Figure 7. Current Transformer Power Meter - Cirrus Logic CDB5480U General Description Manual

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
CDB5480U 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 CDB5480U
evaluation board.
The burden resistor (R11/R22) is necessary in a CT application to convert the secondary current into
voltage. Knowledge of the current transformers turns ratio (N) is key to determining the proper CS5480
input voltage (V ) that the meter places on the system. The optimum secondary voltage (V
burden
the maximum current input should be 10% less than the maximum channel voltage of 250mVp with I-
channel PGA = 10x. The secondary voltage (V
the secondary current. Then the secondary current (I
Law.
The secondary voltage (V
this voltage should not exceed the 250mVp.
GND
IIN1+/IIN2+
IIN1-/IIN2-
GND
LINE
GND
12
V = I
burden burden
) is sourced to the CS5480 through a simple low-pass, anti-alias filter, and
burden
CDB5480U
J1/J12
2.2
R11/R22
J4

Figure 7. Current Transformer Power Meter

) is determined by converting the primary current to
burden
) can be converted into a voltage by Ohm's
burden
I
primary
 
----------------- -
R =
burden
N
J8/J14
1K
R13/R24
J7/J13
1K
R9/R23
J6
R5
1K
J11
CDB5480U
R
burden
J46/J52
R2/R22
100 R50/R53 1K
0.033UF 0.033UF
J54/J55
C6/C12 C35/C2
0.033UF 0.033UF
J53/J56
C5/C11 C34/C1
100 R49/R52 1K
R1/R21
J44/J51
J45
0.027UF
C4
0.027UF
C9
) at
burden
IIN1+/IIN2+
IIN1-/IIN2-
VIN+
VIN-
DS893DB5