Connect with us

Power supply high voltage

Discussion in 'General Electronics Discussion' started by Fractus, Jan 3, 2021.

Scroll to continue with content
  1. Fractus

    Fractus

    18
    0
    Dec 31, 2020
    Why is the power supply has a higher voltage? Power adapter.JPG Multimeter.JPG
     
  2. bertus

    bertus Moderator

    2,506
    977
    Nov 8, 2019
    Hello,

    Could it be that the powersupply is unregulated?
    If so, the voltage should go down under load.

    Bertus
     
  3. Fractus

    Fractus

    18
    0
    Dec 31, 2020

    The powersupply is regulated.
     
  4. bertus

    bertus Moderator

    2,506
    977
    Nov 8, 2019
    Hello,

    How can you tell it is regulated?
    It is not noticed on the power supply.

    Bertus
     
    davenn likes this.
  5. Harald Kapp

    Harald Kapp Moderator Moderator

    12,455
    2,985
    Nov 17, 2011
    That is a contradiction. When regulated, the output voltage should be 4.5 V.
    From the single 220 V input rating I take it this is a transformer based power supply. This type of wall wart quite often consists of a transformer, rectifier and capacitor only. Put a load to the output, around 220 Ω to draw the rated 20 mA, check the voltage again with load.
     
    bertus likes this.
  6. bertus

    bertus Moderator

    2,506
    977
    Nov 8, 2019
    Hello,

    @Harald Kapp , The power supply is rated for 400 mA.
    The given 20 mA is for the 220 Volts side.

    Bertus
     
  7. Fractus

    Fractus

    18
    0
    Dec 31, 2020

    But if I check the voltage on load does it bust my device?
     
  8. bertus

    bertus Moderator

    2,506
    977
    Nov 8, 2019
    Hello,

    As Halrald said, try a resistor (or a small lightbulb from 4.5 or 6 volts torch) as load and see if the voltage goes down.

    Bertus
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

    12,455
    2,985
    Nov 17, 2011
    Oops, I goofed. Thanks for the correction.
    Anyway, 220 Ω should suffice to load the output.
     
  10. Harald Kapp

    Harald Kapp Moderator Moderator

    12,455
    2,985
    Nov 17, 2011
    Use a bare resistor as load, the risk is very low that it gets damaged, And if so, so what? It's only a resistor.
    Do not use an electronic device you want to keep in working order.
     
  11. ColKlonk

    ColKlonk

    15
    3
    Dec 22, 2020
    Those power supplies are rated at the current specified. This is an unregulated power supply.

    In the picture you should get 4.5 Volts when drawing 400mA, the voltage climbing as you draw less current, and visa-versa.
    It's done this way because of the transformer and secondary winding resistance losses, and what you've measured there is the 'no-load' voltage.
    You can now draw a 'straight line' V-I graph to see the voltage-current relationship of the power supply, so if the tranformer can handle a short circuit ;), you would get around 800mA at around 0 Volts. (Don't do this though - it'll cook the transformer)
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads
There are no similar threads yet.
Loading...
Electronics Point Logo
Continue to site
Quote of the day

-