IR2166
Step 5: Program Maximum Ignition Current
Step 3: Program Preheat Frequency
The maximum ignition current is programmed
with the external resistor RCS and an internal
threshold of 1.3 volts. This threshold determines
the over-current limit of the ballast, which can
be exceeded when the frequency ramps down
towards resonance during ignition and the lamp
does not ignite. The maximum ignition current
is given as:
The preheat frequency is programmed with
timing resistors RT and RPH, and timing
capacitor CT. The timing resistors are
connected in parallel internally for the duration
of the preheat time. The preheat frequency is
therefore given as:
1
fPH
=
0.51 RT RPH
RT + RPH
[Hertz] (5)
2 CT
+1475
1.3
IIGN
=
[Amps Peak] (9)
[Ohms] (10)
RCS
or
or
1
− 2892 RT
1.3
1.02 CT fPH
RCS
=
RPH
=
IIGN
1
[Ohms] (6)
RT −
− 2892
1.02 CT fPH
Step 4: Program Preheat Time
The preheat time is defined by the time it takes
for the capacitor on pin CPH to charge up to
10 volts. An internal current source of 3uA flows
out of pin CPH. The preheat time is therefore
given as:
tPH = CPH 3.33e6
[Seconds] (7)
[Farads] (8)
or
CPH = tPH 0.3e − 6
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27
INFINEON [ Infineon ]
