MAE156A October 12, 2006 UCSD H. Ali Razavi

 Electric voltage is similar to height difference: - Electrons start moving under voltage difference - Unless there is a barrier - Balls start moving under height difference - Unless there is a barrier - Work (energy) is needed to move electrons in the reverse direction - Work (energy) is needed to move balls in the reverse direction  Operating an electric circuit if very similar to traveling a closed loop on a 3-D Map: New York San Diego Seattle Miami - As one moves around the map depending on selected road: - One goes through different heights - One experiences different energy requirements and losses - As electrons move around the circuit - Electrons go through different potentials - Electrons go through different energy requirements and losses Voltage

New York San Diego Seattle Miami Denver Kirchhoff's Voltage Law

Kirchhoff's Current Law  Electric currents are very similar to flows Electric Charge # electrons Electron charge Electric Charge Electric Current

Conclusion: To determine the dynamics of circuit, write down Kirchhoff's voltage and current laws Question: How “voltage drop across” and “current passing through a component” are related? * In most cases it is modeled linearly Next: Looking at a few of the following components - Resistor - Capacitor - Inductor - Current source - Voltage source - Transducers - Transistors - Switches - Input impedance - Output impedance Main Points: Impedance of component Current passing “through” component Voltage drop “across” component

Resistors are devices that show resistance to passing electric current - All devices and materials show such resistance - Resistance is similar to friction in mechanical systems - It is always present - It generates heat (energy loss) - It determines how much voltage difference (force) is required to pass electrons (speed) - A simple mathematical model for resistance is a “linear model”  A resistor is very similar to a mechanical damper Resistors

Capacitor are devices that store electrons - Energy storage - It determines how much voltage difference (force) is store electrons (displacement) - A simple mathematical model for capacitor is a “linear model”  A Capacitor is very similar to a spring in mechanical systems Capacitors

Inductors are devices that store energy when there is current (movement of electrons) - Energy storage - It determines how much voltage difference (force) to store energy (velocity) - A simple mathematical model for inductor is a “linear model” Inductors  An inductor is very similar to mass in mechanical systems

Example 1: Low Pass Filtering using a Capacitor A low pass filter is a device that eliminates “high frequency content” content of signals Case 1: No Filtering Open Close Time Valve High Frequency Input Time Q High Frequency Output Case 2: Low Pass Filtering Open Close Time Valve High Frequency Input Time Q2Q2 Low Frequency Output Open Close Time Switch High Frequency Input Time i High Frequency Output Open Close Time Switch High Frequency Input Time i2i2 Low Frequency Output

After Pump The pump (supply) always make sure the collector tank is filled with pressurized water 1 2 Collector Base Bipolar Junction Transistors Pump 1 2 Collector Base Switch Flow Amplifier Emitter (n) Base (P+) Emitter Collector (n) Emitter (n) Base (P+) Collector (n) 1 Switch Current Amplifier npn

Field Effect Transistors Silicon (doped with different impurities at different concentrations at different regions) Drain: n + Source: n + p Dielectric/Insulator (Silicon Oxide) Gate: Metal nMOS FET

PM Motor 10A: Start/Stall 2A: Continuous V: 10-12V Design Example 1: Objective: To Turn On and Off a Permanent Magnet DC motor using a Micro Processor with the requirement of passing 10A during On Time with 10-12V on motor terminals. Problem 1: 10A is too high current to be provided by Microprocessor Problem 2: Switching it off and on using microprocessor Problem 3: Interfacing components and programming Pin x Microprocessor Idea 1: Use of MOSFET to switch the Motor On/Off Idea 2: Use of Bipolar Transistor to switch the Motor On/Off Concept Generation Risk Reduction Trouble Shooting Optimization Problems DefinitionConcept Generation