AN3032

Ballast design

Doc ID 16165 Rev 2

11/26

●

Pin12 PFCS is the inverting input of the current sense comparator. As the voltage

across the sense resistor (proportional to the instantaneous inductor current) crosses

the threshold set by the multiplier output, the power MOSFET is turned off. Equation 12

determines the PFC sense resistor.

Equation 12

●

●

Pin 14 HBCS: assuming that during each lamp’s ignition phase there is a maximum

Equation 13

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Pin 15 GND: device ground.

●

Pin 16 LSD: to drive the external half-bridge low-side MOSFET correctly, the resistor

●

●

Pin 18 out: floating reference of the high-side driver. This pin is connected close to the

source of the high-side power MOSFET.

●

Pin 19 HSD: to drive the external half-bridge low-side MOSFET correctly, the resistor

●

3.2

Design of the PFC power section

3.2.1

Input capacitor

The input high-frequency filter capacitor has to attenuate the switching noise due to the high

frequency inductor current ripple. The worst conditions will occur on the peak of the

●

The coefficient of the maximum high-frequency voltage ripple r = 0.05.

●

Total system efficiency

η = 0.9.

A

27

.

4

PF

V

P

2

2

I

min

in

outTOT

max

L

=

⋅

η

⋅

⋅

=

R

22

V

CSmin

I

Lmax

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

1

4.27

-----------

0.23

Ω

R

22

100m

Ω

=

⇒

=

=

<

Ω

=

=

−

32

.

0

I

V

R

TOT

max

IGN

ign

HBCS

31