We have a giant 48 volt bus, and one plugin board (a jet engine alternator simulator) will have a hunky full-bridge dc/dc converter making +-60 volts. Startup makes hundreds-of-amps current pulses with side effects, so soft start is a good thing.
Here it is:
Version 4 SHEET 1 880 680 WIRE -192 -192 -320 -192 WIRE -112 -192 -192 -192 WIRE 80 -192 -112 -192 WIRE 240 -192 176 -192 WIRE 288 -192 240 -192 WIRE 416 -192 368 -192 WIRE 512 -192 416 -192 WIRE 592 -192 512 -192 WIRE 656 -192 592 -192 WIRE -320 -144 -320 -192 WIRE 240 -96 240 -192 WIRE 416 -96 416 -192 WIRE 592 -96 592 -192 WIRE -320 -16 -320 -64 WIRE -192 -16 -192 -192 WIRE -112 -16 -192 -16 WIRE 48 -16 -32 -16 WIRE 96 -16 96 -144 WIRE 96 -16 48 -16 WIRE 240 32 240 -32 WIRE 416 32 416 -32 WIRE 592 32 592 -16 WIRE 96 96 96 -16 WIRE -272 144 -320 144 WIRE -208 144 -272 144 WIRE -48 144 -128 144 WIRE 32 144 -48 144 WIRE -320 192 -320 144 WIRE -48 224 -48 144 WIRE 96 224 96 192 WIRE 240 224 240 112 WIRE 240 224 96 224 WIRE 96 240 96 224 WIRE 240 256 240 224 WIRE -320 320 -320 272 WIRE -48 352 -48 288 WIRE 96 352 96 320 WIRE 240 352 240 320 FLAG -320 -16 0 FLAG 96 352 0 FLAG -320 320 0 FLAG 416 32 0 FLAG 592 32 0 FLAG 512 -192 Vsoft FLAG -112 -192 +48 FLAG 48 -16 G FLAG -48 352 0 FLAG -272 144 ENAB FLAG 240 352 0 SYMBOL voltage -320 -160 R0 WINDOW 0 36 158 Left 2 WINDOW 3 -52 194 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value PULSE(0 48 1m 1m 1m 9) SYMBOL res -16 -32 R90 WINDOW 0 -10 85 VBottom 2 WINDOW 3 -37 25 VTop 2 SYMATTR InstName R1 SYMATTR Value 10K SYMBOL pmos 176 -144 M270 WINDOW 0 20 180 VLeft 2 WINDOW 3 -10 216 VLeft 2 SYMATTR InstName M1 SYMATTR Value Si7461DP SYMBOL cap -32 288 R180 WINDOW 0 49 41 Left 2 WINDOW 3 43 11 Left 2 SYMATTR InstName C1 SYMATTR Value 10µ SYMBOL res 112 336 R180 WINDOW 0 55 73 Left 2 WINDOW 3 55 42 Left 2 SYMATTR InstName R2 SYMATTR Value 2K SYMBOL voltage -320 176 R0 WINDOW 0 50 144 Left 2 WINDOW 3 -46 187 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value PULSE(0 3.3 5m 1u 1u 2) SYMBOL cap 400 -96 R0 WINDOW 0 66 24 Left 2 WINDOW 3 65 53 Left 2 SYMATTR InstName C2 SYMATTR Value 1m SYMBOL res 576 -112 R0 WINDOW 0 63 40 Left 2 WINDOW 3 59 69 Left 2 SYMATTR InstName R3 SYMATTR Value 100 SYMBOL res 272 -176 R270 WINDOW 0 -40 58 VTop 2 WINDOW 3 -44 57 VBottom 2 SYMATTR InstName R4 SYMATTR Value 1m SYMBOL npn 32 96 R0 WINDOW 0 -44 -52 Left 2 WINDOW 3 -74 -22 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N5210 SYMBOL res -112 128 R90 WINDOW 0 67 54 VBottom 2 WINDOW 3 72 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL cap 224 -96 R0 WINDOW 0 -47 24 Left 2 WINDOW 3 -45 55 Left 2 SYMATTR InstName C3 SYMATTR Value 1µ SYMBOL res 224 16 R0 WINDOW 0 -48 39 Left 2 WINDOW 3 -51 69 Left 2 SYMATTR InstName R6 SYMATTR Value 500 SYMBOL zener 256 320 R180 WINDOW 0 -68 51 Left 2 WINDOW 3 -86 20 Left 2 SYMATTR InstName D1 SYMATTR Value 1N750 SYMATTR Description Diode SYMATTR Type diode TEXT 488 216 Left 2 !.tran 200m TEXT 464 128 Left 2 ;P944 Soft Start TEXT 448 168 Left 2 ;JL June 20 2023 TEXT -40 104 Left 2 ;BCX70 TEXT -48 -104 Left 2 ;IRFR9120N
Peak startup current is just over an amp. We can drive the inverter logic inputs at startup, enable the soft start, and things will ramp up gently.