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Switching losses of mosfet

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srinu9009

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mosfet switching losses

Hi all

i am designing DC-AC full bridge inverter.i am using mosfets.i would like to know power losses of mosfets.I do not know how to caliculate switching losses of mosfet.If any one knows,please kindly send design or application note or your own notes.

I am using irf1010zpbf mosfet and NCP5111 drivers.
 

switching losses in mosfet

Why are you so much worried about switching losses, what's the operating frequency of inverter and how much KW of enegry will pass through it?
 
switching losses of mosfet

Hi

My inverter switching frequency is 20KHz and power is 300VA.Please send caliculations
 

mosfet switching

You can do little maths yourself too.

57_1240040406.jpg



Where:
Pswitching = Losses during turn on and turn off (W)
Pon = Conduction losses when the switch is on (W)
Ptotal = Total losses (W)
Pin = Input Power (W)
n= Efficiency (%)
Vs(off) = Blocking voltage when switch is off (V)
fs = Switching frequency (Hz)
ton = Time taken for the switch to turn on (s)
toff = Time taken for the switch to turn off (s)
Ion = Conduction current (A)
D = Duty Cycle
Rds = “On” resistance of the device ( )
 
switching losses mosfet

Hi umery2k75 sorry i do not u r name.

Thank you very much for your reply.I know whatever the formulas you sent to me.But i do not know how to caliculate ton and toff times theoretically .i would like to know these values before going to testing or practicall implemenation of any converter or inverter.

i have one reference design of pushpull converter.in that they caliculated switching losses but i cannot understand it.

please see attached refernce design
 

switching losses

well in truth,

you just do by intuition.

draw out your I & V waveforms at switch on and switch off....

approximate using straight/slanted lines...........then you get triangles............

find the energy in a triangle by integral of V * i(t) over time.

VIt/t = power loss

then just add 'em up since they happen every time it switches.

please do not look for the formula-from-heaven as you will spend the rest of your life looking for it next time.

otherwise, just say its 30% of on-state losses for each fet
 

fet switching losses

Hi,
I would just like to ask, how to make PSpice calculate the average power disipation on a Mosfet? Basically you have to calculate the integral of W() divided by time. I tired this:
fpa7at.png


But It's an "Error: Invalid expression.". But I'm not sure that the AVG is the right function for the job anyway, since the timestep isn't constant. So, how do you guys measure average power?

George
 

average switching loss for mosfet

avg is the right function for power dissipation.

your expression looks correct. i do not know why there is an error. i have done that many times no problem.

Mr.Cool
 
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