IR21571(S) & (PbF)

10

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During the Startup Mode, the operating frequency is

normally chosen to ensure that the instantaneous

voltage across the lamp during the first few cycles of

operation does not exceed the strike potential of the

decays to the preheat frequency.

During the Preheat Mode, the operating frequency

frequency, along with the Preheat Time, is normally

chosen to ensure that adequate heating of the lamp

filaments occur. Typically, a 4.5:1 ratio of the hot

filament-to-cold filament resistance is desired for

maximum lamp life, as shown in Figure 7.

Figure 6: Oscillator section block diagram with external component connection

0.1

1

10

1

10

100

RDT (Kohms)

tDEAD

(usec)

CT = 220 pF

CT = 470 pF

CT = 1 nF

2

4.0V

5.1V

3

5

7.6V

1.0uA

4

2.0V

I

RT

6

I

7

4.0V

2.0V

CPH

RPH

RT

RUN

CT

DT

Q

S

R2 Q

R1

UNDER-

VOLTAGE

DETECT

C

PH

C

IGN

R

T

C

C

T

R

DT

R

PH

R

RUN