EVLB001 Datasheet, PDF (13/35 Pages) ATMEL Corporation – Automatic microcontroller dimmable ballast

Ballast Demonstrator Operation
the bus current is a good indicator of lamp condition that does not require a high fre-
quency response or a minimal response due to reactive currents.
4.5.2
Lamp Sequential
Step Description
Once the single lamp condition is detected, the minimum run frequency is determined by
lamp current PB4 < 100mV. If the single lamp condition occurs while running, as noted
by a decrease in current of more than 20% from the preset level, increase the frequency
until the PB4 = 90mV. If the PB4 increases to 120mV, assume the lamp has been
replaced by a new one. Increase the frequency to 80 kHz to restart the ignition process.
This is necessary to preheat the new lamp filament to ensure that the hot lamp will not
ignite sooner than the cold lamp, exceeding the balance transformer range. Start the
ignition sequence. With one cold lamp in parallel with one hot lamp, it may be necessary
to restart several times to get both lamps to ignite.
Note that the lamp and resonant circuit use a common return ground separate from the
rest of the circuit. The ballast demonstrator uses active power feedback of the sense
voltage versus drive frequency to meet power objectives. Also note that the differential
amplifier is connected across the current sense resistor R28 to ensure a Kelvin connec-
tion. Layout of the amplifier + and – is critical for fast noise free loop response.
After PB2 (boost voltage at 400V) >= 2.400V (acros R42) start preheat
Enable PD6 rectified lamp voltage sense
Enable PB0 and PB1 half bridge drive output
PB0 & PB1 12.5µS total period (80 kHz) 50% duty 180°out of phase.
Check PB4 > 20mV, then 2 lamps. If PB4 < 20mV, assume a single lamp.
If PB4 < 10mV, assume an empty fixture = fault & shutdown.
4.5.3
Start and Ignition
Sequential Step
Description
Determine the lamp intensity control method: DALI (presence of data stream at PD4), or
Switch (presence of 50/60 Hz modulated at PB6).
Sweep PB0 and PB1 frequency down at 30 kHz/sec or 33µS/sec rate.
Stop sweep at 40 kHz or 25µS period (12.5µS pulses for each half bridge FET)
Check PB4 > 100mV (2 lamps) or > 30mV (1 lamp) for proof of ignition.
Hold ignition frequency for 10mS.
If no PD6 voltage, collapse to < 200mV for proof of ignition, increase frequency to 77
kHz for preheat for 1 second.
Repeat ignition sequence 6 times then if fails, set DALI fail flag or shut down.
Disable if dimmed frequency > 60 kHz. Disable if single lamp.
Proceed to power setting command at 30 kHz/sec rate as established by external con-
trol or if no internal control proceed to PB4 195mV at input terminals before gain (about
32 kHz) for 100% power.
If Switch control, proceed to max power. A continuous pressing of this switch will cause
a progressive increase of frequency at 33 kHz per second. The exception for a single
lamp will be minimum frequency for 97mV (39 watts) at PB4 for 100% brightness. This is
the default power for a single lamp with no dimming.
4-11
7597B–AVR–10/07
ATAVRFBKIT / EVLB001 User Guide