13

RD-0609

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17.Run Mode

During the Run mode the frequency is shifted to the run frequency. The run frequency is determined

only by RT. The 1 V to 3 V end-of-life window comparator in the SD pin is enabled at the beginning

of the Run mode. The full explanation of the functionality of the end-of-life sensing is in the section on

Fault Mode. The Run mode frequency is that at which the lamp is driven to the lamp manufacturer’s

recommended lamp power rating. The running frequency of the lamp resonant output stage for selected

component values is defined as,

f

LC

P

CV

LC

P

CV

V

V

LC

run

Lamp

Lamp

Lamp

Lamp

DCbus

Lamp

=− ⎛

⎝⎜

⎞

⎠⎟

+− ⎛

⎝⎜

⎞

⎠⎟

⎡

⎣

⎢

⎢

⎤

⎦

⎥

⎥

−

− ⎛

⎝⎜

⎞

⎠⎟

1

2

1

2

1

24

1

2

2

2

2

2

2

2

22

π

π

where,

L

= Lamp resonant circuit inductor (L3)

(H)

C

= Lamp resonant circuit capacitor (C14)

(F)

= Lamp running power

(W)

= Lamp running voltage amplitude

(V)

Figure 6 shows the voltage appearing across the lamp during Startup, Preheat, Ignition Ramp and Run

modes.

Fig. 6: Preheat, Ignition Ramp and Run Voltage in the lamp