Cirrus-logic CDB5490U Bedienungsanleitung PDF herunterladen (Seite 13)

CDB5490U

DS923DB5 13

1.6.2 Current Transformer Power Meter Example

A slightly more expensive option is to use a current transformer (CT) to connect the AC current to the

CDB5490U evaluation board. Figure 7 depicts the voltage and current connections for a CT sensor and

its associated filter configurations.

NEVER “open circuit” a CT. Make sure that all signals are well connected before the power source is

turned on. Extreme care should be taken when connecting high-voltage signals to the CDB5490U evalu-

ation board.

The burden resistor (R11) is necessary in a CT application to convert the secondary current into voltage.

Knowledge of the current transformer turns ratio (N) is key to determining the proper CS5490 input voltage

burden

) that the meter places on the system. The optimum secondary voltage (V

burden

) at the maximum

current input should be 10% less than the maximum channel voltage of 250mVp with I-channel

PGA = 10x. The secondary voltage (V

burden

) is determined by converting the primary current to the sec-

ondary current. Then the secondary current (I

burden

) can be converted into a voltage by Ohm's Law.

The secondary voltage (V

burden

) is sourced to the CS5490 through a simple low-pass, anti-alias filter, and

this voltage should not exceed the 250mVp.

burden



primary

------------------------

burden

==

IIN-

IIN+

GND

LINE

CS5490

CDB5490U

PHASE

NEUTRAL

J11

0.033UF

0.027UF

R11

2.2

100

R13

422K

R12

422K

R14

422K

R15

422K

R49 1K

R50 1K

C34

0.033UF

C35

0.033UF

J44

J46

R51

J45

J53

J54

IIN+

IIN-

VIN-

VIN+

Figure 7. Current Transformer Power Meter

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 45 46

CDB5490U 1

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