AN2708 datasheet(12/42 Pages) STMICROELECTRONICS

12 / 42 page

High-frequency ballast

AN2708

12/42

The basic design specifications are listed in Table 4.

For reference, it is useful to define also the following quantities:

●

Input power: Pi (= Po /

η) ≈ 80 W

●

Maximum mains RMS current: Iirms (= Pi/Virms(min))

≈ 1 A

●

Rated output current: Io (= Po/Vo)

≈ 0.2 A

The design guidelines are deeply explained in AN966 ("L6561, enhanced transition mode

power factor corrector"), AN1757 ("Switching from the L6561 to the L6562) and AN1089

("control loop model of L6561-based TM PFC"). The main design formulas are summarized

as follows inTable 5.

Table 4.

PFC operating conditions

Parameter

Value

Mains voltage range: Virms(min) - Virms(max)

90 – 265 Vac

Regulated DC output voltage: Vo

400 Vdc

Rated output power: Po

75 W

Minimum switching frequency: fsw

35 kHz

Maximum output voltage ripple:

∆Vo

< ± 10 V

Maximum overvoltage admitted:

∆VOVP

60 V

Expected efficiency:

ηPFC

> 90 V

Table 5.

Power stage design equations

Input capacitor (C1)

Boost inductor

Power MOSFET (Q1)

Boost diode (D1)

where

Output capacitor (C6)

Irms

π fsw r Vinrmsmin

⋅⋅

⋅

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

0.01

0.1

irms

Virms

⋅

–

()

⋅

⋅⋅

⋅

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

Volume

irms

⋅⋅

≥

K1410

–

Igap

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

⋅⋅

≅

Pcu

---

irms

Rcu

⋅

DSS

∆V

OVP

arg

Pon

Qrms

DS on

()

⋅

Qrms

2 2

Iirms

---

-----------

Virms

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

⋅

–

⋅

Pcross

Iirms

fall

⋅⋅

⋅

Pcap

3.3Coss

1.5

drain

--- Cd

drain

⋅

⎝⎠

⎛⎞

⋅

RRM

1.2

⋅

3Io

⋅

losses

rms

⋅

π fVo ∆Vo

⋅⋅

⋅

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

≥

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