Single-supply DAC controlled bidirectional current source?

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#1
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Hello all,

I have an analogue problem which I hope someone can push a hardware-challenged software person (me) in the right direction :)

What I need to do is precisely set control the amount of current flowing through a coil from software (it generates a magnetic field). I figure a DAC controlled current source of some description is the best option. Nominal coil resistance is 10-20 Ohms with a horrible tempco (3000 ppm/degC, apparently).

The current must be able to flow both ways from -25mA to 25mA.

Ideally, I'd like a single supply to do this, as I already have a clean +5V rail. Any other rails I would need to generate.

The best solution I have managed to dig up so far is a DAC controlling a Howland Current Pump, but requires dual supplies (and, from what I gather, +/-15V supplies for the +/- 25mA current).

Since the coil doesn't need to have one end connected to ground, I'm wondering if there are any better options - say, with the load as part of a feedback loop or bridge arrangement.

Is there a op-amp topology that I should look at that might do the job?

-- Damien

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Use one of these

http://www.analog.com/en/digital...

with a bipolar op amp driver?

You are probably going to need a dual supply, whatever parts you use.

Leon Heller G1HSM

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A single supply full bridge audio power amp ic and a linear tech bi-directional current monitor might do it.

http://cds.linear.com/docs/Application%20Note/an105.pdf

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To get 25mA into 20Ohm requires 0.5 Volts, so
a singe 5V supply design should be possible.

First generate a stable 2.5V mid-point voltage
by using a opamp that can deliver 25mA. Then
design a Howland current source also using this
midpoint as reference. The coils is connected also to the midpoint with one terminal. Problem: the driving
voltage must also be referenced to this midpoint
voltage.