250 kHz Mosfet Switching question

Thread Starter

savage67

Joined Oct 3, 2006
27
Is Switching a power mosfet possible at 250 kHz under 30 A rms current?
Do you have any experiment on this issue.
I want to design a boost converter
Vin=24
Vout=280
P=700W
f=250 kHz is possible for switching.
 

MasterSnow

Joined Jan 18, 2009
22
Those are things that the MOSFET's datasheet ought to tell you I think. I'm no expert, but I believe that the key parameters are how fast you can dump the MOSFET's gate charge as well as if the MOSFET can handle the switching losses at those frequencies.
 

SgtWookie

Joined Jul 17, 2007
22,220
You're going to have a mighty hard time.

Just a quick look at my MOSFET datasheet collection turned up this:
PDP MOSFET
IRFP4242PbF, Vds(min)=300, Rdson=49m, Irp=93A
Total gate charge = 165nC typ; 247nC max (Vdd=150,Id=33,Vgs=10)

Now this PDP MOSFET meets your requirements for Vdss and current.
However, look at that gate charge; it's enormous! (Gate charge is typically a function of Vdss and Rdson/Id ratings)
You would wind up with lots of heat just from trying to quickly charge and discharge the gate that quickly, and don't forget that while you're charging/discharging the gate that the MOSFET is in it's linear region (ie: partially conducting) so it's dissipating power as heat.

I'd say you'd even have a hard time switching that MOSFET at 70kHz, or about 28% of your desired switching speed. You would need a very capable gate driver.

You can compensate for lower switching speeds by increasing the size of your inductor.

I suggest you investigate other/different switch supply topologies.
 

John Luciani

Joined Apr 3, 2007
477
280V out at 700W output is not a trivial design and has lethal voltages.

There are a number of companies that manufacture power converters
that switch FETs at frequencies of 1-2MHz at currents of 30A.
Vicor (http://www.vicr.com) is one of them.

(* jcl *)
 

lmartinez

Joined Mar 8, 2009
224
I would suggest for you to increase the DC voltage source to minimize the ampacity handled by the mosfet devices. Hence, the switching frequency can be reduced to accomplish your goal.
 

steveb

Joined Jul 3, 2008
2,436
Is Switching a power mosfet possible at 250 kHz under 30 A rms current?
Do you have any experiment on this issue.
I want to design a boost converter
Vin=24
Vout=280
P=700W
f=250 kHz is possible for switching.
That switching speed is definitely possible, but achieving the speed, power, voltage and current you specified is difficult.

I can't be sure, but this part might work for this application.

STE45NK80ZD

see attached spec sheet.

I once had an application with similar specs and was thinking about using this device, but the project was cancelled before I got too far. I knew I had this datasheet at work, which I just found when I got back to the office today. That's why it took me so long to answer. Sorry about the delay.
 

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