Figure 7. Current Transformer Power Meter - Cirrus Logic CDB5490U 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
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
(V ) that the meter places on the system. The optimum secondary voltage (V
burden
current input should be 10% less than the maximum channel voltage of 250mVp with I-channel
PGA = 10x. The secondary voltage (V
ondary current. Then the secondary current (I
The secondary voltage (V
this voltage should not exceed the 250mVp.
GND
IIN+
GND
LINE
GND
DS923DB5
) is determined by converting the primary current to the sec-
burden
V burden = I burden
) is sourced to the CS5490 through a simple low-pass, anti-alias filter, and
burden
CDB5490U
J1
IIN-
J4

Figure 7. Current Transformer Power Meter

) can be converted into a voltage by Ohm's Law.
burden
I primary
 
----------------------- -
R burden =
N
J8
1K
R13
2.2
R11
J7
1K
R9
J6
R5
1K
J11
CDB5490U
) at the maximum
burden
R burden
J46
R2
100
R50 1K
0.033UF 0.033UF
J54
C6 C35
0.033UF 0.033UF
J53
C5 C34
100 R49 1K
R1
J44
J45
0.027UF
C4
0.027UF
C9
IIN+
IIN-
VIN+
VIN-
13