Avago Technologies ACPL-224-500E - Manual (Page 59)

AV02-4387EN 56 Avago Technologies
Isolated Inverter Rail Voltage Sensing using an Isolation Amplifier
Motor Control Applications
Description
The HCPL-7840 isolation amplifier
can be used for sensing the rectified
dc power supply voltage in a power
inverter. An isolated 5 V power supply
regulated to 5 V using a simple
three-terminal voltage regulator
powers the HCPL-7840 input circuit.
The resistor divider network is used
so that the full scale voltage at the
HCPL-7840 input is 200 mV. The im-
pedance of the resistor divider must
be less than 1 k Ω so that the input
resistance (500 k Ω) and input bias
current (1 mA) of the isolation am-
plifier do not affect the accuracy of
the measurement. To obtain higher
bandwidths, the input bypass ca-
pacitor (across HCPL-7840’s pins 2
and 3 ) can be reduced, but it should
not be reduced much below 1000 pF
to maintain gain accuracy of the iso-
lation amplifier.
Performance of Circuit
• 15 kV/ µs transient rejection
• 0.05% nonlinearity
• 5% gain tolerance
Benefits
• Few components
• High electrical noise immunity
Avago Alternative Parts
1) HCPL-786J: isolated 15 bit A/D
converter
References
1) HCPL-7860/x870 Technical Data
2) High precision current sensing
resistor suppliers: Dale in USA;
Isabellenhutte in Germany; and
PCN in Japan
2.00 k Ω
10.0 k Ω
10.0 k Ω
2.00 k Ω
0.1 µF
0.1 µF
0.1 µF
0.1 µF
0.1
µF
V
OUT
IN OUT
78L05
HV+
R1
+SUPPLY
39
R2
1
2
3
4
8
8
7
6
5
4
7
150 pF
150 pF
6
5
HV–
+5 V
+5 V
-15 V
+15 V
–
+
MC34082A
HCPL-7840