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Voltage tripler with PWM signals

Discussion in 'General Electronics Chat' started by Gabriel Sá Pinto, Jul 6, 2017.

  1. Gabriel Sá Pinto

    Gabriel Sá Pinto Member

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    I chose the Load to hold 5A for 3.3V rail, thus the 0.66 ohm. The thing is with a gate driver I can't change the current through the load, it's just always the same...
    I'm using a UCC27531 from TI, I can't change neither the gate voltage and by consequence neither does the current. Am I doing something wrong, or is it just how it's supposed to work? Circuit in attachment.
     

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  2. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The output pulses from the gate driver are always at the power supply voltage of 15V. As the capacitor is charged a little with each pulse then the gate voltage increases a little and the Mosfet begins to conduct current through the load.
    Your circuit has nothing to discharge the capacitor so the Mosfet does not vary the output current if you vary the width of the pulses.
     
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  3. Gabriel Sá Pinto

    Gabriel Sá Pinto Member

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    Mosfet Driver is a no-go for this project. I've figured out a decent low Rds logic level mosfet for my applications, however yet another problem has come up (what a surprise).

    Since I'm following the previous referred instructable (https://www.instructables.com/id/Arduino-Programmable-Constant-Current-Power-Resist/) I included an op amp before the MOSFET to make a follower, however the guy from the project in the instructables site used a stability loop between the op amp and the MOSFET and I don't understand how he calculates those values, I used the same values just try to test even though his MOSFET is different than mine.

    The thing is, with or without stability loop I get the same weird response from the output of the op amp, it goes instantly up when responding to a ramp voltage and then slowly, why does this happen? This feature will not allow my application to work as intended... Circuit bellow.

    Once again thank you for your patience.
     

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