# Amplification Circuit for Generating High-Current Sinusoidal Signal to Feed a Coil

I am trying to implement a control algorithm using Arduino Due. I need to generate high-current constant-frequency sinusoidal signals to feed a coil using some batteries. The coil will generate electromagnetic force.

I want to design a circuit that amplifies a reference sinusoidal signal from the DAC0 and DAC1 of the Arduino Due and feeds the coils with the same-frequency but high-current sinusoidal signal. What is a simple, reliable way to do that?

The amplified current should be the same over a frequency range of the reference sinusoid, say 10Hz to 100Hz or some other range, and I want to generate the almost largest possible electromagnetic force.

I have two 12V Li-Po batteries but I can buy other batteries. I also have DC-DC converters if any needed.

There is no restriction on the frequency range. Basically, I have 3 coils and each coil can be fed with an arbitrary frequency but different from other coils. The resistance of each coil is approximately R=16 ohms and the inductance is L=0.070 H. The impedance is (R^2+w^2*L^2)^(1/2), where w is the frequency of the sinusoidal current in rad/s. I need about 3 A but I would like to get higher.

The coil is made with 22 AWG magnet wire with a polyamide overcoat as the material for current-carrying conductor of the coil. Multilayer multirow winding is used. Right now I have 500 turns and the radius of coil is 0.1 m. Max current about 5A and about 0.01 N force. Duration about 30 s.

Design Goal: A simple, reliable circuit that accomplishes the above force

Hope that I have provided enough information

Any help is appreciated.

• I have rolled back your deletion of the question as it already has an answer. Commented May 25, 2020 at 19:24

Force is proportional to current and Inductance.

For 100Hz ( 628rad/s ) your R/L ratio must be T<=1ms .

So using Litz wire with the most turns and diameter and core permeability is what you need with an inductance and resistance calculator for the best Litz wire you can get. (most strands)

Matching the ESR of the batteries to the DCR of the Coil will maximize your power transfer but also load you batteries to the max. which must be minimized by prudent low duty cycle.

Now if you know how to measure battery ESR, and capacitance in kiloFarads , you can use the same conjugate impedance for the coil for the theoretical max. power transfer. Everything is a compromise when you realize how big that is, then you have to cascade coils or think outside the box.

• Thanks for your answer. The focus of the question in my mind was on designing the circuit. After that I need to maximize the power transfer. Can you provide some guidance on one amplification circuit that does what I want? Commented May 21, 2020 at 17:33
• Never design until you have specs, then add more detail until you understand the requirements. Otherwise it is like me telling you how to jump off a cliff and land in water with no experience. Consider DCR of coil and choose an H bridge that can drive 10x the current you plan to use for sufficient efficiency. Commented May 21, 2020 at 17:37
• Okay, I really appreciate your help. I added more details to the question just in case you can provide more guidance. Thanks Commented May 21, 2020 at 17:40
• Not possible unless you define all the physics variables for output and supply Commented May 21, 2020 at 18:41
• I agree that my question is vague. The point is that I want to design a small experiment and I can buy anything with reasonable price. Could you please answer this? For a given coil, if I use an H-bridge, will it provide the same output current when I change the reference frequency say from 100Hz to 50 Hz? Thanks Commented May 21, 2020 at 19:12

Here's a rough estimate of what you need.

You have a coil with an inductance of 70 mH, and you want to pump a sinusoidal current through it of 3 A, at a max frequency of 100 Hz, right?

The coil's reactance at 100 Hz is 44 ohms (6.28*100*.07). The coil's DC resistance is 16 ohms. Adding these two together gives us 60 ohms.

To drive 3 amps through 60 ohms requires 180 V.

So what you basically need is an audio amplifier that can supply an output voltage of 180 V, or +/-180 V if the 3 A sine wave is centered about zero. That's pretty sporty.

Note that the voltage scales inversely with the frequency. If the frequency is only 10 Hz, you only need +/- 60 V, much more manageable.

I may have missed an RMS factor here. If I did, someone will correct this .