I'm looking for a chip amp that can deal with a 0.4ohm load @ 3a - diyAudio
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Old 11th September 2014, 03:48 PM   #1
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Default I'm looking for a chip amp that can deal with a 0.4ohm load @ 3a

Hi all,
I have an application where I want to drive an electromagnetic shaker. This is essentially a speaker but however has a lower impedance (http://www.modalshop.com/filelibrary...-(DS-0073).pdf)

I only need to push about 3a maximum. Are there any chip-amps that can fit the bill?
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Old 11th September 2014, 04:04 PM   #2
AndrewT is offline AndrewT  Scotland
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3Apk or 3Aac?
giving
1.2Vpk or 1.2Vac?

In both cases you are looking for a Buffer, sometimes referred to as a Power Buffer.
There is no amplification, the gain is 0.99Times (-0.1dB)
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Old 11th September 2014, 04:16 PM   #3
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Quote:
Originally Posted by AndrewT View Post
3Apk or 3Aac?
giving
1.2Vpk or 1.2Vac?

In both cases you are looking for a Buffer, sometimes referred to as a Power Buffer.
There is no amplification, the gain is 0.99Times (-0.1dB)
Do you have any part number for a Power Buffer?, I can't turn any up in a simple search.
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Old 11th September 2014, 04:35 PM   #4
AndrewT is offline AndrewT  Scotland
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many on this Forum
or google
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Old 11th September 2014, 04:49 PM   #5
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I still can't turn up much info searching "Power Buffer" or "Voltage Buffer".
Would a high power op-amp be suitable for this application?

http://www.ti.com.cn/cn/lit/ds/symlink/opa549.pdf
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Old 11th September 2014, 06:23 PM   #6
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by AlessandroAU View Post
Hi all,
I have an application where I want to drive an electromagnetic shaker. This is essentially a speaker but however has a lower impedance (http://www.modalshop.com/filelibrary...-(DS-0073).pdf)

I only need to push about 3a maximum. Are there any chip-amps that can fit the bill?
1) please confirm whether your shaker has 0.4 ohms impedance or 0.4 ohms DC resistance.
Not the same by far.

Ok, I checked your datasheet.
Interesting devices

You seem to have chosen the 2007E , 8A Pk, 0.37 ohms DC resistance.
If at all possible (hope you havent boughtb them yet), choose the 2004E which with its 1.5 ohms DCR is MUCH easier to drive.

Supposing it might be late, let's go back to 2007E .

2) DCR is the lowest impedance it will show, and that with very slow movement, or applying some DC to it (or a looooonnnng squarewave pulse) and staying there.

In that case, the coil resistance will drop 3A (your choice) * 0.4 ohms=1.2V DC .... you can call that peak or steady, depending on your waveform or duty cycle, which you have not stated.

So we need to know what will you actually load your shaker with, and at what frequency.

So far we only know that peak current is 3 A, and at any frequency above DC, impedance will be higher, so will required drive voltage.

Please tell us more about the intended application, but so far I can suggest (to begin with something) a TDA2030 which is a "big Op Amp", can supply 3.5A Pk , can supply well above the minimum 1.2 V Pk required , is cheap and plentiful and can work down to DC .

But this is just a preliminary thinking aloud, we need more details.

There are many other options available , such as current buffered Op Amps (conceptually the same as a TDA20xx ) but let's here more from you

But rest assured that this is entirely doable and probably without weird expensive dedicated chips.
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Old 12th September 2014, 05:08 AM   #7
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Unfortunately I already have the shaker. (2007E) I don't have an impedance plot right now but I can certainly take one soon. I'll be running at frequencies from about 30-1000hz given the loading conditions of the shaker its natural frequency is at about 20hz.

I will only be driving pure sine waves, generated from a frequency generator. I would like unity gain so that I know what voltages are being applied to the shaker without taking a direct measurement.

While I specified 3a it would still be useful to know that shaker could be driven at its maximum of 8a momentarily. Although I don't think I will ever exceed 3a continuously.
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Old 12th September 2014, 05:52 AM   #8
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Maybe a current dumper driven by a chip amp would be appropriate? You know where the output transistors are biased class B via dropping resistors in series with the chip's power supply leads.

I have taken apart OEM car "subwoofers" that contained cheesy bridged class D amps driving odd woofers with impedances like 1.6 ohms. There was no switching power supply so the amplifiers ran off of 12 volts. The heatsinks were pretty small too; as were the amplifiers, which were contained inside the compact "subwoofer" enclosures.

So getting an amplifier that can drive enough current off as small a voltage as possible will get you a practical, purpose designed amplifier. You should look at popular chip amps to find one that can deliver your required current and that can operate off of a relatively low voltage. Off the top of my head, I think it will be slim pickings.

There's a lot of el cheapo class D amps for sale on flea bay that you might be able to configure. It is more typical of class D amps to be specified to run off of low voltages like 12 volts than for "hi-fi" class AB chipamps, and still be able to deliver high current. These devices are probably useful for compact car subwoofers with lower impedances (I've seen tabletop "hi-fi" units that came with 3 ohm speakers, and when I measured them they were very low impedance.)

Last edited by Fast Eddie D; 12th September 2014 at 05:58 AM.
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Old 12th September 2014, 05:57 AM   #9
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Transformer coupling will open the horizons open to the audio chipamps.

Gajanan Phadte
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Old 12th September 2014, 06:29 AM   #10
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+1 for the trafo. A mains trafo might even work well enough though losses could become an issue at higher frequencies.
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