×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

High Voltage Bus soft-start

High Voltage Bus soft-start

High Voltage Bus soft-start

(OP)
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!  

RE: High Voltage Bus soft-start

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.

RE: High Voltage Bus soft-start

(OP)
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.

RE: High Voltage Bus soft-start

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.
 

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources