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Old 15th July 2008, 06:36 AM   #1
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Default hwo to identify max switching frequency of a MOSFET

Hi all,

Can anyone help me to identify the maximum operating frequency range of IRPB450 power MOSFET.

http://www.euroelektronik.com.pl/sit...rs/IRFP450.pdf

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Old 15th July 2008, 08:49 AM   #2
Corax is offline Corax  Germany
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The switching speed (measured in V/s for instance) of such MOSFETs is basically determined by the value of the gate resistor (which prevents unwanted oscillation) and the current capability of the gate driving circuit.
Since the gate is isolated from the drain and source pin it reacts as a capacitor and therefore to charge/discharge a capacitor with a certain speed a(n un)limited current is necessary to perform that task.

So, without knowing the circuit, you're using this MOSFET in, it's almost impossible to make any predictions on how far you can drive the switching frequency. Post the schematic and someone might be able to calculate/predict the maximum switching frequency.
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Old 15th July 2008, 03:07 PM   #3
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could that IRFP 450 mosfet operate at 100KHz frequency.
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Old 15th July 2008, 04:59 PM   #4
Eva is offline Eva  Spain
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Your question does not make much sense. You can usually get over 30Mhz bandwidth from 500V/600V TO-247 MOSFET and over 70Mhz from TO-220 ones.

Switching losses and gate drive losses are the actual limiting factors for operating frequency, not the "speed" of the MOSFET itself.

BTW: 100Khz is hardly a problem for any MOSFET.
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Old 15th July 2008, 05:17 PM   #5
Tahmid is offline Tahmid  Bangladesh
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Hi,
100kHz is hardly a problem for IRFP450. I have used it upto 200kHz with no problems.
You can calculate the maximum switching frequency of the MOSFET from the datasheet by calculating the turn on and turn off time / propagation delay time.


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Old 16th July 2008, 01:48 AM   #6
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[QUOTE]Originally posted by Tahmid
[B]Hi,
100kHz is hardly a problem for IRFP450. I have used it upto 200kHz with no problems.
You can calculate the maximum switching frequency of the MOSFET from the datasheet by calculating the turn on and turn off time / propagation delay time.


so u mean to say that the formula to calculate the max switching frequency of a MOSFET is = ( turn on delay time + turn off delay time) / ( rise time + fall time).....please correct if im wrong.
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Old 16th July 2008, 04:16 AM   #7
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jegandren,

Eva answered your question in post #4. Any switching device (MOSFET) has losses associtaed with the switching, and it also has conduction losses. Together these will determine the maximum switching frequency. Stated diffferently,
Psw=(Eon+Eoff)*Freq+DutyCycle*(Pcond). You also need to consider the losses, if any, in the free wheeling diode.

Rick
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Old 16th July 2008, 07:27 AM   #8
Eva is offline Eva  Spain
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In other words:

It's the amount of residual heat produced in every switching event what limits the maximum allowable number of events per second.

You would burn most MOSFET before getting close to the frequency limit imposed by switching times.
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Old 17th July 2008, 07:12 PM   #9
golam is offline golam  Bangladesh
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Hi jegandren,

Do not bother for max. frequency as most of the mosfets can be operated at MHZ range if you can use proper configuration. Since you are new in this field, instead of going for 100 khz, you should try first with 30 khz range, then try 100/200 khz range and you can be rest assured that irfp450 is capable to take you more than that range.

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