Difference between revisions of "Electronics notes/Transistors"

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m (High side versus low side switching/driving)
m (BJTs and FETs)
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==BJTs and FETs==
 
==BJTs and FETs==
 
 
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A transistor is, at the core, a current amplifier  
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A transistor is, at the core, a current amplifier.
: the current you put at the base controls the current across the C and E terminals.
+
  
 +
The basic idea is that the current across C and E is the gain time the current flowing into B
  
It amplifies that current by a particular gain (on the order of a few dozen for power transistors, over a hundred for signal transistors).
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'''Gain''' is fixed for a particular transistor, and is
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: on the order of a few dozen for power transistors
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: over a hundred for signal transistors
  
 
With smaller base current, you amplify a signal fairly linearly (with footnotes).
 
With smaller base current, you amplify a signal fairly linearly (with footnotes).
  
With a large enough base currents, the transistor saturates and essentially just switches freely-running current. In this use, it reacts much faster than things like relays, tubes.
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{{comment|(gain is also known as 'hFE' (apparently short for "Hybrid parameter forward current gain", a measure of DC gain) and 'beta' (presumably because it's shorter to say)}}
(Note also that for larger currents, FETs are way more efficient than BJTs).
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While by itself it's a current amplifier, with a few components it's e.g. a [https://en.wikipedia.org/wiki/Common_emitter common emitter amplifier], which is a voltage amplifier.  
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Beyond a certain amount of base current,
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the transistor saturates and the current between C and E, whatever it is, just passes it as comes in.
 +
 
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This is now effectively a switch, and reacts much faster than things like relays or tubes used as switches.
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(Also note also that for larger currents, FETs are much more efficient than BJTs).
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 +
 
 +
 
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While by itself a transistor is a current amplifier,
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with a few components you can construct e.g. a [https://en.wikipedia.org/wiki/Common_emitter common emitter amplifier], which is a voltage amplifier.  
  
 
Whether such a construction or an [[Electronics_notes/Amplifier_notes#Op_amps_.28and_differential_amplifiers.29|op amp]] is handier for your purpose depends a lot on other details, like  
 
Whether such a construction or an [[Electronics_notes/Amplifier_notes#Op_amps_.28and_differential_amplifiers.29|op amp]] is handier for your purpose depends a lot on other details, like  
whether single-ended is okay or you need differential in the end,
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: output impedance restrictions,
output impedance restrictions,
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: gain and linearity characteristics,
gain and linearity characteristics,
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: whether single-ended is okay or you need differential
and such.
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: some other details
  
  
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* Polarity:
 
* Polarity:
** For BJTs: NPN and PNP
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** For BJTs: NPN or PNP
** For FETs: N-channel and P-channel
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** For FETs: N-channel or P-channel
  
* Amplification factor hfe (transistor beta)
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* Amplification factor hFE (transistor beta)
  
* Maximum power rating
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* Maximum current rating
  
 
* Maximum operating frequency (frequency of transition, at which it yields unity gain)
 
* Maximum operating frequency (frequency of transition, at which it yields unity gain)
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* Semiconductor material: germanium, silicon, gallium arsenide, silicon carbide, etc.
 
* Semiconductor material: germanium, silicon, gallium arsenide, silicon carbide, etc.
  
* Also physical package, intended application
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* Also physical package, intended application, and others
 
+
  
  

Revision as of 18:24, 12 July 2019

This is for beginners and very much by a beginner. It's meant to try to cover hobbyist needs, and as a starting point to find out which may be the relevant details for you, not for definitive information.

Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect


And some more applied stuff:

IO: IO and wired communication · localish communication · wireless (ISM RF, GSM, RFID, more) · 802.11 (WiFi) · 802.15 (including zigbee)


Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · Bluetooth serial · JY-MCU · DMX · ESC/POS notes

Audio notes: basic audio hacks · microphones · amps and speakers · device voltage and impedance, audio and otherwise ·

Less sorted: Common terms, useful basics, soldering · Microcontroller and computer platforms · Arduino and AVR notes · ESP series notes · Electronics notes/Phase Locked Loop notes · mounts, chip carriers, packages, connectors · signal reflection · pulse modulation · electricity and humans · Unsorted stuff


See also Category:Electronics.

BJTs and FETs

Bipolar family

Transistor behaviour, circuit styles

As a switch

High side versus low side switching/driving
This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


Oscillators

As a diode

Identifying a bipolar transistor's legs

FET family

Voltage controlled resistor

Insulated-gate bipolar transistors (IGBT)

A hybrid of the above, basically the high-current ruggedness of a Bipolar with the sensitivity of a FET

https://en.wikipedia.org/wiki/Insulated-gate_bipolar_transistor

Transistor behaviour, circuit styles

Compound pairs

Some practical notes

Tri-state buffer

Phototransistor / optocouple / opto-isolator

These can be seen as transistors that are triggered via light (LED-and-phototransistor combination) instead of using conductors.


Often used for isolation of currents, to avoid communicating some of the voltage noise, or to have simple (one-way) interaction between circuits at different voltages.


Often appear as 4-pin or 6-pin ICs.

  • The 4-pin variants give you the LED cathode and anode, and the transistor's collector and emitter.
  • The 6-pin variant use 5 pins; it adds the transistor's base, which just works as an extra (non-isolated) trigger. In practice it may often be left unconnected, but occasionally it's rather convenient to be able to trigger both ways (e.g. from the same and from the isolated circuit).


ICs with multiple optocouplers also exist.

Specs vary in details such as:

  • current use
  • output voltage
  • how much voltage difference can be isolated
  • added components -- may e.g. be a darlington setup

...and more.


See also: