EOL lamp identification and speed up EOL protection
Publication Date: 2009-Jan-05
The IP.com Prior Art Database
Title: EOL lamp identification and speed-up EOL protection
In the HID lamps, with the ageing of the discharge tube, leaky arc tube can lead to a discharge in the outer bulb, and which may bring about end-of-life (EOL) safety risk. The input electric power to the EOL lamps, is mainly exhausted in heating the electrodes, instead of generating light, as a result, over-heating in the lamp-caps and lamp cables is aroused. EOL risk leads to overheating and thus safety issue, so in the system release for lamp drivers, to pass the EOL test is compulsory.
In the EOL lamps, except for glow discharge mode, arc mode and incandescent mode may also happen, which are the two most dangerous operational modes. Furthermore, in high- filling-pressure EOL lamps, with the increase of ignition striking times, arc and incandescent modes in the outer bulb may easily become unavoidable.
Presently, to lower the EOL risk, so-called burst ignition scheme is widely-applied and is illustrated in Fig. 1, and its basic principle is: 20 min ignition time is required in lamp specifications, but during the 20 min ignition period, at intervals there are some pause without ignition, and then the maximum cumulative ignition time is only 5 min (not 20 min), as a result the EOL risk can be mitigated because of decrease of total ignition on the EOL lamps.
In Fig. 1, during any of the alternately-distributed ignition periods, if lamps are started, then ignition will be interrupted and lamps enter other operational modes. Whether or not the lamps are started is based on the status of so-called Lamp_off signal, as shown in Fig. 2. If lamps are started, then lamp voltage (Vla) connected signal (namely Info(Vla) in Fig. 2) will push down the level of the Lamp_off signal through the bipolar transistor Q1, and this change can be detected by MCU. In other wards, if Vla is high (lamp not started), Info(Vla) will be low, and then Lamp_off signal is high, burst ignition scheme works; whereas, if Vla is low (lamp started), Info(Vla) will be high, and then Lamp_off signal is low, which will disable the ignition. Besides, through adjustment of ratio between R1 and R2 (labeled in Fig.
2), Q1 can be triggered when Vla is around 170V, below which ignition is disabled and above which the burst ignition scheme works.
Fig. 1 widely-used 20 min burst ignition scheme
The circuit in Fig. 2 can be qualitatively used as lamp starting detector, and it also can be quantitatively used as Vla monitor.
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Fig. 2 schematic of lamp voltage monitor (lamp starting detector)
Impartially to say, the presently widely-applied 20 min burst ignition scheme (in Fig. 1), does show good effect in avoiding EOL risk in many types of HID lamps with low filling pressure; but however, in some h...