Speed Up The Single-End Transistor Output Circuit; Speed Up The Single-End Transistor Output Circuit (High/ Medium) - FATEK M Series User Manual

Chapter 6 Digital Output Circuit

6-3 Speed up the Single-End Transistor Output Circuit (High/ Medium)

Either with the SINK or SOURCE structure in single-end output transistor circuit, when the transistor
switches from ON to OFF, the junction capacitor between transistor CE electrodes should be charged to
near the load voltage VDD before it can stop the current running through the photocoupler inside the load,
which increase the OFF time and decrease the response speed. This problem can be solved by adding a
Dummy load to accelerate charging rate and speed up the working frequency of transistor output. For the
transistor output in M-Series PLC, Dummy load that are added to the high- and medium-speed transistor
output and generate a load current of 20~50mA is adequate. For low-speed transistor where its driving
capability (0.5A) but speed is concerned, adding a Dummy load only decreases its driving capability without
any significant improvement and hence is not recommended. The following diagram shows how to add a
Dummy load to SINK and SOURCE transistor output. (Applicable only to high and medium-speed)
VDD
�� = = 20~50����
R

Speed up the Single-End Transistor Output Circuit

6
M-Series PLC Expansion Module User Manual