Section 9 Flashcards
(25 cards)
What does the RC time constant solve?
How long it takes for a capacitor to charge to a certain voltage level
1 RC = 63% full
5RC = 99% of input voltage
How do you calculate the RC Time Constant
How long it takes for a capacitor to charge to a certain voltage
C*R
so 200uF capacitor and 100Ohms of resistance would get you 20 miliseconds or 0.02 seconds
If you want how long it takes all together
you have .02 seconds, just multiple that by the total of 5 RC constants (That’s 99% full) and you have your answer .1 seconds
How does RC time constant work in reverse
1RC = 37% of the inital value
5RC = gets you to about 1%
How do you calculate the time constant if you have a pulsed DC?
How long does it hit and stay at the max voltage?
Do your normal equation, and multiply the answer by how long it hit’s the peak voltage in time constants
What is an inductor and what is it used for?
Looks like coiled copper which creates a magnetic field, which creates inductance
Wrapping in a coil increases the magnetic field
Inductance means the current actively tries to oppose incoming current due to the voltage across it which results in the current through the inductor can’t charge rapidly.
Nearly useless in DC circuits, unless you have a bunch of switches or something that sends a sudden charge.
How do you calculate inductance?
L (inductance) = (N²Au)/l
Inductance is measured in henrys
u = permeability constant (pole piece in the middle)
N = number of turns in the coil
A = are of cole
l = length of coil
What decimal place of henrys are the below:
Mili Henry(mH)
Micro Henry(uH)
Nano Henry (nH)
Pico Henry (pH)
Mili Henry(mH) = 10-3
Micro Henry(uH)=10-6
Nano Henry (nH)=10-9
Pico Henry (pH)=10-12
What is an air core inductor
No core
Low inductance so the rate of current rise is quite fast
Used for high frequency
What is an Iron Core Inductor
Used for low frequency
Ferrit core inductor
Most common
permeability can be finely controlled
What is the inductance of inductors in series
Ltotal = L1 + L2 + L3
What is the inductance of inductors in parallel
Ltotal = 1 / 1/L1 + 1/L2 } 1/L3
What are the differences between a capacitor and an inductor?
Capacitors store energy in an electric field,
When connected to voltage, it’s voltage gradually increases while it’s current decreases
When disconnected it will temporarily maintain voltage
Inductors stores energy in a magnetic field
When connected to voltage, it’s current gradually increases and voltage decreases
When disconnected it will temporarily maintain current
What is back EMF?
It has an amplitude proportional to the rate of change of current.
It has a polarity which opposes the change in current in the inductor that caused it initially.
It sends energy in the opposite direction, often more than you put in innitially
What does it mean that voltage eventually drops to 0 on the inductor after current hits a steady rate?
This just means that it’s using all of that voltage at first to resist the sudden change in current, once the current is steady, it allows it to go to the next component.
It will slowly get that Voltage back to what needs it further in the circuit.
What is used to protect against back EMF?
A diode called a flyback diode
You put it in reverse bias back to the vout in parrallel with the inductor
This works because electron always go for loops with little resistance
What does an inductor do in an AC circuit?
Creates a faze shift
this means voltage and current are not in sync
The current lags behind voltage by 90 degrees
What is a reactive component
Something that resists changes in voltage or current
These components store a bit of energy applied to them
What’s the formula to find inductive reactance
Xl = 2pifreq*l (or inductance measure in henrys)
DON’T DIVIDE ONE BY THIS NUMBER
How does inductive reactance react to high and low frequencies?
High frequencies - inductors have a high reactance
Low frequencies inductors have a low reactance
This is opposite of capacitive reactance
High frequencies are blocked from travelling through a inductor
Inductors are in love with DC since it’s steady
Capacitors are in love with AC since it’s choppy
What’s the mnemonic to remember who leads ahead in terms of voltage and amps in inductors and capacitors
ELI the ICE man
Electricity leads L(inductance)
I(current) leads C(capacitance)
How would you convert the scientific notation below
3.419905271359908e-6
Move the decimal six places
.00000342
What is a RLC?
Resistor Inductor Capacitor
What is RLC resonance
This is where a certain frequency makes the reactance of a capacitor and an inductor overlap
This makes these components cancel each other out
41.1Hz
