Selecting an electronic UV lamp driver in a given application can be an involved task. Many driver design criteria and lamp attributes must be taken into consideration in order to ensure that a suitably matched lamp and driver pair is chosen which will result in a high quality and reliable system with a low annual failure rate.
The application specific driver requirements include number of on/off lamp starting cycles, physical environment i.e., indoor vs outdoor, dry vs moist/wet environment and degree of interaction with other drivers, controllers and nearby electrical/sensitive electronic equipment.
For the back end or output of the driver, the type of lamp wiring configuration it needs to accommodate is one of the first items to consider i.e., 2-wire instant start vs 4-wire preheat. If preheat configuration is chosen it is necessary to know whether continuous or non-continuous filament heating is required. The application will typically dictate this. Following this selection criteria, one needs to ensure or be aware that the output circuit topology of the driver is that of a resonant tank inverter circuit operating between 30-50kHz for lower power applications, i.e., up to 40W lamp power. With today’s modern electronic drivers, this is typically the output circuit topology of choice. Furthermore, for the lower power applications a half bridge MOSFET switching inverter is usually incorporated. For higher power applications, a full bridge MOSFET switching inverter is used.
Moving towards the input circuit topology, the driver should incorporate a full wave bridge rectifier front end feeding a DC bus with good EMI/RFI filtering and proper grounding (to mitigate any EMC issues). Galvanic isolation is preferred but not common in lower power applications. A high power factor (>95%) with low total harmonic current distortion (%Athd) or active PFC front end is the preferred topology of choice. These design requirements/selection criteria will in most cases, if not all, qualify the driver to have UL or CSA agency approval accreditation in addition to FCC or CE accreditation with the respective labels in place, visible on the driver cover. This is a very important consideration when looking at ensuring a given UV lamp and driver system is properly matched resulting in a robust design which will deliver high quality/reliability over the useful life of the system. A useful life between 5 to 10 years for the driver, depending on the application, with an annual failure rate of <1% is an attainable target.
Having application knowledge of the attributes of the physical environment i.e., indoor vs outdoor, dry vs moist/wet environment is key to ensuring the above reliability criteria are met. For example, knowing the maximum ambient air temperature that the driver will be exposed to in addition to knowledge of the humidity levels and/or degree of moisture ingress inside the case of the driver will assist in determining whether a potted driver is required and subsequently will dictate the IP or Nema rating of the driver. This will determine how robust the electronic components need to be within the driver ie. electrolytic capacitor and MOSFET temperature ratings, etc. to name but a few devices.
by Bill Himaras
Aug 5th, 2021