Testing inverters for backlighting
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 12/1/2008 2:00:00 AM
CCFLs (cold cathode fluorescent lamps) provide backlight for many kinds of displays. To get CCFLs started, a DC-to-AC inverter must produce 1000-VAC to 2000-VAC RMS from DC voltages between 5 V and 12 V. After the CCFL illuminates, the inverter must supply from 500 VAC to 1000 VAC RMS to keep the light shining.
Manufacturers of DC inverters must test them for input current and voltage, output current and voltage, output frequency, and power efficiency. Engineers at Endicott Research Group design such inverters and have developed an automated test station for production use. Endicott Research president Tom Novitsky and engineering manager Bob Arnold have written a paper that describes the inverter and test station in detail.
 DC inverters convert DC to AC and require testing for input and output current and voltage. |
The test station (figure) consists of two power supplies, an oscilloscope, a current probe, and two DMMs (digital multimeters). The 12-V power supply provides power for the inverter, and the 0- to 4-V supply provides a control voltage for setting the inverter’s output. A PWM (pulse-width modulator) in the inverter varies its duty cycle based on the control voltage to control the lamp’s brightness.
Test operators use the oscilloscope to measure output current and frequency. They use the DMMs to measure input voltage and current. A PC calculates power efficiency and stores test results for each inverter on the company LAN.
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