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Boost converter with varying input voltage

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dani4438280

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Hi, I am new in power electronics field, I am designing a MOSFET based boost converter with
Vin (0...50V), Vout=150V fixed, D=0.7, R=400 ohm. for CCM when ripple current in inductor is 20%.

required input voltage Vin=?
inductance L=?

Please give me some initial hints to solve this. Thanks

- - - Updated - - -

and f= 80KHz
 

How is the problem specification meaned? Calculate the input voltage for duty cycle of 0.7? Then what's the meaning of varying input voltage? Duty cycle must vary, too.

There's no theoretical input voltage lower limit based on the given parameters but a practical limit, e.g. set by reasonable inductor and transistor current levels.
 

L can be found from di/dt(on) = Vin/L, for your 20% current ripple and dt(on) = 8.8us, from 80kHz & 50 to 150V.

on time will be larger as Vin goes below 50V (99.9% at Vin = 1V) , ckt is for 56W out, so approx 1 amp at 50V in, 2.5 amps at 25V in... etc.
 
p.s. you can not have a fixed duty cycle for this converter, you must have a feed back circuit that reduces the duty cycle to zero as the Vo goes to 150V, either that or a very big 150V zener on the o/p.
 

Thanks for your reply,
1- i have to calculate required input voltage.
2- what does it mean " ripple current in inductor is 20%"???
3-duty cycle and output voltage is fixed, what would be equation to find L then.
 

The peak to peak ripple to be 20% of the max average choke current...

The duty cycle cannot be fixed if you want 150v at no load,

Surely the input volts are fixed by the sources available?
 

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