Disturbance simulator checks lines

Peter Guettler, APS Software Engineering, Cologne, Germany -- EDN, 10/14/1999

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, V_OUT1 and V_OUT2.

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)