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Lecture #13 Power supplies, dependent sources, summary of ideal components

Explore inductors, transformers, power supplies, and dependent sources in electronics engineering lectures. Learn about ideal components such as resistors, diodes, and regulators for efficient circuit design.

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Lecture #13 Power supplies, dependent sources, summary of ideal components

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  1. Lecture #13 Power supplies, dependent sources, summary of ideal components • Reading: Malvino chapter 3, 4.1-4.4 • Next: 4.10, 5.1, 5.8 • Then transistors (chapter 6 and 14) EE 42 fall 2004 lecture 13

  2. Topics Today: • Inductors and transformers • Power supplies • A new type of ideal device, the dependent source. • Summary of ideal devices EE 42 fall 2004 lecture 13

  3. Inductors • Any coil of wire will produce a magnetic field when current flows through it • The magnetic field holds energy. • If the current is changed, the magnetic field will change, and therefore the energy stored will change. • Since the power must come from the circuit, this creates a voltage: EE 42 fall 2004 lecture 13

  4. Symbol for and ideal inductor • The symbol for an inductor is similar to that of a resistor, but with loops EE 42 fall 2004 lecture 13

  5. Transformers • A transformer is a couple of coils of wire which transfer power from one to the other by a changing magnetic field. • By having different numbers of windings, or turns of wire, a transformer can step up or step down an AC voltage. EE 42 fall 2004 lecture 13

  6. Transformers EE 42 fall 2004 lecture 13

  7. Transformer symbols • The symbol for a transformer is a pair of the same loopy lines used for inductors, but close together. If the inductor has a core of a magnetic material, it is shown as a couple of lines between the coils. The number of turns in the coils will Be written nearby. EE 42 fall 2004 lecture 13

  8. Ideal transformer • The voltage across the secondary of the transformer (the output windings) is: • But this only works for changes in the voltage—and therefore for AC only EE 42 fall 2004 lecture 13

  9. Ideal transformer • The transfer of power can increase or decrease the voltage, and the current changes as well. • Remember: so if it is ideal (lossless)) EE 42 fall 2004 lecture 13

  10. Half-wave rectifier • A single diode can be used to take an alternating current, and allow only the positive voltage swing to be applied to the load ~ R EE 42 fall 2004 lecture 13

  11. An AC input is sinusoidal EE 42 fall 2004 lecture 13

  12. The diode blocks the negative voltages EE 42 fall 2004 lecture 13

  13. Full-wave rectifier • If we add an additional diode, it does not pass current at the same time as the first diode, but the load is now disconnected during the negative half cycle. • What if we could flip the connection and use the negative half wave? ~ R EE 42 fall 2004 lecture 13

  14. Full-wave rectifier • The result is called a full wave rectifier ~ R EE 42 fall 2004 lecture 13

  15. Full-wave rectified voltage EE 42 fall 2004 lecture 13

  16. Filtering • A transformer and a full wave rectifier will produce a voltage which is always positive, but varies with time • In order to power electronic devices, we need to smooth out the variations with time. • Another way to look at this is that we need to store energy temporarily while the input voltage changes sign. EE 42 fall 2004 lecture 13

  17. Power supply filter capacitor • If we add a capacitor in parallel with the load, it will charge up when power is available from the voltage source, and then it will slowly discharge through the load when the diodes are off. ~ R EE 42 fall 2004 lecture 13

  18. Full wave rectified, with filtering EE 42 fall 2004 lecture 13

  19. Ripple The result is a DC voltage, with some residual variations at twice the frequency of the AC power. The variation is called ripple. EE 42 fall 2004 lecture 13

  20. Regulated power supply • In order to produce a power supply without ripple, we will need to use an active device called a regulator ~ Constant voltage power supply to load R EE 42 fall 2004 lecture 13

  21. Ideal devices Wire: Current in =current out No voltage differences Resistor EE 42 fall 2004 lecture 13

  22. Ideal devices 2 Inductor: Ideal diode: Reversed bias  no current, open circuit Forward bias  no voltage drop, just like a wire EE 42 fall 2004 lecture 13

  23. Ideal devices 3 + V1 - + V2 - Transformer EE 42 fall 2004 lecture 13

  24. Ideal devices 4 Voltage source: Voltage given, current can be anything Note: the voltage could be given as A function of time ~ Current source Current given, voltage can be anything Note: the current could be given as A function of time EE 42 fall 2004 lecture 13

  25. Ideal devices 5 + V1 - + V2 - Dependent Voltage source: Voltage given as a multiple of another Voltage or a current, current can be anything ~ + V1 - Dependent Current source Current given as a multiple of a different current or voltage, voltage can be anything EE 42 fall 2004 lecture 13

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