Transcript Bio-Electronics for Scientists 1

Power
Stations
House
Generators
Alternating Current & Voltage
AC Power
(Wikipedia)
• In a three-phase system, three circuit
conductors carry three alternating currents (60
Hz) which reach their instantaneous peak
values at one third of a cycle from each other.
This makes it possible to produce a rotating
magnetic field in an electric motor.
• Three-phase systems have a neutral wire. A
neutral wire allows the three-phase system to
use a higher voltage while still supporting lowervoltage single-phase loads.
• Most household loads are single-phase.
2 Phase Y Configuration
120/240 AC Volts
The Standard 3 prong outlet.
Wiring
the
Outlet
Electrical Lab Safety
1. Electricity can kill you, especially alternating
current!
2. Current can pass from your hand through your
feet to ground, or through your heart to your
other hand.
3. Capacitors can hold kilovolts of charge for
years.
4. Static electricity, generated by your feet on a
carpet, can produce kilovolts that can fry solid
state electronics.
5. Wear shoes on a dry floor, use one hand.
DC Circuit Components
Voltage Sources
Bio-Electronics for Scientists 1
Batteries and Source Resistance
Batteries
• An electric battery is a device consisting
of one or more electrochemical cells that
convert stored chemical energy into
electrical energy.
• Each cell contains a positive terminal, or
cathode, and a negative terminal, or
anode.
• Electrolytes allow ions to move between
the electrodes and terminals, which allows
current to flow out of the battery to
perform work (wiki).
How Batteries Work
• Each cell consists of two half-cells connected in series by a
conductive electrolyte containing anions and cations.
• One half-cell includes electrolyte and the negative electrode,
the electrode to which anions (negatively charged ions)
migrate; the other half-cell includes electrolyte and the positive
electrode electrode to which cations (positively charged ions)
migrate.
• Redox reactions power the battery.
• Cations are reduced (electrons are added) at the cathode
during charging, while anions are oxidized (electrons are
removed) at the anode during discharge.
• The electrodes do not touch each other, but are electrically
connected by the electrolyte. (wiki)
Battery Types: Primary
• Primary batteries, or primary cells, can
produce current immediately on assembly.
• Disposable primary cells cannot be reliably
recharged, since the chemical reactions are not
easily reversible and active materials may not
return to their original forms.
• In general, these have higher energy densities
than rechargeable batteries.
• Common types of disposable batteries include
zinc–carbon batteries and alkaline batteries.
(wiki)
Battery Types: Secondary
• Secondary batteries, also known as secondary cells, or
rechargeable batteries, must be charged before first use; they
are usually assembled with active materials in the discharged
state. Rechargeable batteries are (re)charged by applying
electric current, which reverses the chemical reactions that
occur during discharge/use. Devices to supply the appropriate
current are called chargers.
• The oldest form of rechargeable battery is the lead–acid
battery: the modern car battery can deliver a peak current of
450 amperes.
• Mobile phones and laptop computers use (in order of increasing
power density and cost) nickel–cadmium (NiCd), nickel–zinc
(NiZn), nickel metal hydride (NiMH), and lithium-ion (Li-ion)
cells. (wiki)
The
Oscilloscope
Multimeter
(digital)
Power
Supply &
Function
Generator
Unit Analysis
• One of the most important things to do in
manipulating equations involving physical
entitites like power and energy (and everything
is science) is unit analysis.
• Unit analysis means putting the correct units of
various quantities in your equations, and
making sure that the unit type carried through
the equation is correct.
Unit Analysis: An example
• The watt (symbol: W) is a derived unit of power in the
International System of Units (SI), named after the Scottish
engineer James Watt (1736–1819) measures the rate of energy
conversion or transfer.
• One Watt is defined as one joule per second.
• One watt is the rate at which work is done when one ampere
(A) of current flows through an electrical potential difference of
one volt (V).
• Typical large power plants generate about 1000 megawatts.
• In your electric bill you pay for kilowatt hours at a rate of about
5 cents per kilowatt-hour.
• Given that watts is joules per second, and you pay for watts
time hours, you pay for joules, or total energy.
Analog vs. Digital Circuits
• Analog circuits usually have continuous values and
are ‘analogs’ of what they control. For example, a
knob varies a resistance which varies the current
through a light bulb, dimming it.
• Digital circuits implement Boolean logic functions with
all or none states corresponding to 0 or 1. While there
were once analog computers, now virtually all
computers are digital, such as TTL and CMOS.
• The interface between the world and digital circuits is
done via analog to digital and digital to analog
converters.
Devices for Analog Circuits
• Analog circuits use:
1.Operational amplifiers (opamps, which are
composed of transistors and resistors)
2.Transistors
3.Resistors
4.Capacitors
5.Inductors (rarely)
Digital
Logic
Gates
Implement
Boolean
Functions
such as
these
Transistor–transistor logic (TTL)
• Transistor–transistor logic (TTL) is a class of digital circuits
built from bipolar junction transistors (BJT) and resistors.
• It is called transistor–transistor logic because both the logic
gating function (e.g., AND) and the amplifying function are
performed by transistors (contrast with RTL and DTL).
• TTL is notable for being a widespread integrated circuit (IC)
family used in many applications such as computers, industrial
controls, test equipment and instrumentation, consumer
electronics, synthesizers, etc.
• The designation TTL is sometimes used to mean TTLcompatible logic levels, even when not associated directly with
TTL integrated circuits, for example for the properties of the
inputs and outputs of electronic instruments.
TTL
NAN
D
Gate
TTL Interface Properties
• TTL is a current-sinking logic since a current must be drawn
from inputs to bring them to a logic 0 level.
• At low input voltage, the TTL input sources current which must
be absorbed by the previous stage. The maximum value of this
current is about 1.6 mA for a standard TTL gate.[17]
• The input source has to be low-resistive enough (< 500 Ω) so
that the flowing current creates only a negligible voltage drop (<
0.8 V) across it, for the input to be considered as a logical "0".
• If a TTL inputs is simply left floating it will provide a logical "1",
though this usage is not recommended.
• Standard TTL circuits operate with a 5-volt power supply. A TTL
input signal is defined as "low" when between 0 V and 0.8 V
with respect to the ground terminal, and "high" when between
2.2 V and 5 V.
CMOS
• Complementary metal–oxide–semiconductor (CMOS) is a
transistor technology for constructing integrated circuits.
• CMOS technology is used in microprocessors, microcontrollers,
static RAM, and other digital logic circuits.
• CMOS is also sometimes referred to as complementarysymmetry metal–oxide–semiconductor (or COS-MOS).[1]
The words "complementary-symmetry" refer to the fact that the
typical digital design style with CMOS uses complementary and
symmetrical pairs of p-type and n-type metal oxide
semiconductor field effect transistors (MOSFETs) for logic
functions.[2]
CMOS Characteristics
• Two important characteristics of
CMOS devices are high noise
immunity and low static power
consumption.
• Since one transistor of the pair
is always off, the series
combination draws significant
power only momentarily during
switching between on and off
states.
• CMOS also allows a high
density of logic functions on a
chip, primarily for this reason
that CMOS became the most
used technology to be
implemented in VLSI chips.
Interfacing TTL & CMOS
The Diode (rectifier for power)
LEDs (light emitting diode)
How Things are Made: The Lathe
How
Things
are
Made:
The
Milling
Machine
Series Resistors
Parallel Resistors
Current Sources
AC Circuits
Capacitance
AC Circuits & Energy Storage
Capacitance
Cable
properties
Electronic (Resistive) Noise
Resistive
Noise