1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Is it safe to use a 5V-1A USB(Samsung mobile) charger for lm386?

Discussion in 'General Electronics Chat' started by sr13579, Oct 30, 2017.

  1. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    23
    Likes:
    0
    Hello everyone,
    A brother from my hometown told me to make a mini amplifier that can pull the power out from a USB charger(or PC USB).
    I happened to working on a logic gate IC and burned the IC while using a USB(power bank) charger. I want to know is it safe to use a 5V-1A charger to power the LM386? Thanks in advance.
     
  2. JonSea

    JonSea Well-Known Member

    Joined:
    Oct 1, 2012
    Messages:
    1,201
    Likes:
    111
    Location:
    Seattle, WA
    A USB charger will supply very close to 5 volts and should not have damaged your logic chip...unless you had the polarity reversed. it will work fine for your amp circuit too.

    Don't assume anything about color codes on charger wires or USB cables. You must always check. I have one 5vdc module where red is negative and black is positive!
     
  3. dr pepper

    dr pepper Well-Known Member Most Helpful Member

    Joined:
    Oct 6, 2008
    Messages:
    4,763
    Likes:
    259
    Location:
    North west UK
    5v is enough for a little Lm386
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!

    With a 5V supply, an LM386 produces only 0.113W into an 8 ohm speaker which is close to no power. If you turn up the volume then it will cause clipping distortion.

    With a 9V supply it produces 0.45W into an 8 ohm speaker which is almost the power from a cheap clock radio.

    With a 12V supply the output power will sound the same as with a 9V supply but the IC will become hot.
     
  6. JonSea

    JonSea Well-Known Member

    Joined:
    Oct 1, 2012
    Messages:
    1,201
    Likes:
    111
    Location:
    Seattle, WA
    All manner of DC power supplies are available at thrift stores and PC recyclers. I never built ppwer supplies for my projects when high wuality supplies are available for a couple bucks.
     
  7. Pommie

    Pommie Well-Known Member Most Helpful Member

    Joined:
    Mar 18, 2005
    Messages:
    10,162
    Likes:
    340
    Location:
    Brisbane Australia
    If you must run from USB then get a little boost board on ebay such as this module.

    Mike.
     
    • Like Like x 1
  8. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,592
    Likes:
    952
    Location:
    Canada, of course!
    The output of an LM386 with a 9V supply is 0.45W into 8 ohms and its heating will be 0.5W for a total of 0.95W. The boost converter is 97% efficient so its 5V power will be 0.95W/0.97= 0.98W so the 5V current will be 0.98W/5V= 196mA. Can your USB supply 196mA?
     
    • Like Like x 1
  9. sr13579

    sr13579 New Member

    Joined:
    Sep 9, 2017
    Messages:
    23
    Likes:
    0
    Yes it can.Thanks for the calculation
     
  10. ci139

    ci139 Active Member

    Joined:
    Apr 12, 2012
    Messages:
    470
    Likes:
    37
    yes , but the cellular 5V? charger has no load (low load) voltage bit above 7V that is abs max for 74HCxx gates
    the lm386 has (depending on type) 15 or 22 V for the same figure
     
    • Agree Agree x 1
  11. JonSea

    JonSea Well-Known Member

    Joined:
    Oct 1, 2012
    Messages:
    1,201
    Likes:
    111
    Location:
    Seattle, WA
    This is so not true. 5 volt supplies for cell phones whether with a USB socket or cable connection are tightly regulated. I would be surprised to see more than a 0.2 volt swing over the load range.
     
  12. ronsimpson

    ronsimpson Well-Known Member Most Helpful Member

    Joined:
    Apr 17, 2007
    Messages:
    7,375
    Likes:
    975
    Location:
    Loveland, CO USA
    Most 5V cell phone chargers are switching power supplies and have good regulation. (USB must be regulated)
    Many old wall warts use a transformer and likely have no regulation.

    There are many different types of "plug in the wall and give power" type devices.
     
    Last edited: Oct 31, 2017
  13. JonSea

    JonSea Well-Known Member

    Joined:
    Oct 1, 2012
    Messages:
    1,201
    Likes:
    111
    Location:
    Seattle, WA
    Indeed, there are many different types of "wall warts" - the question here was specifically about a plug-in USB power supply for a cell phone, so the voltage regulation will be excellent.

    AC-DC Power Supplies - Using Wall Warts is an article I wrote a few years ago that discusses the different types of power supplies available and provides test data for a number of 12 volt switchers.

    For wall warts, there are 4 major types:

    Transformer - AC - AC supply. These will be cube shaped and relatively heavy for their size. The AC output requires rectification, filtering and regulation. There are very limited times this would be an optimal choice.

    Linear AC DC supply. These use a line frequency transformer, so they will be cube shaped and heavy for their size. These supplies usually have only rectification and minimal filtering and do not include voltage regulation. Under no load conditions, the voltage will be (much) higher than the nameplate voltage. This type of supply is really only useful supplying a voltage regulator. This type of supply is being used less and less, in favor of more efficient switching supplys.

    Switching AC - DC Constant Voltage Supplies: these are the cell phone, laptop and in general the low voltage DC supplies used to power most electronic products now-a-days. They are generally not a cube shape and are relatively light for the power provided. The output voltage will be close the the nameplate voltage across the rated load range. In my experience, most of these handle overloads by reducing output voltage and handle shorted outputs gracefully.

    Switching AC - DC Constant Current Supplies: These are becoming more common and are used to power LED lights. They have the physical characteristics of switchers above but provide a constant current at a varying voltage. If the rating is something like 315mA, 0 - 8 volts, it's a constant current supply and only useful in limited cases, light powering LED lights.
     
    • Like Like x 1

Share This Page