operating a speaker with the output of ua741 n IC

[akshay15]

hi ,, can i drive a 32ohm speaker from the output of a ua741 opamp output in comparator mode.. i.e can dc voltage drive a speaker if yes then how much ??

 

[davenn]

more to the point ... why would you want to put a DC voltage into a speaker ? its not good for the speaker

Dave

 

[Raza]

Driving speaker with DC means only moving the coil in one direction -> UP or DOWN. The coil will move to the supplied voltage strength and will withstand till the coil does not burn up. But I could not get the idea of driving a speaker with DC.

 

[BradtheRad]

You'll get sound, however the volume won't be loud coming from a little 741. Rated power dissipation is 1/2 W.

Say you use a 12V single supply. Through a 32 ohm speaker. You'll overheat the chip if you draw more than 1/8 of an amp.

The speaker can probably endure continuous DC at that rate. However it works better if you put a capacitor in series. 100uF will probably be sufficient. It blocks DC but passes AC.

An improvement would be to use two op amps driving the speaker in bridge mode. (Speaker mounted between the outputs. Outputs at opposite phase.) You'll get more volume.

If you want more volume then a LM386 is a popular choice.

 

[Raza]

Can you upload the circuit in your plan?

 

[Santosh13]

You can go for an POWER AMPLIFIER which is available on many electronic circuit forums and the power amp would probably produce required sound range and can be controlled by using a 100K POT at the input. Use Dual op-amp (NE5532)...NOTE use floating load i.e BRIDGE OUTPUT (SPEAKER connected between the outputs of the op-amp's)



Regards,
Santosh Kumar

 

[FvM]

You'll overheat the chip if you draw more than 1/8 of an amp.

No risk to do so. Maxmum output to the speaker is limited by the LM741 current limit, which is specified as 10 mA minimum, 25 mA typical, 40 mA maximum. Accordingly the output power into 32 ohm (square wave) will be 3 mW min, 50 mW maximum.

 

[BradtheRad]

No risk to do so. Maxmum output to the speaker is limited by the LM741 current limit, which is specified as 10 mA minimum, 25 mA typical, 40 mA maximum. Accordingly the output power into 32 ohm (square wave) will be 3 mW min, 50 mW maximum.

Yes, the Linear Databook says you're correct about max mA output.

As for me I wasn't sure how soon the overload protection takes effect. I saw the spec 500mW max power dissipation, and I did a quick calculation.

Evidently, for the 500mW spec to be relevant at all, the supply V must be high and the load resistance low.

Strange how these max specs don't make it clear whether it's (a) the most we can safely draw from it so we need to be careful, or (b) whether it's the most the device will provide regardless what we attach to it and we don't need to be as careful.

 

[FvM]

The datasheet is clear about short circuit protection for indefinite duration, a common attribute of most classical low bandwith OPs. In my understanding, it refers to nominal +/- 15 V supply, and (I guess) the full voltage range, including supply shorts. Athough there's no thermal shutdown like in voltage regulators or power amplifiers, the limiting current is decreasing according to 1/T. I must admit, that I can hardly remember designs, where I have used the part. But I have still some in a drawer.

 

[E Kafeman]

Many of us do probably think that it is a misuse of an old good IC to let it directly be connected to a speaker, but as that was the question, if it was possible:
Yes, it is possible but an poor design. Think about as if an turtle can tow an Ferrari. Under good condition is it possible but an misuse of both the turtle and the car.
TS want to use comparator mode, and I guess simplest possible construction: single power supply, no speaker decoupling. Under these circumstances will max sound power be ~10 mW at 40 mA. If a serial cap is added is it FvM's numbers that are correct. Not impressive in any case, but audible. It is a good idea to design such that without input signal, let 741 output DC level rest at 0 Volt output, which reduces current consumption if speaker also is connected to ground. This circuit will be enough for simple beeping square-waves.
Just as an example that it still with this simple circuit is possible to play analog sound with decent quality can PWM be used. For PWM do it need that signal source can deliver PWM or that an digital hysteresis inverter is added in serial with analog signal as a modulator (technology level KISS).