denci Posted May 8, 2016 Report Share Posted May 8, 2016 Hello,ia have one question regarding heatsink temperature, so i have two IRFP460 mosfet on pretty big heatsink en testing on 4A current and i measured temperature on heatsink after one hour arround 80 degrees, so high. I made calculation and says:P_Dmax=5A*(12V-(5A*0.1Ω)-5V)=5A*6.5V=32.5WSo max power dissipation is one transistor is 32.5W, thermal resistance THj-c is 0.45C/W. why then so high temperature, i select pretty bigger heatsink that it sould be regarding my calculations?? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 9, 2016 Report Share Posted May 9, 2016 Simple arithmetic error.5A x 0.1 ohms= 0.5V. 12V - 0.5V= 11.5V. 5A x 11.5V= 57.5W.The heatsink thermal resistance might be 1 degree C per Watt and the thermal grease might be 0.5 degrees C per Watt. The ambient might be 30 degrees C. Then the heatsink will be very hot and the chips inside the Mosfets might be hotter than allowed. Quote Link to comment Share on other sites More sharing options...
denci Posted May 9, 2016 Report Share Posted May 9, 2016 Yes, but what with 5V voltage drop on 0.5E dischatge resistor? Is this nedd to take into account, or? Now i tasted with 4A, so 2A only through each mosfet and i measured 75degree per C on heatsink so from calculation is junstion temperature is allowed range.Is that not truth? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 9, 2016 Report Share Posted May 9, 2016 The datasheet for your Mosfet will tell you its maximum rated temperature and its thermal resistance. Quote Link to comment Share on other sites More sharing options...
vialop Posted May 30, 2016 Report Share Posted May 30, 2016 You didn't say if the current is AC or DC, and you didn't say how much current or voltage. Quote Link to comment Share on other sites More sharing options...
Lulu123 Posted September 7, 2016 Report Share Posted September 7, 2016 Hi, you mentioned that you wanted to build a current monitor/sensor like the voltage monitor. I have some information for you and I really hope this will help you. It is that Monitor-Current/Voltage product. You can check my link to see the detailed description of the product. Hope you find the solution soon. Lulu Quote Link to comment Share on other sites More sharing options...
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