Hi...
I am looking for an amp to drive a 'voice coil actuator'... During a conversation with an engineer for the manufacture I was told that they use a simple audio amp for 'testing' purposes to drive these devices, but I'm concerned that my requirements will place an intolerable load on an audio amp. In particular, I will be driving these devices at very low frequency... (expected frequency range will be 0.1 hz to 10hz) and with a DC offset to boot. Another significant problem with these devices is that they utilize a very substantial coil (one device that I'm considering has a 2 lb voice coil) and consequently produce significant back EMF. This same device has an impedence of 2.8 ohms and produces 100 lbs of force at 41 volts. I think that I will only require a small percentage of that force, but this motor has other charateristics that are important (for one... it's surplus). Anyway, my question is this, is there an audio amp design which would be appropriate for such a load, or should I look elsewhere?
thanks,
steve
I am looking for an amp to drive a 'voice coil actuator'... During a conversation with an engineer for the manufacture I was told that they use a simple audio amp for 'testing' purposes to drive these devices, but I'm concerned that my requirements will place an intolerable load on an audio amp. In particular, I will be driving these devices at very low frequency... (expected frequency range will be 0.1 hz to 10hz) and with a DC offset to boot. Another significant problem with these devices is that they utilize a very substantial coil (one device that I'm considering has a 2 lb voice coil) and consequently produce significant back EMF. This same device has an impedence of 2.8 ohms and produces 100 lbs of force at 41 volts. I think that I will only require a small percentage of that force, but this motor has other charateristics that are important (for one... it's surplus). Anyway, my question is this, is there an audio amp design which would be appropriate for such a load, or should I look elsewhere?
thanks,
steve
to be honest..... no.
There is a very long (and mostly irrelevant) story behind this, but the short explanation is that I'm trying to build a device to introduce pressure waves (at low frequency) into tissue. I currently have a device called a 'foredom percussor' which is used for this purpose, but it is limited to a sine wave of fixed amplitude, with only limited control of frequency. I am interested in more complex patterns, and need to have more control of amplitude and frequency, in particular I am looking for feedback control.
I have found a 'voice coil actuator' which should be capable of reproducing the motions and power of the foredom device (at least the low frequency aspects), with the additional capacities that interest me, and it is this device that I mentioned in my previous post.
I would be happy to 'start out' with an amp that is able to produce a quarter of the force that the motor is rated for, I'd guess about 10 volts at 2.8 ohms, but at the same time, I think that this amp might need to deal with wildly unsymeteric swings as well as DC offset, and the back EMF will be horrendous at any sort of speed..
And the truth is that I'm just experimenting here, and I don't know what requirements I'll end up with... It would be nice to just get to a point where I could produce a simple sine wave with the contraption... but I am hoping to eventually utilize a linear transformer as a feedback device. I actually want to introduce a 'feedback' effect in the tissue
hope this helps,
thanks,
steve
There is a very long (and mostly irrelevant) story behind this, but the short explanation is that I'm trying to build a device to introduce pressure waves (at low frequency) into tissue. I currently have a device called a 'foredom percussor' which is used for this purpose, but it is limited to a sine wave of fixed amplitude, with only limited control of frequency. I am interested in more complex patterns, and need to have more control of amplitude and frequency, in particular I am looking for feedback control.
I have found a 'voice coil actuator' which should be capable of reproducing the motions and power of the foredom device (at least the low frequency aspects), with the additional capacities that interest me, and it is this device that I mentioned in my previous post.
I would be happy to 'start out' with an amp that is able to produce a quarter of the force that the motor is rated for, I'd guess about 10 volts at 2.8 ohms, but at the same time, I think that this amp might need to deal with wildly unsymeteric swings as well as DC offset, and the back EMF will be horrendous at any sort of speed..
And the truth is that I'm just experimenting here, and I don't know what requirements I'll end up with... It would be nice to just get to a point where I could produce a simple sine wave with the contraption... but I am hoping to eventually utilize a linear transformer as a feedback device. I actually want to introduce a 'feedback' effect in the tissue
hope this helps,
thanks,
steve
hm, i don't know really, how some standard amplifier chip can tolerate currents returned from your device, but loudspeakers has same "practice"...
You can posibly try some "gainclone" project, it's widely available both at this forum, and at world wide web.
It's simple, inexpensive, and with other components (large power supply capacitors... for example) you can do anything with it...
They is like "power opamp", you can do DC with it, etc.
-Current limit is 7A typical
-and you can use +/-20V power supply
-if your currents are too high, you can do "parallel mode" configuration with two LM3886, and then drive low impedance with him...
Ok, I probably speculate only, but there isn't much more informations...
best regards,
-boggy
You can posibly try some "gainclone" project, it's widely available both at this forum, and at world wide web.
It's simple, inexpensive, and with other components (large power supply capacitors... for example) you can do anything with it...
They is like "power opamp", you can do DC with it, etc.
-Current limit is 7A typical
-and you can use +/-20V power supply
-if your currents are too high, you can do "parallel mode" configuration with two LM3886, and then drive low impedance with him...
Ok, I probably speculate only, but there isn't much more informations...
best regards,
-boggy
Thanks again... I know that I didn't have much info to provide, but you actually addressed my major concern which had to do with the DC offset that I anticipate.... I actually have a couple of 3875's... not to good for the loads that I anticipate.. but I could try to parallel a couple.. Or I could look at the 4870(?)...
I just wanted assurance that I wasn't going to toast my amp by trying to drive such a crazy load.
thanks,
steve
I just wanted assurance that I wasn't going to toast my amp by trying to drive such a crazy load.
thanks,
steve
I would say this sort of driving capability is beyond a chipamp. I would build a discrete amp with a heavy output stage, probably switching mosfets. The emphasis here would be on the output stage having to provide lots of current and deal with quite a severe back EMF.
It might also be an idea to look at discrete, high current regulated power supply circuits. These are normally very similar to amps in design, but with emphasis on handling current.
It might also be an idea to look at discrete, high current regulated power supply circuits. These are normally very similar to amps in design, but with emphasis on handling current.
Either that or use a standard amp design, remove the input and feedback coupling caps and you have a DC amplifier. Beef up the drivers and outputs and away you go. Bigger heatsink and you now have full power.
MikeB just finished a simple amp that would be a good base for this project. Thread starts here
-Chris
MikeB just finished a simple amp that would be a good base for this project. Thread starts here
-Chris
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