H Exp – Electricity and Electronics 21 – The inverting amplifier used to control heavier loads.

Aim – To show how the Op-Amp can be used in a circuit to switch on a high current device. .

Instructions

Click on the right side of the potentiometer to increase the input voltage V₁.
Click on the left side of the potentiometer to decrease the input voltage V₁.
▪ Gradually increase the input voltage V₁. At some point the relay contacts should close and the motor will work.
▪ Note the current value A₁, A₂ and A₃. Comment on the size of these currents.
▪ State the gain of this circuit.
▪ At what value of V₁ does the transistor switch on?
▪ What is the value of the output voltage of the Op-Amp at this value of V₁?
▪ The output voltage of the Op-Amp is also the input voltage of the transistor. At what voltage does the n-p-n transistor switch on?

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