hi all,
This is the information i have attached...
Introduction:
Each output card drives 16 outputs through solid-state FET switches. Each switch can drive typically 3 Amps from 110Vdc supply for driving external relays. Again each of the switches is also provided with short circuit protection so that in case of accidental overload or external short-circuit the switch is tripped to protect the switches.
Functional Description of the Output card:
The system has a provision for 80 digital outputs. All outputs are optically isolated. The system is a two out of two system i.e. two processor will work simultaneously and in case of failure of one the other will take the whole responsibility of the system.
Output data from the two-processor cards are first latched on individual buffers. This is crossed checked by the individual processor through feedback ports. The data is then passed through an OR gate to combine the activation signals from the individual processor. A second stage of feedback is provided from this stage. This ORed output is used to drive opto-isolators, which in turn switch ON the MOSFET for driving the external relay.
The driver circuit is short circuit current protected. The current protection is achieved by considering the resistance drop due to over current flowing in the input side, as a result a thyristor will be ON, which pulls the gate to the high voltage towards source; hence put the FET into cut-off. A Zener diode is used between source and gate of the FET, to protect gate to source break down, due to some fault in the circuit.