Inductor saturation during smps startup

Sylvia Else · 2016-08-04T09:27:46+00:00

I was looking at using an LT1170 in a Positive-to-Negative Buck-Boost Converter, as per page 14 of this data sheet Thing is, when I put this into LTSpice (using Linear Techology's own model of their part), it shows that the current through the inductor rises to 10 amps, during start-up, settling to something more reasonable later. I don't want to have to use a 10 amp inductor, and the part they suggest isn't 10 amps anyway. I can limit the current by including a clamp circuit on the Vc connection, but it increases the component count, and would probably need to include a trimpot because the relationship between current limit and clamp voltage isn't specified. Does it matter if the inductor saturates during start-up? Note that in the spice schematic below, I've included the switching on and off of the 2 amp load at regular intervals to look at the transient response, and regulation (the latter not being good at all, though good enough in my application). Sylvia. Version 4 SHEET 1 1704 788 WIRE 96 -64 64 -64 WIRE 256 -64 176 -64 WIRE 368 -64 256 -64 WIRE 528 -64 368 -64 WIRE 368 -48 368 -64 WIRE 528 -48 528 -64 WIRE 64 16 64 -64 WIRE 64 16 -144 16 WIRE 64 32 64 16 WIRE -144 96 -144 16 WIRE -144 96 -160 96 WIRE 256 112 256 -64 WIRE 256 112 192 112 WIRE -160 128 -160 96 WIRE 256 176 192 176 WIRE 320 176 256 176 WIRE 368 176 320 176 WIRE 368 224 368 176 WIRE 480 224 448 224 WIRE 544 224 480 224 WIRE 640 224 608 224 WIRE 752 224 720 224 WIRE 816 224 752 224 WIRE 896 224 896 128 WIRE 896 224 816 224 WIRE 992 224 944 224 WIRE 224 240 192 240 WIRE 240 240 224 240 WIRE 320 240 320 176 WIRE 480 256 480 224 WIRE 816 256 816 224 WIRE 752 272 752 224 WIRE 896 272 896 224 WIRE 992 272 992 224 WIRE 1136 272 1040 272 WIRE 1040 288 1040 272 WIRE 240 352 240 320 WIRE 944 352 944 224 WIRE 944 352 896 352 WIRE 1040 352 1040 336 WIRE 1072 352 1040 352 WIRE 1136 352 1072 352 WIRE -160 416 -160 192 WIRE 16 416 -160 416 WIRE 64 416 64 320 WIRE 64 416 16 416 WIRE 240 416 64 416...

Aug 04, 2016 21 Replies

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Don Kuenz 9 years ago

FWIW my LTSpice is two and a half years old. These two lines

SYMATTR SpiceLine Ipk=7 Rser=0.013 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX50-7-52"

had to be joined into a single line

SYMATTR SpiceLine Ipk=7 Rser=0.013 Rpar=0 Cpar=0 mfg="Coiltronics" pn="CTX50-7-52"

to eliminate my crash. YMMV.

Don Kuenz KB7RPU Sing a song of saucers Flown from outer space. Four-and-twenty generals, Crimson in the face. The saucers conquered gravity So they all began to spin- And, Gentlemen, if you'll pardon me, This is where I came in.

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Sylvia Else 9 years ago

Thanks for tracking that down. So it looks like the problem is line wrapping in people's Usenet browsers, since my post doesn't actually contain a line break there. Something to be aware of in future.

Sylvia.

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