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Agilent Effective Transformer/ LF Coil Testing Application Note 1305-3 Introduction Transformers and LF coils are used in power supplies, digital networks (for example, ADSL) and various communication instruments to step up (or down) an AC voltage or for impedance conversion or filtering purposes. Though production of transformers is increasing year after year, there are problems that QA test efficiency and production test throughput cannot be easily improved because several different measurement instruments and setups need to be used for testing various transformer parameters. This application note introduces the cost-effective solutions to the transformer parameter measurements by using the Agilent 4263B LCR Meter. 2 Current Problems on The primary parameters that need to be known for transformer/LF coils are Transformer/LF Coil self-inductance, dc resistance, turns ratio and inter-winding capacitance. Conventional low-cost LCR meters have the following shortcomings when used Evaluation for transformer/LF coil evaluation. 1. DC resistance of primary and secondary windings cannot be measured with LCR meters. (The DC resistance measurement requires using a separate test instrument such as a multimeter.) 2. The turns ratio, a key transformer parameter, cannot be measured with LCR meters. 3. The transformer parameters cannot be measured at 100 kHz because many low-cost LCR meters do not cover high frequencies up to 100 kHz. 4. The test signal level is automatically selected according to the measurement range, the test signal level cannot be user-defined for a specified level. 5. Total test throughput on production lines cannot be maximized because of slow measurement speed. 6. The connections of a transformer to the instrument (test fixture) must be changed to measure parameters for the primary and secondary windings. The required connection changes make it difficult to enhance the measurement efficiency. 3 Agilent 4263B LCR 1. DC resistance measurement capability Meter Solution The Agilent 4263B with option 001 (N/M/DCR measurement capability) can sequentially measure self-inductance and dc resistance (Rdc) by alternately applying AC signal and DC signal to the DUT, as shown in Figure 1. DC resis- tance measurement function covers a wide range from 1 m to 100 M and enab