learning a.c. theory

[Mark S.]

Hi,

I am working my way through a number of theory books and they all seem to seperate d.c. theory and a.c. theory. At this stage i am doing basic d.c. experiments with a breadboard using a 6v battery source.

At the moment i would'nt risk using the a.c. mains to do any tests for fear of my own safety. So my question is if i am only using a d.c. voltage source for my experiments does a.c. theory come into play?

If so can you give me examples please.

Also when using a 555 timer as an oscillator is the output signal classed as a.c. or does the direction of the conventional current have to move from negative to positive?


Thanks

Mark S.

 

[BrownOut]

Hi,

I am working my way through a number of theory books and they all seem to seperate d.c. theory and a.c. theory. At this stage i am doing basic d.c. experiments with a breadboard using a 6v battery source.

At the moment i would'nt risk using the a.c. mains to do any tests for fear of my own safety. So my question is if i am only using a d.c. voltage source for my experiments does a.c. theory come into play?

Depends. AC is not only mains voltage/current, but also small signals. You could use an oscillator to generate small AC signals, then you are in the AC domain.

Also when using a 555 timer as an oscillator is the output signal classed as a.c. or does the direction of the conventional current have to move from negative to positive?

The output of the 555 is pulsed DC, however it exhibits many of the same effects as AC, and can be thought of in a similar way.

 

[MrAl]

Hi,

I am working my way through a number of theory books and they all seem to seperate d.c. theory and a.c. theory. At this stage i am doing basic d.c. experiments with a breadboard using a 6v battery source.

At the moment i would'nt risk using the a.c. mains to do any tests for fear of my own safety. So my question is if i am only using a d.c. voltage source for my experiments does a.c. theory come into play?

If so can you give me examples please.

Also when using a 555 timer as an oscillator is the output signal classed as a.c. or does the direction of the conventional current have to move from negative to positive?


Thanks

Mark S.

Hi there Mark,


If you can learn DC theory real good then you will be able to adopt to AC theory pretty quick because AC theory is an extension of DC theory with a few little tricks. It helps to know complex numbers too.
You didnt say if you were using resistors too, do you have some?

 

[JimB]

I am working my way through a number of theory books and they all seem to seperate d.c. theory and a.c. theory.

Generally speaking DC is less complex than AC, so DC comes first, and when you have got the idea, move on to AC.

At the moment i would'nt risk using the a.c. mains to do any tests for fear of my own safety.
At this stage i am doing basic d.c. experiments with a breadboard using a 6v battery source.

Very wise to keep away from the mains for basic experiments.
When you want to move on to AC, use a transformer which converts the mains down to 12 or 24volts and experiment with that, safely.

So my question is if i am only using a d.c. voltage source for my experiments does a.c. theory come into play?
If so can you give me examples please.

DC could be considered as a special case of AC where the frequency is zero.
As an example, consider an inductor, it has resistance and inductance. Both of these properties affect the behaviour in a DC circuit, but only the resistance will affect the steady state of the circuit after switch on and before switch off.

In an AC circuit, because of the inductance, there is reactance which opposes the current flow as well as the resistance.
If the frequency is high enough, there will also be AC resistance, in addition to the DC resistance.
(This can get complicated!)

Also when using a 555 timer as an oscillator is the output signal classed as a.c. or does the direction of the conventional current have to move from negative to positive?

This is one of those questions which will cause a thread to run for 10 pages here on ETO!
Yes it is AC, but it has a DC offset so that the polarity of the output is always +ve (with respect to the circuit 0v line).

By the way, the output of a 555 is not a good source for simple AC experiments, it is a square wave not a sinewave, it does not have a 50:50 mark-space ratio and is unipolar.

JimB

 

[Jony130]

But you can easily buy a step-down transformer.
Or AC to AC power supply
**broken link removed**

And then you can make experiments with AC.
For example you can check that capacitor act like resistors in AC circuits.
And there is no "plus" or "minus" in AC signal.

 

[Mark S.]

Hi there Mark,


If you can learn DC theory real good then you will be able to adopt to AC theory pretty quick because AC theory is an extension of DC theory with a few little tricks. It helps to know complex numbers too.
You didnt say if you were using resistors too, do you have some?

I have done a load of experiments with resistors coming up with difficult networks and succesfully predicting measurements. I have diodes, LED's, transistors, capacitors but I am guilty of reading electronics theory more rather than experimenting.

Can someone please give me a list of a.c. theory subjects that i can work with using a battery voltage supply and a 555 oscillator circuit.

 

[crutschow]

Experimenting with actual circuits is good experience, but an even easier way to learn about various circuits, AC or DC, is to use a Spice simulator such as LTspice (free) or PSpice. It allows you to easily construct virtual circuits, and test them with various signals while viewing the voltages and currents anywhere in the circuit. You can even make measurements and tests that would be very difficult or impossible to do in real circuits. You can start out with simple resistor circuits with a DC source, and go more complicated from there. There are models for ICs such as the 555 that will fairly accurately predict its operation in circuits.

There is a learning curve with the programs of course, but once you understand how they work, you will find it quite easy way to observe circuit operation and test them before you build them. I believe they are a great learning tool that is well worth the effort to understand their use. There is even a users forum for LTspice that will help you get started and answer questions about its operation.