Lectures 5-6 Flashcards
Transformer equation is
V p / V s = N p / N s = I s / I p
V - voltage
N - number of turns
I - current
Transformer power can be calculated as
P =
V p X I p = V s X I s
Power in a transformer has units of
Why
VA rather than W
Volt ampere
Watt is used to measure P when the voltage and current are in phase
How much more does a full wave rectified signal lose its output voltage by, compared to a half wave rectified signal? Why?
Double, as the full wave signal requires the conduction of two diodes
Capacitor equation linking I, C and V is
I = C (dV / dt)
Capacitance has the unit of
Farad (F)
Capacitors are used to smooth out
the voltage variation in a rectified signal
What is the change in voltage due to charging and discharging a capacitor, in a rectified signal called?
Ripple voltage
As Capacitance increases, —- —- decreases
ripple voltage
The ripple voltage equation is
Change in V =
( I / C ) X change in t
change in t is the discharging time
Two approximations we make about the capacitor
- Capacitor current is not constant
- Capacitor discharges for the full time between the voltage peaks
What do we assume as we know capacitor current is not constant
Capacitor current is constant at its maximum ripple value
Equivalent to the load current
Equation linking t and f for a half wave rectified signal
change in t = 1 / f
Equation linking t and f for a full wave rectified signal
change in t = 1 / 2f
as two waves peaks occur in the space of one “wavelength”
Inputting the time period equation into the capacitance equation for each rectifier gives us…
C =
For half wave: (I 0 X change in t) / change in V = I 0 / (change in V X f)
For full wave: (I 0 X change in t) / change in V = I 0 / (change in V X 2f)
An op-amp stands for ——– and is ——
Operational amplifier, an integrated circuit of many transistors and resistors
On an op-amp, the V+ and V- are
the power supplies, positive and negative
Where do you count the notches from on an op-amp?
The first notch is near the indented circle
then count anticlockwise up
What happens to the input signal in a non-inverting and inverting op-amp
Non-inverting: signal remains in phase as the input and is amplified
Inverting: signal is inverted (or 180 degrees out of phase and is amplified
Op amps have gain so the output voltage is calculated by
V diff X gain
V diff =
V p - V n
Offset null is
when the two common inputs into an op-amp cancel each other out to give no output
Realistically, there is always a slight signal so offset null allows this to be cancelled out
Op-amps amplify what?
They amplify the difference between the two inputs
The op-amp bandwidth is
the frequency at which the voltage gain of the amplifier is above 70.7% of its maximum input value
Negative feedback for op-amps is
to reduce the potential difference between the inverting and non-inverting inputs so that the signal does not saturate
Saturation in op-amps is
What is the main feature of the wave form showing this signal
when the input p.d is larger than that of the limits of that op-amp, so the peaks of the waves are flatened
Saturation in op-amps is
What is the main feature of the wave form showing this signal
when the input p.d is larger than that of the limits of that op-amp, so the peaks of the waves are flattened
Negative feedback is obtained by
feeding some of the input signal back into the output
3 pros of negative feedback
- Stabilises the gain
- Increase the bandwidth
- Reduces output impedance (the amount by which the wave is cut off)
Inverting A cl =
Closed loop gain =
V out / V in = - R f / R i
Non inverting A cl =
Closed loop gain =
V out / V in = 1 + ( R f / R s )
