IRPLMB1E datasheet(6/13 Pages) IRF

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IRPLMB1E

Figure 6.3 shows the VS (HB) Voltage, the lamp

voltage and the lamp current during Run Mode.

Figure 6.3:

VS (HB) Voltage (blue), Lamp Voltage (yellow) and the

Lamp Current (green) during Run Mode.

7. Fault Conditions

In case of fault conditions such as open filaments,

failure to strike, deactivated lamp or no lamp, the

IR2520D will go into Fault Mode. In this mode the

oscillator is latched off. To reset the IC back to pre-

heat mode, VCC must be recycled below and above

the UVLO thresholds. Resetting the mains does this.

In case of low AC line, the IR2520D will automati-

cally increase the frequency to maintain ZVS. In this

way, the ballast will work at a lower power during a

low AC line condition and will operate at the proper

power again when the line increases again.

7.1. Failure To Strike/ Deactivated Lamp Protection

This protection relies on the crest factor protection

together with the non-ZVS circuit of the IR2520D, both

enabled when the voltage in pin VCO reaches 4.6V.

In order to detect failure to strike conditions, the

IR2520D performs an internal crest factor measure-

ment for detecting excessive dangerous currents or

inductor saturation that can occur during a lamp non-

strike fault condition or deactivated lamp condition.

The IR2520D measures the VS pin during the entire

on-time of the low-side MOSFET. Should the peak

current exceed the average current by a factor of 4

during the on-time of LO, the IC will enter Fault Mode

and both gate driver outputs will be latched ‘low’.

Performing the crest factor measurement provides

a relative current measurement that cancels tem-

perature and/or tolerance variations of the RDSon

of the low-side half-bridge MOSFET and does not

need to be programmed differently for different

lamp types. During normal operation, the current

will increase until the lamp ignites. After lamp ig-

nition the current will decrease down to the nomi-

nal current. Should a lamp non-strike condition

occur where the filaments are intact but the lamp

does not ignite, the lamp voltage and output stage

current will increase during the ignition ramp until

excessive currents occur or the resonant induc-

tor saturates. The non-ZVS circuit or the crest

factor circuit will detect this condition and the IC will

enter Fault Mode and both gate driver outputs will be

latched ‘low’. This will prevent damaging of the half-

bridge MOSFETs.

Fig. 7.1 shows the inductor current and the lamp

voltage in case of failure to strike condition together

with the VCO pin voltage. At initial turn-on of the bal-

last, the frequency will ramp down from fmax, through

resonance, to fmin. If the lamp does not ignite, the

inductor current will saturate and high-voltages will

occur across the lamp as the frequency sweeps

through resonance. The voltages and currents in the

output stage will decrease as the frequency contin-

ues to decrease to the capacitive side of resonance.

The voltages and currents will be low but hard-switch-

ing will occur (non-ZVS). When the frequency reaches

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