Omron SYSMAC C500, Installation Manual

Page: 56 / 112

Section 7
Safety Considerations
51
Output Leakage Current
If there is a possibility of leakage current causing a transistor or triac to mal-
function, connect a bleeder resistor across the output as shown below.
PC
Load Power Supply
OUT
COM
Bleeder resistor
L
R
Determine the value and rating for the bleeder resistor using the following
formula.
E
ON
I
R
Where
E
on
= ON voltage of the load
I = leakage current in mA
R = bleeder resistance
Output Surge Current
When connecting a transistor or triac Output Unit to an output device having
a high surge current (such as an incandescent lamp), care must be taken to
avoid damage to the Output Unit. The transistor and triac Output Units are
capable of withstanding a surge current of ten times the rated current. If the
surge current for a particular device exceeds this amount, use the circuit
shown below to protect the Output Unit.
R
L
+
OUT
COM
Another way of protecting the Output Unit lets the load draw a small current
(about one third the rated current) while the output is OFF, significantly re-
ducing the surge current. This circuit (shown below) not only reduces the
surge current, but also reduces the voltage across the load at the same time.
R
L
+
OUT
COM
Transistor Output
Residual Voltage
When connecting TTL circuits to transistor Output Units, connect a pull-up
resistor and a CMOS IC between the two. This is because of the residual
voltage left on the transistor output after the output turns OFF.