High Voltage Bus soft-start

[masa6614]

Hi,
If I was trying to use provide a soft-start to a High Voltage bus, i was thinking of PWMing the bus FET and using an inductor to limit the inrush current while the Load's input Caps are charging. I couldnt find any mosfet or igbt gate driver chips that would stay on 100% duty cycle after the soft start, so was thinking of doing something like this pics. Does this seem like it'd work? Anyone know of a half-bridge IC that would work, and would also have the ability to switch on the high side permanently once i'm done with the soft-start? Or would i need to just turn off the chip completely, and provide control for another high side switch to keep the +315V at the bus FET gate?
And im having no luck finding the 600 to low voltage DC converters.

Thanks alot!

 

[RCinFLA]

In rush current limiting is usually done with a current sense on input line. You can do a slow output voltage ramp if you know the load and filter cap value. Some buck switcher I.C. have this current sense function but I doubt you can find an I.C. for 600 vdc control. When you reach desired voltage you could shut down the buck switcher and force the series pass MOSFET into full on.

 

[masa6614]

thanks alot

 

[MikeMl]

I do this for the 3500V supply on my KiloWatt RF amp. It is a 240V-primary transformer, rectifier, filter-capacitor, and bleeder resistor supply. I put a current-limiting resistor in series with the transformer primary. The 50W wire-wound resistor is sized to limit the in-rush current while the capacitors charge. A relay (120Vac coil in-series with a 10W wire-wound slider adjustable resistor) is wired across the transformer primary downstream from the current-limiting resistor.

The adjustable slider resistor in series with the relay coil is adjusted so that the relay does not pull-in until the initial current surge (for charging the filter capacitors) is over (about 1/2 second). When the relay pulls-in, its N.O. contacts short out the current-limiting resistor, applying the full 240V line voltage to the transformer from that point on...

This has been in service for 20+ years.