Protection Or Quality? With AC Power For Systems, It’s Vital To Know The Difference

Power Line Noise Filter. Surge diverters clamp transient voltage disturbances at around 250 volts to 300 volts but do nothing to prevent power disturbances of lower amplitudes from reaching the electronic load. Surge diverters also prevent destruction, but they do little to prevent degradation of electronic components. This is the job of the noise filter.

Filters address lower amplitude power disturbances, and they also function by diverting these disturbances to ground. Filters are excellent at preventing degrading power disturbances but because they function like surge diverters, they also create potentially disruptive disturbances by converting normal mode to common mode.

Filters are constructed of inductors and capacitors and are tuned to offer a low impedance path to ground for a specific range of power disturbance frequencies. A negative aspect of noise filters is that the impedance of the filter combines with the impedance of the branch electrical circuit, which often results in a shift in the frequency response of the filter.

Gain in noise amplitude at certain frequencies is frequently observed. As a result, filters work best when they are individually tuned to the unique impedance characteristics of each application.

Installing a surge diverter and a filter on the secondary of a low impedance isolation transformer offers the best of both worlds. The filter may be designed around the fixed impedance of the transformer secondary so that its performance is the same regardless of where it is installed. The surge diverter handles the large amplitude transients and the filter addresses what slips by the surge diverter.

Also, if the transformer has a neutral to ground bond, the filter and surge diverter can do their jobs without creating a neutral to ground disturbance that might be disruptive for a microprocessor based system.

Voltage Regulator. Intended to stabilize the voltage that powers an electronic system. A variety of devices can function as a voltage regulator. These include ferro-resonant transformers, buck/boost autoformers, tap switching autoformers, and tap-switching isolation transformers. Unfortunately, voltage regulators are frequently misapplied for two primary reasons.

Voltage regulation is seldom necessary when the electronic system uses a power supply design that is tolerant of supply voltage variations. Many modern systems are powered by switch mode power supplies (SMPS), which “gulp” power from the power line in a discontinuous fashion.

SMPS are constant power devices. In other words, when line voltage decreases, the current gulp gets bigger. When line voltage increases, the current gulp gets smaller. Either way, power consumed (volts times amps) stays the same.

SMPS technology is largely immune to voltage regulation issues provided the branch electrical circuit has adequate ampacity, which leads to the second reason why voltage regulators are misapplied.
The job of a voltage regulator is to address both over voltages and under voltages.

While we perceive that the voltage regulator is stabilizing voltage, it’s actually accomplishing that task by regulating current flow in the electrical circuit. While it’s relatively easy for a regulator to reduce over voltage, an under voltage condition is something else entirely – especially if the under voltage is the result of an overloaded branch circuit, distribution panel, or service transformer.