Opamp maximum output current (NE5532 or similar) - diyAudio
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Old 14th July 2011, 10:45 AM   #1
pvh1987 is offline pvh1987  Denmark
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Default Opamp maximum output current (NE5532 or similar)

I don't know if this is the right place to ask about opamps, but I'll try anyway:

Does anybody know how much current a NE5532 can supply on it's output? I guess it is about 20-50 mA or something like that, but I can't find any datasheet of the NE5532 stating that parameter. Nor does it say anything about maximum power dissipation.

Is it possible to calculate maximum output current by other parameters or do I have to make a test circuit that might destroy it?

I could use power opamps instead, but they seem to be expensive - even the smaller ones, that will supply up to 200 mA.

So, If anybody knows of some opamps similar priced to the NE5532 that can supply 50-100 mA or more, or at least states how much it can handle, I would be very happy to know about it. And - it has to be unity-gain stable, so I can use it as a voltage follower without problems.
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Old 14th July 2011, 11:07 AM   #2
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The datasheet I have (TI) says typically the current limit is 38mA, but the minimum is 10mA. Doug Self has a paralleled NE5532 design working as a power amp, so you could do worse than to copy that and reduce the number of opamps to suit.
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Old 14th July 2011, 11:44 AM   #3
pvh1987 is offline pvh1987  Denmark
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Yes, I know that design and it works extremely well for me in my headphone amplifier where I paralleled 8 NE5532 voltage followers for each channel. That's why I now want to do something similar in a power supply with power opamps or a lot of low power opamps like NE5532, to reduce noise and make a very clean and low impedance power source. It is all experimental and it might turn out to be a bad idea, but I have to try it.

So I guess if I need to supply 1 ampere with reasonable margins, so it should be able to deliver about 2 amps without breaking down, I need a whole lot of NE5532's. If I could get a similar priced opamp with min. output current about 50 mA or more, that would be very nice. I am very open for suggestions :-)
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Old 14th July 2011, 12:26 PM   #4
jcx is offline jcx  United States
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the 5534 and many older op amps have very asymmetric output stages, performance can be really poor near one rail, less so at the other

I have measured a large increase in distortion near 1/2 fo the rated output current with some op amps - just because the short circuit rating is ~40 mA doesn't mean you get good performance there

paralleling for higher output current is "inefficient" for performance because you still have internal thermal feedback, power supply pin current coupling, and the N extra op amp's loop gain isn't adding to the feedback around the output stages


a better approach is to use a multiloop composite amplifier with a purpose designed high current output amp/buffer and your preferred good quality/low noise audio op amp for input servoing the output of the fast, high current output amp

the output amp/current buffer needs to be much faster than the input op amp to avoid stability compensation issues when including it in the input op amp feedback loop

CFA op amps make good high current outputs - heat removal becomes a problem at higher power - LT1210 is a 1A output 35 MHZ CFA op amp in a TO-220 package



extreme op amp heatsinking (6x TPA6120, paralleled and totem pole/cascaded in a multiloop with OPA627 input/overall feedback)

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Last edited by jcx; 14th July 2011 at 12:36 PM.
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Old 14th July 2011, 12:50 PM   #5
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At 1-2 A that just doesn't seem sensible. You want an external pass transistor to get the heat away from the error amplifier part of the circuit. There's no advantage to having it all on one die. Output impedance will be determined more by the feedback arrangement than anything else. I do remember some small tab package opamps with a few hundred mA of output (LM759) but don't know what's currently available. You could get there with 3 or 4 of those if you just have to try it.
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Old 14th July 2011, 12:57 PM   #6
lineup is offline lineup  Sweden
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Quote:
Originally Posted by pvh1987 View Post
So, If anybody knows of some opamps similar priced to the NE5532 that can supply 50-100 mA or more
"similar priced to the NE5532"
This is a mission impossible.
There are very few OPamps in the class of NE5532 and similar price.
In fact, I don't know any!!!
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Old 14th July 2011, 01:16 PM   #7
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by lineup View Post
"similar priced to the NE5532" This is a mission impossible.
There are very few OPamps in the class of NE5532 and similar price.
In fact, I don't know any!!!
Hi, I agree totally, for its price nothing gets near current wise (or anything else), rgd, sreten.
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Old 15th July 2011, 11:46 AM   #8
pvh1987 is offline pvh1987  Denmark
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Thanks for your replies :-) Seems like my idea probably won't work, or will be very expensive, inefficient, break down because of heat issues or something like that.

I have thought about using one single power opamp or maybe 2 paralleled power opamps instead of a whole lot of NE5532's. It seems like some of the power op amps are specifically made for power supplies. Would that be a better idea? It might be cheaper as well, if I need 1-2 A. What about noise levels and output impedance? I know that paralleling NE5532 reduces noise and output impedance, and that's what I want. But I think I need too many of them to make 1-2 A and it will be hard to mount them on a heatsink compared to the power opamps in TO220-housing?

I don't know anything about multiloop composite amplifiers. Is that opamps coupled with discrete transistors with some kind of advanced feedback loop?
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Old 15th July 2011, 11:57 AM   #9
Mooly is offline Mooly  United Kingdom
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Unless I have missed it somewhere... what is the load you are trying to drive ?
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Old 15th July 2011, 12:43 PM   #10
jcx is offline jcx  United States
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composite amplifiers can use descrete or other IC amps to improve the performance over that of just 1 op amp

for application that fit in the supply rail range of integrated chip amps they are convenient

http://focus.ti.com.cn/cn/lit/an/sboa002/sboa002.pdf

http://waltjung.org/PDFs/ADI_2002_Se..._Drivers_I.pdf

you can combine ideas, if you just need 2x more than a otherwise adequate op amp's current then paralleling output current buffer amps can be practical

the 2 output chips can still be inside the feedback loop of a good quality audio input op amp

people have added a good quality op amp to a power chip amp (LM3886, TDA7293, ect. ), but it is a little more dificult to stabilize since many power audio chip amps are decompensated for minimum gain >10 already and are slow compared to today's better audio op amps
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