Active Devices Flashcards
What is a diode?
A two terminal device that will pass current in one direction but will block it in the other.
What are the characteristics of an ideal diode?
As soon as the forward voltage is applied across the diode, there will be an instantaneous increase in the current flow through the diode.
What are the characteristics of a real diode?
Once the forward voltage is applied, the current takes a small amount of time to change. Although large currents can flow through the diode with small changes in voltage.
At what voltage will a BJT start to conduct?
0.7V normally for a silicon diode.
How is the collector current controlled?
Ic is controlled by Ib with a constant beta that can range from 10 to 1000.
Ic = B*Ib
What is the equation for emitter current?
Ie = Ic + Ib
What happens when Ib is 0?
What region will the BJT be in?
This means that Ic will be zero for any value of the collector emitter voltage. This means that the BJT is in the cutoff region. It will be fully off and act as an open switch.
What happens to the BJT when the collector emitter voltage is greater than 1V?
The collector current will not be linear and the BJT will be in saturation mode. The BJT will be fully on and act as an open switch
What happens to the collector current Ic when it is the active region?
It will be constant for any value of collector emitter voltage
What are the properties of an ideal op amp (4)
Infinite input resistance so no current will flow into the op amp.
Zero output resistance so no power will be wasted as heat.
Infinite open loop gain so we can use the virtual earth principle.
Infinite bandwidth so that any range of frequencies can be amplified.
What is the equation for the output voltage of an op amp?
Vout = (v2-v1) * Gain
What are the properties of Ideal Op Amps?
Infinite input resistance so no current flow into the op amp.
Zero output resistance so no power is wasted as heat.
Infinite open loop gain so the virtual earth principle applies.
Infinite bandwidth so that any range of frequencies can be amplified.
How does the virtual earth principle work?
Vout = deltaV * Gain.
Therefore deltaV = Vout / Gain. If Gain = infinity then deltaV will equal 0.
deltaV = v1 - v2, so this is how v1 = v2.
What does an inverting amplifier do?
It will amplify the input voltage and reverse the polarity so that the output has a different sign to the input.
