Diodes & Transistors ¡ Semiconductors ¡ Diodes ¡ Transistors ¡ Are metals good conductors? § Yes, the electrons are highly mobile ¡ Semiconductors are materials that on their own do NOT conduct like metals…
¡ We DOPE them § We add materials with additional electrons OR § We add materials with missing electrons, called holes http://www.filmscanner.info/en/CCDSensoren.html ¡ Semiconductors doped with additional electrons are called n-Type
¡ Semiconductors doped with missing electrons, called holes, are called p-Type ¡ Semiconductors ¡ Diodes ¡ Transistors ¡ Lets put doped materials together!
¡ The P-N junction is a building block for electronics
p n
+ Vdiode -
Idiode ¡ P-N Junction § P doped side is the p n Anode § N doped side is the anode cathode Cathode
+ Vdiode - § AKA a Diode
Idiode p n ¡ Current only flows from anode to cathode anode cathode
+ Vdiode - § If Vdiode > Von Idiode § For silicon diodes, Von ~ 0.7 V Idiode
Vdiode Von ¡ Diodes are used for § Stop valve § LEDs § Convert AC to DC (Rectifiers) § … ¡ Nick Holonyak § 1928- § Invented the first practical visible LED in 1962 while at GE § EE Prof at University of Illinois § Also invented laser diode and light dimmer
en.wikipedia.org/wiki/File:Nick_Holonyak_Jr.jpg ¡ LED – Light Emitting Diode § Electron-hole recombination in a diode releases photons § GaAs and related materials glow red, yellow, green, or blue
§ Von depends on material, typically ~1.7 V § Typically 5-20 mA gives satisfactory brightness www.desktopedia.com ¡ Semiconductors ¡ Diodes ¡ Transistors ¡ William Shockley § 1910-1989 § Son of a mining engineer § B.S. Caltech, Ph.D. MIT § Invented BJT (Bipolar Junction
Transistor) in 1948 @ Bell Labs computerhistory.org § Supervised Bardeen & Brattain ▪ who invented first transistor in 1947 ▪ The three received the Nobel Prize in Physics in 1956 collector ¡ Made of two back-to-back diodes n ¡ Behaves as a current-controlled base p switch n ¡ 3 Terminals emitter § Base (control) § Emitter (negative switch terminal) collector § Collector (positive switch base terminal) emitter ¡ Base-to-emitter junction is a diode
¡ Small base current allows larger collector current to flow ¡ Small current from base to emitter (works like diode) ¡ Larger current from collector to emitter ¡ Applications § Current Amplifier § Switch 1. When Vbe ≈ 0.7V, transistor turns
Ic ON c + b Vce 1. If Vce > 0, transistor behaves as a + Ib - current amplifier Vbe e - Ic = β Ib c
2. If V falls t0 0, I ceases to rise Ic = bIb ce c b with Ib I SATURATION b e ¡ Turn on or off a high-current load § Such as the motor V § Needs more current than digital I/O bat
¡ If D2 = 0, transistor is cutoff M § No current flows to load
¡ If D2 = 1 (5V), transistor saturates 215 W x D2 § Ib = (5-0.7) / 215 = 20 mA
§ Ic of up to ~2A flows to load § Enough to pull x down close to 0