Modelling Roman Black's boost converter in LT spice. - Page 1
Forum section: electronics / projects

author: richard.cs
author_rank: Super Contributor
timestamp: May 14, 2015, 09:55:47 pm
content: http://www.romanblack.com/smps/conv.htmI'm trying to get a spice simulation of this to oscillate, with the intention to tweak it for another purpose. I have tried:The "startup" option (ramps DC source)Driving it from a pulsed voltage source to get a sharper startup transient.ic for inductor current.ic for the initial voltage on the 1nReal inductor models from the libraryAn inductor model that includes saturation (at various currents)Tweaking various component values hopefullyCombinations of the above.Whatever I do it settles down to a steady DC state- I'm not sure if I've made some silly wiring error or if it's fundamentally un-simulatable because it relies on some component parasitic that isn't modeled. I could use another pair of eyes on it please.Edit: Not being allowed to upload .asc files on an electronics forum is a bit sucky.

author: fmaimon
author_rank: Unknown
timestamp: May 14, 2015, 10:18:31 pm
content: Try using the BC337-40, as it has higher hfe, or maybe lower R1. In my first try, Q1 (Q3 in your schematic) collector current was limited by it.I've attached my circuit, renamed to .txt instead of .asc

author: Anand
author_rank: Contributor
timestamp: May 14, 2015, 10:22:48 pm
content: In thehttp://www.romanblack.com/smps/conv.htmI see the collector of Q2 connected to the base of Q3, not the emmiter.

author: c4757p
author_rank: Super Contributor
timestamp: May 14, 2015, 10:33:00 pm
content: Quote from: Anand on May 14, 2015, 10:22:48 pmYes!That transistor resets the switching cycle by pulling Q3's base low. It doesn't make any sense to pull its emitter instead.

author: richard.cs
author_rank: Super Contributor
timestamp: May 14, 2015, 10:44:12 pm
content: Quote from: Anand on May 14, 2015, 10:22:48 pmThank you! I have no idea how I missed that.And lo it springs into life.

author: Zero999
author_rank: Super Contributor
timestamp: May 15, 2015, 05:06:22 pm
content: It's more efficient to connect Q2's base to D2 so it shuts off when D2 conducts.Copy and paste the code into a text editor and save as an .asc.Code:Version 4SHEET 1 1012 680WIRE -272 -112 -480 -112WIRE -80 -112 -272 -112WIRE -32 -112 -80 -112WIRE 112 -112 48 -112WIRE 304 -112 112 -112WIRE 416 -112 304 -112WIRE 672 -112 480 -112WIRE 816 -112 672 -112WIRE 944 -112 816 -112WIRE -80 -48 -80 -112WIRE 304 32 304 -112WIRE 112 80 112 -112WIRE -80 128 -80 32WIRE 16 128 -80 128WIRE 48 128 16 128WIRE -480 176 -480 -112WIRE 944 176 944 -112WIRE -272 208 -272 -112WIRE 16 208 16 128WIRE 400 208 16 208WIRE 816 208 816 -112WIRE 672 224 672 -112WIRE 400 256 400 208WIRE -480 288 -480 256WIRE 112 304 112 176WIRE 192 304 112 304WIRE 304 304 304 112WIRE 304 304 272 304WIRE 336 304 304 304WIRE 672 304 672 288WIRE 672 304 336 304WIRE 112 336 112 304WIRE 304 368 304 304WIRE -272 480 -272 272WIRE 112 480 112 416WIRE 304 480 304 432WIRE 400 480 400 352WIRE 816 480 816 272WIRE 944 480 944 256FLAG 112 480 0FLAG 304 480 0FLAG 400 480 0FLAG 816 480 0FLAG 944 480 0FLAG -272 480 0FLAG -480 288 0SYMBOL npn 48 80 R0SYMATTR InstName Q1SYMATTR Value BC337-40SYMBOL npn 336 256 R0SYMATTR InstName Q2SYMATTR Value BC337-40SYMBOL res -96 -64 R0SYMATTR InstName R1SYMATTR Value 10kSYMBOL res 96 320 R0SYMATTR InstName R2SYMATTR Value 6.8SYMBOL res 288 16 R0SYMATTR InstName R3SYMATTR Value 15kSYMBOL res 288 288 R90WINDOW 0 0 56 VBottom 2WINDOW 3 32 56 VTop 2SYMATTR InstName R4SYMATTR Value 1kSYMBOL ind -48 -96 R270WINDOW 0 32 56 VTop 2WINDOW 3 5 56 VBottom 2SYMATTR InstName L1SYMATTR Value 470µSYMATTR SpiceLine Rser=4.9SYMBOL cap 288 368 R0SYMATTR InstName C1SYMATTR Value 1nSYMBOL cap -288 208 R0SYMATTR InstName C2SYMATTR Value 47µSYMBOL diode 416 -96 R270WINDOW 0 32 32 VTop 2WINDOW 3 0 32 VBottom 2SYMATTR InstName D1SYMATTR Value 1N4148SYMBOL cap 800 208 R0SYMATTR InstName C3SYMATTR Value 10µSYMBOL zener 688 288 R180WINDOW 0 24 64 Left 2WINDOW 3 24 0 Left 2SYMATTR InstName D2SYMATTR Value BZX84C12LSYMATTR Description DiodeSYMATTR Type diodeSYMBOL res 928 160 R0SYMATTR InstName R5SYMATTR Value 10kSYMBOL voltage -480 160 R0WINDOW 123 0 0 Left 2WINDOW 39 0 0 Left 2SYMATTR InstName V1SYMATTR Value 5TEXT -512 504 Left 2 !.tran 10m

author: richard.cs
author_rank: Super Contributor
timestamp: May 15, 2015, 05:53:18 pm
content: What I'm actually doing with it:Modifying for 9V in, ~100V output open-circuitAdding feedback for constant 1mA (might make this switchable to 100 uA)Combine with cheap ebay DMM module for measuring breakdown voltages of zeners, forward voltages of HV diode stacks, etc. the item under test takes the place of R6.I can always use a bench supply to do the same thing but it's a bit of a pain when I only want a quick check. I've just realised that it needs a further tweak - I want the current to be limited even for things that breakdown at <9V. Maybe I'll make L1 a transformer so there's no DC path.Thanks for the help :-)