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1 www.irf.com ir21571 ballast control ic design kit features drives: 1 x 32w t8 lamp (irpllnr2u) 1 x 36w t8 lamp (irpllnr2) input: 90-140vac/60hz (irpllnr2u) 185-265vac/50hz (irpllnr2) high power factor/low thd high frequency operation (42khz) lamp filament preheating lamp fault protection with auto-restart brownout protection ir21571 hvic ballast controller description the irpllnr2 is a high efficiency, high power factor, fixed output electronic ballast designed for driving rapid start fluorescent lamp types. the design contains an emi filter, active power factor correction and a ballast control circuit using the ir21571. this demo board is intended to ease the evaluation of the ir21571 ballast control ic, demonstrate pcb layout techniques and serve as an aid in the development of production ballast?s using the international rectifier ir21571. ballast block diagram emi filter rectifier pfc half-brid g e output sta g e line lamp pfc control ir21571 uvlo lamp fault international rectifier ? 233 kansas street, el segundo, ca 90245 usa irpllnr2
2 www.irf.com parameter units value (irpllnr2) value (irpllnr2u) lamp type 36w t8 32w t8 input power [w] 36 32 input current [arms] 0.300 0.300 preheat mode frequency [khz] 44 44 preheat mode lamp voltage [vrms] 220 220 preheat time [s] 0.9 0.6 ignition ramp mode frequency [khz] 38 38 run mode frequency [khz] 42 42 lamp run current [arms] 0.34 0.34 input ac voltage range [vacrms] 185..255/50..60hz 90..140/50..60hz input dc voltage range [vdc] 250..350 100..180 power factor 0.98 0.99 total harmonic distortion [%] <15 <10 maximum output voltage [vpk] 600 600 electrical characteristics note: measurements performed with input ac line voltage = 120vrms (irpldim1u) 230vrms (irpldim1) fault ballast restart operation line voltage low deactivates increase line voltage upper filament broken deactivates lamp exchange lower filament broken deactivates lamp exchange failure to ignite deactivates lamp exchange open circuit (no lamp) deactivates lamp exchange fault protection characteristics functional description overview he irpldim1 demo board consists of an emi filter, an active power factor correction front end, a ballast control section and a resonant lamp output stage. the active power factor correction section is a boost converter operating in critical mode conduction, free-running frequency mode. the ballast control section provides frequency modulation control of a traditional rcl lamp resonant output circuit and is easily adaptable to a wide variety of lamp types. the ballast control section also pro- vides the necessary circuitry to perform closed-loop dimming, lamp fault detection, shutdown and auto-restart. all functional descriptions refer to the irpldim1 schematic diagram.
3 www.irf.com l1 c2 br1 c3 r1 r2 r3 r4 r5 r6 r7 c4 c5 l2 d1 c6 m1 r9 r10 d2 c8 cramp cph c9 r11 cstart rstart rt c13 ct rrun rph rdt c11 d4 c10 r14 r13 rcs m3 r16 r15 c12 m2 d5 r17 c17 l3 d6 c15 c16 r18 r12 note: thick traces represent high-frequency, high-current paths. lead lengths should be minimized to avoid high-frequency noise problems l n r8 rv1 gnd c1 roc 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 ir21571 vdc cph rph rt run ct dt oc lo com vcc vb vs ho sd cs r19 coc d3 8 7 6 5 4 3 2 1 mc34262 c7 c14 r20 r21 irpllnr2/irpllnr2u schematic diagram
4 www.irf.com irpllnr2u bill of materials lamp type: t8/32w line input voltage: 90..140 vac/50..60 hz note: different lamp types require different frequency programming components. item # qt manufacturer part number description reference 1 1 international rectifier df10s bridge rectifier, 1a 1000v br1 2 1 roederstein wy0222mcmbf0k capacitor, 2.2nf 275 vac y cap c1 3 1 roederstein f1772433-2200 capacitor, 0.33uf 275 vac c2 4 1 wima mkp10 capacitor, 0.01uf 400 vdc c3 5 3 panasonic ecu-v1h103kbm capacitor, 0.01uf smt 1206 c4, cramp, cstart 6 3 panasonic ecj-3yb1e474k capacitor, 0.47uf smt 1206 c5, c6, c13 7 5 panasonic ecu-v1h104kbm capacitor, 0.1uf smt 1206 c9,cph, coc, c10, c11 8 1 panasonic eeu-eb2v100 capacitor, 10uf 350vdc 105c c8 9 1 panasonic ecu-v1h471kbm capacitor, 470pf smt 1206 ct 10 1 panasonic ece-a1hge010 capacitor, 1uf 50vdc 105c c12 11 1 vitramon 1812a152kxe capacitor, 1.5nf 1kv smt 1812 c14 12 1 wima mkp10 capacitor, 0.1uf 400vdc c15 13 1 vitramon 1812a102kxe capacitor, 1nf 1kv smt 1812 c16 14 1 panasonic ecw-h16103jv capacitor, 0.01uf 1.6kv c17 15 1 panasonic ecu-v1h101kbm capacitor, 100pf smt 1206 ccs 16 3 diodes ll4148dict-nd diode, 1n4148 smt dl35 d1, d5, d6 17 2 international rectifier 10bf60 diode, smt smb d2, d4 18 1 diodes zmm5250bct diode, zener , 20v smt dl35 d3 19 1 motorola mc34262 ic, power factor controller ic1 20 1 international rectifier ir21571 ic, ballast driver ic2 21 1 panasonic elf-15n007a emi inductor, 1x10mh 0.7apk l1 22 1 rg-allen pfc inductor, 2.0mh 2.0apk l2 23 1 rg-allen inductor, 2.0mh 2.0apk l3 24 3 international rectifier irf730 transistor, mosfet m1, m2, m3 25 5 panasonic erj-8geyj680k resistor, 680k ohm smt 1206 r1, r2, r4, r5, r17 26 1 panasonic erj-8geyj10k resistor, 10k ohm smt 1206 r3 27 1 panasonic erj-8geyj12k resistor, 12k ohm smt 1206 r6 28 1 panasonic erj-8geyj100k resistor, 100k ohm smt 1206 r7 29 3 panasonic erj-8geyj22k resistor, 22k ohm smt 1206 r8, rstart, rt 30 3 panasonic erj-8geyj22 resistor, 22 ohm smt 1206 r9, r13, r15 31 1 dale cw-1/2 resistor, 0.5 ohm ? watt r10 32 1 panasonic erj-8geyj130k resistor, 130k ohm smt 1206 r11 33 1 yageo 2.2mqbk-nd resistor, 2.2megohm ? watt r12 34 1 dale cw-1/2 resistor, 0.68 ohm ? watt rcs 35 1 panasonic erj-8geyj5.6k resistor, 5.6k ohm smt 1206 rdt 36 1 panasonic erj-8geyj30k resistor, 30k ohm smt 1206 roc 37 1 panasonic erj-8geyj91k resistor, 91k ohm smt 1206 rph 38 1 panasonic erj-8geyj150k resistor, 150k ohm smt 1206 rrun 39 1 yageo 390kqbk-nd resistor, 390k ohm ? watt r14 40 1 panasonic erj-8geyj1k resistor, 1k ohm smt 1206 r16 41 1 panasonic erj-8geyj2.2m resistor, 2.2megohm smt 1206 r18 42 1 yageo 100kqbk-nd resistor, 100k ohm ? watt r19 43 1 panasonic erz-v05d471 transient suppressor rv1 44 2 panasonic erj-8geyj10 resistor, 10 ohm smt 1206 r20, r21 total 67
5 www.irf.com irpllnr2 bill of materials lamp type: t8/36w line input voltage: 180..255 vac/50..60 hz note: different lamp types require different frequency programming components. item # qt manufacturer part number description reference 1 1 international rectifier df10s bridge rectifier, 1a 1000v br1 2 1 roederstein wy0222mcmbf0k capacitor, 2.2nf 275 vac y cap c1 3 1 roederstein f1772433-2200 capacitor, 0.33uf 275 vac c2 4 1 wima mkp10 capacitor, 0.01uf 400 vdc c3 5 3 panasonic ecu-v1h103kbm capacitor, 0.01uf smt 1206 c4, cramp, cstart 6 3 panasonic ecj-3yb1e474k capacitor, 0.47uf smt 1206 c5, c6, c13 7 5 panasonic ecu-v1h104kbm capacitor, 0.1uf smt 1206 c9,cph, coc, c10, c11 8 1 panasonic eeu-eb2v100 capacitor, 10uf 350vdc 105c c8 9 1 panasonic ecu-v1h471kbm capacitor, 470pf smt 1206 ct 10 1 panasonic ece-a1hge010 capacitor, 1uf 50vdc 105c c12 11 1 vitramon 1812a152kxe capacitor, 1.5nf 1kv smt 1812 c14 12 1 wima mkp10 capacitor, 0.1uf 400vdc c15 13 1 vitramon 1812a102kxe capacitor, 1nf 1kv smt 1812 c16 14 1 panasonic ecw-h16103jv capacitor, 0.01uf 1.6kv c17 15 1 panasonic ecu-v1h101kbm capacitor, 100pf smt 1206 ccs 16 3 diodes ll4148dict-nd diode, 1n4148 smt dl35 d1, d5, d6 17 2 international rectifier 10bf60 diode, smt smb d2, d4 18 1 diodes zmm5250bct diode, zener 20v smt dl35 d3 19 1 motorola mc34262 ic, power factor controller ic1 20 1 international rectifier ir21571 ic, ballast driver ic2 21 1 panasonic elf-15n007a emi inductor, 1x10mh 0.7apk l1 22 1 rg-allen pfc inductor, 2.0mh 2.0apk l2 23 1 rg-allen inductor, 2.0mh 2.0apk l3 24 3 international rectifier irf830 transistor, mosfet m1, m2, m3 25 5 panasonic erj-8geyj680k resistor, 680k ohm smt 1206 r1, r2, r4, r5, r17 26 1 panasonic erj-8geyj10k resistor, 10k ohm smt 1206 r3 27 1 panasonic erj-8geyj8.2k resistor, 8.2k ohm smt 1206 r6 28 1 panasonic erj-8geyj100k resistor, 100k ohm smt 1206 r7 29 3 panasonic erj-8geyj22k resistor, 22k ohm smt 1206 r8, rstart, rt 30 3 panasonic erj-8geyj22 resistor, 22 ohm smt 1206 r9, r13, r15 31 1 dale cw-1/2 resistor, 1.0 ohm ? watt r10 32 1 panasonic erj-8geyj56k resistor, 56k ohm smt 1206 r11 33 1 yageo 2.2mqbk-nd resistor, 2.2megohm ? watt r12 34 1 dale cw-1/2 resistor, 0.68 ohm ? watt rcs 35 1 panasonic erj-8geyj5.6k resistor, 5.6k ohm smt 1206 rdt 36 1 panasonic erj-8geyj30k resistor, 30k ohm smt 1206 roc 37 1 panasonic erj-8geyj75k resistor, 75k ohm smt 1206 rph 38 1 panasonic erj-8geyj150k resistor, 150k ohm smt 1206 rrun 39 1 yageo 390kqbk-nd resistor, 390k ohm ? watt r14 40 1 panasonic erj-8geyj1k resistor, 1k ohm smt 1206 r16 41 1 panasonic erj-8geyj2.2m resistor, 2.2megohm smt 1206 r18 42 1 yageo 100kqbk-nd resistor, 100k ohm ? watt r19 43 1 panasonic erz-v05d471 transient suppressor rv1 44 2 panasonic erj-8geyj10 resistor, 10 ohm smt 1206 r20, r21 total 65
6 www.irf.com power factor correction the power factor correction section consists of the motorola semiconductor mc34262 power factor controller ic (ic1), mosfet m1, inductor l2, diode d2, capacitor c8 and additional biasing, sens- ing and compensation components (see schematic diagram). the ic was chosen for its minimal component count, low start-up supply current and robust error amplifier. this is a boost topology designed to step-up and regulate the output dc bus voltage while drawing sinusoidal current from the line (low thd) which is ? in phase ? with the ac input line voltage (hpf). the design of the power factor correction section was taken from the motorola semiconductor mc34262 data sheet and information on the operation and design considerations for the mc34262 are contained therein. ballast control the ballast control section is built around the ir21571 ballast control ic, ic2 of the demo board. the ir21571 contains an oscillator, a high voltage half-bridge gate driver and lamp fault protection circuitry. a block diagram of the ir21571 ic is shown in figure 1 and a state diagram of the ir21571 is shown in figure 2. following is a breakdown of the operation of the ballast in all of the different modes of operation. over- temp detect level shift pulse filter & latch 2 4.0v 5.1v 3 5 7.6v 3.0v 5.1v 1 1.0ua 4 2.0v i rt 6 i ct = i rt 7 4.0v 2.0v cph rph rt run ct dt vdc q s r2 q r1 q t rq 16 14 15 vs ho vb 13 11 12 com lo vcc 15.6v 9 sd 10 0.2v cs q s rq qd r q clk qs r q under- voltage detect 2.0v 8 oc 50ua 7.6v 7.6v 7.6v figure 1: ir21571 block diagram
7 www.irf.com uvlo mode 1 / 2 -brid g e off i qcc ? 150 a cph = 0v oscillator off preheat mode 1 / 2 -brid g e @ f ph cph char g in g @ i ph = 1 a rph = 0v run = open circuit cs disabled ignition ramp mode f ph ramps to f min cph char g in g @ i ph = 1 a rph = open circuit run = open circuit cs+ threshold enabled run mode f min ramps to f run cph char g es to 7.6v clamp rph = open circuit run = 0v cs- threshold enabled vcc > 11.4v ( uv+ ) and vdc > 5.1v ( bus ok ) and sd < 1.7v ( lamp ok ) and t j < 140c ( t jmax ) cph > 4.0v ( end of preheat mode ) cph > 5.1v ( end of ignition ramp ) vcc < 9.5v ( vcc fault or power down ) or vdc < 3.0v ( dc bus/ac line fault or power down ) or sd > 2.0v ( lamp fault or lamp removal ) power turned on fault mode fault latch set 1 / 2 -brid g e off i qcc ? 150 a cph = 0v vcc = 15.6v oscillator off t j > 140c ( over-temperature ) cs > cs+ threshold ( failure to strike lamp or hard switchin g) or t j > 140c ( over-temperature ) cs > cs+ threshold ( over-current or hard switchin g) or cs < 0.2v ( no-load or below resonance ) or t j > 140c ( over-temperature ) sd > 2.0v ( lamp removal ) or vcc < 9.5v ( power turned off ) figure 2: ir21571 state diagram
8 www.irf.com startup mode when power is initially applied to the ballast, the voltage on the vcc pin of ic2 (ir21571) begins to charge up. the voltage for ic2 is derived from the current supplied from the rectified ac line through startup resistor r14. during this initial startup when the vcc voltage of ic2 is below its rising under- voltage lock-out threshold (11.4v), ic2 is in its uvlo and also its micro-power mode. the micro- power mode of the ic2 allows the use of a large value, low wattage startup resistor (r14). when the voltage on ic2 reaches the rising under-voltage lockout thresh- old, the oscillator is enabled (this assumes that there are no fault conditions) and drives the half-bridge out- put mosfets (m2 and m3). when the half-bridge is oscillating, capacitor c16, diodes d5 and d6 form a snubber /charge pump circuit which limits the rise and fall time at the half-bridge output and also supplies the current to charge capacitor c12 to the vcc clamp volt- age (approx. 15.6v) of ic2. the voltage for ic1 is de- rived from the current supplied from another snubber/ charge pump circuit formed by capacitor c14 and di- odes d1 and d3. when the rising under-voltage lock- out threshold of ic1 is reached, it starts to oscillate and drive mosfet m1 to boost and regulate the bus voltage to 400 vdc. an oscillograph of the startup of the vcc of ic1, vcc of ic2 and half-bridge output voltage are shown in figure 3. (for a complete de- scription of the operation of ic1, refer to the motorola semiconductor mc34262 data sheet.) preheat mode when the ballast reaches the end of the uvlo mode, the preheat mode is entered. at this point the oscillator of ic2 has begun to operate and the half-bridge output is driving the resonant load (lamp) circuit. the oscillator section of ic2 is similar to oscillators found in many popular pwm voltage regulator ics and consists of a timing capacitor and resistor connected to ground. resistors rt and rph program a current which determines the ramp up time of capacitor ct and resistor rdt deter- mines the ramp down time. the downward ramping time of ct is the deadtime between the switch- ing off of the lo (ho) and the switching on of the ho (lo) pins on ic2. the preheat mode frequency of oscillation is selected such that the voltage appearing across the lamp is below the minimum lamp ignition voltage while supplying enough current to preheat the lamp filaments to the correct emission temperature within the preheat mode period. the preheating of the lamp filaments is performed with a constant current during the preheat mode. the waveform in figure 4 shows the lamp filament current while figure 5 shows lamp filament voltage during the normal startup, preheat, ignition ramp and run modes of the ballast. figure 3: top trace: half-bridge output voltage middle trace: vcc of ic2 bottom trace: vcc of ic1
9 www.irf.com figure 4: lamp filament current during startup, preheat, ignition ramp and run (500ma/div) figure 5: lamp filament voltage during startup, preheat, ignition ramp and run figure 6 shows a plot of the half-bridge oscillation frequency as a function of time for all of the normal modes of operation: preheat mode, ignition ramp mode and run mode. as shown in figure 6 there is an initial startup frequency that is much higher than the steady state preheat mode frequency that lasts for only a short duration. components cstart and rstart are used to program this initial startup frequency. this is done to insure that the initial voltage appearing across the lamp at the startup of oscillation does not exceed the minimum lamp ignition voltage. if, at the initiation of oscil- lation of the half-bridge, the voltage across the lamp is large enough, a visible flash of the lamp occurs which should be avoided. this in effect is a cold strike of the lamp which could shorten the life of the lamp. an oscillograph of the lamp voltage at startup is shown in figures 7 and 8 (next page). figure 7 shows the lamp voltage without the high initial startup frequency while figure 8 shows the lamp voltage with the high initial frequency startup. f osc t preheat ignition run f preheat f run f ignition figure 6: oscillator frequency versus time, normal operating conditions
10 www.irf.com figure 7: typical lamp voltage at startup; f startup = f p reheat figure 8: improved lamp voltage at startup; f startup > f p reheat the duration of the preheat mode as well as which mode of operation the ballast is operating in is determined by the voltage on the cph pin of ic2. at the completion of the uvlo mode, preheat mode is entered and an internal current source is activated at the cph pin of ic2 which begins to charge up capacitor cph. the ballast remains in the preheat mode until the voltage on the cph pin of ic2 exceeds the ignition ramp mode threshold (4v). ignition ramp mode at the completion of the preheat mode (4v < cph pin < 5.1v) the ballast switches to the ignition ramp mode and the frequency ramps down to the ignition frequency. the frequency ramping is accomplished by turning off the internal open drain mosfet on the rph pin of ic2 (see figure 1, ir21571 block diagram). resistor rph is no longer connected di- rectly in parallel with resistor rt. the shift in frequency does not occur in a step function but rather with an exponential decay because of capacitor cramp in series with resistor rph to ground. the duration of this frequency ramp is determined by the time con- stant of the rc combination of capacitor cramp and resistor rph. the minimum frequency of oscil- lation occurs at the end of this ramp and is deter- mined by resistor rt and capacitor ct. during this ramping downward of the frequency, the voltage across the lamp increases in magnitude as the frequency approaches the resonant frequency of the lc load circuit until the lamp ignition voltage figure 9: upper trace: voltage on capacitor cramp during ignition ramp mode lower trace: lamp voltage during ignition ramp mode.
11 www.irf.com 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, figure 10: top trace: cph pin ic2 middle trace: rph pine ic2 bottom trace: run pin ic2 2 2 2 2 2 2 2 2 2 1 4 2 1 2 1 2 1 c l v v cv p lc cv p lc f lamp dcbus lamp lamp lamp lamp run ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? = (3)
12 www.irf.com c = lamp resonant circuit capacitor (c14) (f) p lamp = lamp running power (w) v lamp = lamp running voltage amplitude (v) l = lamp resonant circuit inductor (l3) (h) where, figure 11 shows the voltage appearing across the lamp while figure 12 shows the current flowing through the lamp during startup, preheat, ignition ramp and run modes. figure 11: lamp voltage during startup, preheat, ignition ramp and run figure 12: lamp current during startup, preheat, ignition ramp and run (100ma/div.) normal powerdown a normal powerdown occurs when the ac line voltage is disconnected from the ballast. when this occurs the voltage on the vdc pin of ic2 drops below the line fault threshold (3v) and ic2 shuts down in a controlled fashion. the oscillator is stopped, the half-bridge driver outputs (lo and ho) are turned off and capacitors cph, cramp, cstart and ct are discharged. ic2 also goes into its uvlo/micro-power mode and the bus voltage begins to collapse. fault mode fault mode is when the ballast driver is shutdown due to the detection of a lamp fault. note that when the ballast is in this fault mode the power factor correction section of the ballast is also shutdown and the bus voltage will drop to the non-boosted/unregulated level. there are several lamp fault conditions which can put the ballast into the fault mode. the lamp fault conditions detected include: near/below resonance (under-current) detection, hard-switching detection and over-current detec- tion. resistor rcs in the source lead of the low side mosfet (m3) serves as the current sensing point for the half-bridge which is used to detect these lamp fault conditions. in operation when the half-bridge is oscillating, a voltage appears across rcs whenever the low side mosfet, m3, is
13 www.irf.com 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
15 www.irf.com 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
16 www.irf.com data sheets lighting ballast control ic - designer ? s manual

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