Difference between revisions of "Passives"
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== Inductors == | == Inductors == | ||
+ | |||
+ | An inductor reacts to current, but not to its value, but rather its change. It “tries” to keep the current through it constant. Any change in current causes a voltage across the inductor. The key equation for an inductor ( it is a bit complicated, but anyway here it ) is: | ||
+ | |||
+ | === equation here soon === | ||
+ | |||
+ | where | ||
+ | L = inductance ( units: henry ) | ||
+ | V = voltage ( unit: volts ) | ||
+ | I = current ( unit: Ampere ) | ||
+ | t = time ( unit: seconds ) | ||
+ | |||
+ | Uses: | ||
+ | *tuned circuits: a circuit that responds in a special way to some frequencies( s ). | ||
+ | *power supply filter: remove the pulsing DC left from rectification or other noise in the signal. | ||
+ | *Decoupling: usually blocking high frequencies from one part of a circuit from getting in another part. | ||
+ | *boost buck regulators: voltage regulators that decrease or increase voltage. | ||
+ | |||
+ | Links | ||
+ | *[http://en.wikipedia.org/wiki/Inductors Inductor From Wikipedia, the free encyclopedia] | ||
+ | |||
+ | Comments: | ||
+ | |||
"Ferrites? I don't know much about 'em, I only use ferrites in switching regulators." --National Semiconductor's Bob Pease | "Ferrites? I don't know much about 'em, I only use ferrites in switching regulators." --National Semiconductor's Bob Pease | ||
Revision as of 15:09, 7 February 2008
Contents
Capacitors
Basics
You can think of a capacitor as sort of a rechargeable battery, connect it to a voltage and a current will flow into it charging it up, later it will have a voltage of its own that can push the current back out. The key equation for a capacitor is:
Where:
- C = capacitance ( units: farad = volts /coulomb )
- V = voltage ( unit: volts )
- Q = charge in the capacitor ( unit: coulomb )
A simple application of the formula above occurs when a constant or near constant current flow into a capacitor: then the voltage across it increases at a constant rate, the graph of the voltage against time will be a line rising ( or falling for a negative current ) from the left to the right. If the current is constant the line is straight.
Another way of thinking of a capacitor ( which is only partly correct ) is that it is a resistor with infinite resistance for DC and lower and lower resistance as the frequency goes up. This is a fair model for sinusoidal voltages and currents, but is less useful for signals such as square waves.
Uses:
- ac coupling –- blocking -- isolation
- timing
- Time for a capacitor to charge or discharge is very roughly RC where R is the resistor in series with the capacitor.
- Filter ( often power supply filter )
- decoupling
- tuned circuits
All capacitors are formed by having 2 conductors ( or plates ) connected to the two terminals of the capacitor. The conductors are separated from each other by insulator, typically very thin. Adding charge to one side forces like charge off the opposite plate because like charges repel. The larger the plates and the closer together they are the less voltage it takes to force in the charge. If the insulator ( called the dielectric ) is too thin it will be pierced by the charge and the capacitors becomes a conductor. Typically the basic specifications for a capacitors are its capacitance and the maximum voltage that can be used without causing the dialectic to break down.
There are many diferent technologies for manufacturing capacitor each with its own advantages and disadvantages.
External Links
- Capacitor From Wikipedia, the free encyclopedia
- RC circuit From Wikipedia, the free encyclopedia
- RC Timers and Timing Circuits
- Decoupling capacitor From Wikipedia, the free encyclopedia
- Components: Capacitors
Electrolytic
In electrolytic capacitors the insulating layer is formed by electro chemical action between the plates and other chemicals in the capacitor. This forms a very thin layer which allows large capacitance in a small package. Typically this works for one polarity and not another so electrolytic capacitors are marked with their polarity. There are some non-polarized electrolytics, but they are not common.
Some electrolytic capacitors manufactured between 1999 until today are made with bad electrolyte. Avoid these, see capacitor plague for more info.
Aluminum
Tantalum
Ceramic
Film
Polyester (Mylar)
Polystyrene
Polycarbonate
Polypropylene
Teflon
Exotics
Mica
Glass
Oil
Vacuum
Inductors
An inductor reacts to current, but not to its value, but rather its change. It “tries” to keep the current through it constant. Any change in current causes a voltage across the inductor. The key equation for an inductor ( it is a bit complicated, but anyway here it ) is:
equation here soon
where L = inductance ( units: henry ) V = voltage ( unit: volts ) I = current ( unit: Ampere ) t = time ( unit: seconds )
Uses:
- tuned circuits: a circuit that responds in a special way to some frequencies( s ).
- power supply filter: remove the pulsing DC left from rectification or other noise in the signal.
- Decoupling: usually blocking high frequencies from one part of a circuit from getting in another part.
- boost buck regulators: voltage regulators that decrease or increase voltage.
Links
Comments:
"Ferrites? I don't know much about 'em, I only use ferrites in switching regulators." --National Semiconductor's Bob Pease
Can be replaced in many circumstances with an impedance inverter using only an opamp, a capacitor, and a few resistors.
Resistors
List of standard 1% resistors. If you want 1% resistors, you must pick from this list or you will pay a fortune for the resistor, assuming you can ever get it. Interpret these numbers as the "mantissa" of the value. You can multiply the value by anything from 0.01 to about 100,000.
100 102 105 107 110 113 115 118 121 124 127 130 133 137 140 143 147 150 154 158 162 165 169 174 178 182 187 191 196 200 205 210 215 221 226 232 237 243 249 255 261 267 274 280 287 294 301 309 316 324 332 340 348 357 365 374 383 392 402 412 422 432 442 453 464 475 487 499 511 523 536 549 562 576 590 604 619 634 649 665 681 698 715 732 750 768 787 806 825 845 866 887 909 931 953 976
External Links: