Characteristics

FLC01

4/11

DocID3616 Rev 7

The applications of the lighter using the capacitance discharge topology operate in 2

phases:

Phase 1

The energy coming from the mains is stored into the capacitor C. For that, the AC voltage is

rectified by the diode Ds.

Phase 2

At the end of the phase 1, the voltage across the capacitor C reaches the avalanche

threshold of the zener. Then a current flows through the gate of the thyristor Th which fires.

–

The firing of the thyristor causes an alternating current to flow through the

capacitor C

–

The positive parts of this current flow through C, Th and the primary of the HV

transformer

–

The negative parts of the current flow through C, D and the primary of the HV

transformer

RS resistor calculation

The Rs resistor allows, in addition with the capacitor C, the spark frequency to be adjusted

and the current from the mains to be limited. Its value shall allow the thyristor Th to fire even

in the worst case. In this case the system must fire with the lower RMS mains voltage value

while the breakdown voltage and current of the FLC are at the maximum.

The maximum Rs value is equal to:

(1) See Figure 4

Figure 6. Spark frequency versus RS and C

The couple Rs/C can be chosen with the previous curve.

Keep in mind the Rs maximum limit for which the system would not work when the AC

mains is minimum.

Rsmax

(V

2)

V

1 +

αTT

am b

25

–

()

⋅

()

⋅

[]

–

⋅

kI

BO

1

()

⋅

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

=

4.7

6.8

10

12

15

18

22

27 30

1

2

3

5

10

20

F (Hz)

Rs (k )

Ω

Vac=220Vrms, Vbo=225V, Tamb=25°C

C=3.3

F

μ

C=2.7

F

μ

C=2.2

F

μ

C=0.47

F

μ

C=0.47

F

μ

C=1

F

μ

C=1

F

μ

C=1.5

F

μ

C=1.5

F

μ