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DAC0801 with OPA541 as voltage follower, single supply

  1. Aug 8, 2014 #1
    Hi all,

    I'm attempting to use a DAC0801 and an Arduino to control the current through an LED ranging between 0.0 and 1.0 Amps. I tried to supply the DAC with a single power supply as shown in This Tutorial. Unfortunately, the maximum output current is several mA. Would I be able to power an OPA541 opamp with the same (12V) power supply and raise the max output current to 1 Amp?

    Any suggestions are welcome!

    (Also sorry if this is too basic a question, I'm just starting to dive into EE!)
     
  2. jcsd
  3. Aug 9, 2014 #2

    Baluncore

    User Avatar
    Science Advisor

    I do not believe that the solution needs to use a high current op-amp.
    An op-amp is designed to produce a voltage output, here you need a current.

    If you set the Iref of the DAC to 1 mA, then you can get the 1 amp maximum current by selecting the ratio of two resistors.

    The attached circuit uses an op-amp with a P'channel MOSFET to generate the output current. The maximum output of 1 mA from the DAC will drop 1 volt across the 1k resistor. The op-amp will adjust the MOSFET gate until a current sufficient to drop 1V across the 1 ohm resistor flows through the LED. LED current will be proportional to DAC output current.

    The MOSFET will need to dissipate a maximum of 12 watt, it will need a heatsink. The op-amp must be chosen to operate with common mode voltages including the +ve supply rail. The 1 ohm resistor will need to be rated at 1 watt.
     

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