BL0921
CT
RF
VAP
CF
Single Phase Energy Meter IC
with Integrated Oscillator
+
-
±660mV
RF
CF
AGND
VN
Phase Neutral
AGND
AGND
Ra
CF
Rb
AGND
AGND
Rv
±660mV
VAP
Phase Neutral
AGND
RF
VN
CF
AGND
AGND
+
-
Ra >> RF
Rb+Rv=RF
Figure 5.
Typical Connections for Voltage Channels
Current Channel Input
The voltage outputs from the current transducers are connected to the BL0921 here. As Figure6
shows that channel V1 has two voltage inputs, namely V1A and V1B. These inputs are fully
differential with respect to V1N. However, at any one time, only one is selected to perform the
power calculation.
V1
V2P
V1
V2N
+660mV
Maximun input differential voltage
±660mV
+
-
V2
V2
Maximun input common-mode voltage
±100mV
-660mV
AGND
Figure 6.
Current Channels
The analog inputs V1A, V1B and V1N have same maximum signal level restrictions as V2P and
V2N. However, Channel 1 has a programmable gain amplifier (PGA) with user-selectable gains of
1 or 16. These gains facilitate easy transducer interfacing. Figure illustrates the maximum signal
levels on V1A, V1B, and V1N. The maximum differential voltage is
±
660 mV divided by the
gain selection. Again, the differential voltage signal on the inputs must be referenced to a common
mode, e.g., GND. The maximum common-mode signal is
±
100 mV.
Figure7 shows a typical connection diagram for Channel V1. Here the analog inputs are being
used to monitor both the phase and neutral currents. Because of the large potential difference
between the phase and neutral, two CTs (current transformers) must be used to provide the
isolation. The CT turns ratio and burden resistor (Rb) are selected to give a peak differential
voltage of
±
660 mV/gain.
http://www.belling.com.cn
-9-
Total
13 Pages
3/15/2007
BELLING [ SHANGHAI BELLING CO., LTD. ]
