Isolating a board from actuator and position sensors

Brian, I had a customer ask this recently.  How can we help?

I have a processor board that needs to be isolated from an actuator and position sensor.  From the processor board I need to provide 5V of isolated power at about 1W to the actuator. The switching regulator that I built with an optocoupler feedback seems to be fine for static loads but when the motor runs the output voltage does not stay stable and bounces around by several volts.  The problem is that the load current on the isolated 5V changes from 50mW to 1W when the actuator runs at a rate of 10ms/cycle.  Using a simple open loop switcher and linear regulator is not an option because the efficiency loss.  I am looking for a simple isolated 5V to 5V regulated DC supply that is less expensive than a module. Also, the  FPGA on the processor board has a standard SPI port to communicate with the actuator and position sensor that also needs to be isolated.  I don’t have a lot of space on in my PCB.

Message was edited by: rdowning

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    •  Analog Employees 
    on Mar 16, 2011 5:10 PM

    Sometimes if you don’t choose the correct L and C to filter the load current or if the feedback is not compensated correctly, the switching regulator feedback loop can become unstable.  Maybe if you used a switching controller that had the feedback built in and is stable under all conditions then you won’t have to worry about the load variation causing the output voltage to become unstable.  The ADuM3471  is a switching controller that has an iCoupler PWM feedback built in and should be stable for the types of loads that you are talking about.  In the data sheet there are application circuits that have transformers specified from Halo and Coilcraft for 5V to 5V applications.   The ADuM3471 also has 4 channels of digital isolation that you can use to isolate the SPI port to further save space and eliminate any optocouplers that you might be using for the data channels.

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  • 0
    •  Analog Employees 
    on Mar 16, 2011 5:10 PM

    Sometimes if you don’t choose the correct L and C to filter the load current or if the feedback is not compensated correctly, the switching regulator feedback loop can become unstable.  Maybe if you used a switching controller that had the feedback built in and is stable under all conditions then you won’t have to worry about the load variation causing the output voltage to become unstable.  The ADuM3471  is a switching controller that has an iCoupler PWM feedback built in and should be stable for the types of loads that you are talking about.  In the data sheet there are application circuits that have transformers specified from Halo and Coilcraft for 5V to 5V applications.   The ADuM3471 also has 4 channels of digital isolation that you can use to isolate the SPI port to further save space and eliminate any optocouplers that you might be using for the data channels.

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