Announcements
Download
1 / 18

Announcements - PowerPoint PPT Presentation


  • 84 Views
  • Updated On :

Announcements. Assignment 1 solutions posted Assignment 2 due Thursday First mid-term Thursday October 27 th (?). Lecture 8 Overview. Inductors in transient circuits Semiconductors Diodes Rectifying circuits Other Diode Applications Transistors. Time response of Inductors.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Announcements' - brittany


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Announcements l.jpg
Announcements

  • Assignment 1 solutions posted

  • Assignment 2 due Thursday

  • First mid-term Thursday October 27th (?)


Lecture 8 overview l.jpg
Lecture 8 Overview

  • Inductors in transient circuits

  • Semiconductors

  • Diodes

  • Rectifying circuits

  • Other Diode Applications

  • Transistors


Time response of inductors l.jpg
Time response of Inductors

Switch to position a:

Integrate and apply boundary condition t=0, i=0

Time constant τ=L/R.

Talk about "Charging a capacitor"

"Current build-up" in an inductor

Switch to position b:


Time response of inductors4 l.jpg
Time response of Inductors

A battery is connected to an inductor. When the switch is opened does the light bulb:

1.Remain off

2.Go off

3. Slowly Dim out

4. Keep burning as brightly as it did before the switch was opened

5. Flare up brightly, then dim and go out

Answer 5


Semiconductors l.jpg
Semiconductors

Simple review of basic concepts: What is a semiconductor?

(for more detail see e.g. Simpson Ch. 4)

Elements such as Silicon and Germanium have 4 valence electrons in their outer shell

They form covalent bonds with neighbouring atoms to form strong crystal lattice structures.

In pure silicon, all valence electrons are bound in the lattice structure


Semiconductors6 l.jpg

depletion region E-field

(~0.2V Ge, ~0.5V Si)

Semiconductors

The addition of impurities ("doping"), such as Sb(Antimony) with 5 valence electrons, leaves one electron unbound and free to move and create a current flow (n-type semiconductor). Alternatively, an impurity with 3 valence electrons can be used to create positive "holes".

When a p-type and an n-type are joined (p-n junction), mobile electrons diffuse from the n-type to the p-type, forming positive and negative ions at fixed positions in a state of equilibrium which inhibit further transfer of electrons (depletion region)

-

+


What happens when you apply a voltage l.jpg
What happens when you apply a voltage?

For the device to conduct, electrons from the n-type region must cross the junction

Depletion region E-field

Reverse bias: Apply an electric field in this direction, mobile electrons are driven away from the junction (unlike fixed charged ions). Mobile holes are also driven away in the opposite direction. Depletion region acts like an insulating slab - No current flows

applied E-field

Depletion region E-field

Forward bias: Helps electrons overcome the depletion region. Current flows easily

applied E-field


Ideal diode l.jpg
Ideal diode

  • A diode is a non-linear circuit element

  • Only passes current in one direction

  • Constructed from a p-n semiconductor junction


Real diode l.jpg
Real diode

Diode law:

IS = reverse-leakage current

v = voltage across the diode

kB = Boltzmann's constant

e- = electron charge

T = Temperature (K)

Strong dependence on T

IS is small ~ 10-6A (Ge), ~10-8(Si)


Diode circuit l.jpg
Diode Circuit

  • Diodes are non-linear; how do we calculate the operating conditions? (Can’t easily use V=IR)

  • Consider the simplest diode circuit

KVL:

When ID=0; VD=VDD

When VD=0; ID=VDD/R

Must satisfy both equations: Operating point can be calculated by seeing when diode law line intersects load line


Rectifying circuit l.jpg
Rectifying Circuit

Ideal transformer: VS/VP=NS/NP

Real transformers are ~98% efficient

One of the most important applications of a diode is in rectifying circuits: used to convert an AC signal into the DC voltage required by most electronics


Half wave rectifier l.jpg
Half-wave rectifier

  • Only lets through positive voltages. Rejects negative voltages


Full wave rectifier l.jpg

-

-

+

-

+

+

Full-wave rectifier

  • To use both halves of the input sinusoid,can use a centre-tapped transformer:

e.g. Battery Charger


Or use a bridge rectifier l.jpg
or use a Bridge rectifier

  • Does not require centre-tapped transformer

  • Requires 2 diodes in each direction – cheap, but voltage drop is double


Bridge rectifier l.jpg
Bridge rectifier

  • Current flow in the bridge

vO

vO

+

-

-

+


Peak rectifier l.jpg
Peak rectifier

  • Most devices need steady DC

  • To smooth out the peaks and obtain a DC voltage

When source voltage < capacitor voltage

Diode is reversed biased

Capacitor discharges through resistor


Another diode application voltage doubler l.jpg
Another diode application: Voltage doubler

  • High Voltage transformers are expensive and impractical at voltages above a few thousand Volts. How do we get higher?

C1 charges to 2Vsec

C2 charges to Vsec


Voltage doubler l.jpg
Voltage doubler

  • Can extend this circuit to produce extremely high voltages (~750kV).

  • Cockroft-Walton voltage multiplier

  • 1932, Cavendish Labs

  • reached 250 kV

  • Accelerated protons onto a Lithium target

  • Split the atom!

  • http://www.youtube.com/watch?v=RdBqMtioh6U

Voltage Quadrupler