R2 and R3 are the loads. R2 load always between 5mA and 15mA. R3 load not always on.
Acceptable for the +10V rail to drop down to +7V on low input voltage.
5V rail must always be at 5V
Needs to operate from 9V to 34V input. But it also needs to survive ISO
7637-2. That dictates upto -600V spikes with rise times of 1uS or so and repetive +200V spikes with similar rise times.
So I thought about switching but due to a few problems this isn't really workable. Mainly due to ISO 7637-2 and the high +ve voltages causing a problem with the size of the inductor.
So I thought maybe linear at input voltages upto the first regulated output voltage (10V), then switching regulation upto the max input V of
34V. Input voltages above that then revert to a linear reg feeding the switcher (because voltages higher than this are only spikes so dissipation isn't such a problem). Sounds ridiculously complicated. But I got this....
Version 4 SHEET 1 1176 776 WIRE 48 208 -512 208 WIRE 208 208 112 208 WIRE 384 208 208 208 WIRE 512 208 384 208 WIRE 208 224 208 208 WIRE 384 288 384 208 WIRE -512 336 -512 208 WIRE 112 336 -32 336 WIRE 208 336 208 304 WIRE 208 336 112 336 WIRE 320 336 256 336 WIRE 112 352 112 336 WIRE 512 384 512 208 WIRE 944 400 640 400 WIRE 1024 400 944 400 WIRE 1120 400 1024 400 WIRE 256 416 256 336 WIRE 256 416 208 416 WIRE 384 432 384 384 WIRE 448 432 384 432 WIRE 112 448 112 432 WIRE 272 448 112 448 WIRE 944 448 944 400 WIRE 1120 448 1120 400 WIRE 528 480 512 480 WIRE 640 480 640 400 WIRE 640 480 608 480 WIRE 640 496 640 480 WIRE 656 496 640 496 WIRE 768 496 736 496 WIRE 848 496 768 496 WIRE 880 496 848 496 WIRE -32 512 -32 336 WIRE -80 528 -336 528 WIRE 272 528 272 448 WIRE 640 528 640 496 WIRE -336 544 -336 528 WIRE 112 544 112 448 WIRE 512 544 512 480 WIRE 768 544 768 496 WIRE 848 544 848 496 WIRE 944 560 944 544 WIRE -512 576 -512 416 WIRE -80 576 -144 576 WIRE -32 656 -32 592 WIRE 112 656 112 608 WIRE 272 656 272 592 WIRE 512 656 512 608 WIRE 640 656 640 608 WIRE 768 656 768 608 WIRE 848 656 848 608 WIRE 944 656 944 640 WIRE 1120 656 1120 512 WIRE -336 672 -336 624 WIRE -144 704 -144 576 WIRE 1024 704 1024 400 WIRE 1024 704 -144 704 FLAG -512 576 0 FLAG 848 656 0 FLAG 944 656 0 FLAG 112 656 0 FLAG 768 656 0 FLAG 640 656 0 FLAG -32 656 0 FLAG -336 672 0 FLAG 512 656 0 FLAG 1120 656 0 FLAG 272 656 0 SYMBOL voltage -512 320 R0 WINDOW 123 0 0 Left 0 WINDOW 39 24 132 Left 0 SYMATTR SpiceLine Rser=1m SYMATTR InstName V1 SYMATTR Value 35 SYMBOL diode 48 224 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D2 SYMATTR Value BYG21M SYMBOL npn 320 288 R0 SYMATTR InstName Q1 SYMATTR Value MMBTA42 SYMBOL npn 448 384 R0 SYMATTR InstName Q2 SYMATTR Value FZT658 SYMBOL npn 880 448 R0 SYMATTR InstName Q3 SYMATTR Value 2N2222 SYMBOL res 752 480 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 5k SYMBOL zener 864 608 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D3 SYMATTR Value BZX84C6V2L SYMBOL res 928 544 R0 SYMATTR InstName R2 SYMATTR Value 360 SYMBOL cap 752 544 R0 SYMATTR InstName C1 SYMATTR Value 10n SYMBOL res 624 512 R0 SYMATTR InstName R3 SYMATTR Value 720 SYMBOL sw -32 496 R0 SYMATTR InstName S1 SYMATTR Value cmp SYMBOL voltage -336 528 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 10.85 SYMBOL ind 512 496 R270 WINDOW 0 32 56 VTop 0 WINDOW 3 5 56 VBottom 0 SYMATTR InstName L1 SYMATTR Value 0.01 SYMATTR SpiceLine Rser=10m SYMBOL schottky 528 608 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 0 Left 0 SYMATTR InstName D6 SYMATTR Value PMEG3005AEA SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 1104 448 R0 SYMATTR InstName C2 SYMATTR Value 1µ SYMBOL res 192 208 R0 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL res 192 320 R0 SYMATTR InstName R6 SYMATTR Value 2k SYMBOL res 96 336 R0 SYMATTR InstName R5 SYMATTR Value 10k SYMBOL cap 256 528 R0 SYMATTR InstName C3 SYMATTR Value 1µ SYMBOL zener 128 608 R180 WINDOW 0 24 72 Left 0 WINDOW 3 24 -22 Left 0 SYMATTR InstName D1 SYMATTR Value BZX84C39L TEXT -664 248 Left 0 !.tran 0 100m 0 TEXT -728 712 Left 0 !.model cmp SW(RON=50 ROFF=1E6 VT=1m VH=5m)
Dissipation in Q2 is about 1/3 an equivalent linear reg at max input (34V)
Nothing like optimised, just testing the idea. Anyone done anything similar? Any better ideas?
Have I missed something simple?