Amplifier generates a new voltage in the same shape as the input voltages. The input is amplified as the output is usually higher.
The gain of the amplifier is the ratio of its output and input
Gain (A) = Vout/Vin
Amplifier essentially takes an DC source and covert it to a AC output based on the same of a smaller AC input. Efficiency of an amplifier indicates how well this DC-AC conversion is
%Eff = (Power-out/Power-in) * 100%
Lost power is usually converted to heat. Efficient is sometime traded off for better linearity, fidelity and lower distortion of the signal.
Another property of amplifier is frequency response. This indicate the range of frequency that an amplifier covers. DC amplifier covers only frequency up to a few hundred Hz. Audio amplifier covers frequency up to 20kHz
Saturday, July 12, 2014
Diodes
Diode is a semiconducting device that allow current flow in one direction only. When used with capacitor, it can convert AC to DC, a process called rectification.
Inductor
Inductors are coil of wire. When current flows, it generates a magnetic field which in turn develop a voltage in itself. The voltage has opposite polarity (direction) and thus impeding to the initial current flow, making the inductor behaves like a resistor. The opposition to current flow is called inductive reactance. Inductor is often used to control the current flow in an AC circuit.
Capacitor
Capacitor stores charge. It composed of 2 metallic plates with a insulation gap (ceramic, plastic, air etc) in between. When a voltage is applied to the capacitor, it takes a finite time to charge up. The duration of charging depends on the capacitance value of the capacitor. The capacitor provides a DC voltage to the load when discharging. Again, the discharge will take a period of time.
When used with AC, capacitor behave like a resistor and the opposition of current flow is called capacitive reactance. Unlike a resistor, capacitor resistance varies depending on the frequency of the AC and the capacitance values. In other words, the capacitor will only passes voltage of a certain frequency range and it attenuate the frequency outside the range rapidly.
Capacity can also use to block DC and allow AC to pass through.
When used with AC, capacitor behave like a resistor and the opposition of current flow is called capacitive reactance. Unlike a resistor, capacitor resistance varies depending on the frequency of the AC and the capacitance values. In other words, the capacitor will only passes voltage of a certain frequency range and it attenuate the frequency outside the range rapidly.
Capacity can also use to block DC and allow AC to pass through.
Sunday, July 6, 2014
Electrical Signals
Analog signals are voltages that vary smoothly and continuous over time. Analog signal can be either AC or DC.
Digital signals are pulses (on/off).
Analog-to-digital converters (ADC) and DAC converts the signals from one form to another.
Fourier theory said that any sinusoidal wave (like a square-wave digital signal) can be approximated by adding the base sine wave with its harmonics. Usually the approximation is good enough for using 5 to 7 harmonics.
Digital signals are pulses (on/off).
Analog-to-digital converters (ADC) and DAC converts the signals from one form to another.
Fourier theory said that any sinusoidal wave (like a square-wave digital signal) can be approximated by adding the base sine wave with its harmonics. Usually the approximation is good enough for using 5 to 7 harmonics.
Generators
Generator at power plant is operated by a mechanical sources such as steam turbine powered by oil, coal or nuclear energy. The turbine turns the generator which consists of metallic coil in a strong magnetic field, The speed of rotation determine the frequency (60Hz).
Wind generator produce AC but of different varying frequency. The electricity firstly will be convert to DC and then back to AC of the correct frequency before feeding to the electricity grid.
Car alternator is actually an AC generator. The alternator is turned by the engine via a belt. The AC current is converted to DC by diodes to charge the car battery.
Inverter produces AC from DC source.
Wind generator produce AC but of different varying frequency. The electricity firstly will be convert to DC and then back to AC of the correct frequency before feeding to the electricity grid.
Car alternator is actually an AC generator. The alternator is turned by the engine via a belt. The AC current is converted to DC by diodes to charge the car battery.
Inverter produces AC from DC source.
Batteries
A battery is a collection of cells. A cell generates electricity by chemical reaction. It consists of 2 metal conductor called electrodes immersed in a solution called electrolyte. The chemical interaction between the electrodes and the electrolyte produce a separation of charge - one electrode become positively charged and one become negatively charged.. When a conductor connects up the terminals of the cell, a current flow from the negative terminal to the positive one. The voltage generated depends on the choice of the types of electrodes and electrolyte.
A cell is represented schematically by 2 lines. The longer on represents positive terminal and the shorter one is the negative one.
Primary cells cannot be recharged. When the chemical reaction stops, no charge will be produce and the battery needs to be replaced.
Alkaline - 1.5v (AA, AAA, C, D cells)
Mercuric Oxide - 1.35v (for watches and calculator)
Silver Oxide - 1.6v (for hearing aids, watches)
Secondary cells can be recharged. In other words, the chemical reaction can be reversed when the battery is connected to an external DC voltage. The electrodes and electrolyte can be rejuvenated.
Nickel-cadmium - 1.2v (tools)
Nickel metal hydride - 1.2v (laptop, cell phone)
Lead acid - 2.1v (cars)
Lithium ion - 4.1v (cell phone, laptop, iPod)
The amount of current produced by cell depends on the its size and the quantity of the materials use. Large electrodes and electrolyte produce more current but voltage stays the same. The type of material, not the volume determine the voltage.
For example, both AA and the D cell made of same material produce 1.5v cell. The D cell can last longer because of its larger size.
When connect batteries in series, the overall voltage increases proportionally. When connect battaries in parallel, the current increases but the voltage stays the same.
Solar cell (photovoltaic PV cell) convert light into electrical energy. A solar cell in space satellite is often used to charge the secondary cell (Nickel-cadmium) rather than operating the equipment directly.
Fuel cell combines oxygen and hydrogen to produce voltage and current. Heat and water is the byproducts. Fuel cell generates about 0.5v to 0.9v and so many of them is needed to produce work.
A cell is represented schematically by 2 lines. The longer on represents positive terminal and the shorter one is the negative one.
Primary cells cannot be recharged. When the chemical reaction stops, no charge will be produce and the battery needs to be replaced.
Alkaline - 1.5v (AA, AAA, C, D cells)
Mercuric Oxide - 1.35v (for watches and calculator)
Silver Oxide - 1.6v (for hearing aids, watches)
Secondary cells can be recharged. In other words, the chemical reaction can be reversed when the battery is connected to an external DC voltage. The electrodes and electrolyte can be rejuvenated.
Nickel-cadmium - 1.2v (tools)
Nickel metal hydride - 1.2v (laptop, cell phone)
Lead acid - 2.1v (cars)
Lithium ion - 4.1v (cell phone, laptop, iPod)
The amount of current produced by cell depends on the its size and the quantity of the materials use. Large electrodes and electrolyte produce more current but voltage stays the same. The type of material, not the volume determine the voltage.
For example, both AA and the D cell made of same material produce 1.5v cell. The D cell can last longer because of its larger size.
When connect batteries in series, the overall voltage increases proportionally. When connect battaries in parallel, the current increases but the voltage stays the same.
Solar cell (photovoltaic PV cell) convert light into electrical energy. A solar cell in space satellite is often used to charge the secondary cell (Nickel-cadmium) rather than operating the equipment directly.
Fuel cell combines oxygen and hydrogen to produce voltage and current. Heat and water is the byproducts. Fuel cell generates about 0.5v to 0.9v and so many of them is needed to produce work.
Voltage Sources
For current to flow, there must have voltage.
Direct Current (DC) is a fixed steady current flow from one direction to the other. The voltage can be positive or negative, measure relative to a point called ground.
Alternate Current (AC) flows in two directions over the conductor. In other words, electron flows in one direction for a moment and then reverse to flow in the opposite direction later, and so on. The AC signals that comes into home are in the shape of sine wave. The frequency refers to the number of reversion per second. In the case of AC signal, it is generally at a frequency of 60Hz.
AC is represented by a symbol of circle with a varying wave in the middle.
Direct Current (DC) is a fixed steady current flow from one direction to the other. The voltage can be positive or negative, measure relative to a point called ground.
Alternate Current (AC) flows in two directions over the conductor. In other words, electron flows in one direction for a moment and then reverse to flow in the opposite direction later, and so on. The AC signals that comes into home are in the shape of sine wave. The frequency refers to the number of reversion per second. In the case of AC signal, it is generally at a frequency of 60Hz.
AC is represented by a symbol of circle with a varying wave in the middle.
Electromagnetic Induction
When a conductor moves in a magnetic field, a voltage will be induced in the conductor and causes current to flow. Current is also induced if the the conductor is held still but the magnetic field moves relative to the conductor.
The direction of the current depends on the direction of the magnetic field and the relative movement of the field. The strength of the voltage depends on the density of the flux line (how strong the magnetism field is) and the speed of the movement. The highest induced strength is achieved when the line cut the force field in right angle. If the wire move in the same direction as the force field, no voltage is induced.
The direction of the current depends on the direction of the magnetic field and the relative movement of the field. The strength of the voltage depends on the density of the flux line (how strong the magnetism field is) and the speed of the movement. The highest induced strength is achieved when the line cut the force field in right angle. If the wire move in the same direction as the force field, no voltage is induced.
Static and Dynamic Electricity
These are 2 types of electricity.
Static electricity refers to two charge objects. One with an excess of electrons and one with a shortage. A electric (force) field exists between the 2 objects. The charge stored in the object is called static electricity.
If the 2 objects become too close or the charge build up become too great, the attractive force will caused electrons to jump across the space from one object to the other. This is called electrostatic discharge (ESD). ESD is generally not useful as the charges are dissipated quickly in sparks or quick flow of electricity.
Dynamic electricity refers to the electricity that we know to power appliance. This is a constant flow of electrons. There must be voltage source that cause the electrons to flow from negative terminal to the positive terminal. Current is measured as the number of electrons that pass through a certain point in a specific period of time. One ampere of current equals to 1 Coulomb of charge per second. One Coulomb of charge equals to 6.242 x 10^18 electrons.
Static electricity refers to two charge objects. One with an excess of electrons and one with a shortage. A electric (force) field exists between the 2 objects. The charge stored in the object is called static electricity.
If the 2 objects become too close or the charge build up become too great, the attractive force will caused electrons to jump across the space from one object to the other. This is called electrostatic discharge (ESD). ESD is generally not useful as the charges are dissipated quickly in sparks or quick flow of electricity.
Dynamic electricity refers to the electricity that we know to power appliance. This is a constant flow of electrons. There must be voltage source that cause the electrons to flow from negative terminal to the positive terminal. Current is measured as the number of electrons that pass through a certain point in a specific period of time. One ampere of current equals to 1 Coulomb of charge per second. One Coulomb of charge equals to 6.242 x 10^18 electrons.
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