16

RD-0613

www.irf.com

The Run Mode frequency (Figure 11) 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 (LRES)

(H)

C

= Lamp resonant circuit capacitor (CRES) (F)

= Lamp running power

(W)

(V)

Fig. 11: Half-Bridge Mid-Point Voltage (VS Pin) During Run Mode

Normal Power Down

A normal power down occurs when the AC line voltage is disconnected from the ballast. When this

occurs, the voltage on the VBUS pin of the IRS2168D drops below the VBUS pin under-voltage reset

threshold of 3 V. This will cause VCC to be discharged internally to UVLO- (10.5 V). The IC enters