MOSFET ratings
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Posted by Jon Slaughter on April 7, 2008, 9:23 pm
Please log in for more thread options circumstances under normal operating circumstances? e.g., basically if it says X amps and I run it < 80%X or so will everything be ok? i.e., does it essentially include the power dissipation in that value too(in the sense that P_max = X*Rds_ON)? Just not sure if I actually need to calculate anything else if I'm running it under "normal operating conditions"? I'm just trying to find some decent, but not too derated, mosfets(actually H-Bridge) for motor control of about 15A but not sure if they can handle the power dissipation but not sure if the max current rating takes that into account or not. I do see the max power dissipation on the data sheet but I'm a bit confused at how they got it: Dual N & P-Channel PowerTrench® MOSFETN-Channel: 40V, 20A, 24m? P-Channel: -40V, -20A, 54m? Features Q1: N-Channel ??Max rDS(on) = 24m? at VGS = 10V, ID = 9.0A ??Max rDS(on) = 30m? at VGS = 4.5V, ID = 7.0A Q2: P-Channel ??Max rDS(on) = 54m? at VGS = -10V, ID = -6.5A ??Max rDS(on) = 70m? at VGS = -4.5V, ID = -5.6A ??Fast switching speed ??RoHS Compliant How can it be both 20A and 9A? Thanks, Jon | ||||||||||||||||
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Posted by Joerg on April 7, 2008, 9:28 pm
Please log in for more thread options Because the marketing guy sez so? Seriously, look at the guaranteed Rdson at your drive level and nothing else. Graphs are just typical data and I never design by those. And the marketing glitz, well, you know. Be conservative. If in doubt take a biger FET. -- Regards, Joerg http://www.analogconsultants.com/ | ||||||||||||||||
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Posted by Eeyore on April 8, 2008, 12:26 am
Please log in for more thread options
Jon Slaughter wrote: > Does the current rating of a mosfet take into account all maximum
> circumstances under normal operating circumstances? e.g., basically if it > says X amps and I run it < 80%X or so will everything be ok? i.e., does it > essentially include the power dissipation in that value too(in the sense > that P_max = X*Rds_ON)? There's more to power dissipation that that alone if it's switching such as turn on and off losses during which it's operating in a linear way. Graham | ||||||||||||||||
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> circumstances under normal operating circumstances? e.g., basically if it
> says X amps and I run it < 80%X or so will everything be ok? i.e., does it
> essentially include the power dissipation in that value too(in the sense
> that P_max = X*Rds_ON)?
>
> Just not sure if I actually need to calculate anything else if I'm running
> it under "normal operating conditions"? I'm just trying to find some decent,
> but not too derated, mosfets(actually H-Bridge) for motor control of about
> 15A but not sure if they can handle the power dissipation but not sure if
> the max current rating takes that into account or not. I do see the max
> power dissipation on the data sheet but I'm a bit confused at how they got
> it:
>
> Dual N & P-Channel PowerTrench® MOSFETN-Channel: 40V, 20A, 24m?
> P-Channel: -40V, -20A, 54m?
> Features
> Q1: N-Channel
> ??Max rDS(on) = 24m? at VGS = 10V, ID = 9.0A
> ??Max rDS(on) = 30m? at VGS = 4.5V, ID = 7.0A
> Q2: P-Channel
> ??Max rDS(on) = 54m? at VGS = -10V, ID = -6.5A
> ??Max rDS(on) = 70m? at VGS = -4.5V, ID = -5.6A
> ??Fast switching speed
> ??RoHS Compliant
>
> How can it be both 20A and 9A?
>