IRPLLNR2U Datasheet IRPLLNR2E, IRPLLNR2U | P13-P15

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turned on or the high side MOSFET, M2, is turned off. The magnitude of this voltage directly relates

to the current in the lamp resonant circuit. Figure 13 shows the voltage which appears across resis-

tor RCS during normal Run mode conditions while Figure 14 shows the voltage appearing across the

lamp during the end of Preheat mode, Ignition Ramp mode and the beginning of Run mode. Also

shown in Figure 13 are the gate drive signals for the low side MOSFET (LO pin) and the high side

MOSFET (HO-VS pin).

Figure 13: Normal Run mode, Upper trace: voltage

across RCS, Middle trace: IC2 LO pin voltage,

Lower trace: IC2 HO-VS pin voltage

Figure 14: Normal lamp ignition: Lamp voltage during

the end of Preheat mode, Ignition Ramp mode

and the beginning of the Run mode

During the Preheat mode the voltage across resistor RCS is not measured. However, at the end of

Preheat mode (the beginning of the Ignition Ramp mode) the hard-switching and over-current detec-

tion are enabled. If at any time thereafter the voltage magnitude across resistor RCS rises above the

over-current (CS+) threshold of the CS pin of IC2, a lamp fault condition is signaled and the half-

bridge output MOSFETs’, (M2 and M3) are turned off and the ballast goes into Fault mode. This can

happen if the lamp fails to ignite or if the upper filament is open. For failure to ignite the lamp, the

current in the half-bridge increases and thus the voltage across resistor RCS increases above the

over-current threshold signaling a fault. Figure 15 shows the voltage across resistor RCS and the

voltage appearing across the lamp when the ballast detects a failure to ignite the lamp and goes into

Fault mode. The CS+ threshold is determined by resistor ROC. An internal current source of 50uA is

connected to the OC pin of IC2 which when applied to resistor ROC sets a voltage at the OC pin.

This voltage is the CS+ threshold of IC2. Figure 16 shows the voltage appearing across the lamp

during the tail end of the Preheat mode and the Ignition Ramp mode for a failure of the lamp to ignite

condition. If the upper filament is open, the half-bridge output hard-switches and each time the low

side MOSFET (M3) is turned on a large current pulse occurs and thus a large voltage pulse occurs

across resistor RCS signaling a fault, Figure 17 shows this hard-switching condition. Figure 18 shows

the lamp voltage during the Preheat mode and beginning of Ignition Ramp mode for this hard-

switching condition when the lamp fault condition is detected. The ballast will remain in Fault mode

until either the line voltage is cycled or a lamp replacement is performed.

14 www.irf.com

Figure 15: Failure of lamp to ignite condition (lamp

filaments good): Upper trace: voltage across

RCS, Lower trace: lamp voltage

Figure 16: Failure of lamp to ignite condition (lamp

filaments good): Lamp voltage during the end

of Preheat and Ignition Ramp modes

Figure 17: Hard-switching condition (upper filament

open): Upper trace: voltage across RCS,

Middle trace: IC2 LO pin voltage,

Lower trace: IC2 HO-VS pin voltage

Figure 18: Hard-switching condition (upper filament open):

Lamp voltage during Preheat mode and beginning of

Ignition Ramp mode when lamp fault is detected

At the completion of the Ignition Ramp mode (beginning of the Run mode) the near/below resonance

(under-current) detection is also enabled. Near/below resonance detection is performed by synchro-

nously sensing the voltage across resistor RCS, which relates to the current flowing in the low side

MOSFET (M3), just prior to the turn off of M3. If this voltage is lower than the near/below resonance

threshold (CS- = 0.2V) of the CS pin of IC2, a lamp fault condition is signaled and the ballast goes

into Fault mode. This could occur if the frequency of oscillation becomes too close to the resonant

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frequency of the load circuit and the current in the load circuit commutates to close to zero. Figure 19

shows a near/below resonance condition where the voltage on resistor RCS falls below the 0.2V

threshold on the CS pin of IC2.

Figure 19: Near/Below Resonance conditions

Upper trace: voltage across RCS

Lower trace: half-bridge output voltage

Resistors R17, R18 and capacitor

C13 form a divider/filter network

which is used to detect an open lower

lamp filament and/or lamp replace-

ment. Under normal conditions, the

voltage across C8 is approximately

zero volts. However, if the lower fila-

ment becomes open or the lamp is

removed, the voltage across C13 in-

creases above the 2V threshold for

the SD pin of IC2 and signals a lamp

fault condition which in turn puts the

ballast into Fault mode. The ballast

remains in the Fault mode until the

line voltage is cycled or a lamp re-

placement is performed. If the lamp

is replaced with a lamp with a good

lower filament, the voltage on the SD

pin of IC2 is pulled back below the

2V threshold and the ballast will go

through a restart. Line voltage cycling

is also used to restart the ballast for all lamp fault conditions. The ballast will go through a full

Preheat, Ignition Ramp and Run modes any time a restart is performed. Note that the SD pin of IC2

is active during all modes of operation.

Another way that the ballast can go into Fault mode is if the AC line voltage falls below approximately

170Vrms. Resistors R11, R12 and capacitor C9 form a voltage divider/filter network which is con-

nected to the VDC pin of IC2 and is used to determine if the line voltage falls below permissible

levels. This happens when the line voltage is cycled or possibly a brownout condition occurs. The

VDC pin of IC2 senses a fault if the voltage at the pin falls below 3 volts and shutdown of the ballast

occurs. The ballast remains shutdown until the voltage at the VDC pin rises above 5.1 volts. At this

time if there are no other fault conditions the ballast will go through a full Preheat, Ignition Ramp and

Run mode. As in the case of the SD pin of IC2, the VDC pin of IC2 is active during all modes of

operation of the ballast.

IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245 Tel: (310) 252-7105

Data and specifications subject to change without notice. 10/28/2000

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

IRPLLNR2U

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BALLAST 32W/T8 120V AC IR21571

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