Troubleshooting a Boost Circuit: Voltage Rise & Gate Issues

In summary, the designer is having trouble testing their boost circuit, and may need to use a transformer to avoid overloading the circuit and causing problems.
  • #1
core7916
56
3
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?.
 
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  • #2
core7916 said:
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.

core7916 said:
* 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.
 
  • #3
core7916 said:
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.

core7916 said:
* 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.

core7916 said:
* 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.
 
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  • #4
core7916 said:
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.
 
  • #5
Rive said:
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.
 

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