Development of super-small floating power supply circuit for current measurement system of high voltage power line

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In this research, a floating power supply circuit for current measurement systems of high voltage power line is developed. The specifications for the power supply are that the input is 3, 810V/60Hz (distribution-line voltage), the output voltages are ±12V (dual DC voltages), and the output power is 0.5W. The output power is obtained from distribution-line voltage by a capacitor voltage divider, without using heavy coils.In the 2007 fiscal year, the fundamental characteristics were measured, for example (1) the load-resistances, (2) the distribution-line voltage, and (3) the distribution-line frequency, are changed. These measured results are good agreement with the hspice simulations.In the 2008 fiscal year, the transient responses, the heat tests, and the noise experiments are verified. First, for the transient responses, (1) power failure and return, (2) half-cycle power failure, and (3) n cycles power failure are measured. The output voltages reach ±12V after 1.5 seconds from return of a power failure. Even if a power failure during 100ms (six cycles) occurs, the output voltage can hold more than 10V, since the time constant of the circuit is as long as 576ms.Next, the characteristics are measured when the temperature is changed from -15 to 80 degree. There is no problem when the value of the capacitance can keep 25 nF or more in the temperature range. Moreover, the temperature dependency of the output voltages is determined by the temperature characteristics of the used zener diodes, and the output voltage regulation of the test circuit is less than ±4%. Since the proposed circuit is not kind of a switching regulator, there is no generation of a noise which causes a problem.In future, the characteristics under the conditions that a quasi-surge voltage is applied by thunderbolt will be measured, since there is no test equipment now.