LM 386 AUDIO AMPLIFIER

[jimtylee]

LM386 running hot....do not worry they all do......been using them for ages
too hot to keep a finger on ???? they never fail use one in my R209 radio at full volume no trouble...
JIM G4REK

 

[Nigel Goodwin]

Post your schematic and a picture of it's layout (use 'upload a file').

 

[MikeMl]

They are a Class A Power amp, after all...

 

[jimtylee]

They are a Class A Power amp, after all...

Its class ab surely not class a

 

[MikeMl]

It is more class A than Class AB even though it has a totem-pole output stage; hence the rather high quiescent power dissipation... National made various grades which had a lower quiescent current that were more suitable for battery powered applications...

 

[Nigel Goodwin]

It is more class A than Class AB even though it has a totem-pole output stage; hence the rather high quiescent power dissipation... National made various grades which had a lower quiescent current that were more suitable for battery powered applications...

Sorry, but it's nothing like class A - which wouldn't even be possible in a small plastic casing.

According to the datasheet typical quiescent current is only 4mA - if it's getting hot like he said, then it's likely a design or layout problem - and ALL of them were designed for battery usage.

 

[JimB]

LM386 running hot....do not worry they all do......been using them for ages
too hot to keep a finger on ???? they never fail use one in my R209 radio at full volume no trouble...
JIM G4REK

Can someone please explain to me, is there a question here?
If there is I cannot see it.

There just seems to be a statement that all LM386s run hot and that it is not a problem.
What am I missing in this thread?

JimB

 

[audioguru]

They are a Class A Power amp, after all...

Absolutely NOT! It is class-AB like most audio amplifiers. Its idle current is typically only 4mA, not hundreds of mA like in a class-A amplifier.

I suspect that bad wiring on a solderless breadboard or a missing supply bypass capacitor causes the LM386 to oscillate at hundreds of kHz which makes it get hot.
Or the supply voltage is too high then its output power and heating are high.

 

[jimtylee]

Absolutely NOT! It is class-AB like most audio amplifiers. Its idle current is typically only 4mA, not hundreds of mA like in a class-A amplifier.

I suspect that bad wiring on a solderless breadboard or a missing supply bypass capacitor causes the LM386 to oscillate at hundreds of kHz which makes it get hot.
Or the supply voltage is too high then its output power and heating are high.

 

[jimtylee]

No oscillation at all scope tells me that, th....ey just get hot even when driven lightly

 

[Nigel Goodwin]

No oscillation at all scope tells me that, th....ey just get hot even when driven lightly

You still haven't posted either a schematic, or a layout photo - so we've no idea what you're doing?.

Are you claiming ALL LM386's run hot at idle?, because they don't.

Have you measured the supply current?.

 

[jimtylee]

You still haven't posted either a schematic, or a layout photo - so we've no idea what you're doing?.
12.3 voltage on the ic......quiescent current 5 milliamps.... 190 mills when drive fairly lightly


Are you claiming ALL LM386's run hot at idle?, because they don't.

Have you measured the supply current?.

 

[Nigel Goodwin]

If it's only taking 5mA, then it can't be running hot quiescent - as it's only consuming 61.5mW

190mA isn't 'driven lightly' - it's probably highly over-driven, and consuming 2.337W - so I would expect it's quite hot when over-driven in that way.

Presumably you're using too low a speaker impedance?, and thus greatly over-loading the IC?.

 

[jimtylee]

If it's only taking 5mA, then it can't be running hot quiescent - as it's only consuming 61.5mW

190mA isn't 'driven lightly' - it's probably highly over-driven, and consuming 2.337W - so I would expect it's quite hot when over-driven in that way.

Presumably you're using too low a speaker impedance?, and thus greatly over-loading the IC?.

 

[jimtylee]

8 OHM SPEAKER.....measured on Avo8 and dig meter

 

[jimtylee]

8 OHM SPEAKER.....measured on Avo8 and dig meter

Not running hot on no signal...quiescent current never said it was.

 

[Nigel Goodwin]

8 OHM SPEAKER.....measured on Avo8 and dig meter

Too low an impedance for a 12V supply - overloading the chip - you probably want a 32 ohm speakers for 12V?.

 

[audioguru]

The datasheet shows that An LM386 works well with a 6V or 9V supply. It shows that with a 12V supply its output power is not increased much but its heating increases a lot.
Yours is in a socket instead of being soldered to the copper traces on the circuit board. The copper traces help carry heat away when it is soldered to them.
With a 6V supply, the output voltage swing into an 8 ohm speaker at clipping is 4V peak-to peak which is 0.25W. Its heating is 0.22W.
With a 9V supply, the output voltage swing into an 8 ohm speaker at clipping is 6V peak-to peak which is 0.56W. Its heating is 0.52W.
With a 12V supply, the output voltage swing into an 8 ohm speaker at clipping is 6.5V peak-to peak which is 0.66W. Its heating is 0.82W.
Its maximum allowed heating when it is not enclosed and is in 25 degrees C air is 1.25W when it is extremely hot (150 degrees C inside it).

You measured its current as 190mA when driven lightly then its total power is 12V x 190mA= 2.28W. Then its output power and heating are much more than shown on the graph in the datasheet so it is probably oscillating. At clipping its total power is 0.66W + 0.82W= 1.48W. Then its current is 1.48W/12V= 123mA.

 

[audioguru]

In my clock radio I put an LM390 amplifier IC which is in a 14 pins package and is not made anymore.
With a 9V supply its output swing into an 8 ohm speaker at clipping is 8.2V p-p which is 1.05W. Then its heating is 1.2W.

Its output swing and power are much more than the LM386 because the LM390 uses an extra resistor and capacitor to bootstrap its output stage.

 

[jimtylee]

The datasheet shows that An LM386 works well with a 6V or 9V supply. It shows that with a 12V supply its output power is not increased much but its heating increases a lot.
Yours is in a socket instead of being soldered to the copper traces on the circuit board. The copper traces help carry heat away when it is soldered to them.
With a 6V supply, the output voltage swing into an 8 ohm speaker at clipping is 4V peak-to peak which is 0.25W. Its heating is 0.22W.
With a 9V supply, the output voltage swing into an 8 ohm speaker at clipping is 6V peak-to peak which is 0.56W. Its heating is 0.52W.
With a 12V supply, the output voltage swing into an 8 ohm speaker at clipping is 6.5V peak-to peak which is 0.66W. Its heating is 0.82W.
Its maximum allowed heating when it is not enclosed and is in 25 degrees C air is 1.25W when it is extremely hot (150 degrees C inside it).

You measured its current as 190mA when driven lightly then its total power is 12V x 190mA= 2.28W. Then its output power and heating are much more than shown on the graph in the datasheet so it is probably oscillating. At clipping its total power is 0.66W + 0.82W= 1.48W. Then its current is 1.48W/12V= 123mA.

Okay thank you for the information, very enlightening
jim g4rek