Electronic Component Questions

Discussion in 'General Electronics Chat' started by Guest3123, Aug 13, 2016.

  1. Guest3123

    Thread Starter Member

    Oct 28, 2014
    What is a capacitor used for?

    I understand so far that a capacitor is used mainly for leveling out voltage spikes and ripples is a voltage supply. Like for a voltage regulator LM7805.

    ** At any time, please correct me if I'm wrong, because I'm not a professor, nor an electronics expert, instead, I'm a 24/7 student. I'm always trying to learn something about electronics, even if it's very simple to some people.

    I also hear recently that a capacitor is used for motors. In order for the motor to start up, it needs a capacitor.

    So is that basically what Julian is talking about, because when the wireless transceiver starts up, it draws a lot of power, and the capacitor is used to do something about the current?

    2m 29s Into the video. The "link" is supposed to start the video at that time, but it doesn't seem to work.

    Why do you use a 0.1uF capacitor on one circuit, and use a 20uF capacitor on another.

    According to Google, farads is the SI unit of electrical capacitance, equal to the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt.

    I'm pretty good with buying and using n-Channel MOSFETs, and I have no problem finding the resistor value for an LED. But I've been trying, slowly, to get a better understanding of different electronic components.

    If I needed a reply for this, a specific reply, I'd request it was a reply to what capacitors are used for. Maybe in the form of a neat list.. something similar to the following example.

    Also, what is the difference between a 1uF and a 1F capacitor.
    Farads being a unit of

    1. Voltage spikes, and ripples in voltage.
    A little more explanation of #1.
    2. Current.. motors, IDK.
    A little more explanation of #2.
    3. Something else.
    A little more explanation of #3.

    I'm not young, and I'm not in school. I'm in my early 30's, and have a slight interest in electronics. I simply would love to learn and have a better understanding of how electronic components are used, and what they are used for.

    I could watch videos and search the entire internet for hours, or even days, and not learn, get, or understand what I'm trying to learn. When I could just come here and ask a specific question, and get a straight answer, and have a very clear understanding of what they're used for, and why. By people that have experience and knowledge under their belt about stuff that people like myself, have no clue about.
  2. ISB123

    Well-Known Member

    May 21, 2014
    Can you be more specific with your question for capacitors? There is too much to explain without specific question.
  3. MrChips


    Oct 2, 2009
    In order to provide you with a clear understanding I will answer this in three stages:
    1. What is a capacitor physically.
    2. What it looks like electrically.
    3. What are some usage.
    1. Physical - A generic capacitor consists of two electrically conductive plates brought close to each other but not touching.
    Hence you have a gap between the two plates. You may have nothing filling the gap (as in a vacuum) or the gap may be filled with any material that is an electrical insulator, for example, air, paper, glass, mica, plastic.

    In order to make a capacitor physically small in size, the plates can be constructed with metal foil (for example aluminum foil) and then rolled tightly into a cylinder.

    2. Electrical properties
    First of all, the plates are not touching, hence to an electrical circuit it might appear as an open circuit. No charge can flow from one plate to the other. However, because the plates have physical dimensions, they can hold a charge. When one plate has a charge, an equal charge of opposite polarity is induced on the opposite plate.

    How much charge can the plate hold? That depends on the area of the plates, the separation between the plates and the type of material filling the gap.

    Larger area = more charge storage
    Smaller gap = more charge storage
    The material has a special electric property called dielectric constant. If we use air as a reference baseline, paper has a dielectric constant that is 1.5 times that of air whereas glass, mica and many plastics have a dielectric constant that is 4 times that of air. What this means is that if we fill the gap between the plates with plastic we can store 4 times more charge on the capacitor.

    What does it really mean to store charge?

    If we put charge on an air filled capacitor, the voltage will go up.
    If we put the same amount of charge on a capacitor of the same dimensions but with mica as the insulator, the voltage will only go up a quarter as much. That is because the mica capacitor has four times the capacity and can hold four times more charge at the same voltage.

    3. Usage
    The first thing we note is that a capacitor can store charge, like a storage tank of charge. What this means is that we can use this in a power supply circuit to keep the voltage constant even if the charge drawn from it is fluctuating. In other words, a capacitor smooths out the voltage.

    This is also called a low-pass filter. Why? Because all the high-frequency fluctuations have been smoothed out. It is like the shock absorber on your car, it dampens the bumps from the potholes but does nothing about the hills and valleys on the road. So that is a second application - as a filter to remove fast changing voltage fluctuations.

    We note that a capacitor looks like an open circuit to DC current. If we place a capacitor in series with a signal path, no DC current can get through. What happens if the voltage of the signal is changing? An opposite charge is induced on the opposite plate and the voltage of the opposite plate will move in unison with the applied voltage. Yet no DC current can get through because, remember, this is an open circuit.
    In this scenario, the capacitor is called a DC blocking capacitor. Fast fluctuations are mimicked on the other plate but not slow fluctuations. This is called a high-pass filter. High-frequencies get through but not low frequencies and DC.

    Lastly, since a capacitor can hold charge, we can charge or discharge the capacitor as we wish through current limiting resistors or similar circuit. It takes time for the capacitor to charge and discharge. This is very useful for timing applications. One of the most ubiquitous applications is seen in the 555-timer circuit where the pulse duration and frequency is determined by a capacitor and two resistors.
    Bernard, bwilliams60 and Guest3123 like this.
  4. noam ezra

    New Member

    Jul 20, 2016
    usually a cap is on every electronic component in order to filter noise and supply power.
    the value is chosen according to the filter factor, the power supply frequency to the part and the part frequency.
  5. Abdel_Rahman


    Jul 19, 2016
    Yes , Capacitors are used for starting ac-single phase motors,
    ac single phase motor consists of two coils, simply capacitor is used for making a difference in the phase angle between the two coils.

    capacitor usage in power/machines systems is totally different from electronics.
  6. bertus


    Apr 5, 2008
  7. Guest3123

    Thread Starter Member

    Oct 28, 2014
    What are capacitors used for in DC Circuits?
  8. Guest3123

    Thread Starter Member

    Oct 28, 2014
    Thank you. Very nice brief explanation of the different uses for a Capacitor.
  9. Veracohr

    Distinguished Member

    Jan 3, 2011
    Storing energy, generically.
  10. MrChips


    Oct 2, 2009
    The photo flash in your camera (at least in the ones gone by) has capacitor of about 330μF. The xenon flash tube needs a significant amount of energy in order to give off such a bright flash in a short duration. The capacitor is charged up to 300V from the tiny batteries in the camera. That is why you have to wait before you can take another photo after taking one photo.

    When the photo is taken, most of the charge stored in the capacitor is dumped through the xenon flash tube in microseconds. Then it takes seconds to recharge the capacitor back to 300V.

    It is like dumping a barrel full of water and then having to fill it again from the faucet.
    bwilliams60 likes this.