TS19452
AC/DC WLED Driver with Internal MOSFET
Universal Switch Mode
4/7
Version: A12
Application Information (Continue)
Where L is the inductance value, and C
L
is the coil capacitance. Charging and discharging this capacitance every
switching cycle causes high-current spikes in the LED string. Therefore, connecting a small capacitor C
O
(~100nF)
is recommended to bypass these spikes.
Using an ultra-fast rectifier diode for D1 is recommended to achieve high efficiency and reduce the risk of false
triggering of the current sense comparator. Using diodes with shorter reverse recovery time t
rr
and lower junction
capacitance C
J
achieves better performance. The reverse voltage rating V
R
of the diode must be greater than the
maximum input voltage of LED lamps.
The total parasitic capacitance present at the Drain pin of the TS19452 can be calculated as:
C
P
= C
DRAIN
+ C
PCB
+ CL + C
J
When the switching MOSFET turns on, the capacitance C
P
is discharged into the Drain pin of the IC. The discharge
current is limited to about 150mA typically. However, it may become lower at increased junction temperature. The
duration of the leading edge current spike can be estimated as:
T
PSIKE
= ((V
IN
x C
P
) / (I
SAT
)) + t
r
EMI Filter
As with all off-line converters, selecting an input filter is critical to obtaining good EMI. A switching side capacitor,
albeit of small value, is necessary in order to ensure low impedance to the high frequency switching currents of the
converter. As a rule of thumb, this capacitor should be approximately 0.1~0.2µF/W of LED output power.
