1. Engineering
2. Electrical Engineering
3. Electronic Engineering
4. 625925

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!

(b) The diagram of FIGURE 2 shows a bi-directional opto coupler input interface circuit. When a supply voltage of 20 V is applied the LED carries a current and 2 V is dropped across it. Calculate the value of the LED current and the value of current through the 3 k resistance.

External wiring

Separate supply used for inputs.
Note: Either polarity.

Internal wiring

FIG. 2

(c) The circuit shown in FIGURE 3 is part of the interface of a relay output module. Ib is 1 mA and VCC is 9 V. The relay requires a
minimum of 50 mA to energise.

Complete the values of the assumptions listed below in order to calculate:

• voltage across R1
• value of R1
• voltage across the relay coil
• voltage across R2
• value of R2
• collector of current Ic.
Assumptions: Logic '1' = V
Logic '0' = V
Transistor forward current gain hfe = LED current = 10 mA LED voltage drop at 10 mA = V Base/emitter voltage = V
Collector emitter voltage when transistor is on = 1 V

External Terminals

Logic Signal

0 volts

FIG. 3