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Problem selecting constant current DC/DC solution

user1661804
Prodigy 20 points
Other Parts Discussed in Thread: INA138, LM3150

Hi guys, Im looking for a synchronous controller able to deliver a constant current of 5 to 10 amp to a 24v 300w haloguen projection lamp.  The trick is, I need to ramp up the current from a cold filament in a controlled way and there is where the constant current powerup mode comes in. Then the lamp will operate in half intensity (pwm) and full power mode( where the pwm controller gets bypassed) and the full power of the external power supply takes over.

The selector guide is mostly directed to constant voltage or led driving but Im having trouble finding a controller suitable for the needs.

Thanks in advance.

  • 0
    TI__Genius 13700 points
    Hello,

    One approach that might be worth looking into is a Power Limiting / Current Limiting hot swap controller.

    Since for >90% of the time this circuit will be in 100% conduction.

    How long is the "warm-up" period?

    This link gives you a parametric search that i have paired down do a handful of devices that might work in your application. The I2C controlled devices would allow you to more dynamically control between warm-up and full power.
    www.ti.com/.../power-protection-monitoring-and-hot-swap-products.page Only;Always&p1498=Catalog

    You will want to parallel FETs for this application to handle the power dissipation during "warm-up" and to reduce conduction losses during full power.

    How accurate does your current limit need to be for the "warm-up" period?
  • 0
    Prodigy 20 points
    Thanks Ryan I was already looking at the current sensing IC's like the MAX4173 or the INA138 to do the job.
    The startup time depends on the temperature of the environment, if I preglow the filament with let's say 5Amp, it takes 3-4 sec for the voltage to rise from almost zero to nominal. Thats why I cannot rely on the overcurrent features of pwm controllers because they monitor the FB voltage and when it falls below 60% vref, they jump into short circuit protection, not what I want.

    The current regulation during preglow is not that critical, I just need to avoid the inrush by limiting the startup current to something around 10A.

    The CC/CV solultion I'm prototyping right now is a LM3150 + MAX4173/INA138 and mixing the current fb with the voltage fb by means of an opamp based superdiode "analog max", this allows the feedback loop to regulate on voltage and on current, whichever rises first above the vref.

    What I am trying to avoid now is the shunt resistor(efficiency).
    Anyone tried before to use these current sensors with the inductor's DCR+ RC matched LPF?