ACTIVE DEVICES OBJECTIVES

Transcription

1 ACTIVE DEVICES OBJECTIVES To become familiar with basic Tubes and Semiconductors To be able to name their parts To understand their basic function To be able to answer exam questions

2 ACTIVE DEVICES To be an active device, the component must in some way control electron flow. To be an electronic circuit (rather than an electrical circuit) the circuit must contain at least one active device.

3 ACTIVE DEVICES Controlling electron flow means controlling current and/or voltage. Static Current = current-controlled Static Voltage = voltage-controlled Active Devices allow small signals to control large signals. Most common benefit of a control circuit is AMPLIFICATION.

4 Classification of Materials INSULATORS - GLASS - WOOD - PLASTICS CONDUCTORS - GOLD - SILVER - COPPER - ALUMINUM SEMICONDUCTORS - SILICON - GERMANIUM

5 INSULATOR No free Electrons to move in orbit Atoms require a large amount of energy input to allow the electrons to jump (conduct)

6 CONDUCTOR Free electrons are flying about atom Small amounts energy required to move electron from one atom to the next (conduction)

7 Electron Current Flow

8 SEMICONDUCTOR Conductive impurities added to insulators

9 SEMICONDUCTORS Some Types: Silicon Germanium Gallium Arsenide ALMOST THE SAME AS AN INSULATOR CONDUCTION (current flow) IS CONTROLLED BY DOPING (IMPURITIES) AND BY ELECTRIC FIELDS (BIASING)

10 Semiconductors Impurities are added to the germanium, silicon etc to create flavours of each variety (called doping). This makes germanium or silicon with: P type material (more positive, missing a valence electron) N type material (more negative, additional valence electron)

11 Semiconductors -JUNCTION-The point where the P and N material meets -BIAS- The polarity of the electricity required to make current flow -REVERSE BIAS- The polarity of the electricity required to make current stop flowing

12 DIODE Anode- positive Cathode - negative

13 Diode

14 Diode- Equilibrium some holes move to N region some electrons move to P region and no current flows. Creates depletion zone.

15 Diode-Zero Bias no current flows in circuit

16 Diode Zero Bias

17 Diode-forward bias current flows ve to +ve

18 Diode reverse bias blocks current (or unwanted signals)

19 Diode Voltage Drops Cause by depletion zone. Once a diode conducts you always measure the same voltage across it Silicon diode = 0.7v Schottky diode = 0.3v Germanium diode = 0.2v

20 DIODES Simple P N junction semiconductor Electrons build up in the depletion zone until current flows (si.7v, ge.2 v) Conducts in one direction (forward bias) Blocks current in reverse direction (reverse bias) Electrical equivalent to a valve (on/off)

21 DIODES

22 DIODES Used as detectors of weak radio signals (crystal radio) by taking high frequency and converting to the envelope Used to convert A.C. to D.C. (rectify) Used as a voltage regulator (constant voltage) Used to block or isolate circuitry (in a battery operated device it prevents damage by reverse battery installation)

23 WhaT IS a transistor 1:20

24 Diode Rectifiers ½ wave rectified- pulsing D.C. (negative cycle blocked)

25 Full Wave Rectifiers Power supply. Centre tap transformer, each diode conducts on half cycle. Provides a D.C. output with ripple.

26 Full Wave Rectifiers Bridge Rectifier- four Diodes each

27 Diode Bridge Rectifier Each half cycle is rectified using two diodes

28 Diode Rectifiers Input A.C ½ wave rectifier Full wave rectifier or DC. This output is filtered with capacitors to make as smooth as required

29 Zener Diodes Zener is designed to be mounted backwards (positive of battery to cathode). In forward bias it acts like a normal diode. Voltage Regulator - Voltage remains constant at output for its designed value. (R limits current), even when input voltage varies.

30 LED light emitting diode Emit light when current flows through them. Colour is dependent on LED. Tri- colour, two diodes

31 TRANSISTORS All have three legs or conductor leads Collector Emitter Base (usually control) Made from semiconductor sandwich NPN or PNP

32 TRANSISTOR

33 TRANSISTOR MODEL Base- small amount of water goes in and lifts up flapper Collector has huge reservoir of water Flapper opens, water rushes from collector to the emitter Base also adds water. An increase in base water forward biases the circuit and amplifies with the extra water

34 Transistor Types

35 Transistor Types and Parts

36 Transistor Configurations Typically three types of configurations: Common Emitter -both the signal source and the load share the emitter Common Collector - both the signal source and the load share the collector Common Base - both the signal source and the load share the base

37 Transistor Configurations Common Emitter Input base, output collector. Amplifies weak radio signals Common Collector Input base, output is emitter. ( emitter follower). Unity output voltage but follows input very closely, good current gain.

38 Common Base: Transistor Configurations Emitter is input, collector is output, base is common Used for audio preamps and VHF and UHF due to its impedance matching

39 Transistor clip How a transistor works First transisitor

40 FETfield effect transistor A type of transistor but leads called: Drain Source Gate (controls) FETS are normally on and gate bias (controls) flow. (voltage at gate stops the FET output) Acts most like a vacuum tube

41 MOSFET metal oxide field effect transistor

42 n-channel JFET p-channel JFET

43 Field effect transistors 3:50

44 Advantages of Transistors/FETS Small Inexpensive Easily Manufactured Good Amplification Fast Switching Low Power Consumption Easily matches stages in circuits

45 IC s (Integrated Circuits) Entire circuits on a single substrate (blanket) Smaller chassis required Reliable and reproducible results Low cost Require less power to perform the control function

46 IC-complex circuits build on a substrate

47 Semiconductors Worst Enemies HEAT- protected by heat sinks, fans, air openings in cases. High power devices require special coolants. Static Discharge protected by good grounding in A.C. line, ground plates, shields, straps (away from carpets) EMF/EMI electromagnetic frequency/interference. Protected by grounding and shielding, circuit design.

48 PERFECT MACHINE efficiency

49 TRUE MACHINE Energy cannot be created or destroyed

50 AMPLIFICATION Energy cannot be created or destroyed The amplified signal is achieved by adding another power source. The transistor (amplifier) takes this power and uses it to duplicate the input signal and make it larger

51 AMPLIFIER GAIN A=GAIN

52 AMPLIFICATION AMPLIFIED Current Voltage Power NOT AMPLIFIED Resistance Capacitance Inductance

53 Commonly Amplified Signals in Amateur Radio AUDIO 20 Hz 20 khz (high fidelity) SPEECH Hz (radio audio) RF (radio frequency) 3 khz 300 GHz (allotted band within this range) Microwave 300 MHz 300 GHz (EHF)

54 Vacuum Tubes Glass or metal tube with air pumped out (vacuum) DIODE Filament (heater) Cathode (inner tube) Anode (plate- outer cylinder) Grid ( grid acts as a control - becomes a triode)

55 Vacuum Tube Operation Filament (Cathode) heats Cathode emits electrodes into the space charge Anode surrounding cathode is charged more positively Current flows from cathode to anode Creates a Rectifier A.C. becomes pulsating D.C. Diode

56 Triode Amplifier Addition of Grid between plate and cathode Grid made negative to plate, and plate made positive with respect to cathode Some electrons are repelled back (feedback,heat give amplification) Grid very negative no current (cut-off) Grid less negative more current flows

57 Rectifier Tube

58 Tube Advantages/ Disadvantages Tubes provide amplification of infinite harmonics for audio amps- warm rich sound High power Bulky Dissipates large amounts of Heat Costly Fragile Unreliable

59 Transistor vs Tube (NPN Transistor and N-Channel FET) Transistor FET Triode Input Emitter Source Cathode/ filament Output Collector Drain Plate/ Anode Control Base Gate Control Grid

60 Troubleshooting Plugged in? Each individual assembly, sub assembly, board or chip on board. Turned on? Each individual assembly. Inputs at each stage ok (connectors)? Outputs at each stage ok (connectors)? Power Supply (wall warts), cord. Swap it if you can t measure it. Batteries present, ok.

61 Troubleshooting Look for burnt chips, swollen components, bad/loose solder connections, burnt cooper traces, broken wires, burnt wires, bent pins. Microprocessor equipment. POST power on self test. Resets, software or hardware switches, power cycle/reboot.