ADLINK LPCI-7230 - Manual (Page 51)

Operation Theory 43
4.2 Isolated Digital Output Circuits
On the 7230/7234 series, an external voltage source, minimum
5V, maximum 35 VDC, is necessary to power the internal isolated
circuits. It is connected with the VDD pin, When the isolated digital
output goes to high, the sink current will be from VDD.
On the 7230/7234 series, the VDD pin is used as a “fly-wheel”
diode, which can protect the driver if the loading is inductance
loading such as relay, motor, or solenoid.
The VDD must connect to the external power to form a fly-wheel
current loop.
Figure 4-2: Isolate output circuits of PCI-7234 (sink current)
Figure 4-3: Isolate output circuits of PCI-7234P (source current)
+
DC (5-35V)
Load
VDD
IDOn
Darlington
Sink Driver
PC 817
V5V
I.GND
+
DC (5-35V)
Load
VDD
IDOn
I.GND
Darlington
Source Current
V5V
PC 817