Toshiba T2N - Manual (Page 69)

3.Application Precautions for I/O Modules
54 PROSEC T2N
(4) Pay attention to the following cases caused by the diode mentioned in (3).
〈
Case1
〉
When connecting to the external equipment in which DC power supply
is provided from internal,if the voltage of P1 is higher than one of P2 or
if P2 turns to OFF when P1 is ON, the external equipment may turn to
ON in spite of the output status.
Because a load current flows through D:a diode.
A power supply should be basically used for P1 and P2.
In the above case,insert a diode for preventing a back current
in the position A so that a back current is prevented from
flowing into P2.
〈
Case2
〉
When the power cable connected to the P24 terminal is cut off,
external load may be driven because the load current of OFF output
circuit(OUT0) flows through the diode and the transistor of ON output
circuit(OUT1) as shown below.
Pay attention for preventing a P24 line from cutting off.
External eguipment DC Output module
D
COM COM
P24
A
IN
+
P1
-
+
P2
-
OUT
DC Output module
OFF
ON
OUT0
OUT1
P24
COM
Cutting off
24Vdc
Load
Load
L
L