Troubleshooting a Boost Circuit: Voltage Rise & Gate Issues

[core7916]

Hello. I am creating a boost circuit and there is a lot of problems while testing.
Before creating circuit i have simulated circuit in modelsim.
Problems.
1. Sudden voltage rise from 40% to 50 % dury cycle. ( i am checking each duty cycle )
2. When applying a gate voltage to mosfet the the pulse is behave like charging and discharging (like capacitor charge and discharge). In 90% duty cycle the pulse is not reaching zero, similarly in 10 % pulse is not reaching pulse voltage ( 5v - from function generator). Frq= 300khz
* I am designing 5v input to 100v output.
Why this is happenig ?
* Should i use any other driving component to use drive the gate of mosfet?.

 

[Baluncore]

When applying a gate voltage to mosfet the the pulse is behave like charging and discharging (like capacitor charge and discharge).

A power MOSFET is made from many MOSFETs in parallel. There is a very high total gate input capacitance that must be charged quickly. With a high output voltage, the miller capacitance between the gate and drain may become significant.

* Should i use any other driving component to use drive the gate of mosfet?.

Yes. The driver you need would depend on your choice of MOSFET and the circuit employed. It might only need a couple of BJTs to drive the gate.
Please post your circuit diagram.

 

[Rive]

Sudden voltage rise from 40% to 50 % dury cycle.

By my limited experience such thing often means continuous/discontinuous operation mode transition. Check your knowledge/design regarding operation modes.

* Should i use any other driving component to use drive the gate of mosfet?.

At 300kHz, likely yes. There are some ICs for this specific role as 'gate driver'. You can do it with discrete components too, but far more simple with ICs.

* I am designing 5v input to 100v output.

That feels like a bit too big step to do it efficiently. A transformer might be required, instead of a simple buck converter.

 

[berkeman]

Hello. I am creating a boost circuit and there is a lot of problems while testing.

Can you upload a copy of your schematic please? Use the "Attach files" link below the Edit window to upload a PDF or JPEG copy of your schematic. Thank you.

 

[DaveE]

That feels like a bit too big step to do it efficiently. A transformer might be required, instead of a simple buck converter.

Yes, easier with a flyback topology. You have to have big magnetics anyway, might as well put on another winding (or tap) and get back to a more reasonable duty cycle. Your peak to average current ratios will be stressful on things. OTOH, it can be done with a buck converter.