Push and Pull current from voice coil linear actuator from ADC output of 0-5V

[faizan_zaheer]

Hi members

I am Faizan. I am designing a circuit for driving a voice coil linear actuator with R=18 ohms and operates fully at a 5V supply. I want to make a current source and sink circuit so that I can source and sink current from the voice coil to produce back-and-forth linear motion. Right now, I am using an op-amp with a transistor as a current source buffer which provides variable voltage supply by varying input voltage between 0-5V at op-amp input generated by ADC and it also varies source current according to voltage set.
But, to produce reverse backward movement, I need to place negative voltage on a coil or sink current from it after supplying it with 5V. How can I design a circuit to both source and sink varying current from it by varying voltages from 0-5V with a 2.5V split? The Howland current pump is the way but it will always maintains a fixed current regardless of the input voltage to the load? Thanks.

[Terry Bites]

H-bridge motor driver?
L9110H will handle 800mA continuous.

[Benta]

H-bridge motor driver?
L9110H will handle 800mA continuous.

That would work for bang-bang control.
For linear control, I'd suggest a bridge-coupled audio power amplifier.

[Tim S]

Voice coil motors are not easy to implement, they require something to push/pull against otherwise all they do is shoot end to end like a doorbell solenoid.
Options are
1) use a spring to push it to one end then drive against the spring. The position is dependant upon current flow. The spring must be arranged to exert a constant force over the range which excludes sticking it on the end. The spring cannot move more than 10% of it's length - the shorter the better.

2) use a position feedback and servo to the required position. Difficult as you will need a linear position feedback.

Whatever you do, analogue class B like a speaker driver is the way to go. Things may get warm, but get it working on analogue first.
Good luck!

[mawyatt]

An LM1875 might work in a bridge configuration. The Juntek 1698 has a pair of LM1875s that is used for a DC Coupled Buffer Amp for AWGs. Should be easy to configure to check out how these LM1875s behave driving a Voice Coil Motor.

Best