| neutron7 |
I was wondering if it would be safe to power an electromagnet from a chip amp. since an electromagnet is similar to a speaker coil.
I would use/make electromagnets with properties as similar as possible to a speaker.
According to my rough calculations the electromagnet would need to be powered by about 5 watts (at audio frequencies)
It is for an electromechanical music synthesiser experiment. |
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| johnnyx |
| Yes, I've done it, but an opamp with complementary output transistors is cheaper. No need to bias the transistors, tie the bases together and connect to the opamp output via a 100R resistor. I used the latter method to drive a motor. I would use power diodes connected between the output and the supply rails to catch back emf spikes from the solenoids. It's a case of matching the requirements of the solenoid to the capabilities of the chip amp. The problem is fast switching spikes, they can destroy a chip.:bawling: |
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| jackinnj |
| yeah, you can do it, but better off and much more effective using an H-Bridge chip or a quad of MOSFET's arranged in an H-bridge. The chipamp is really set up for bipolar operation. |
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| neutron7 |
Well the thing is i would like to vary the strength of the electromagnet with an audio signal. it will not be switching on and off any quicker than a speaker would be moving.
anyways i will give it a try. |
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| jackinnj |
so you use a pulse modulating chip -- like the LM3524 (SG3524) or SG3525 -- Velleman has a kit which is only a few Euro which demonstrates the principal. By varying the duty cycle (time on/total time) you can control the strength of the magnet. There is an error amplifier input on these chips which can take the audio input,
the LM3524 also has current limiting -- something lacking in the chipamp.
this is much simpler than using a chip-amp, it can be single supply so no head games with biasing the chipamp, and no compensation worries, etc. |
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| macboy |
| quote: | | so you use a pulse modulating chip |
You are assuming that the magnet needs to be fully on or fully off. That is not necessarily the case.
Simply feeding an audio signal into the electromagent could have interesting results.
neutron7: make sure that the electromagnet's coil has a resistance about the same as a speaker: 4 to 8 ohms (or higher). |
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| jackinnj |
| think of it as a digital amplifier. |
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| xocoatl |
macboy,
You meant total impedance, not resistance. Right?
Sorry but i'm a newbie.
--
Szymon |
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| jackinnj |
Szymon -- dzien dobry
exactly, di/dt isn't instantaneous! |
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| xocoatl |
Jack,
Thanks. ;)
I think I'll go back to my "teoria obwodow", as i have an exam next month. :dead:
I was asking becouse i'm planning an experiment. OPA541, some magnetic wire and neodymium magnets...
An I'm curious if i need to place additional resistor between OPA and the coil.
Szymon - trying to reinvent a transducer |
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