I am designing a SEPIC power supply using the LT3758. I have simulated the circuit in LTSpice and all the waveforms are as expected except the L1 current.
Here I see massive overshoots when the MOSFET switches on (eg normal current is about 3A pk-pk and overshoot goes up to over 20A). The spike is extremely narrow (< 1nS).
I am new to LTSpice, so might be missing something obvious.
Is this spike real or a simulator aboration? What could be causing it and what can I do about it?
Input +28V, Output +40V 1A.
[Edit] I have posted a follow on question here LTSpice SEPIC design low freq ringing
Best Answer
The only place this can come from is stored charge in D1 (or gate drive on Q1, but that's not the case).
Your currents look non-linear with time -- likely your circuit is not very efficient.