What is SMPS...(Switch Mode Power Supply)

                                     How to Easily Understand The Functions
                                Of Switch Mode Power Supply 

Troubleshooting linear power supply was quite easy as compare to switch mode power supplies (SMPS). AC voltage enters to the primary side of linear transformer and then converted the AC into a lower or higher AC voltage depending on the secondary winding. The output AC voltage is then rectified and filtered by a diode and capacitors to produce a clean DC voltage.
If there is a problem in the linear transformer circuit, I can say that it is very easy to locate the fault. This is somehow different in the case of a switch mode power supply. The designs were complicated and some technicians found it quite hard to fully understand how the switch mode power supplies work.
The working principle of switch mode power supply is different from the linear type. First the AC voltage will enter to a full wave rectifier (bridge rectifier) which produces an uneven DC output and then filtered by a large capacitor (usually 220 micro farad and up to 450 volts).

The clean DC voltage will then enter to start up resistors and to the input of switch mode power transformer. Once the voltage passed through the high ohms resistor (start up resistors) the voltage would drop to a value where it then enters to the VCC supply pin of Pulse width modulation IC.

Once the PWM IC received the voltage it will output a signal to drive the transistor (or FET) and produces a changing in magnetic field in the transformer primary winding. The changing magnetic field induces voltage in the secondary windings.
Each of these AC voltage produced by the secondary windings is then rectified, filtered, and regulated to produce a clean DC voltage. One of the main DC output voltage is the B+ that supply to flyback transformer (for TV and Monitor Circuit)

The output from the B+ voltage supply is then connected, through a “feedback” loop (which consist of optoisolator ic and an error amplifier TL431 IC), back to the PWM IC. When the voltage from the B+ supply rises or drop a bit, the PWM IC will act to correct the output.
You must ask your self what is the purpose and its function of the components in the SMPS circuit and how to check them if they fail. Find out the function of these components in SMPS circuit:
Bridge rectifier,

Filter capacitor, Start up resistors Chopper/Power FET
Pulse Width Modulation (PWM IC) Current sense resistor Switch mode power transformer Optoisolator/optocoupler Error Amplifier IC (TL431) Secondary diodes Secondary filter capacitors

Push yourself further by searching the internet for the datasheet of a PWM IC part number. For example, UC3842 PWM IC is mostly used in SMPS. Do you know what the function of pin 5 of this IC is? Do you know which pin is the supply voltage (VCC)? Do you know what is the actual voltage that enters to the IC? Do you know which pin that drives the power FET? Can I get a replacement for this IC? And so on………
Let’s take a soldier as an example. Soldiers not only good in handling rifle but also knows all the details about it. They know how to dismantle and assemble back their rifle fast (imagine in the middle of war the rifle jammed-they can repair it fast). They know how much each bullet cost, how far the shooting distance, how big is the diameter of the bullet, how many cm the length of the bullet and so on. Hope you don’t get bored with the soldier’s story, did you get the ideas?

Any SMPS that comes across my repair bench, I would not immediately repair it, in fact I will take couples of minutes to analyze the circuit design and see it from all angles before I begin to repair. Troubleshooting SMPS is not limited to only one procedure in fact many electronic repairers have their own unique ways and methods to solve SMPS problems. Some prefer to use light bulb to isolate SMPS faults while others like to use resistors. Troubleshooting SMPS is fun and flexible but in some cases could make you get very frustrated too.
Remember, don’t limit yourself to only one or two sources to get you understand and be able to repair SMPS. If you have the budget, get the books that have related to SMPS repair-study and start doing practical about it. Share your problems with other fellow electronic repairers and the most important thing is don’t give up. There’s lot of mountain in the journey of our live and you yourself have to climb and conquer it. All the best!

WHT IS AN OLED...?

OLED Components

Like an LED, an OLED is a solid-state semiconductor device that is 100 to 500 nanometers thick or about 200 times smaller than a human hair. OLEDs can have either two layers or three layers of organic material; in the latter design, the third layer helps transport electrons from the cathode to the emissive layer. In this article, we'll be focusing on the two-layer design.

An OLED consists of the following parts:

Substrate (clear plastic, glass, foil) - The substrate supports the OLED.

Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.

Organic layers - These layers are made of organic molecules or polymers.

Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.

Emissive layer - This layer is made of organic plastic molecules (different ones from the conducting layer) that transport electrons from the cathode; this is where light is made. One polymer used in the emissive layer is polyfluorene.

Cathode (may or may not be transparent depending on the type of OLED) - The cathode injects electrons when a current flows through the device.

The biggest part of manufacturing OLEDs is applying the organic layers to the substrate. This can be done in three ways:

• Vacuum deposition or vacuum thermal evaporation (VTE) - In a vacuum chamber, the organic molecules are gently heated (evaporated) and allowed to condense as thin films onto cooled substrates. This process is expensive and inefficient.
• Organic vapor phase deposition (OVPD) - In a low-pressure, hot-walled reactor chamber, a carrier gas transports evaporated organic molecules onto cooled substrates, where they condense into thin films. Using a carrier gas increases the efficiency and reduces the cost of making OLEDs.
• Inkjet printing - With inkjet technology, OLEDs are sprayed onto substrates just like inks are sprayed onto paper during printing. Inkjet technology greatly reduces the cost of OLED manufacturing and allows OLEDs to be printed onto very large films for large displays like 80-inch TV screens or electronic billboards.

How do OLEDs Emit Light?

OLEDs emit light in a similar manner to LEDs, through a process calledelectrophosphorescence.

The process is as follows:

1. The battery or power supply of the device containing the OLED applies a voltage across the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons). The cathode gives electrons to the emissive layer of organic molecules. The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive layer.)
3. At the boundary between the emissive and the conductive layers, electrons find electron holes. When an electron finds an electron hole, the electron fills the hole (it falls into an energy level of the atom that's missing an electron). When this happens, the electron gives up energy in the form of a photon of light (see How Light Works).
4. The OLED emits light.
5. The color of the light depends on the type of organic molecule in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays.
6. The intensity or brightness of the light depends on the amount of electrical current applied: the more current, the brighter the light.

SMALL MOLECULE OLED VS. POLYMER OLED

The types of molecules used by Kodak scientists in 1987 in the first OLEDs were small organic molecules. Although small molecules emitted bright light, scientists had to deposit them onto the substrates in a vacuum (an expensive manufacturing process called vacuum deposition -- see previous section).

Since 1990, researchers have been using large polymer molecules to emit light. Polymers can be made less expensively and in large sheets, so they are more suitable for large-screen displays.

Types of OLEDs: Passive and Active Matrix

There are several types of OLEDs:

• Passive-matrix OLED
• Active-matrix OLED
• Transparent OLED
• Top-emitting OLED
• Foldable OLED
• White OLED

Each type has different uses. In the following sections, we'll discuss each type of OLED. Let's start with passive-matrix and active-matrix OLEDs.

Passive-matrix OLED (PMOLED)

PMOLEDs have strips of cathode, organic layers and strips of anode. The anode strips are arranged perpendicular to the cathode strips. The intersections of the cathode and anode make up the pixels where light is emitted. External circuitry applies current to selected strips of anode and cathode, determining which pixels get turned on and which pixels remain off. Again, the brightness of each pixel is proportional to the amount of applied current.

PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly due to the power needed for the external circuitry. PMOLEDs are most efficient for text and icons and are best suited for small screens (2- to 3-inch diagonal) such as those you find in cell phones, PDAs and MP3 players. Even with the external circuitry, passive-matrix OLEDs consume less battery power than the LCDs that currently power these devices.

Active-matrix OLED (AMOLED)

AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the circuitry that determines which pixels get turned on to form an image.

AMOLEDs consume less power than PMOLEDs because the TFT array requires less power than external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh rates suitable for video. The best uses for AMOLEDs are computer monitors, large-screen TVs and electronic signs or billboards.

OLED TUTORIAL

     

What is an OLED?

•Organic Light Emitting Devices are solid state devices comprising a thin electroluminescent organic (carbon-based) semiconductor layer that emits light when electricity is applied by adjacent electrodes
•In order for light to escape from the device, at least one of the electrodes must be transparent
•Intensity controlled by amount of current applied
•Color of light determined by emissive material used   

• Organic material can be deposited by vapor phase or solution deposition
• Intensive research into creating more efficient materials and structures

Structure of OLED Stack...

Why Are OLEDs Appealing?

SSL FEATURE

1. Higly Efficient
2. Long Life
3. Durable
4. No HarmFul Substance
5. Low Voltage
6. Instant On
7. Dimmable
8. Colour Tuneable

                                                 
Why Are OLEDs Appealing?

1. Diffuse, low brightness, large area
2. Any Colour Shape
3. Thin Light Weight
4. Flexible
5. Transparent
6. Mirror Surface

Unique Features...?

  ANY COLOR SHAPE

TRANSPARET LIKE NOVALED

DIFFUSE LIGHT  THIN (LUMIOTEC)

                                                                       LIKE A MIRROR

OLED Potential 

OLED Panel Status & Targets

Changhong LCD TV Repairing Tips

                             
                               

21K39PH – 21K51PH – PF2114PH – PF2115PH

DEAD SET

R528, FUSE, R502, L502, L503, V512, VD515,

BRIDGE RECTIFIER DIODES

CHANGING CHANNEL NOT FINE TUNED
DEFECTIVE DIODE NEAR JUNGLE IC

NO MENUR733 10K Ohms OPEN

ADJUST SCREEN RETRACE GREEN HAVE SCREEN

GOOD B+ STANDBY ONLY NO HIGH VOLTAGE OUT
PUT VIDEO IN AND OUT = GOOD = GOOD SYSTEM IC AND JUNGLE GOOD
AUTO PROGRAM THE UNIT CHANNEL CHANGING BUT NO SOUND
= DEF JUNGLE IC

BURNT RX02
RXO1 NOT MATCH THE ORIGINAL

OVERHEAT H-OUT
LEAKAGE H-OUT OR CAPACITOR

STANDBYEEPROM, SENSOR
PINCUSIONING CAPACITOR BLOWN
RM11C SHORTED

WHITE SREEN
JUNGLE IC,( LA76814K )

NO PICTURE
TUNER, DEMODULATION IC, IF TRANSFORMER, JUNGLE IC, SYSTEM IC

VIDEO PRESS MANY TIMES PICTURES GONE
BC SUPPLY UP TO 7.5 VOLTS , REPLACE 8.2V DIODE AS BLOCKING DIODE TO PRODUCED 0.28V BASE OF R G B

ABNORMAL VERTICAL ONE LINEHANG PIN#7 OF SYSTEM IC IF VERTICAL RETRACE APPEARS ON SCREEN ,

V702 = A1015 DEFECTIVE

BURN THE REGULATORC3807 AND VD515 OPEN

NO MENUR722, R723, V704, V703

OSCILATE NO RASTER BLACK SCREEN
CHECK: VIDEO OUT- GOOD
- VIDEO IN – GOOD
- V704 & V703 COLLECTOR = 5VOLTS
- RESISTOR BIAS 10K Ohms
- R725 & R733 OPEN
- DEF V704

NO HEATER
RF481, FLYBACK TRANSFORMER,

HORIZONTAL LINE OUTPUT TRANFORMER,

HORIZONTAL LINE OUTPUT TRANSISTOR,

HORIZONTAL DRIVE TRANSISTOR, AND

JUNGLE IC ( LA76814K )

NO VIDEO INCPU OR SYSTEM IC DEFECTIVE

RETRACE LINEV901, V902, V903, AND

COLOR DRIVE TRANSISTORS

ABNORMAL VOLTAGERF551, VD586, V582, V583

NO SIGNAL
TUNER ( TDQ-6F2M )

IF TRANSFORMER, SAW TOOTH FILTER,

CHECK 5 VOLTS AND 45 VOLTS
NOTE: 45 VOLTS MUST BE 21-22.5 VOLTS VCC,

5 VOLTS MUST BE 4.8 VOLTS IF

45 VOLTS MEASURES 31 VOLTS

IT MEANS NO 5 VOLTS SUPPLY OR LOOSE CONTACTS,
MEMORY MAY POSSIBLE
JUNGLE DEFECTS IF NO RASTER

PF2914PH NOT OSCILATESCHECK:

POWER SUPPLY TO ACTUAL
- NO 5V-2
- 8V = 1V ONLY
- NO STANDBY VOLTAGE
- SUSPECTED AREAS:
- BCJA18D OSCILATOR DEFECTIVE
- CPU
- JUNGLE IC
- MEMORY

21F SERIES

CAUSE AND DEFECTS

OSCILATE NO PICTURE
CHECK- 3.3 VOLTS ( V512 ) = A1569 TRANSISTOR,
- PIN # 33 OF IC BUS OMS 837X ,

PIN# 54, 56, AND 61 IS 3.3 VOLTS
- HANG PIN# 10 OF JUNGLE IC

IF TV SET POWER UP DEFECTIVE JUNGLE IC
- V805 =A1015
- HANG UP C839
- PIN#33 JUNGLE IC 0.48V TO H-DRIVE BASE
- 1200MGhz REPLACE IF HIGH VOLTAGE TOO HIGH

OUTPUT OR NO OUTPUT
- C824A DEF

NO PICTURE BLACK SCREEN
OSCILATE NOT POWER ON

– CHECK
- +B 115 VOLTS.
- COLLECTOR OF HORIZONTAL OUTPUT 115V UP TO 118.5V
- BASE OF H-OUT 0.22VOLTS IF NOT FIND OTHER CAUSE
- V810, V811, D831
- COLLECTOR OF V810 = 1.98V IF NOT D831 LEAKAGE
- PIN# 45 OF IC BUS OPEN IF VOLTAGE EXCIST TO 4.5V
- HANG UP THE C839 THEN TRY TO RUN THE TV SETS IF IT WORKS PROPERLY REPLACED THE D831 OR OTHER RELATED X-RAY PROTECTION CICUITS

oscilate only not power on

CHECK +B 115 TO 118.5 VOLTS, STANDBY VOLTAGE 90 TO 93 VOLTS
- 3.3 VOLTS OF PIN# 45, 54, 56, & 61 IF GOOD CHECK
- 3.3V BECOME 1.6V IF ATTACHED TO JUNGLE IC JUNGLE IC

REPLACE THE A1569 3.3V REGULATOR
- MEMORY VOLTAGE 5V, 4.56V, & 4.58V IF GOOD
- REPLACE EEPROM 24C16
- AUDIO DEMODULATOR IC( N106 ) = TDA9859
- DEMODULATION IC ALSO RESPONSIBLE FOR THE OSCILATION

OR SWITCHING LOW VOLTAGE SECTION
- REPLACE THE TDA9859 IF DEFECTIVE

HANG PIN#15, 16, 17 &18
- CHECK ALSO 5V REGULATOR 7805

NO LEFT AUDIO
CHANGE EEPROM

NO VIDEO INPUT SIGNAL AND SOUND WITH AIREAL OR CABLE SIGNALV213 DEFECTIVE = C1815
R309 OPEN 1K OHMS

NO AIREAL SIGNAL WITH VIDEO INPUT SIGNAL
V214 DEFECTIVE = A1015,

N808=LM317T 8.2 VOLTS REGULATOR,

C824A= 35V/1000uf , C861= 16V/1000uf
RAINBOW COLOR APPEARS ON SCREEN
REPLACE VERTICAL IC

BURN RY22SHORTED TO GROUND THE CRT SOCKET AND

NEED TO REPLACED A NEW ONE

IF NO GREEN COLOR OR VOLTAGE UP TO 185V VY06 NEED TO REPLACE

STANDBY NO OTHER ACTION OF THE TV SETHANG UP C839, IF IT WORKS D831 DEFECTIVE AND

OTHER RELATED X-RAY PROTECTION CIRCUITS.
- TRY TO CHANGE EEPROM,
- AUDIO DEMODULATOR
- A1569=3.3V REGULATOR
- REGULATOR = STR G8653 OR 8656

OSCILATE NO PICTURE NO HEATER
NO VOLTAGE IN D831 CHANGE IC BUS AND MEMORY
- 190V = 150 ONLY AND ABNORMAL
- 30V GOOD IF FLYBACK HANG UP BUT DECREASE IF CONNECTED
- H-DRIVE AND PRE-DRIVE GOOD
- R841 CHANGE VALUE = 15K BECOME 25K Ohms
- R260 OPEN

OSCILATE AUTO PICTURE
LOOSE CONTACT IN JUNGLE IC BUS NEED RESOLDER OR CHANGE IC

OSCILATE NO PICTURE BLACK SCREEN WITH HEATER
CHECK: R G B SUPPLY FROM JUNGLE IC BUS 2.0 OR 1.98V TO 2.53V

IF IT EXCEEDED OR 3.0

CHECK 8.2 VOLTAGE SUPPLY FROM LM317T AND

THE FILTER CAPACITOR
L805 MUST 8.2 VOLTS IF ITS ALL GOOD

REPLACE THE JUNGLE IC MAY DEFECTIVE
R867 DEFECTIVE AND D838

AUTO SHUT ON AND OFF H-OUT NOT RUN
H-DRIVE TRANSISTOR C2688 LEAK
VERTICAL RETRACE UPPER LINE
R402 CHANGE VALUE

AUTO SHUT ON BLUE BACK AND NO OTHER ACTIONS
JUNGLE IC DEFECTS

OSCILATE NOT POWER UP STILL STANDBY MODE
JUNGLE IC DEFECTIVE

POWER BLINKS ONLY BACK TO STANDBY MODE680 Ohms = R804 OPEN,

STR G8653 LEAKGE,

EEPROM
D822 SHORTTED= RG2,

NO PICTURE BLACK SCREEN BUT HAVE MENU
LM317T SECTION 8.2 VOLTS DEFECTIVE

OUT OF HORIZONTAL SYNCR255 SHORTED TO GROUND
C388 DEFECTIVE
JUNGLE IC

29F PIN CUSTIONING DEFECTS
EW SECTION CANT ADJUST,

68K Ohms =R409 OPEN

29F18 RETRACE LINE UPPER SIDE
R403 CHANGE VALUE

29F18 BURN SUPPLY TO HEATER & G2 BRIDGE CAPACITOR
CHANGE FLYBACK

FLECKERING WHEN AUTO PROGRAMR841 CHANGE VALUE,

C206 LEAKAGE

VERTICAL NOT ENOUGHR403 CHANGE VALUE 0.33Ohms TO 0.15 Ohms

LIGHTNING EFFECTS
C206A OPEN OR SHORTED AND

R841 CHANGE VALUE

LOW VOLTAGE B+V802 COLLECTOR TO EMITTER OPEN

LOW VOLTAGE BLINKING DEFECTSB+ ABNORMAL = R804 680 Ohms CHANGE VALUE AND

C810 LEAK

PF29F15PH AND PF29F18PH WIDE VERTICAL OR STRETCHED
MEASURE THE VD501 OR VD402 & VD437

IF GOOD WHILE HANG UP BUT

SHORTED WHEN ATTACHED= VERTICAL IC DEFECTIVE

SMALL RETRACE APPEARS ON SCREEN R G BREPLACE JUNGLE IC

NO SIGNAL
TUNER,

SAW TOOTH FILTER, JUNGLE IC,

NO PICTURE WITH SOUNDS
H-DRIVE OPEN

INTERMITTENT DEADSET
H TRANSFORMER LOOSE CONNECTION

NO RIGHT AUDIODEFECTIVE AUDIO PROCESSOR TDA9859

PRESS ANY BUTTONS EVEN REMOTE MENU APPEARS ON SCREEN
JUNGLE IC DEFECTIVE

NO COLORMEMORY AND 1200MGhz DEFECTIVE

H1418PH IN COMPLETE CHANNELSTUNER OR JUNGLE IC

ONE CLICK ONLY AND LIGHT INDECATOR BLINKS ONLYCHANGE MEMORY

NO SIGNAL RECIEVEDCHECK: VIDEO IN = GOOD- TUNER
- SHORTING THE SAW FILTER WILL

DETECTS OR ISULATE THE CAUSE ETHEIR

JUNGLE OR TUNER SECTION IF RASTER APPEARS JUNGLE OK
- MEMORY= GOOD
- TUNER = GOOD
- FR AMP = GOOD
- DEMODULATION = GOOD
- 3.3V= GOOD
- 5V = GOOD
- 3.39V = GOOD
- 22V = GOOD
- 8.2 VOLTS MAY LEAK

H1418PH WHITE VERTICAL LINES STRIPSCHECK: VIDEO OUT = GOOD
- RGB VOLTAGE = 6V INSTEAD OF 3.0 VOLTS
- RGB AMP = 55V- 190V = GOOD
- VD301= A1015 DEFECTIVE

STANDARD CRT TUBE SHUT OFF AFTER 30 MINUTES TO 2HrsLY01 NOT CONNECTED AN

GROUND TO HEATER GROUND OPEN

AUTO PROGRAM = GOOD BUT NO CHANNEL APPEARS AFTER FINISH
SERVICE MODE NOT FUNTION TOO
REPLACE THE MEMORY

B+ GOOD BUT NO FLYBACK B+R501 OPEN AND H-OUT

14F98PH BURN R406R406 = 10 Ohms
REPLACE D402

STANDBY ONLYC823 DEF

AUTO POWER ON NO PICTURE
MEMORY DEFECTIVE

BLURD PICTURE
G2= 50 VOLTS ONLY
CY04 = OPEN

BURN R821
MEMORY REVERSED CONNECTION

OVERHEAT H-OUT
LEAK H-OUT
C502 &C501 = DEFECTIVES

NO SECONDARY VOLTAGECHECK: PHOTO COUPLER
- REGULATOR
- B+ DIODE RG2
- R803 CHANGE VALUE= 0.27 Ohms
- D805 = RU2 OR AK03
- C808= 2KV/680P

COLOUR CODING OF RESISTENCE...

                   

The 4-band code is used for marking low precision resistors with 5%, 10% and 20% tolerances. Identifying the value will become easy with a little practice, as there are only a few simple rules to remember: The first two bands represent the most significant digits of the resistance value. Colors are assigned to all the numbers between 0 and 9, and the color bands basically translate the numbers into a visible code. Black is 0, brown is 1, red is 2 and so on (see the color code table below). So, for example, if a resistor has brown and red as the first two bands, the most significant digits will be 1 and 2 (12). The third band indicates the multiplier telling you the power of ten to which the two significant digits must be multiplied (or how many zeros to add), using the same assigned value for each color as in the previous step. For example, if this band is red (2), you will multiply it by 102 = 100 (or add 2 zeros). So, for the resistor we used in the previous example, the value would be: 12 x 100 = 1200Ω (1.2kΩ). Note: If the multiplier band is gold or silver, the decimal point is moved to the left by one or two places (divided by 10 or 100). The tolerance band (the deviation from the specified value) is next, usually spaced away from the others, or it's a little bit wider. A color is assigned to each tolerance: gold is 5%, silver is 10%. 20% resistors have only 3 color bands

Basic Electronics Part2

Diode

•A diode is a 2 lead semiconductor that acts as a one way gate to electron flow.
– Diode allows current to pass in only one direction.
•A pn-junction diode is formed by joining together n-type and p-type silicon.
•In practice, as the n-type Si crystal is being grown, the process is abruptly altered to grow p-type Si crystal. Finally, a glass or plastic coating is placed around the joined crystal.
•The p-side is called anode and the n-side is called cathode.
•When the anode and cathode of a pn-junction diode are connected to external voltage such that the potential at anode is higher than the potential at cathode, the diode is said to be forward biased.
–In a forward-biased diode current is allowed to flow through the device.
•When potential at anode is smaller than the potential at cathode, the diode is said to be reverse biased. In a reverse-biased diode current is blocked.

Diode: How it Works —I

•When a diode is connected to a battery as shown, electrons from the n-side and holes from the p-side are forced toward the center by the electrical field supplied by the battery. The electrons and holes combine causing the current to pass through the diode. When a diode is arranged in this way, it is said to be forward-biased.

 

Transistor

A three lead semiconductor device that acts as: – an electrically controlled switch, or
– a current amplifier.
• Transistor is analogous to a faucet.
–Turning faucet’s control knob alters the flow rate of water coming out from the faucet.
–A small voltage/current applied at transistor’s control lead controls a larger current flow through its other two leads.


               Transistor Types: BJT, JFET, and MOSFET

• Bipolar Junction Transistor (BJT)
– NPN and PNP
• Junction Field Effect Transistor (JFET)
– N-channel and P-channel
• Metal Oxide Semiconductor FET (MOSFET)
– Depletion type (n- and p-channel) and enhancement type (n- and p-channel)

BJT Types


• NPN and PNP.
–NPN: a small input current and a positive voltage applied @ its base (with VB>VE) allows a large current to flow from collector to emitter.
–PNP: a small output current and a negative voltage @ its base (with VB<VE) allows a much larger current to flow from emitter to collector.

Basic Electronics...

Basic Electronics....


Semiconductor —I

•Materials that permit flow of electrons are called conductors (e.g., gold, silver, copper, etc.).
•Materials that block flow of electrons are called insulators (e.g., rubber, glass, Teflon, mica, etc.).
•Materials whose conductivity falls between those of conductors and insulators are called semiconductors.
•Semiconductors are “part-time” conductors whose conductivity can be controlled.


Semiconductor —II

• Silicon is the most common material used to build semiconductor devices.

•Si is the main ingredient of sand and it is estimated that a cubic mile of seawater contains 15,000 tons of Si. 
•Si is spun and grown into a crystalline structure and cut into wafers to make electronic devices.

Semiconductor —III

• Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence electrons).
– Germanium is another semiconductor material with four valence electrons.
• In the crystalline lattice structure of Si, the valence electrons of every Si atom are locked up in covalent bonds with the valence electrons of four neighboring Si atoms.
–In pure form, Si wafer does not contain any free charge carriers.
–An applied voltage across pure Si wafer does not yield electron flow through the wafer.
–A pure Si wafer is said to act as an insulator.
• In order to make useful semiconductor devices, materials such as phosphorus (P) and boron (B) are added to Si to change Si’s conductivity.


N-Type Silicon

 

•Pentavalent impurities such as phosphorus, arsenic, antimony, and bismuth have 5 valence electrons.
•When phosphorus impurity is added to Si, every phosphorus atom’s four valence electrons are locked up in covalent bond with valence electrons of four neighboring Si atoms. However, the 5th valence electron of phosphorus atom does not find a binding electron and thus remains free to float. When a voltage is applied across the silicon-phosphorus mixture, free electrons migrate toward the positive voltage end.
•When phosphorus is added to Si to yield the above effect, we say that Si is doped with phosphorus. The resulting mixture is called N-type silicon (N: negative charge carrier silicon).
•The pentavalent impurities are referred to as donor impurities.


P-Type Silicon—I

•Trivalent impurities e.g., boron, aluminum, indium, and gallium have 3 valence electrons.
•When boron is added to Si, every boron atom’s three valence electrons are locked up in covalent bond with valence electrons of three neighboring Si atoms. However, a vacant spot “hole” is created within the covalent bond between one boron atom and a neighboring Si atom. The holes are considered to be positive charge carriers. When a voltage is applied across the silicon-boron mixture, a hole moves toward the negative voltage end while a neighboring electron fills in its place.
•When boron is added to Si to yield the above effect, we say that Si is doped with boron. The resulting mixture is called P-type silicon (P: positive charge carrier silicon).
• The trivalent impurities are referred to as acceptor impurities.