DocID026370 Rev 1

11/18

AN4496

Designing a high PF wide range LED driver with the HVLED815PF

18

Mean output voltage [V]:

Equation 22

The mean voltage LED string drop is the output voltage.

Overvoltage protection [V]:

Equation 23

proportional to the output current and reverse proportional to output capacitance. This

application has a high ripple voltage (due to the high power factor and small bulk capacitor).

With a mean output voltage of 22 V the peak is at 25 V.

For reliability the output capacitor has a rated voltage of 35 V.

The selected OVP threshold of 29 V is set between these two limits (the peak output voltage

and output capacitor rated voltage).

Supply voltage of the device [V]:

Equation 24

In this design the supply voltage Vcc is low. That value is selected, because in this design

the output voltage is fixed to 22 V. A higher value of Vcc is recommended (until 18 - 21 V)

in case of application with variable output voltage [example: Iout = 460 mA,

Vout = 14 V ~ 22 V)].

The efficiency is better if the supply current is sourced from the auxiliary winding rather than

from the high voltage startup.