Resistors, Capacitors, Diodes, and Inductors

[zpyder]

Resistors restrict current and dissapate the energy as heat [ I = V/R ]
Resistors are linear, in that the graph of resistance to voltage or current is a straight line
Photoresistors (LDR's) are resistors whose resistance value is dependant upon the amount of light hitting its surface.  Resistance goes down as light goes up.

Capacitors store and release a charge (based on their Farad rating)
Capacitors also present reactance (resistance) to current relative to AC frequency [ R = 1/(2*pi*f*C) ].  As frequency goes down, reactance goes up.
Capacitors also present infinite reactance (resistance) to DC voltage (since the frequency of DC is 0).  Useful for coupling an AC signal to a DC voltage.
Electrolytic Capacitors (and Tantalum, among others) are polar and only allow current flow in one direction, all other capacitors are non-polar
Capacitors are non-linear

Diodes are polar and only allow current flow in one direction
Diodes also, if plugged in backwards (reverse-biased), do allow a certain "leakage" current through (exploited in the Millenium bypass)
Diodes also have an activation threshold rated in volts(??), called a "knee".  Below the knee, no current flows, above it, large amounts of current flow.
Silicon Diodes are said to have a "knee" at ~.7V
Germanium Diodes are said to have a "knee" at ~.3V
Diodes also create a "voltage drop", but I have no idea what this is
Since diodes are polar, they will transfer only one half (the top or bottom) of an AC signal wave.  This is half-wave rectification.
A Bridge Rectifier is nothing more than 4 diodes, and transfers an AC signal, but flips all wave parts to the positive.  This is full-wave rectification.
Diodes are non-linear

Inductors are



Anything I missed or got wrong?
Anything anyone has to add?
What the f is an inductor?   

cheers,
zpyder

[Paul Marossy]

An inducor is an electrical component that generates a magnetic field when a current is passed through it and stores the energy in the form of the magnetic field. It also tends to resist changes in current.

[R.G.]

Inductors are the alter ego of capacitors.

Capacitors store energy in an electrical field created by separating charges into the two different plates. The energy stored is E = (C*V^2)/2.
Inductors store energy in a magnetic field, created by charge moving (i.e. current) through a coil of conductor. The energy stored is E = (L*I^2)/2.

Capacitors have an impedance of their leakage resistance at DC, infinity for a "pefect" cap. Their impedance to AC is Xc = 1/(2*pi*F*C).
Inductors have an impedance of theirDC wire resistance (zero for a "perfect" inductor). Their impedance to AC is Xl = 2*pi*F*L.

Inductors are useful for extracting the AC content of a signal while letting the DC component flow unopposed. Inductors are useful for transformer coupling, which connects signals across a non-conductive boundary by mutually coupling two coils. There is no analog of mutual magnetic coupling for capacitors.

Electrolytic Capacitors (and Tantalum, among others) are polar and only allow current flow in one direction,

Electrolytic caps are polar and must have a DC voltage across them in the correct direction. They will allow current to flow either way, but the cap will be damaged if the voltage is connected in the wrong direction.

Capacitors are non-linear

All components are non-linear to some degree. It's no worse with caps than with other types of components. You just have to know what the nonlinearities are like and work with (or around) them.
Resistors are nonlinear ( voltage and temperature coefficient of resistance)
Photo resistors are nonlinear (bulk photoresistivity nonlinearities)
Capacitors are nonlinear (dielectric absorption and mechanical stress)
Inductors are nonlinear (B-H curve nonlinearities, minor loops, and saturation)

And that's just the supposedly linear components.

Diodes also create a "voltage drop", but I have no idea what this is

All components create a voltage drop. It's the same as that activation voltage/clipping voltage. Diodes have this quirk that they don't conduct at all (mostly...) in the reverse direction, and not in the forward direction until the threshold voltage is reached. After that, you can supply lots of current and the voltage does not increase much. So if you bias the diode with a resistor from a voltage source, the voltage source my vary, and the current in the diode will vary, but the voltage across the diode will vary by much less than the source driving it. So it creates a more constant voltage source. A string of several diodes creates a voltage source - when properly biased with DC - equal to the number of diodes times the activation voltage.

The activation voltage is not a fixed voltage, only a kind of fixed voltage. What is actually happening is that the current through the diode is an exponential function of the applied voltage. For a diode, I = K e^(mv/Vt) Where k and m are some numerical constants which make the numbers come out right for the material of the diode. The function e^h where e is the base of natural logarithms has a value of one for h=0, between 0 and 1 for h less than 0, and greater than one for h>0. For h<0 up to h=0, the value only changes from 0 to 1. When h goes positive, the result when graphed turns up and heads almost for infinity. This is the "activation voltage" value in the diode equation. After that, current goes up hugely, but the "knee" where it turns from non-conduction to conduction is slightly rounded.

[zpyder]

Resistors are nonlinear ( voltage and temperature coefficient of resistance)

A Resistor's resistance in ohms varies with voltage?  I guess this is in line with R = V/I.  What about with current then!?

zpyder

[Single Coil]

I have wondered  and probably wrongly. But, I've had this notion that since capacitors store charge, if you used sufficiently large capacitors, could capacitors be used for delay effects? If caps store charge and if you could control/gate the charging/discharge process, then it seems that delay capabilities would exist. Are capacitors ever used in this way?

Thanks for humoring me...

[R.G.]

A Resistor's resistance in ohms varies with voltage?  I guess this is in line with R = V/I.  What about with current then!?

Changing the voltage across a normal resistor also changes the current at the same time, not the resistance.

A perfect resistor does not vary with voltage, or temperature, or other conditions. Any variation of resistance is a special case.

Resistance is defined as the relationship between the DC voltage and DC current in a part. That is, to find resistance, you measure the voltage across the part, and the current through it, then divide. This gives a number that is the resistance of that part. In general, a normal resistor's value is viewed as not changing.

Another definition of one Ohm is "one volt per ampere". If you put one volt across one ohm, one ampere flows. If you put one ampere through one ohm, the voltage across the resistor will be one volt. The resistance is the constant of proportionality between voltage and current.

Then there are the imperfections.
Resistors do have some small variation in resistance with heat, voltage, aging, etc. These are ignored for the most part in simple designs. They are small effects, usually well under the manufacturing tolerance of the resistance itself. A 1.000 ohm resistor might change to a 1.003 ohm resistor when soldered into a board from the heating effect. A 100.00K resistor might become a 100.1K resistor with 100V across it.

Some special resistors are intended to vary with light, voltage, etc. These are used as variable resistors and are special and costly. This category is things like LDRs, thermistors, and some early MOVs. These are indeed special cases. Normal resistors do not vary very much with such effects.

But, I've had this notion that since capacitors store charge, if you used sufficiently large capacitors, could capacitors be used for delay effects? If caps store charge and if you could control/gate the charging/discharge process, then it seems that delay capabilities would exist. Are capacitors ever used in this way?

As a matter of fact, yes. However, not the way you think.

Big capacitors are kind of "DC delays". If you charge them up, they "remember" the charge for a long time and you can take it out again. But big capacitors would simply eat AC signals.

All "analog" delays are arrays of microscopically small capacitors and MOSFET switches. The way these delays work is that at the input, a MOSFET switch connects a capacitor to the input terminal. The input voltage charges the tiny capacitor in a veyr short time, then the MOSFET switch turns off. A second MOSFET switch turns on and connects the input capacitor to a follower amplifier which charges a second capacitor. Then the input switch turns on again as the second switch turns off. This repeats forever, the input capacitor taking a snapshot of the input voltage, then transferring this snapshot to a second capacitor.

So far, it's not a very interesting delay.

But if we had a line of maybe a thousand of these caps and MOSFET switchs set up so that half the MOSFET switches turn on while the other half is off and vice versa, we can make the capacitors pass little snapshots of the input voltage down the line one step every time the switch states change. At the end,  a high impedance buffer puts the snapshots coming off the end on the output pin for us to use. ]

And that is what really happens inside every analog delay chip.

Digital delays do the same thing, by the way, except that they take a digital snapshot in the form of a number representing the input voltage, and they then delay this number in digital memory arrays. The digital memory arrays are ... yep, you guessed it ... arrays of tiny capacitors and MOSFET switches to charge up and discharge the tiny caps. The caps in a digital memory don't have to be as good as the ones in an analog delay, as they only have to remember "more than half full" or "less than half full" so they can be read out.

[Single Coil]

But, I've had this notion that since capacitors store charge, if you used sufficiently large capacitors, could capacitors be used for delay effects? If caps store charge and if you could control/gate the charging/discharge process, then it seems that delay capabilities would exist. Are capacitors ever used in this way?

As a matter of fact, yes. However, not the way you think.

Big capacitors are kind of "DC delays". If you charge them up, they "remember" the charge for a long time and you can take it out again. But big capacitors would simply eat AC signals.

All "analog" delays are arrays of microscopically small capacitors and MOSFET switches. The way these delays work is that at the input, a MOSFET switch connects a capacitor to the input terminal. The input voltage charges the tiny capacitor in a veyr short time, then the MOSFET switch turns off. A second MOSFET switch turns on and connects the input capacitor to a follower amplifier which charges a second capacitor. Then the input switch turns on again as the second switch turns off. This repeats forever, the input capacitor taking a snapshot of the input voltage, then transferring this snapshot to a second capacitor.

So far, it's not a very interesting delay.

But if we had a line of maybe a thousand of these caps and MOSFET switchs set up so that half the MOSFET switches turn on while the other half is off and vice versa, we can make the capacitors pass little snapshots of the input voltage down the line one step every time the switch states change. At the end,  a high impedance buffer puts the snapshots coming off the end on the output pin for us to use. ]

And that is what really happens inside every analog delay chip.

Digital delays do the same thing, by the way, except that they take a digital snapshot in the form of a number representing the input voltage, and they then delay this number in digital memory arrays. The digital memory arrays are ... yep, you guessed it ... arrays of tiny capacitors and MOSFET switches to charge up and discharge the tiny caps. The caps in a digital memory don't have to be as good as the ones in an analog delay, as they only have to remember "more than half full" or "less than half full" so they can be read out.
[/quote]

Thanks RG for that great information. You're right. That's not the way I had it figured out. I sure didn't have the thousands of small capacitors figured out that's very cool....that is what's going on in those delay chips. Thanks for the education.

If I am understanding your description, digital delays are digital as far as the timing goes but the actual signal remains in analog form?

[R.G.]

If I am understanding your description, digital delays are digital as far as the timing goes but the actual signal remains in analog form?

Sorry - I wasn't being clear. That's what an analog delay does.

In both analog and digital delays, the delay steps and timing are digital. In analog delays, the signal is converted to a series of DC voltages that hold the signal's actual level at one instant in time. In digital delays, the signal is converted to a digital number. This digital number is then delayed by a number of timing steps.

Digital and analog delays are the same in that the timing is digital. The only thing analog about an analog delay is that the signal is held in an analog form as it's passed down the delay chain. In a digital delay, the signal is made into a binary number representation and that number is delayed, then re-converted into analog form at the end.