Hi !
I want to make an inverter from 12VDC to 220 VDC with UC3845 IC with a flyback transformer.
Transformer needs 8A and i choosed IRF740 N-FET.
I don't know of my math is good when i calculate the juction temperature and if will work.
ThetaJc is 1 degC/W and RDSon is 0.55
P = I^2 * RDSon.
P = 8^2 * 0.55
P = 35.2W
Junction temperature is 35.2W * 1 = 35.2 degC <- much smaller than Tj = 150 deg
or This one
(max temperature - ambient temperature) / degrees per Watt = Max Watts
(150 - 25) / 1 = 125W
P = I^2 * RDSon
125 = I^2 * 0.55
I^2 = 125*0.55
I^2 = 68.75
I = sqrt(68.75)
I= 8.29A max else it will melt
How do i know what's the real temperature ?
I want to make an inverter from 12VDC to 220 VDC with UC3845 IC with a flyback transformer.
Transformer needs 8A and i choosed IRF740 N-FET.
I don't know of my math is good when i calculate the juction temperature and if will work.
ThetaJc is 1 degC/W and RDSon is 0.55
P = I^2 * RDSon.
P = 8^2 * 0.55
P = 35.2W
Junction temperature is 35.2W * 1 = 35.2 degC <- much smaller than Tj = 150 deg
or This one
(max temperature - ambient temperature) / degrees per Watt = Max Watts
(150 - 25) / 1 = 125W
P = I^2 * RDSon
125 = I^2 * 0.55
I^2 = 125*0.55
I^2 = 68.75
I = sqrt(68.75)
I= 8.29A max else it will melt
How do i know what's the real temperature ?