Datasheet AP1910 (Anwell Semiconductor) - 7

AP1910 Anwell Semiconductor Corp. Detail Description (Continued) Operating Frequency
Knowing the nominal rectified input line voltage VIN=120V*1.414=170V. The switching duty ratio The operating frequency of AP1910 can be set by can be determined as: the external resistor connected to RT pin. Connecting the resistor from RT to GND for D  V /V  30 /170  0.176 LEDS IN constant frequency operation mode or RT to GATE for constant off-time operation mode. Following Then, given the switching frequency 50KHz. The diagram is the reference data for setting switching required on time of the MOSFET transistor can be frequency. calculated:
Constant Freqency mode
T  D / f  3.52s , T 16.48s ON OSC OFF
180 160
The required value of the inductor is given by:
z) 140 H K 120 (
 V V
y
IN LED
100
*T  30% * I
c
ON LED
n 80
L
e u 60 q
L  (V V ) *T / (0.3* I )  4.69mH
e
IN LED ON LED
r 40 F 20 0 0 200 400 600 800 1000 Input Bulk Capacitor RT (KΩ)
An input filter capacitor should be designed to hold
Constant Off-time mode
the rectified AC voltage above twice the LED string
60
voltage throughout the AC line cycle.
50 )
Assuming 15% relative voltage ripple across the
S 40 u(
capacitor, a simplified formula for the minimum
e 30
value of the bulk input capacitor is given by:
mi t-f f 20
1
O
2 I * 30% *V  C V LED LED MIN IN
10
2 2   
0
C I * 0.06 *V / V 22 F MIN LED LED IN
0 200 400 600 800 1000 RT (KΩ)
A passive PFC circuit at the input requires using two series connected capacitors at the place of
Inductor Design
calculated CMIN. Each of these identical capacitors should be rate for 0.5 of the input voltage and Referring to the typical application circuit below the have twice as much capacitance. value can be calculated from the desired peak-to-peak LED ripple current in the inductor. Typically, such ripple current is selected to be 30% of the nominal LED current in the example given here, the nominal current ILED is 350mA. The next step is determining the total voltage drop across the LED string. For example, when the string consists of 10 HB LEDs and each diode has forward voltage drop of 3V at its nominal current. The total LEDs voltage VLEDS is 30V. All reserved by AnSC © 2012 Page: 7/11 V1.6-2014/09/29