i have a problem with driving a MOSFET in a converter, let me explain. I need to build a Buck Converter with the following requirements:
- Input 180 V (From a 120 VRMS rectifier circuit)
- Output 24 V
- No Feedback, is a specific load for demostration purposes.
By designing formulas i came with the following circuit, 10 kHz switching frequency, the only change is the use of a RURG3060 as D1, proteus didn't have this model. The load is a set of 3 light incandescent bulbs in paralel, making 24 V and 120 W output. So a 5 A current is expected in the output. I simulated theorically with PSIM the circuit and the output and ripple requirements are met.
Because of the high input voltage, i use an optocoupler 6N135 to protect the microcontroller from the circuit, and connected like this: Here comes the problem: I notice that the NMos source pin is floating, i tried to connect the negative of the 12V from the optocoupler to the source pin of the NMos, thus, making a floating ground but that don't work, then, i connect the same negative pole to the circuit ground but i don't get any output even. Researching, i tried to connect a MOSFET Driver IC like the IR2112 to solve this problem but the MOSFET don't conmute. All of this is obtained by simulation, because of the use of High Voltage i want to make sure that the simulation works before making any PCB.
How i can drive the MOSFET then? Collegues suggested me to change to a PMos but how i can drive then? I'm not limited to use a MOSFET as switch, only to use a 6N135 as isolation between uC and the circuit. the output and load is fixed.
Any suggestion, advice, will be appreciated
So, i think the problem is in the output side of the optocoupler, because i connected as i show both ground and floating referenced mosfet and don't work. I tested the output of the opto without the converter and i have a slightly slow PWM but Works, until i connected to the converter. How i can connect the output side of the opto then? I use this model because of availability and switching frequency used.
EDIT2: I finally found a way to make it work, i just connect the 6N135 as an example in his datasheet to the Q1's gate, using 5 instead of 12 V and with the floating ground. I get a working simulation and real implementation. The final circuit is shown:
Thanks for the help!