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Transistor symbols

Types

Symbols (new sub title)

Symbols for main types shown on right. variations will be found. Included diodes. Separate substrate connection. Circle optional was for included in chip. Half arrow used in past to indicate silicon.

Packaging (add to existing sub title)

Referred to as case, package, and form factor. Latter used maily when laying out PCCts. JEDEC registered & propietary. xlink to pak illustration. Image shows T03 etc. Surface mount. BGA

Type Identity (new sub title)

JEDEC, Pro electron, Japanese, and Proprietry

Thermal aspects (new title)

Temperature is important consideration/has big effect on transistors. Too much heat will destroy transistor & semiconductors generally. High temp = reduced reliability. Heat final barrier to chip complexity. Dec Ace microprocessor 5v@ 50A?? = 250W. Move to lower voltages from standard 5V to 3.3V, 2.7V down to 0.9V ??? core often lower voltage with built in power converter (ie pentium).

Applications require wide heat range -50°C?? (goose bay Labrador) to 120°C?? (sahara desert) early transistors being Ge thus temp problem (high leakage) thermal runaway. Junc temp max Ge = ???. Si much higher 150?°C. Domestic (office), Autos (engine compartment especially wide range), airoplanes, military

Temperature effects

BJT increase temp =

incresed leakage
lower Vbe (-2.1 mV/°C)
Inc current gain
therefore increased conductivity

(makes BJT poor for paralleling Secondary break down, consider as many small trans in parallel. Domino effect destroys whole device)

Thermal runaway danger especially Ge.

FET incresed temp =

decreased leakage
reduced conductivity (Gm)
FETs simple to parallel (automatic)

Temperature ranges

Standard temp ranges commercial= 0 to 70°C, industrial= -20?? to 85°C, military= -55 to 120°C better temp more expensive because of more testing often same transistor chip, but better case sealing etc.

Small signal tran just speced to ambient air temp

Heatsinks

Many heatsink types: just to ambient, cold wall, peltia?, heat pipe, fans mounted on chip (ie pentium) oil (high voltage). insulating washer between transistor case and heatsink= mica, conductive foam, anodised ally. Sometimes case insulated so washer is not needed. Silicon grease used on mating faces to improve thermal conduction

Case affects thermal rating. TO3 First on right in image) case high dissipation (but bigger cases used for very high power) but big expensive and difficult to mount. TI pioneered the plastic case which could fit a TO3 pcb footprint but only has single hole fixing TO220?? (scond from right)

Thermal budget

Power simply = V*I Many transistors overrated in equipment.

Take 2n3055, what does 115W rating mean: not much can't actually dissipate 115W

Tj controlling factor also secondary break down prevented by operating within Safe Operating Area Rating (SOAR). For esample 2n3055 (example of VI profile)

Example:

Tj>Tcase>Insulating washer>heatsink>local air temp take 2n3055 Tj max (150 °C)> Junct to case (2°C/W)> Electrically Insulating Washer (1°C/W)>Heatsink to ambient(4°C/W)> ambient air temp (70 deg C)

So total thermal resistance to ambient =2+1+4= 7°C/W

Tj max = 150°C - T amb = 70°C 150-70= 80°C ignore base current Therefore maximum allowable dissipation = 80/7 = 11.4W along way from 115W also check SOA.

Other applications

2n3055 used as a heater showed how jelly bean transistors have become, even power types.

Oven Xtals

precision temperature sensor (example)

Use in Power Supplies (new title)

Term PSU used loosely for either power source of power conditioning including: converting from AV to DC (and vica versa: inverter), smoothing, stabilisation, provides low output impedance, changing polarity, filtering (EMC). PSU has major impact on performance of equipment especially HiFi amps. In this section PSU means power conditioner. Power sources include: domestic supply, battery, solar panel, generator. Used in automobile generator to charge batt.

Semiconductors (rectifiers and transistors) have transformed PSUs and thus transformed equipment including: radio, TV, computer (main frame & PC, radar systems, etc. Bench psu. Uninteruptable Power Supplies (UPS) : expplain. Inverters. high voltage PSU (ie TV). In the last 15 years there has been a revolution in SMPSU design with frequencies increasing resulting in smaller components. Small high frequency SMPS. SMPS are more efficient.

PSU building block in most equipment. Foundation of good equipment. Early vacuum tube computer PSU nightmare: give example (size & power: failures)

Before transistors and semiconductor rectifiers, PSUs were big, expensive and low performance, also inefficient. Large mains transformer to provide power for heater and poor efficiency of vacuum tubes.

Vacuun tube PSUs comprised 60% of equipment volune and weight (ie audio amp).

Copper Oxide rectifier and Selinium rectifier first semiconductor rectifiers: improved efficiency and no heater. But Germamium and Silicon junction rectifiers much more efficient. Schotckey? diode even efficient and faster (lower switching losses), but lower reverse blocking voltage, higher leakage and more expensive: but they have taken over for most modern PSUs.

Stabilising with vacuum tubes difficult and even more inefficient. Neon voltage stabilisers not to good. First recs germanium: efficient but not rugged or high current. Zenner diode good voltage reference (explain why reference voltage needed).

Early solid state PSUs similar architecture to vacuum tube supplies but BJTs allowed more sophisticated supplies including voltage stabilisation.

Progression: recitified non stabilised> rectifyed stabilised> swith mode low frequency. Early SMPSUs 400hz but then increased to 4 mhz (gives smaller, lighter components especially transformer and reservoir capacitor). Volume of transformer and reservoir inversly proportional to frequency. High frequency SMPSs require careful layout and high frequency components (especially Tx and res C) to ensure high efficiency and minimise EMC. Extensive filtering required, but modern chips much better.

PSUs catergorised as linear or switch mode. Linear PSU voltage transformation SMPS voltage and current transformation thus more efficient and flexible. Consider varying power source (ie solar cells ??) Inverter converts DC (from batt for example) to AC (110V, 60 Hz) to power mains equipment from a 12V automobile batt for example. High voltage PSU ie TV 25kV for TV Cathode Ray Tube CRT Extra High Tension (EHT) voltage (find exact term?).

Linear regulators

For example, the LM317[1] /LM137[2] are popular adjustable positive/negative voltage regulators capable of sourcing 1.5 ampres. explain use. They have been around for years. Cost $1.00 U.S. New generation of Low Drop Out (LDO) regulators will eventually replace these: explain LDO principal and advantages.

Switch Mode Power Supplys (SMPs)

Progression, recitified non stabilised> rectifyed stabilised> swith mode low frequency 400hz but then increased to 4 mhz Early types discrete, then chip & descrete, then all chip

Now very simple to use: few other components. National simple switcher. Early chip PSUs expensive and quirky: liable to oscillate.

Electromagnetic Compatibility (EMC) considerations

High frequency gives smaller components especially transformer and resorvour capacitors. Early SMPSs 400 Hz but now some 4 MHz but normal about 200 kHz

Tran good synchronous rectifiers especially IGFET. More efficient than diode but Scotky diode more efficient than junction diode (rectifier): lower forward drop and faster, but lower reverse voltage and more expensive. Speed gives more efficiency. Efficiency = power out/power in. Rectifier just diode designed for high current and high reverse voltage.

SWMPSs efficiency now typically 85%

Chip Types:

Polarity: Positive, Negative, Positive Inverting, Negative Inverting,
Input/ output voltage: Buck, Boost, ?? ?? ?? ?? ?? (SEPIC)

(use table to show above characteristics ?)

Isolated, non isolated: explain

Off line switching: explain

Voltage mode, current mode: explain

Data sheet for good psu chip. Maxim or national ?

PC PSU= Off line switcher, compact. Costs around $20.00 U.S. 5V at 50A, +-12V @ 5A -5v @ 500mA. (??? Watts)

from tran page revised 28-10-06

Bipolar junction transistor

The bipolar junction transistor (BJT) was the first type of transistor to be mass-produced. Bipolar transistors are so named because they conduct by using both majority and minority carriers. The three terminals of the BJT are named emitter, base and collector. Two p-n junctions exist inside a BJT: the base/emitter junction and base/collector junction. The BJT is commonly described as a current-operated device because the collector/emitter current is controlled by the current flowing between base and emitter terminals. Unlike the FET, the BJT is a low input-impedance device. As the base/emitter voltage (Vbe) is increased the base/emitter current and hence the collector/emitter current (Ice) increase exponentially (Ice ∝ K^Vbe where K is a constant). Because of this exponential relationship the BJT has a higher transconductance than the FET. Bipolar transistors can be made to conduct by light (photons) as well as current. Devices designed for this purpose have a transparent window in the package and are called phototransistors.

Field-effect transistor

The field-effect transistor (FET), sometimes called a unipolar transistor, uses either electrons (N-channel FET) or holes (P-channel FET) for conduction. The four terminals of the FET are named source, gate, drain, and body (substrate). On most FETs the body is connected to the source inside the package and this will be assumed for the following description. But, note that it is actually the voltage applied between the gate and body that controls the FET.

A voltage applied between the gate and source (body) controls the current flowing between the drain and source. As the gate/source voltage (Vgs) is increased the drain/source current (Ids) increases parabolically (Ids ∝ Vgs ²). In FETs the drain/source current flows through a conducting channel near the gate. This channel connects the drain region to the source region. The channel conductivity is varied by the electric field generated by the voltage applied between the gate/source terminals. In this way the current flowing between the drain and source is controlled. Like bipolar transistors, FETs can be made to conduct by light (photons) as well as voltage. Devices designed for this purpose have a transparent window in the package and are called phototransistors.

FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as metal-oxide-semiconductor FET (MOSFET), from their original construction as a layer of metal (the gate), a layer of oxide (the insulation), and a layer of semiconductor. Unlike IGFETs, the JFET gate forms a PN diode with the channel which lies between the source and drain. Functionally, this makes the N-channel JFET the solid state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. Also, both devices operate in the depletion mode, they both have a high input impedance, and they both conduct current under the control of an input voltage.

MESFETs are JFETs, in which the reverse biased PN junction is replaced by a semiconductor-metal Schottky-junction. These, and the HEMFETs (high electron mobility FETs), in which a two-dimensional electron gas with very high carrier mobility is used for charge transport, are especially suitable for use at very high frequencies (microwave frequencies; several GHz).

FETs are further divided into depletion-mode and enhancement-mode types. Mode refers to the polarity of the gate voltage with respect to the source at the threshold of conduction. For N-channel depletion-mode FETs the gate is negative with respect to the source while for N-channel enhancement-mode FETs the gate is positive, at the threshold of conduction. For both modes, if the gate voltage is made more positive the source/drain current will increase. For P-channel devices the polarities are reversed. Nearly all JFETs are depletion-mode types and most IGFETs are enhancement-mode types.

Tran Talk Phototransistor 30-10-06

The following two sentences are in discussion:

Photo BJT

"Bipolar transistors can be made to conduct by light (photons) as well as current. Devices designed for this purpose have a transparent window in the package and are called phototransistors."

Photo FET

"Like bipolar transistors, FETs can be made to conduct by light (photons) as well as voltage. Devices designed for this purpose have a transparent window in the package and are called phototransistors."

Edit Comment

"(phototransistors don't "conduct" photons (or voltage, for that matter); the photons cause RG current... Plus the effect isn't limited to bipolar transistors)"

H11F3 FET optocoupler

http://www.fairchildsemi.com/ds/H1/H11F3.pdf

Revision

My understanding now, having read the discussion and done some light investigating, is that there are very few descreet photo FETs (and those are "bastards"). Most photo FETs are embodied into optocouplers and fibre receivers. Manufacturers seem to describe three arrangements as photo FETs: 1) photo diode driving a FET, 2) FET driven by a "substrate photodiode" and 3) FET where photons impinge directly on the "channel" and cause conduction. Can anyone confirm or refute arrangement 3)? I have come across various statements on the web supporting it but nothing authorative.

While all that has been said is valied it is true that in each case the FET is made to conduct by the action of light. I suggest that for the purpose of the tran page the following be used: Suggest keep it simple and consistent with the technical level of tran page. "FETs can be made to conduct by light (photons) as well as voltage. Devices designed for this purpose have a transparent window in the package and are called photo FETs."

The statement ("Bipolar transistors can be made to conduct by light (photons) as well as current. Devices designed for this purpose have a transparent window in the package and are called phototransistors."). seems to fit with the discussion so far. Suggest this be put on tran page.

External links and references

(From transistor page 15 March 05 22:45)

[3] AudioUK's Milestones. Photograph of first working transistor
[4] Transistorized. Historical and technical information from the Public Broadcasting Service (PBS) web site
[5] The Transistor Legacy Then and Now. From Lucent Technologies ( Bell Telephone Laboratories) (AT&T)
[6] This Month in Physics History: November 17 to December 23, 1947: Invention of the First Transistor. From the American Physical Society (APS)
[7] 50 Years of the Transistor. From Science Friday, December 12, 1997
[8] The CK722 Museum. Website devoted to the "classic" hobbyist germanium transistor
[9] Bob's Virtual Transistor Museum & History. Treasure trove of transistor history
[10] 1954 to 2004, the TR-1's Golden Anniversary. In depth coverage of Regency radio.
[11] Jerry Russell's Transistor Cross Reference Database.
Riordan, Michael & Hoddeson, Lillian (1998). Crystal Fire. W.W Norton & Company Limited. ISBN 0393318516.{{cite book}}: CS1 maint: multiple names: authors list (link) The invention of the transistor & the birth of the information age
Amos S W & James M R (1999). Principals of Transistor Circuits. Butterworth-Heinemann. ISBN 0750644273.
Horowitz, Paul & Hill, Winfield (1989). The Art of Electronics. Cambridge University Press. ISBN 0521370957.{{cite book}}: CS1 maint: multiple names: authors list (link)

Math_symbols

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References Links etc

http://en.wikipedia.org/wiki/Wikipedia:Copyrights