Troubleshooting Flyback Converter Simulation in Multisim

[greg997]

Hello, I am having the following problem. Basically, I am supposed to create a simulation in multisim for a flyback converter. A basic model, no feedback needed.
I have 120 dc power supply, transformer with ratio of 26. Output voltage 5 V and power delivered 35W. All that controlled by mosfet, and the switching frequency at 45kHz.So I created a model, And I get 5 Vol output , but the current is 10 less to what I want, and instead 35 W I see 3.5 W.The expected I average shoudl be 6.9A. I have played with different mosfets, some give me miliV a some give kvolts. I use the PWM controller, where in the Edit Model, I removed everything apart from T= 22.2u and Duty cyclemax =Dutycycel min=0.5. If anyone could have a look at my schematic and tell what is wrong with that I would be grateful.And according to my previous calculations the max I in primary is 1.4 A whereas in the probe it shows 4 different values of current, I don know at which I should look, but all of them are too high.

 

[Wirrrthink]

In my opinion just the resistor is wrong. If you want 35W at the right side, you need 35W/5V=7A and a 5V/7A=0.714Ohm resistor. After changing the resistor it should work.

I have the same Problem with the high current on the left side. When I measured the voltage at the mosfet Ii figured out that the MOSFET in Multisim does not switch. I tested a Resistor and a Mosfet in a row, and when the resistor is smaller than 10k there is a huge voltage drop at the MOSFET, so less voltage drop at the transformer.

Which transformer did you use to simulate the storage of energy? This is my main Problem

 

[greg997]

hi, thanks for the info, but it still does not work. I used normal transformer TS_XFMR1.
That resisor in series with capacitor is uded to reduce some spikes when switching , I suppose, but not sure. It is not really needed to have proper simulation.