I am using the LT4320-1 (LT4320IN8-1#PBF) with 4 mosfets (SQP120N10-3m8_GE3) in order to make a rectifier for 13.5VAC but I am having some issues. Indeed, I have a nice DC voltage at the output but the mosfets are getting really hot (100°C) when passing 10A. I followed exactly the diagram presented here:
Do you have any idea about what could be wrong ? Are the chosen mosfets not suitable for this ?
What frequency is your 13.5VAC input? Have you double checked your output with a scope to confirm that it is DC? What is your measured DC output voltage?
The frequency of the input is 50Hz. I did a test with 12VAC/50Hz and the following image shows the voltage measured at the output:
I know I should use a bigger capacitor to have a smoother signal but the circuit seems to work correctly since it rectifies the current. The only problem is the heat released by the mosfet and I cant find the reason...
Can you probe the gates of these MOSFETs? They should match Figure 2 in the datasheet.
Thank you for your quick answer.
So I probed the gates:
Yellow: VTG1, Blue: VTG2, Pink: VOUTP, 5V/div
Yellow: VBG1, Blue: VBG2, Pink: VOUTP, 5V/div
Do you see something wrong ?
The part seems to be functioning properly, the gate signals are correct. These waveforms tell me the top gates are being fully driven, so reducing the RDSON of the MOSFETs would improve efficiency and reduce heat.
How are your MOSFETs mounted, are they near one another and do they have any heatsinking? RDSON increases with junction temperature. If you're measuring a case temperature of 100C, then the junction will be slightly hotter and the RDSON may be in the 6mOhm to 8mOhm range. Can you try mounting the MOSFETs further away from each other or using different TO-220 MOSFETs with lower RDSON?