Boost converter load problem

Neglecting the losses of any kind thus assuming a 100% efficiency, one can thing about a boost convert as a voltage translator with constant power. I mean that Pin = Pout.

$$ P_{in} = V_{in}I_{in}$$ $$ P_{out} = V_{out}I_{out}$$

thus

$$ V_{in}I_{in} = V_{out}I_{out} $$

of rewritten differently:

$$ \frac{V_{in}}{V_{out}} = \frac{I_{out}}{I_{in}} $$

thus if you boost 3.3V to 30V and see a power consumption of 9A, then

$$ \frac{3.3V}{30V} = \frac{I_{out}}{9A} $$

$$ I_{out} = 1A $$

If you designed your boost convert to supply roughly 1A then it is working fine. Because we assumed a 100% efficiency, the real available output current would be less than 1A.

Usually you do the computation backward, you know your output current requirement and you can compute what would be the input current.

If the Spice model of the IRFP4668 is at all accurate, it will not be turned on well with only 5V gate drive. You should increase the gate drive to 10V to support higher current. Expect the power modulator to have a resonant frequency of ~ 1200 Hz, with a Q of ~ 4. So, it will take a lot of simulated time to settle, probably at least a second and the output will be ringy.

Peak switch current with a 34W output and 11V input and 64uH inductor will be ~3.4A. The LM2585 switch can limit as low as 3A, so don't expect to get 2A output. It might be able to put out 1.75A with a 3A switch limit. The inductor will need at least a 5A rating to avoid saturation and thermal problems.

Also, the 12V input will need to be able to supply the 3+ amps.