IRPLLNR2U International Rectifier, IRPLLNR2U Datasheet - Page 11

• Manufacturer Part Number: IRPLLNR2U
• Description: BALLAST 32W/T8 120V AC IR21571
• Manufacturer: International Rectifier

Specifications of IRPLLNR2U

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *IRPLLNR2U

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is exceeded and the lamp ignites. Figure 9 shows the ramping of voltage appearing across the lamp
and also the voltage on capacitor CRAMP. Note that the sudden drop in lamp voltage indicates that
the lamp has ignited. Also note that the voltage on capacitor C12 is still increasing at the point when
the lamp has already ignited meaning the frequency is still ramping down to the final minimum
ignition frequency. This minimum frequency corresponds to the absolute maximum ignition voltage
required by the lamp under all conditions.
During the Ignition Ramp mode the voltage on the CPH pin of IC2 continues to ramp up until the
voltage at the CPH pin of IC2 exceeds the Run mode threshold (5.1V). Over-current sensing is also
enabled at the beginning of the Ignition Ramp mode. A full explanation of the functionality of the
over-current sensing is in the section on Fault Mode.
Run Mode
At the end of the Ignition Ramp mode (CPH pin
> 5.1V) the ballast switches to the Run mode at
which point the frequency is shifted to the run
frequency. The run frequency is determined by
the parallel combination of resistors RT and
RRUN and capacitor CT. Resistor RRUN is
connected in parallel by turning on the internal
open drain MOSFET connected to the RUN pin
of IC2 (see Figure 1, IR21571 block diagram).
The sensing of under-current conditions is also
enabled at the beginning of the Run mode. The
full explanation of the functionality of the under-
current sensing is in the section on Fault Mode.
Figure 10 shows the functionality of the CPH,
RPH and RUN pins of IC2 during Startup, Pre-
heat, Ignition Ramp and Run modes.
The Run mode frequency is that at which the lamp is driven to the lamp manufacturer’s recom-
mended lamp power rating. The running frequency of the lamp resonant output stage for selected
component values is defined as,
f
run
2
1
LC
1
2
CV
P
Lamp
2
Lamp
2
LC
1
2
CV
P
Lamp
2
Lamp
Figure 10: Top trace: CPH pin IC2
2
Middle trace: RPH pine IC2
Bottom trace: RUN pin IC2
2
4
1
2
V
L
V
2
Lamp
C
DCbus
2
2
(3)
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