mouser.com/vishay / 21
-
6
+
5
7
U2B
VOA300
A
2
C
1
C1
3
A1
4
C2
6
A2
5
7, 8 NC
K2 K1
U1
R3
-
2
+
3
1
U12A
V(OUT)
GND_HVP AGND
V(OUT) = (IP1 * K3) * R3
V(OUT) = IS * RS / R1 * K3 * R3
R1
RS
WSBM8518-35
IP1 = IS * RS / R1
IS
K3 = K2/K1
GND_HVP
-
6
+
5
7
U2B
VOA300
A
2
C
1
C1
3
A1
4
C2
6
A2
5
7, 8 NC
K2 K1
U1
R3
-
2
+
3
1
U12A
V(OUT)
GND_HVP AGND
V(OUT) = (IP1 * K3) * R3
V(OUT) = V(HV+) * Rb / (Ra + Rb) / R1 * K3 * R3
Ra
TNPV1210
IP1 = V(HB+) / R1
HV+
K3 = K2/K1
GND_HVP
Rb
TNPW0805
GND_HVP
-
2
+
3
1
U2A
R1
HB+
V(HB+) = Rb / ( Ra + Rb )
Figure 4: Voltage
measurement schematic
(Source: Vishay)
Figure 3: Current
measurement schematic
(Source: Vishay)
Learn More
Learn More
Learn More
TNPV e3 Thin Film
High-Voltage Chip
Resistors
WSBS8518-35 Power
Metal Strip
®
Battery
Shunt Resistors
VOA300 Linear
Optocouplers
The WSBS8518-35 has a very low TCR (down to +-10 ppm/°C)
that maximizes the accuracy of the output signal, and offers the
highest linearity (from milliamps to kiloamps). Using a current
shunt method is also very cost effective as compared to a Hall
effect sensor implementation.
The resistor divider (Ra/Rb in Figure 4) using Vishay high-
voltage TNPV1210 and TNPW0805 is used for the isolated
voltage measurement. Very high resistance values were selected
to minimize the losses. The low TCR (down to 10ppm) and
tolerance (down to 0.1 percent) of the TNPV/TNPW provide
excellent accuracy, so no further calibration is required. Only the
transfer factor K3 in the VOA300 must be calibrated by software.
Depending on the application, adjusting the series resistance of
the IRLED and adding filter capacitors might be necessary. Also,
transmitting unipolar signals is straight-forward because of the
nature of single-channel optical paths. However, transmitting
bipolar signals, as in bi-directional current measurements,
requires some additional hardware. The idea is to either split
or shift the bipolar signal to obtain one or two unipolar signals,
which can be transmitted as shown.
A cost effective approach to providing isolated voltage and
current signals between the low-voltage and high-voltage buses
has been presented. In this case, an optically isolated device
was used to safely maintain the isolation barrier that is required
in any electric/hybrid vehicle. ▼
