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Derating MOSFET for High Frequency Application

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pradhan.rachit

pradhan.rachit

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Hello Experts,

I am building a Full Bridge DC-DC Converter with the following ratings:

Vin: 150V
Iin: 10.5A
fs: 35kHz

I'm having problems in selection of the MOSFETs. How do I derate the MOSFETs and operate it in the SOA on the basis of high frequency operation?

I couldn't find any plots of the derating to be made on the basis of switching frequency. I assume that I cannot take the continuous drain current while selecting the MOSFET? If not, is there any way to derate the MOSFET at the selected operating frequency?

- Rachit
 

Hi,

there is no "derating vs frequency" chart in the datasheet.

Look for "switching loss". It mainly depends on:
* Mosfet (gate charge)
* gate driver capability (gate driving current)
* DC voltage (150V)
* switching current (usually more than the 10.5A)
* switching frequency (35kHz)
There are lots of application notes. Look at MOSFET manufacturer´s internet sites.

****
and the MOSFET has conducting loss:
about: I_avg ^2 * R_DS_on / duty_cycle

Klaus
 

Total transistor losses of power switch are comprised of conduction and switching losses.

Switching losses depend on off-state voltage, on-state current, rise-/fall time and switching frequency. It's no datasheet parameter because it varies according to application circuit and respective waveforms.
 

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