Ballast design

AN3032

8/26

Doc ID 16165 Rev 2

●

Pin4 TCH is the time counter and is activated during the preheating phase as well as

after a protection is triggered (HBCS crossing during ignition/run mode, window

Equation 4

be calculated.

Equation 5

●

Pin5 EOLP is a 2 V reference and allows programming the window comparator of Pin6

(EOL) according to the values defined inTable 4 in the L6585DE datasheet. Working in

a lamp-to-ground configuration, a fixed reference mode has been selected, and for a

●

Pin6 EOL is the input of the window comparator. Concerning this comparator, the fixed

reference configuration requires two Zener diodes to shift the mean value of the lamp

voltage to 2.5 V. The values of the two Zener diodes relate to the symmetry of the

protection intervention, and the best symmetry is obtained by choosing two values

whose difference is equal to twice the reference voltage.

Referring to the first series lamp (Figure 7):

Equation 6

maximum/minimum voltage on the low resistance of the voltage divider of the lamp is

.

deviation voltage lamp

F

1

C

10

26974

.

0

C

t

7

6

7

reduced

,

Tch

μ

=

⇒

⋅

⋅

≅

Ω

⇒

Ω

=

⋅

⋅

−

=

k

750

k

755

5

.

1

63

.

4

ln

C

63

.

4

I

C

t

R

7

CH

7

pre

15

2

W

V

V

5

.

2

V

16

ZD

15

fD

max

K

+

+

+

=

(

)

2

W

V

V

5

.

2

V

16

fD

15

zD

min

K

−

+

−

=

V

10

V

,

V

1

.

5

V

V

V

5

.

2

2

15

zD

16

zD

16

zD

15

zD

=

=

⇒

−

=

⋅

V

K

8.2V

=

V

lamp

18V

=