Power Adapters 1 Power Adapters 2 Introductory Question Introductory Question If you install a pocket radio’s batteries If you install a pocket radio’s batteries � backward, it won’t work because its backward, it won’t work because its Power Adapters Power Adapters speaker will move the wrong direction. speaker will move the wrong direction. k k ill ill h h di di i i A. A. parts can only conduct current one way. parts can only conduct current one way. B. B. batteries will absorb power and recharge. batteries will absorb power and recharge. C. C. Power Adapters 3 Power Adapters 4 5 Questions about 5 Questions about Observations about Power Adapters Observations about Power Adapters Power Adapters Power Adapters � They obtain power from AC electrical outlets They obtain power from AC electrical outlets � Why isn’t a power adapter simply a transformer? Why isn’t a power adapter simply a transformer? � � They provide DC power to electronic devices They provide DC power to electronic devices � Why can electrons move in metals not insulators? Why can electrons move in metals not insulators? � � They somehow fix the AC versus DC problem They somehow fix the AC versus DC problem � How does charge move in a semiconductor? How does charge move in a semiconductor? � � They come in various voltages and other ratings They come in various voltages and other ratings � How does a diode carry current only one way? How does a diode carry current only one way? � How does a capacitor store electric charges? How does a capacitor store electric charges? Power Adapters 5 Power Adapters 6 Question 1 Question 1 Power Adapter Components Power Adapter Components (part 1) (part 1) � Why isn’t a power adapter simply a transformer? Why isn’t a power adapter simply a transformer? � A basic power adapter completes three steps A basic power adapter completes three steps � � to convert household AC power to convert household AC power � into low into low- -voltage DC power. voltage DC power. � A tr n f rm r p rf rm � A transformer performs only one of those steps. A transformer performs only one of those steps. A tr n f rm r p rf rm nl nl n n f th f th t p t p � Step 1: household AC to low Step 1: household AC to low- -voltage AC voltage AC � Performed by a step Performed by a step- -down transformer down transformer � Household AC flows into the primary coil Household AC flows into the primary coil � Low Low- -voltage AC flow out of the secondary coil voltage AC flow out of the secondary coil 1
Power Adapters 7 Power Adapters 8 Power Adapter Components Power Adapter Components (part 2) Power Adapter Components (part 3) Power Adapter Components (part 2) (part 3) � Step 2: low Step 2: low- -voltage AC to low voltage AC to low- -voltage pulsed DC voltage pulsed DC � Step 3: low Step 3: low- -voltage pulsed DC to low voltage pulsed DC to low- -voltage DC voltage DC � Performed 1 to 4 diodes: one Performed 1 to 4 diodes: one- -way devices for current way devices for current � Performed by a capacitor: a charge storage device Performed by a capacitor: a charge storage device � Low Low- -voltage AC flows into the system of diodes voltage AC flows into the system of diodes � Low Low- -voltage pulsed DC flows into the capacitor voltage pulsed DC flows into the capacitor � The diodes switch the current so that it always flows � Th di d The diodes switch the current so that it always flows Th di d it h th it h th rr nt rr nt th t it l th t it l fl fl � Capacitor stores charge when voltage is increasing � C p C p Capacitor stores charge when voltage is increasing it r t r it r t r h r h r h n h n lt lt i in r i in r in in out through one wire and returns through the other out through one wire and returns through the other � Capacitor releases charge when voltage is decreasing Capacitor releases charge when voltage is decreasing � Because the AC reversals cause the voltage to pulse, Because the AC reversals cause the voltage to pulse, � The capacitor smoothes out the voltage pulses The capacitor smoothes out the voltage pulses � low low- -voltage pulsed DC flows out of the diodes voltage pulsed DC flows out of the diodes � Low Low- -voltage DC flows out of the capacitor voltage DC flows out of the capacitor Power Adapters 9 Power Adapters 10 Question 2 Question 2 Metals, Insulators, and Diodes Metals, Insulators, and Diodes � Why can electrons move in metals not insulators? Why can electrons move in metals not insulators? � Three different electrical behaviors: Three different electrical behaviors: � Metals can carry current in any direction Metals can carry current in any direction � Insulators can’t carry current Insulators can’t carry current � Di d � Diode carry current only in one direction Diode carry current only in one direction Di d rr rr rr nt nl in n dir rr nt nl in n dir ti n ti n � To understand a diode, To understand a diode, � we need to understanding metals and insulators we need to understanding metals and insulators � so we must take a peek at quantum physics. so we must take a peek at quantum physics. Power Adapters 11 Power Adapters 12 Quantum Physics (Part 1) Quantum Physics Quantum Physics (Part 2) Quantum Physics (Part 1) (Part 2) � Classical physics (pre Classical physics (pre- -1900) thought that 1900) thought that � Example 1: light Example 1: light � everything in nature is a particle everything in nature is a particle or or a wave a wave � travels as waves (electromagnetic waves) travels as waves (electromagnetic waves) � electrons, atoms, and billiard balls are particles electrons, atoms, and billiard balls are particles � is emitted and absorbed as particles (photons) is emitted and absorbed as particles (photons) � li ht nd � light and sound are waves light and sound are waves li ht nd nd r nd r � Example 2: electrons E E Example 2: electrons l 2 l 2 l l � Modern physics (post Modern physics (post- -1900) recognizes that 1900) recognizes that � are emitted and detected as particles (electrons) are emitted and detected as particles (electrons) � everything in nature is both particle everything in nature is both particle and and wave wave � travel as waves (matter waves) travel as waves (matter waves) � things are most wave things are most wave- -like as they move unobserved like as they move unobserved � reside in atoms and solids as standing waves reside in atoms and solids as standing waves � things are most particle things are most particle- -like when they interact like when they interact 2
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