, a value of 0.55mA is suggested. The resistance of R
1
can be calculated by dividing
the nominal input voltage in RMS by the start up current suggested.
So, R
1
= 110V/0.55mA = 200K
Ω
is recommended.
Transformer Turn Ratio
The transformer winding turn ratio, n is governed by the MOSFET Q1 maximum rated voltage, (V
Q3(MAX)
), highest
line input peak voltage (V
AC-PEAK
) and output diode maximum reverse voltage rating (V
D3(MAX)
). The output diode
rating limits the lower bound of the turn ratio and the MOSFET rating provide the upper bound of the turn ratio.
The transformer turn ratio must be selected in between the bounds. If the maximum reverse voltage of D3
(V
The transformer turn ratio must be selected in between the bounds. If the maximum reverse voltage of D3
(V
D3(MAX)
) is 100V. the minimum transformer turn ratio can be calculated with the equation in below.
(4)
In operation, the voltage at the switching node, V
SW
must be small than the MOSFET maximum rated voltage
V
Q1(MAX)
, For reason of safety, 10% safety margin is recommended. Hence, 90% of V
Q1(MAX)
is used in the
following equation.
(5)
(6)
where V
OS
is the maximum switching node overshoot voltage allowed, in this example, 50V is assumed. As a
rule of thumb, lower turn ratio of transformer can provide a better line regulation and lower secondly side peak
current. In here, turn ratio n = 3.8 is recommended.
current. In here, turn ratio n = 3.8 is recommended.
Copyright © 2012, Texas Instruments Incorporated
13
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