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According to the IRF740 data-sheet from IR or from Vishay (they are nearly the same, the Vishay is better to read), the Qg is specified as 63nC under Id = 10A Vds = 320V and Vgs = 10V.

But at page 4, Fig. 6 - Typical Gate Charge vs. Drain-to-Source Voltage, The graph shows that under the same conditions the Qg is ~45nC. Its 63nC at a Vgs = ~15V.

Is the data-sheet that have a error or I'm interpreting it wrong?

Typical Gate Charge vs. Drain-to-Source Voltage graph

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Sorry, but you're interpreting it wrong. The 63 nC is a maximum figure, while your graph shows typical Qg - which is, as you might expect, less than the maximum.

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The value in the table is a maximum value.

The curve in the chart is a typical characteristic.

The charts almost always show typical values, not specification limits.

I assumed the graph showed the maximum value too

enter image description here

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  • \$\begingroup\$ As it generally better to dimension the gate-drive for the worst case, I assumed the graph showed the maximum value too. Anyway that's just talking about the data-sheet, thanks for the answer. \$\endgroup\$ – Diego C Nascimento Feb 10 '15 at 4:55
  • \$\begingroup\$ It's on page 3, the title of the section of the datasheet that contains all the charts is "Typical Characteristics". \$\endgroup\$ – The Photon Feb 10 '15 at 4:56
  • \$\begingroup\$ Yes, even that's only present at the Vishay datasheet, the graph itself says "Typical Gate Charge vs. Drain-to-Source Voltage". \$\endgroup\$ – Diego C Nascimento Feb 10 '15 at 5:01
  • \$\begingroup\$ As the graph seems linear above certain Vgs (but this is a so dynamic property), would interpolating between the max/typical value at Vgs = 10V to get the maximum value at Vgs = 15V or some common safety margin? \$\endgroup\$ – Diego C Nascimento Feb 10 '15 at 5:15
  • \$\begingroup\$ @DiegoCNascimento 1. You say " ...Yes, even that's only present at the Vishay datasheet, ..."-> NO both data sheets make it clear what is max and what is typical. 2. Also, graphs are always typical unless stated otherwise. 3. This is engineering !!!!!!!!!!! 45 = = 63 = = 50 == 45 ==70. ie you are extremely unlikely to have to have the sort of precision you are aiming at in Q. \$\endgroup\$ – Russell McMahon Feb 10 '15 at 5:22

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