I'm building current limiter for my circuit, I saw a nice one in Maxim's document (Figure 2a): https://www.maximintegrated.com/en/app-notes/index.mvp/id/2158
I need current limiting for 100mA, so I modified that circuit and simulated in LTspice:
It works, it limits current well, but there is some glitch/spike when power is switched on (current across R1):
Spike in detail (power is turned at 10μs, spike starts at 10μs):
I tried different transistors (Q1 and M1) but it didn't help.
What causes this spike?
Is there any problem in that circuit?
Or is it just some problem in LTspice simulation?
Is it possible to get rid of this spike?
Best Answer
After my failed attempts in the comments, I point the finger to
V1
, who has (machine) zero internal resistance and is forced to deliver the charging current for the capacitors (through the other series resistances in the circuit). Normally, you'd have both a limited resistance from the input supply, and some capacitor at the input, so simulating that by addingRser=1m Cpar=1m
toV1
, seems to solve it.