Disturbance simulator checks lines

-October 14, 1999

The simple line-disturbance simulator in Figure 1 helps you check the immunity of line-powered devices to line disturbances and noise; you can build the device from leftover parts found in a junk drawer. The key elements are a ballast inductor (L3) and a slightly modified glow-discharge starter (ST1) from a fluorescent lamp. Starters for fluorescent lamps usually contain a glow-discharge tube together with a noise-suppression capacitor in a small housing. You must remove the capacitor for this application. Electronic starters are unsuitable for this simulator. Operation of the circuit is straightforward: When S1 closes, the glow-discharge starter switches on and off at a random rate. The abrupt current variations through L3 induce noise at the output terminals, VOUT1 and VOUT2.

L1, L2, C1, C2, and R1 through R4 form a decoupling filter to keep noise from flowing back into the ac mains. L1 and L2 must have a 3A current rating. You can wind them yourself, with 40 turns of 1-mm-diameter magnet wire wound on a ferrite rod of 10-mm diameter and 50-mm length. R1 and R2 are 47?, 5W wirewound types. You mount all parts in a shielded enclosure. This simple circuit does not replace accurate, calibrated test equipment, but it provides a handy tool for a quick check during development. (DI #2423)

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