Chargers like voltage sources

Discussion in 'General Electronics Chat' started by fektom, Jan 10, 2013.

  1. fektom

    Thread Starter Member

    Aug 20, 2012
    Hello Everybody!

    I have probem with measuring some voltage sources which were chargers of various electronic equipments (for example beard trimmer, mobile phones).

    I have exactly 3 chargers and have problem with 2. Each have an own characteristic table which clearly says how much voltage can you use with and how much voltage does it produce (with the current value as well).
    Let me call the three charger first, second and third.

    The first charger made me surprise. It's table says:
    PRI: 220-240V 50-60Hz, SEC: 2,3V 100mA (DC)
    So I expected 2,3V when I measured the voltage with no load (I mean I measured only the terminal voltage). However, I got 6.9V.
    No problem, I said, because I connected less and less resistance into the circuit, and realised that the voltage decreases. It's a good result, because I know that a correct generator works like this: the load is connected in series with the internal resistance of the generator, so the generator is a voltage divider circuit with the load in series.
    After this measure, I interpret the characteristic table of the charger like it shows correct values only if you connect it to expected resistance.

    Later, just to make it completely sure, I tried the second and third chargers.
    Second is: INPUT: 100-240V, 50-60HZ, OUTPUT: 5V 0.7A (DC)
    Third is: INPUT: 100-240V, 50-60HZ, OUTPUT: 4.9V 450mA (DC)

    I expected very similar results, namely, the terminal voltage must to be much higher than the values presented on the cover.
    However, I got the same results shown on the charger. I tried it over and over again with different value resistances but didn't succeed to measure lower voltage (the lowest value resistance was 200ohm).

    So, because of these results, I have got the following questions:
    1, First is why? If it is true that all voltage source has an internal resistance and I connect in series some resistance, I make a voltage divider circuit. So I should measure different voltages with different resistances.
    2, Is it possible that the reason is in the different technology used by the chargers? Because the first has lot more weight than the second and the third (maybe because it uses coils inside)?
    3, If it is true that the characteristic table shows correct values only if you connect it to specified resistance, you should get a different voltage if you wire it with higher or lower resistance. Or if im wrong, what does a table like this exactly mean? How can I interpret a table like this?

    If anyone has good explanation or answer which might help, please don't hold back!
  2. panic mode

    Senior Member

    Oct 10, 2011
    there are different beasts out there;

    - regulated power supply will provide stable regulated output regardless of load (as long as within specification)

    - unregulated power supply will provide higher voltage with no load, lower voltage with load

    - basic charger can be just a transformer and rectifier (no filter) so output is not even stable (there is a large ripple). if you add filter, you get unregulated power supply. if you also add regulator, you get regulated power supply.
    fektom likes this.
  3. Audioguru


    Dec 20, 2007
    Do not call them a "charger" because the charger circuit is inside the cell phone.
    They are simply a cheap power supply that might or might not have its voltage regulated.
    fektom likes this.
  4. BillB3857

    AAC Fanatic!

    Feb 28, 2009
    One indicator of the type supply you have is the input voltage range. Your fist supply, 220-240V 50/60Hz tells me it is a transformer type with rectifier and possibly filtering.

    The other two with the wide input range of 100-240V tells me they are switching type power supplies with output regulation.

    Like Panic Mode says, there are different beasts out there.
    fektom likes this.
  5. fektom

    Thread Starter Member

    Aug 20, 2012
    I didn't know voltage regulator, it's new for me!
    You guys, helped me a lot! Thank you!