LM386 Amplifier With A Class AB Push-Pull Stage - 2 Watts

Thread Starter

aac044210

Joined Nov 19, 2019
178
hi aac,
I agree with 'Ram'',
I have split the Output stage on this sim to show the LTSpice response, with the modification.

There seems to be a problem with your LM386 model.
E
I wondered about the LM386 model. I got it from Bordodynov. It surprises me that with LTSpice
being so popular, that it is hard to get workable models of such common components. I kind of
wondered about the class ab biasing but figured maybe it was just another way to do it.
 

ericgibbs

Joined Jan 29, 2010
11,122
hi,
Auto gen is when you use LTS to create a model from the model sub or mod file.

Ref image.
Note the Create Symbol in the pop up menu.

What part does not work in the example I posted.?
E
Rename LM386.txt to LM386.mod and open it with LTS


Update:
Added the LM386 zip
 

Attachments

ericgibbs

Joined Jan 29, 2010
11,122
hi,
You are using a different LM386 model, so thats what I see as in post #11.

Look in F2 Auto Generated, you should see a LM386 model.

E
 

ericgibbs

Joined Jan 29, 2010
11,122
hi,
If you cannot get that to work, lets try the following.
1. Download this zip to your Desktop.
2. Unzip it, you should see on the desktop a LM386_2 Folder
3. Open the folder
4. Run the LM386_test3.asc in LTS

You should get the same circuit I posted in Post #6.

Do that and post what you see.

E
 

Attachments

Thread Starter

aac044210

Joined Nov 19, 2019
178
Hi E:

I did all that and the sim schematic is missing a lot of parts and connections.
Thanks for trying to help. I am not going to bother with it.
 

Audioguru again

Joined Oct 21, 2019
2,067
An LM386 has an output power of only 0.45W into 8 ohms when its supply is 9V.
2W into 8 ohms is 4V RMS which is 11.3V RMS. Use a real power amplifier that is powered with a 15V or 16V supply.

The LM386 with an 18V supply might be zapped since 12V is the max for most of them.
Your original circuit (with RB2 changed to a 1k resistor) with a 12V supply is shown in the datasheet of the LM386 to drive the output transistors with about 10.5Vp-p which is 5.25V peak. The diodes driving the output transistors use 0.7V and the base of each output transistor uses about 0.8V then the 5.25V peak is reduces to 3.75V. The 8 ohm speaker has a 2.2 ohm emitter resistor in series with it and the 3.75V peak will be reduced to maybe 2.5V peak since the 1k base resistors have a voltage drop.
Then the output of 2.5V peak is in the series 8 ohms plus 2.2 0hms which is a current of 2.5V/10.2)= 245mA which is the peak current in the 8 ohm speaker which calculated to be a whopping power of 0.24W in the speaker.

Double checking, a TIP31 and TIP32 has a minimum current gain of 20. Then the base current is 245mA/20= 12.25mA.
But 12.25mA in the 1k base resistor causes a voltage drop of 12.25V so the circuit does not work!. Even if the transistors have their typical current gain of 100 then the circuit will only barely work.
 
Last edited:

345wspo

Joined Jul 10, 2020
15
An LM386 has an output power of only 0.45W into 8 ohms when its supply is 9V.
2W into 8 ohms is 4V RMS which is 11.3V RMS. Use a real power amplifier that is powered with a 15V or 16V supply.

The LM386 with an 18V supply might be zapped since 12V is the max for most of them.
Your original circuit (with RB2 changes to a 1k resistor) with a 12V supply is shown in the datasheet of the LM386 to drive the output transistors with about 10.5Vp-p which is 5.25V peak. The diodes driving the output transistors use 0.7V and the base of each output transistor uses about 0.8V then the 5.25V peak is reduces to 3.75V. The 8 ohm speaker has a 2.2 ohm emitter resistor in series with it and the 3.75V peak will be reduced to maybe 2.5V peak since the 1k base resistors have a voltage drop.
Then the output of 2.5V peak is in the series 8 ohms plus 2.2 0hms which is a current of 2.5V/10.2)= 245mA which is the peak current in the 8 ohm speaker which calculated to be a whopping power of 0.24W in the speaker.

Double checking, a TIP31 and TIP32 has a minimum current gain of 20. Then the base current is 245mA/20= 12.25mA.
But 12.25mA in the 1k base resistor causes a voltage drop of 12.25V so the circuit does not work!. Even if the transistors have their typical current gain of 100 then the circuit will only barely work.
YOU ARE ALWAYS SO NEGATIVE. GET LOST AG!
 
Last edited:

Audioguru again

Joined Oct 21, 2019
2,067
I am not negative. I simply explained the many voltage losses in the hopeless circuit and why it will not work.
Instead get a real audio power amplifier IC.
 
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