TC62D902FG Datasheet, PDF (11/19 Pages) Toshiba Semiconductor – Offline Isolated AC/DC Flyback LED Controller built-in PFC

TC62D902FG
Switching Frequency of MOSFET)
The recommendation range of switch frequency fOSC is 30 - 200 kHz.
As explained by the function of the average LED current, it controls the pulse width tS of current IS at
the frequency in the standard. Roughly the following estimating is possible from the inductance
value LS, peak current IS(Peak) and the LED forward-voltage VF of the secondary.
Switch frequency fOSC = 1/(Secondary on time tS*(7/4))
= 1÷(Inductance of primary LS*Peak secondary current IS(peak)/VF of LEDs)*(7/4)
There is a following relation about the primary inductance LP and secondary inductance LS.
Primary inductance LP=Secondary inductance LS * Turn ratio Ntr^2
At this time, the primary inductance LP is big and recommends above 50μH.
Single state PFC)
This device does power-factor-improvement in making VIN terminal-voltage ISEN pin voltage
threshold and controlling an IP(Peak). Because the primary current is a discontinuity (DCM), it is
difficult for the power factor of the light-load to be high.
The power factor depends on the operating condition and it is possible for approximately and
PF=0.75~0.9 to be realized.
It inputs to the VIN pin voltage after doing AC voltage in the divide at the resistor.
This waveform becomes the voltage threshold of the ISEN pin voltage as gain 1. The VIN pin voltage
input-voltage-range is from 0V up to 1.8 V.
VIN
AC voltage in the divide at the resistor.
GATE
Primary
Current IP
ILED
Secondary
Current IS
Because the main system is single stage PFC, the LED current waveform of the secondary side
includes a ripple. To make LED current waveform smoother, it makes a secondary output capacitor
big. The GATE pin is modulating a frequency.
Remark)
This waveform is a function image and the actual waveform and the figure above
are sometimes different.
11
2014-10-01