DSH 755 measurement frequency of Limited Current Circuits (LCCs) capacitance

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DSH 755 ) }" m8 N" a7 {3 l

measurement frequency of Limited Current Circuits (LCCs) capacitance 4 B1 T1 X' \5 {% Q4 J0 x

2.4

60950-1(ed.1) & 60950-1(ed.2)

Question:
When measuring the circuit capacitance according to clause 2.4, what frequency should be used, 1kHz, the measured frequency of the circuit or another frequency?

Proposal:

For frequencies not exceeding 1kHz, the circuit capacitance shall be measured at a frequency of 1kHz.

For frequencies above 1kHz, the circuit capacitance shall be measured under the actual circuit frequency or the nearest frequency point of the measuring equipment.

Decision:

LCC limit values per 2.4.2 typically are applied to two different types of circuits, those

providing:

(a) steady state current, or

(b) capacitively driven current.

In a single product, one or multiple measurements may be required based on the type

of individual circuits involved.

·          For circuits with steady state current of a single frequency, a measurement through a 2000 ohm resistor is conducted. There is no capacitance determination.

·          For circuits with steady state current of multiple/complex frequencies, a measurement using one of the measurement instruments of Annex D is conducted. There is no capacitance determination.

·          For a circuit with a capacitance driven current, such as found in a lamp driver circuit, where the current typically is driven by a ‘single’ capacitor, the circuit capacitance can be determined via either the marked nominal capacitor rating or measurement of the single capacitor via LCR measurement equipment. For circuits that have capacitance driven currents, there are no additional current measurements. It is purely a capacitance determination or measurement, with maximum capacitance defined per 2.4.2, based on the maximum Working Voltage of the circuit.

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