Electronics OverviewBasic Circuit AnalysisThe Basic RelationsExample: Voltage dividerReal Batteries: Output ImpedancePower Supplies and RegulationDiodesDiode MakeupLEDs: Light-Emitting DiodesGetting DC back out of ACDoing Better: Full-wave Diode BridgeFull-Wave Dual-SupplySmoothing out the BumpsHow smooth is smooth?Regulating the VoltageThe Zener RegulatorVoltage Regulator ICVoltage RegulatorsTransistorsBJT Amplifier ModeSwitching: Driving to SaturationTransistor BufferImproved Zener RegulatorSwitching Power SuppliesSwitcher topologiesStep-Down CalculationsStep-down waveformsCable ImpedancesImpedances, cont.Impedance Phasor DiagramTransmission Line ModelTypical Transmission LinesWhy impedance mattersImpedance matters, continuedSo Beware!References and AssignmentElectronics OverviewElectronics OverviewBasic Circuits, Power Supplies,Basic Circuits, Power Supplies,Transistors, Cable ImpedanceTransistors, Cable Impedancediode bridgeWinter 2012UCSD: Physics 121; 20122Basic Circuit AnalysisBasic Circuit Analysis•What we won’t do:What we won’t do:–common electronics-class things: RLC, filters, detailed analysis•What we will do:What we will do:–set out basic relations–look at a few examples of fundamental importance (mostly resistive circuits) –look at diodes, voltage regulation, transistors–discuss impedances (cable, output, etc.)Winter 2012UCSD: Physics 121; 20123The Basic RelationsThe Basic Relations•VV is voltage (volts: V); is voltage (volts: V); II is current (amps: A); is current (amps: A); RR is is resistance (ohms: resistance (ohms: ); ); CC is capacitance (farads: F); is capacitance (farads: F); LL is inductance (henrys: H)is inductance (henrys: H)•Ohm’s Law: Ohm’s Law: VV = = IRIR; ; VV = = ; ; VV = = LL((dIdI//dtdt))•Power: Power: PP = = IVIV = = VV22//RR = = II22RR•Resistors and inductors in series addResistors and inductors in series add•Capacitors in parallel addCapacitors in parallel add•Resistors and inductors in parallel, and capacitors in Resistors and inductors in parallel, and capacitors in series add according to:series add according to:€ 1CIdt∫ € 1Xtot=1X1+1X2+1X3+ KWinter 2012UCSD: Physics 121; 20124Example: Voltage dividerExample: Voltage divider•Voltage dividers are a classic way to Voltage dividers are a classic way to set a voltageset a voltage•Works on the principle that all charge Works on the principle that all charge flowing through the first resistor goes flowing through the first resistor goes through the secondthrough the second–so V  R-value–provided any load at output is negligible: otherwise some current goes there too •So So VVoutout = = VV((RR22/(/(RR11 + + RR22))))•RR22 here is a variable resistor, or here is a variable resistor, or potentiometerpotentiometer, or “pot”, or “pot”–typically three terminals: R12 is fixed, tap slides along to vary R13 and R23, though R13 + R23 = R12 always123R1R2VVoutWinter 2012UCSD: Physics 121; 20125Real Batteries: Output ImpedanceReal Batteries: Output Impedance•A power supply (battery) is characterized by a A power supply (battery) is characterized by a voltagevoltage ( (VV) and an ) and an output impedanceoutput impedance ( (RR))–sometimes called source impedance•Hooking up to load: Hooking up to load: RRloadload, we form a voltage , we form a voltage divider, so that the voltage applied by the battery divider, so that the voltage applied by the battery terminal is actually terminal is actually VVoutout = = VV((RRloadload/(/(RR++RRloadload))))–thus the smaller R is, the “stiffer” the power supply–when Vout sags with higher load current, we call this “droop”•Example: If 10.0 V power supply droops by 1% Example: If 10.0 V power supply droops by 1% (0.1 V) when loaded to 1 Amp (10 (0.1 V) when loaded to 1 Amp (10  load): load):–internal resistance is 0.1 –called output impedance or source impedance–may vary with load, though (not a real resistor)VRD-cell example: 6Aout of 1.5 V batteryindicates 0.25  outputimpedanceWinter 2012UCSD: Physics 121; 20126Power Supplies and RegulationPower Supplies and Regulation•A power supply typically starts with a transformerA power supply typically starts with a transformer–to knock down the 340 V peak-to-peak (120 V AC) to something reasonable/manageable•We will be using a We will be using a center-tapcenter-tap transformer transformer–(A’  B’) = (winding ratio)(A  B)•when A > B, so is A’ > B’–geometry of center tap (CT) guarantees it is midway between A’ and B’ (frequently tie this to ground so that A’ = B’)–note that secondary side floats: no ground reference built-inABA’CTB’AC inputAC outputWinter 2012UCSD: Physics 121; 20127DiodesDiodes•Diodes are essentially one-way current gatesDiodes are essentially one-way current gates•Symbolized by: Symbolized by: •Current vs. voltage graphs:Current vs. voltage graphs:VIVIVIVI0.6 Vplain resistor diode idealized diode WAY idealized diodeno current flowscurrent flowsthe direction thearrow points in thediode symbol is thedirection that currentwill flowacts just like a wire(will support arbitrarycurrent) provided thatvoltage is positiveWinter 2012UCSD: Physics 121; 20128Diode MakeupDiode Makeup•Diodes are made of semiconductors (usually silicon)Diodes are made of semiconductors (usually silicon)•Essentially a stack of Essentially a stack of pp-doped-doped and and nn-doped-doped silicon to silicon to form a form a p-n junctionp-n junction–doping means deliberate impurities that contribute extra electrons (n-doped) or “holes” for electrons (p-doped)•Transistors are Transistors are n-p-nn-p-n or or p-n-pp-n-p arrangements of arrangements of semiconductorssemiconductorsp-type n-typeWinter 2012UCSD: Physics 121; 20129LEDs: Light-Emitting DiodesLEDs: Light-Emitting Diodes•Main difference is material is more exotic than silicon used in ordinary Main difference is material is more exotic than silicon used in ordinary diodes/transistorsdiodes/transistors–typically 2-volt drop instead of 0.6 V drop•When electron flows through LED, loses energy by emitting a When electron flows through LED, loses energy by emitting a photonphoton of of light rather than vibrating lattice (heat)light rather than vibrating lattice (heat)•LED efficiency is 30% (compare to incandescent bulb at 10%)LED efficiency is 30% (compare to incandescent bulb at 10%)•Must