Application information

HVLED007

14/33

DS12866 Rev 1

no difference in the voltage stresses apart from those caused by parasitics and resulting

from the different peak currents.

The timing, the control and electrical quantities of a Hi-PF QR flyback converter based on

the HVLED007, needed for a proper design, are summarized in Table 6, 7 and 8

respectively. The symbolism used has been defined already or is obvious.

 the voltage drop across the EMI filter, the input bridge and the power switch in the ON-

state are negligible as compared to the instantaneous line voltage;

 transformer's efficiency is 100% and its windings are perfectly coupled;

boundary between the continuous and the discontinuous current conduction mode.

Please refer to [Reference 1] for more information on their derivation. It is worth noting that:

 Switching frequency along a line half-cycle is at a minimum on the peak of the sinusoid (θ

= π/2) and rises along the edges to reach the maximum value at the zero-crossings of the

line voltage (θ = 0 and θ = π/2).

 The absolute minimum of the switching frequency occurs on the peak of the sinusoid at

 The ON-time of the power switch behaves exactly the other way round: it is at a maximum

on the peak of the sinusoid, goes to a minimum at the zero-crossings and increases with

Table 6. Timing quantities in a HVLED007-based Hi-PF QR flyback converter

Eq. #

Parameter

Expression

1

Power switch ON-time

2

Switching period

3

Switching frequency

4

Duty cycle

 = 4 Lp

2

2

-----------------------------

T



 = 4 Lp

2

-----------------------------





2

 = 1

T





------------ = 1

4

---

2

-----------------

-----------------------------





2

D



 =



T





--------------------- =

1

-----------------------------