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

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sr13579

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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.
 

JonSea

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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!
 

dr pepper

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5v is enough for a little Lm386
 

audioguru

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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.
 

JonSea

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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.
 

audioguru

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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?
 

sr13579

Member
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?
Yes it can.Thanks for the calculation
 

JonSea

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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
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.
 

ronsimpson

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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.
 
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JonSea

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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.
 
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