Help with LM386 audio amp

[orangemanorman]

Hello all,

I am new to audio amp and I need your help/opinion

What I am trying to do is maximize the current out of the audio amp. Out of Pin 5, I noticed a lot of diagrams have a small resistor in series with a capacitor connected to ground as well as the capacitor connected in series with the load speaker. Can you tell me what the capacitor and the resistor is for?

How can I max the current output if I have a load of 30 Ω? and what would the maximum current be?

I am also interested in the LM384 which delivers 5W output, but I am not sure how to max the current there either (and there is also a resistor and capacitor in series connected to ground), the load is 30Ω also.

Thanks

 

[Dragon Tamer]

The wattage of the amplifier is under ideal conditions, I can tell you right now your conditions are most likely not ideal as they rarely ever are. The LM386 has a max output of 0.5W and it is impossible to exceed that limit for any number of reasons. The main reason is that if you try to exceed that you will destroy the amp. The output power is defined by the input power, the gain and the supply power. It sounds like you are trying to gain power out of the amp that isn't there.

The capicitor and resistor in series connected to the output are for stabalising the amplifier. Without them the IC will oscillate wildly and it will sound horible. The large capacitor in series with the speaker is a decoupling capacitor, also known as a DC blocking capacitor in some aplications. It is there so that the output of the amp is not shorted when the speaker is connected. Try to bypass this cappacitor and you will destroy your IC.

The maximum current coming out of most amplifiers is realatively small unless it is specified as a power amp. You can find out how much current you can get out of an amp if you look up it's data sheet. A good place to get data sheets is http://datasheetcatalog.com/

The max output power of an LM386N-4 with a supply voltage of 16V and a load of 32 ohms, the power can be between 750mW (0.75W) to 1000mW (1W). Trying to aim for a higher current is probably useless and I would not even try.

As for the LM384 the max output is 5.5W with an 8 ohm load, but it doesn't specify a supply voltage for that power output so I'm assuming that it is 28V. The max ouput current is 1.3A when shorted, shorted is the key word here.

It would help us more if we knew specificaly what you were trying to do with your circuit.

 

[orangemanorman]

thanks for the reply

I am trying to amplify a 134.2kHz signal for a RFID application. The reason i want to use an audio amp is because the fast speed. The 134.2kHz is coming out an Atmel chip at 3.3V TTL.

I want to boost the current to around 1-2A to drive an antenna.

Do you think an ordinary amp will do it? I think I need to have a current gain of at least 100? Will an normal amp be fast enough?


If you think there is a better way of amplifying a signal at that frequency with no distortion to 1-2A, please let me know

 

[carbonzit]

134kHz? I don't think so.

The National Semicircular datasheet is your friend. Sure, it claims a bandwidth of 300kHz (page 2). But take a look at the graph of distortion vs frequency on page 4. Above 20kHz, distortion rises (from about 1.5%) at a very steep rate. No telling what it ends up being at your desired F. So who knows what kind of waveform you'll get at your antenna. (Not to mention that it'll be a horrible impedance mismatch.)

What you need is a low-frequency RF amp. Dunno what's available, but I don't think this is a very good choice. Could it work? Maybe.

 

[4pyros]

You need an rf amp. The outputs of audio amps are not ment to drive antennas. Thare are many rf amps out there and cupling to the antenna is the key.

 

[ronv]

What's the plan for the antenna?