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!

 

[sreid]

Possibly a Power Thermistor.

http://www.ametherm.com/

 

[sdavis123]

masa,
As far as switching devices that are capable of being pulsed and 100% duty cycle, have you checked into IGBT's? look at Semikron.com

As far a soft start for the buss. Have you considered a permanent soft start? Quite simply high wattage resistors across the buss fet. You would need to determine their wattage based on short circuit load conditions.

If permanent soft start is not feasible, use soft start resistors and a separate fet that is turned on 100% duty cycle until the buss is charged to the desired level.

If you could provide more details as to what you are trying to accomplish, it may help people to guide you down a reasonable path.

 

[masa6614]

Thanks for your suggestions,
It's just the load will have some large capacitances to charge up to a very high voltage, and I'm afraid the power required of resistors in the path would make them huge and involve alot of heatsink space in what is a space-constrained area already. I just figured the inductor would slow down the inrush and hopefully not be as a big as the resistors.

 

[sdavis123]

Any inductance will in fact limit the rate of charge to the capacitor. And, using the following formula's you can determine the inductance required to achieve the desired charge time. However, I do believe you will find the inductance to be much larger than you expected.

I=c(dv/dt) Plug in desired charge time. solve for I

V = L(di/dt) plug in di based on 0A to I above. Solve for L.