Why is this happening? SMPS

[binvytas]

Hi guys has any one of you came across this problem on multisim. So I am trying to design a simple SMPS circuit using a 555 timer but for some reason the transistor after the first pulse just seems to not switch off at all i have even tried to replace it with a switch everything is OK until you switch it on and then off the voltage across the coil remains the same even though there is no connection. I am attaching the screenshots and the circuit file. And when I have removed the filter cap it get even weirder check it out. I have spent ages trying to figure why it does not work until i have tried to use a simple switch instead when i realized there's something else that i missed.switch offswitch onswitch off after it has been switched on

[Riley_Ilieva]

Hi Binvytas, 

for some reason I cannot run the simulation on my computer so cannot test this but is there any reason you have a ground on the load next to the rectifier? This might not be the problem but I cannot see a ground in similar circuits so could you possibly check if anything happens if you remove it? 

Kind Regards, 

Riley Ilieva

Applications Engineer

National Instruments

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