I'm trying to design a quick startup network for the controller UCC28704. See picture attached. The datasheet suggests using a depletion MOSFET, but in my case it is hard to find them with high voltage for this application, so I'm using a enhancement MOSFET. The circuit attached is from a reference design, and I'm trying to calculate the time it takes to charge C7 and start the controller at the minimum and maximum input voltage levels. I mean, how much it takes when input voltage is 100VAC, and when it is 600VAC? The NTC pin just supplies a current when the controller starts so it turns off the MOSFET. I want to have startup time about ~10 ms, and the circuit with the FET is meant to substitute the commonly used lossy RC network.
Do you know other startup approaches?
Do you know other startup approaches?
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