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Instruction:
Press the switch S1 and then released. You can observes how the voltage at V+, V-, V0 and VCE changes with time.
If no curves are seen, press "pause" and them the "yellow triangle t" on the bottom right to restart the simulation.
Principles
In this timer circuit, when the S1 is pressed, the capacitor C will discharge, so V+=20V (orange curve) > V-=12.6V (pink curve), so opamp Vo = 18V (blue curve), and LED will turn ON and the transistor Q1 will ON causing the RELAY to ON (VCE is green curve). When S1 is released, C1 is now charging and V+ is falling, when V+=V- (orange and pink curve is cross over each another), Vo=0 and LED will OFF and Q1 will OFF also.
Please follow the color curves with respective to time.
If you want to change a component value, simply click the component and alter its values.
To restart the simulation, press S1 and release again.
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