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Author Topic: How best to supply 1v output for a low impedance device  (Read 595 times)
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Letchworth Garden City
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Dear Forum,
I wish to control an acousto-optic modulator MOD input which requires a variable input between 0 and 1 Volt. This input control the power output from the device. I have tried this with a National Instruments DAQ card but it doesn't supply enough current. Since I need to build something to provide more current for this low impedence device, I thought I could use an Arduino instead.

Any suggestions for either a low cost variable voltage driver that can be controlled via the arduino using logic commands, or a circuit to convert a PWM signal to a voltage but with an amplifier to provide more current.

I will need to provide 3 separate outputs for three different acousto-optic devices.

Thanks,
Nick H
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Montreal
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Quote
it doesn't supply enough current.
And what is that?
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Letchworth Garden City
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I am not sure exactly how much current is required. I cannot find that information in the specifications but I think that 500 mA per 0-1V output would be plenty.
NickH
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500 mA is about battery charging current, so same design would works. Download AVR451 app. note from atmel.com, there is drawings 3-3 which shows two channel PWM - current converter based on OPA + MOSFET.  Be aware, that PWM may be not right approach, as there is low response time and low resolution 8-bit (default). External DAC may be better solution, interfaced with same OPA+MOSFET driver.   
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Shannon Member
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Do you have the specifications to hand - there might be a clue - I'd not recommend trial and error for something like this, rather expensive.  Also it doesn't sound right that a control input would need 0.5A at 1V.   Does this control input have a BNC socket perchance?  That would be a mighty big clue.

Also what are the output specs for that DAQ card?
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Letchworth Garden City
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Thanks for the various replies. I think I will use a benchtop power supply with a current readout to find out how much current is required. The PWM-op amp-mosfet idea is a nice one and I had not thought of a battery charger as a model to follow. Although the response time and sensitivity of a PWM approach is not going to be fantastic, this shouldn't be an issue because once set, it is not likely to be changed. I have a Pockels cell to control the power and that will be controlled with a DAQ device with a much faster update rate and sensitivity.

Thanks,
Nick
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Thanks for the various replies. I think I will use a benchtop power supply with a current readout to find out how much current is required. The PWM-op amp-mosfet idea is a nice one and I had not thought of a battery charger as a model to follow. Although the response time and sensitivity of a PWM approach is not going to be fantastic, this shouldn't be an issue because once set, it is not likely to be changed. I have a Pockels cell to control the power and that will be controlled with a DAQ device with a much faster update rate and sensitivity.

Thanks,
Nick

Yes, find out the actual requirements of the control signal, then the best/simplest method will be much easier to determine. Can't believe there would be a 500ma requirement for a control signal.

Lefty
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My money is on 50 or 70 ohm BNC input.
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