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micropower boost circuit

I need a DC to DC boost circuit with an output defined not with respect to ground, but with respect to the input, which is variable. Output about 15 volts above the input, over a wide range -- from less than a volt in, up to

15 or 16 volts in. But can be inefficient and only needs to put out a few milliamps. I pasted an LTspice netlist of a possible solution. R15 simulates a grain-of-wheat incandescent. For Q6, if the Zetex is hard to find I might use a DSS416 or some such. What's the consensus about the vulnerability of Q6 when Vin = 16 volts?

Version 4 SHEET 1 1388 680 WIRE 496 -160 -80 -160 WIRE 384 -144 352 -144 WIRE -80 -128 -80 -160 WIRE 352 -112 352 -144 WIRE 512 -112 352 -112 WIRE 560 -112 512 -112 WIRE 352 -80 352 -112 WIRE 448 -80 448 -144 WIRE 448 -80 416 -80 WIRE 512 -64 512 -112 WIRE -528 -16 -528 -48 WIRE -528 -16 -560 -16 WIRE -464 -16 -528 -16 WIRE -368 -16 -464 -16 WIRE -352 -16 -368 -16 WIRE -304 -16 -352 -16 WIRE -288 -16 -304 -16 WIRE -192 -16 -288 -16 WIRE -160 -16 -192 -16 WIRE 208 -16 -160 -16 WIRE 272 -16 208 -16 WIRE 288 -16 288 -112 WIRE 288 -16 272 -16 WIRE 304 -16 288 -16 WIRE 448 -16 448 -80 WIRE 448 -16 384 -16 WIRE -464 0 -464 -16 WIRE -192 0 -192 -16 WIRE 272 32 272 -16 WIRE 384 32 272 32 WIRE -368 48 -400 48 WIRE -256 48 -288 48 WIRE 272 48 272 32 WIRE 496 80 496 -160 WIRE 496 80 448 80 WIRE -464 96 -592 96 WIRE -448 96 -464 96 WIRE -384 96 -288 48 WIRE -352 96 -352 -16 WIRE -272 96 -368 48 WIRE -192 96 -208 96 WIRE -128 96 -192 96 WIRE 144 96 -128 96 WIRE 208 96 208 -16 WIRE -464 112 -464 96 WIRE -192 112 -192 96 WIRE -528 128 -528 -16 WIRE -304 128 -304 -16 WIRE -80 144 -80 -48 WIRE 16 144 -16 144 WIRE 272 144 272 128 WIRE 272 144 96 144 WIRE 352 144 352 -80 WIRE 352 144 336 144 WIRE 272 160 272 144 WIRE -464 208 -464 192 WIRE -416 208 -464 208 WIRE -352 208 -352 176 WIRE -192 208 -192 192 WIRE -192 208 -240 208 WIRE -160 208 -160 64 WIRE -160 208 -192 208 WIRE 208 208 208 176 WIRE 208 208 112 208 WIRE 208 224 208 208 WIRE -560 240 -560 64 WIRE -464 240 -464 208 WIRE -464 240 -560 240 WIRE -352 256 -304 208 WIRE -352 256 -400 256 WIRE -304 256 -352 208 WIRE -256 256 -304 256 WIRE -80 256 -80 144 WIRE -16 256 -80 256 WIRE 48 256 -16 256 WIRE 144 272 144 176 WIRE -592 320 -592 176 WIRE -528 320 -528 208 WIRE -528 320 -592 320 WIRE -464 320 -464 304 WIRE -464 320 -528 320 WIRE -384 320 -384 176 WIRE -384 320 -464 320 WIRE -352 320 -384 320 WIRE -304 320 -352 320 WIRE -272 320 -272 176 WIRE -272 320 -304 320 WIRE -192 320 -192 304 WIRE -192 320 -272 320 WIRE -128 320 -128 176 WIRE -128 320 -192 320 WIRE -80 320 -128 320 WIRE -16 320 -80 320 WIRE 112 320 112 304 WIRE 112 320 -16 320 WIRE 208 320 112 320 WIRE 272 320 272 256 WIRE 272 320 208 320 FLAG 560 -32 0 FLAG -528 -48 Vin FLAG 512 -64 Vout FLAG -80 320 0 SYMBOL npn -256 208 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL npn -400 208 M0 SYMATTR InstName Q2 SYMATTR Value 2N2222 SYMBOL pnp -400 96 R180 WINDOW 0 51 37 Left 2 WINDOW 3 31 60 Left 2 SYMATTR InstName Q3 SYMATTR Value 2N2907 SYMBOL pnp -256 96 M180 WINDOW 0 36 42 Left 2 WINDOW 3 -10 95 Left 2 SYMATTR InstName Q4 SYMATTR Value 2N2907 SYMBOL cap -240 192 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C1 SYMATTR Value 1n SYMBOL cap -352 192 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 1n SYMBOL cap -384 80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 1n SYMBOL cap -208 80 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 8 14 VTop 2 SYMATTR InstName C4 SYMATTR Value 1n SYMBOL res -320 112 R0 WINDOW 0 1 -2 Left 2 WINDOW 3 -13 62 Left 2 SYMATTR InstName R1 SYMATTR Value 47k SYMBOL res -400 80 R0 WINDOW 0 0 40 Left 2 WINDOW 3 -5 70 Left 2 SYMATTR InstName R3 SYMATTR Value 47k SYMBOL res -288 80 R0 WINDOW 0 1 42 Left 2 WINDOW 3 -2 72 Left 2 SYMATTR InstName R4 SYMATTR Value 4k7 SYMBOL voltage -528 112 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 -42 -248 Left 2 WINDOW 0 -13 58 Left 2 SYMATTR Value PULSE(0 1 0 100n) SYMATTR InstName V1 SYMBOL res -480 96 R0 WINDOW 0 3 55 Left 2 WINDOW 3 13 80 Left 2 SYMATTR InstName R5 SYMATTR Value 10 SYMBOL res -208 96 R0 WINDOW 0 -16 36 Left 2 WINDOW 3 -2 70 Left 2 SYMATTR InstName R6 SYMATTR Value 10 SYMBOL diode -288 320 R180 WINDOW 0 3 -13 Left 2 WINDOW 3 -84 -14 Left 2 SYMATTR InstName D1 SYMATTR Value 1N4148 SYMBOL diode -336 320 R180 WINDOW 0 88 -13 Left 2 WINDOW 3 -1 -12 Left 2 SYMATTR InstName D4 SYMATTR Value 1N4148 SYMBOL diode -272 48 R180 WINDOW 0 8 108 Left 2 WINDOW 3 -29 82 Left 2 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL diode -352 48 R180 WINDOW 0 31 45 Left 2 WINDOW 3 9 94 Left 2 SYMATTR InstName D3 SYMATTR Value 1N4148 SYMBOL res -368 80 R0 WINDOW 0 6 32 Left 2 WINDOW 3 9 71 Left 2 SYMATTR InstName R2 SYMATTR Value 4k7 SYMBOL res -608 80 R0 WINDOW 0 17 38 Left 2 WINDOW 3 2 88 Left 2 SYMATTR InstName R7 SYMATTR Value 4k7 SYMBOL res -576 -32 R0 WINDOW 0 -3 53 Left 2 WINDOW 3 -12 89 Left 2 SYMATTR InstName R8 SYMATTR Value 4k7 SYMBOL res -144 80 R0 WINDOW 0 15 38 Left 2 WINDOW 3 7 73 Left 2 SYMATTR InstName R9 SYMATTR Value 4k7 SYMBOL res -176 -32 R0 SYMATTR InstName R10 SYMATTR Value 4k7 SYMBOL npn 144 224 R0 SYMATTR InstName Q5 SYMATTR Value 2N2222 SYMBOL npn 208 160 R0 WINDOW 0 56 45 Left 2 SYMATTR InstName Q6 SYMATTR Value FZT849 SYMBOL ind 256 32 R0 WINDOW 3 64 53 Left 2 SYMATTR Value 100µ SYMATTR InstName L1 SYMATTR SpiceLine Rser=.5 SYMBOL schottky 272 160 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D5 SYMATTR Value 1N5819 SYMATTR Description Diode SYMATTR Type diode SYMBOL pnp 384 80 M180 SYMATTR InstName Q8 SYMATTR Value 2N2907 SYMBOL zener 416 -96 R90 WINDOW 0 -4 32 VBottom 2 WINDOW 3 37 -14 VTop 2 SYMATTR InstName D6 SYMATTR Value BZX84C15L SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 352 -128 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 1µ SYMBOL res 544 -128 R0 SYMATTR InstName R14 SYMATTR Value 4k7 SYMBOL res 192 80 R0 WINDOW 3 -254 -27 Left 2 WINDOW 0 -5 2 Left 2 SYMATTR Value R=100+sqrt(54000*V(Vin)) SYMATTR InstName R15 SYMBOL res 128 80 R0 WINDOW 0 -2 40 Left 2 WINDOW 3 -2 83 Left 2 SYMATTR InstName R16 SYMATTR Value 1k SYMBOL res 400 -32 R90 WINDOW 0 9 81 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R11 SYMATTR Value 1k SYMBOL npn 48 208 R0 SYMATTR InstName Q7 SYMATTR Value 2N2222 SYMBOL res -96 -144 R0 SYMATTR InstName R12 SYMATTR Value 1k SYMBOL res 112 128 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R13 SYMATTR Value 10k SYMBOL cap -16 128 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C7 SYMATTR Value 100p SYMBOL diode 0 320 R180 WINDOW 0 24 64 Left 2 WINDOW 3 -17 25 Left 2 SYMATTR InstName D7 SYMATTR Value 1N4148 SYMBOL cap 448 -160 R90 WINDOW 0 27 65 VBottom 2 WINDOW 3 5 -6 VTop 2 SYMATTR InstName C5 SYMATTR Value 1n TEXT -320 -136 Left 2 !.tran 0 5m 0

Reply to
Michael Robinson
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--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

But it's "compact" >:-} ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

On Sun, 22 Sep 2013 09:27:35 -0700, Jim Thompson wrote:

All drawings should be clean, commented, titled and dated.

LT Spice should have a title block. There is a checkbox "show title block" but it's "for internal use."

Version 4 SHEET 1 1920 968 WIRE 240 144 112 144 WIRE 320 144 240 144 WIRE 464 144 400 144 WIRE 528 144 464 144 WIRE 656 144 608 144 WIRE 816 144 768 144 WIRE 960 144 896 144 WIRE 1040 144 960 144 WIRE 1184 144 1104 144 WIRE 1232 144 1184 144 WIRE 1360 144 1312 144 WIRE 1424 144 1360 144 WIRE 112 176 112 144 WIRE 768 208 768 144 WIRE 240 240 240 144 WIRE 320 240 240 240 WIRE 464 240 464 144 WIRE 464 240 384 240 WIRE 1184 240 1184 144 WIRE 1232 240 1184 240 WIRE 1360 240 1360 144 WIRE 1360 240 1296 240 WIRE 1360 288 1360 240 WIRE 112 320 112 256 WIRE 656 320 656 144 WIRE 720 320 656 320 WIRE 768 320 720 320 WIRE 768 368 768 320 WIRE 960 368 960 144 WIRE 304 384 240 384 WIRE 400 384 368 384 WIRE 1360 400 1360 352 WIRE 48 416 -32 416 WIRE 96 416 48 416 WIRE 240 416 240 384 WIRE 240 416 176 416 WIRE 656 432 656 320 WIRE -32 448 -32 416 WIRE 240 448 240 416 WIRE 304 448 240 448 WIRE 400 448 400 384 WIRE 400 448 368 448 WIRE 768 480 768 448 WIRE 960 480 960 448 WIRE 240 512 240 448 WIRE 304 512 240 512 WIRE 400 512 400 448 WIRE 400 512 368 512 WIRE 432 512 400 512 WIRE 560 512 512 512 WIRE 608 512 560 512 WIRE -32 528 -32 512 WIRE 48 576 48 416 WIRE 80 576 48 576 WIRE 128 576 80 576 WIRE 240 576 240 512 WIRE 240 576 192 576 WIRE 304 576 240 576 WIRE 400 576 400 512 WIRE 400 576 368 576 WIRE 656 592 656 528 WIRE 768 592 768 544 WIRE 960 592 960 544 WIRE 1184 592 1136 592 WIRE 1360 592 1264 592 WIRE 1408 592 1360 592 WIRE 1424 592 1408 592 WIRE 48 608 48 576 WIRE 1136 640 1136 592 WIRE 1360 656 1360 592 WIRE 240 688 96 688 WIRE 320 688 240 688 WIRE 448 688 384 688 WIRE 480 688 448 688 WIRE 240 720 240 688 WIRE 1136 800 1136 720 WIRE 1360 800 1360 720 WIRE 48 832 48 704 WIRE 240 832 240 800 FLAG 1424 144 VP FLAG 656 592 0 FLAG 112 320 0 FLAG 720 320 DRAIN FLAG 560 512 GATE FLAG 768 208 0 FLAG 960 592 0 FLAG 1136 800 0 FLAG 1408 592 EFF FLAG 768 592 0 FLAG 1360 800 0 FLAG -32 528 0 FLAG 80 576 rc FLAG 48 832 0 FLAG 240 832 0 FLAG 448 688 VP FLAG 1360 400 0 SYMBOL ind2 512 160 R270 WINDOW 0 -41 56 VTop 2 WINDOW 3 -53 53 VBottom 2 SYMATTR InstName L1 SYMATTR Value 10µ SYMATTR Type ind SYMATTR SpiceLine Rser=0.06 SYMBOL schottky 1040 160 R270 WINDOW 0 -41 30 VTop 2 WINDOW 3 -49 27 VBottom 2 SYMATTR InstName D1 SYMATTR Value 10MQ060N SYMATTR Description Diode SYMATTR Type diode SYMBOL voltage 112 160 R0 WINDOW 0 48 55 Left 2 WINDOW 3 54 83 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 9 SYMBOL nmos 608 432 R0 WINDOW 0 -48 -65 Left 2 WINDOW 3 -87 -29 Left 2 SYMATTR InstName M1 SYMATTR Value Si7218DN SYMBOL ind2 800 160 R270 WINDOW 0 -32 56 VTop 2 WINDOW 3 -41 57 VBottom 2 SYMATTR InstName L2 SYMATTR Value 90µ SYMATTR Type ind SYMATTR SpiceLine Rser=0.06 SYMBOL res 528 496 R90 WINDOW 0 77 56 VBottom 2 WINDOW 3 84 57 VTop 2 SYMATTR InstName R3 SYMATTR Value 25 SYMBOL res 1216 160 R270 WINDOW 0 47 31 VTop 2 WINDOW 3 74 86 VBottom 2 SYMATTR InstName R6 SYMATTR Value 1m SYMBOL cap 1296 224 R90 WINDOW 0 68 59 VBottom 2 WINDOW 3 42 -8 VTop 2 SYMATTR InstName C3 SYMATTR Value 100m SYMBOL res 304 160 R270 WINDOW 0 48 28 VTop 2 WINDOW 3 76 86 VBottom 2 SYMATTR InstName R8 SYMATTR Value 1m SYMBOL cap 384 224 R90 WINDOW 0 73 60 VBottom 2 WINDOW 3 47 -14 VTop 2 SYMATTR InstName C6 SYMATTR Value 100m SYMBOL res 944 352 R0 WINDOW 0 -50 38 Left 2 WINDOW 3 -57 75 Left 2 SYMATTR InstName R9 SYMATTR Value 500 SYMBOL cap 944 480 R0 WINDOW 0 -46 35 Left 2 WINDOW 3 -50 68 Left 2 SYMATTR InstName C7 SYMATTR Value 30p SYMBOL bv 1136 624 R0 WINDOW 3 -558 118 Left 2 WINDOW 0 -89 56 Left 2 SYMATTR Value V= LIMIT (0, 100 * I(R6) * V(VP) / ( I(R8) * 9 ), 100 ) SYMATTR InstName B1 SYMBOL res 1280 576 R90 WINDOW 0 70 60 VBottom 2 WINDOW 3 78 61 VTop 2 SYMATTR InstName R1 SYMATTR Value 1K SYMBOL res 752 352 R0 WINDOW 0 57 39 Left 2 WINDOW 3 51 80 Left 2 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL cap 752 480 R0 WINDOW 0 60 34 Left 2 WINDOW 3 56 72 Left 2 SYMATTR InstName C1 SYMATTR Value 50p SYMBOL cap 1344 656 R0 WINDOW 0 -37 63 Left 2 WINDOW 3 -43 94 Left 2 SYMATTR InstName C2 SYMATTR Value 50n SYMBOL Digital\\schmtinv 128 512 R0 SYMATTR InstName A1 SYMATTR Value2 Vhigh=5 Vt=2.5 Vh=1 SYMATTR SpiceLine Td=5n SYMBOL cap -48 448 R0 WINDOW 0 42 14 Left 2 WINDOW 3 42 51 Left 2 SYMATTR InstName C4 SYMATTR Value 1n SYMBOL res 80 432 R270 WINDOW 0 -36 57 VTop 2 WINDOW 3 -43 57 VBottom 2 SYMATTR InstName R4 SYMATTR Value 1K SYMBOL Digital\\schmtinv 304 448 R0 SYMATTR InstName A2 SYMATTR Value2 Vhigh=5 Vt=2.5 Vh=1 SYMATTR SpiceLine Td=5n SYMBOL Digital\\schmtinv 304 384 R0 SYMATTR InstName A3 SYMATTR Value2 Vhigh=5 Vt=2.5 Vh=1 SYMATTR SpiceLine Td=5n SYMBOL Digital\\schmtinv 304 512 R0 SYMATTR InstName A4 SYMATTR Value2 Vhigh=5 Vt=2.5 Vh=1 SYMATTR SpiceLine Td=5n SYMBOL Digital\\schmtinv 304 320 R0 SYMATTR InstName A5 SYMATTR Value2 Vhigh=5 Vt=2.5 Vh=1 SYMATTR SpiceLine Td=5n SYMBOL nmos 96 608 M0 WINDOW 0 100 28 Left 2 WINDOW 3 79 72 Left 2 SYMATTR InstName M2 SYMATTR Value 2N7002 SYMBOL res 224 704 R0 WINDOW 0 -55 50 Left 2 WINDOW 3 -63 91 Left 2 SYMATTR InstName R5 SYMATTR Value 10K SYMBOL zener 320 704 R270 WINDOW 0 -47 34 VTop 2 WINDOW 3 -54 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value ZNR48 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap 1344 288 R0 WINDOW 0 56 10 Left 2 WINDOW 3 56 55 Left 2 SYMATTR InstName C5 SYMATTR Value 5µ TEXT 1032 488 Left 2 !.tran 0 5m 0 10n uic TEXT 1064 392 Left 2 ;DUMB BOOST TEXT 1048 440 Left 2 ;JL June 28 2013 TEXT 648 104 Left 2 !K L1 L2 0.95 TEXT 144 624 Left 2 ;74HC14

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

How is it you say, "Net dumb"? ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.
Reply to
Jim Thompson

Wow, did you knead it afterwards or compress it with vise grips? :-)

A 30V transistor is the wrong choice here, it'll like go *PHUT* and I'd suggest looking at some with at least 50V rating. At 16V input it sees around 32V and you need some margin. Also, mind ESD. There should be a capacitor on the VIN side.

[...] 
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Snarky comments about the layout of the schematic aside, why don't you want to use a chip for the switcher, or a chip + op-amp? You're going to consume a lot of board space with what you have here.

--
Tim Wescott 
Control system and signal processing consulting 
www.wescottdesign.com
Reply to
Tim Wescott

The LT8410 does what you want, if by "a few mA" you mean 5 or so, and if you can stand the difference between Vin and Vboost to be close to, but not exactly, your set value:

(What a waste of a Sunday -- but it was fun)

Version 4 SHEET 1 1136 680 WIRE 768 -32 304 -32 WIRE -144 -16 -192 -16 WIRE -32 -16 -144 -16 WIRE 16 -16 -32 -16 WIRE 176 -16 96 -16 WIRE 768 -16 768 -32 WIRE -144 16 -144 -16 WIRE 176 32 176 -16 WIRE 304 32 304 -32 WIRE -32 96 -32 -16 WIRE 96 96 -32 96 WIRE 816 96 384 96 WIRE 944 96 816 96 WIRE 976 96 944 96 WIRE -144 112 -144 80 WIRE 944 112 944 96 WIRE 816 128 816 96 WIRE 480 176 384 176 WIRE 672 176 480 176 WIRE 480 192 480 176 WIRE 672 240 672 176 WIRE -352 256 -432 256 WIRE -32 256 -32 96 WIRE 96 256 -32 256 WIRE 416 256 384 256 WIRE -432 272 -432 256 WIRE 416 304 416 256 WIRE 480 304 480 272 WIRE 480 304 416 304 WIRE 480 320 480 304 WIRE 560 320 480 320 WIRE 768 320 768 48 WIRE 768 320 640 320 WIRE 816 320 816 192 WIRE 816 320 768 320 WIRE 944 320 944 192 WIRE 944 320 816 320 WIRE 976 320 944 320 WIRE 480 336 480 320 WIRE -432 384 -432 352 WIRE 240 448 240 320 WIRE 480 448 480 416 WIRE 672 448 672 304 FLAG 240 448 0 FLAG 480 448 0 FLAG 672 448 0 FLAG -432 384 0 FLAG -144 112 0 FLAG -352 256 Vin FLAG -192 -16 Vin FLAG 976 320 Vin FLAG 976 96 Vout SYMBOL PowerProducts\\LT8410 240 176 R0 SYMATTR InstName U1 SYMBOL ind 0 0 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 5 56 VBottom 2 SYMATTR InstName L1 SYMATTR Value 470µ SYMBOL cap 752 -16 R0 SYMATTR InstName C1 SYMATTR Value 100n SYMBOL cap 800 128 R0 SYMATTR InstName C2 SYMATTR Value 100n SYMBOL cap 656 240 R0 SYMATTR InstName C3 SYMATTR Value 100n SYMBOL res 464 176 R0 SYMATTR InstName R1 SYMATTR Value 772k SYMBOL res 464 320 R0 SYMATTR InstName R2 SYMATTR Value 559k SYMBOL cap -160 16 R0 SYMATTR InstName C4 SYMATTR Value 100n SYMBOL voltage -432 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 124 Left 2 SYMATTR InstName V1 SYMATTR Value PWL(0 12 400u 12 500u 5 3000u 16 5000u 5) SYMATTR SpiceLine Rser=10 SYMBOL res 928 96 R0 SYMATTR InstName R3 SYMATTR Value 3300 SYMBOL res 656 304 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 10meg TEXT -424 432 Left 2 !.tran 5m

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

BTW:

To get perfect* tracking, set

1/R4 = (1/31.85) * (1/R1 + 1/R2 + 1/R4)

To get your desired offset voltage, Vd, set

R4/R1 = Vd / Vref

Where the 31.85 and Vref come from the LT8410 data sheet.

Or:

R4 = whatever, but make it big enough for the chip (I chose 10 meg -- that's big).

Then calculate R1 from R4 and your desired Vd.

Then calculate R2 from R1, R4, and your desire for perfect tracking.

  • You'll never really perfect tracking, because (a) the 31.85 comes from the chip design, and will vary from chip to chip and probably with temperature and aging, and (b) you'll need to set your resistor ratios perfectly, which you can't, and (anyway) the resistor ratios will change, and R4 needs to be big to keep the chip happy, meaning you'll have leakage issues.
--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

Sundays are supposed to be wasted.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

Can you suggest a chip which will work in a range from less than a volt to fifteen volts.

Reply to
Michael Robinson

DSS416 has a 60 volt rating. And thanks for reminding me, I forgot the bypass.

Reply to
Michael Robinson

I don't think they work at less than 2.2V and abs max is 16V. Close call for the abs max because Michael needs to use it up to there.

There are some micro-power devices that will start at less than 1V but I haven't looked if any of them would go to 18V or more, so there'd be some margin.

[...] 
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Whoops -- I missed the "less than a volt in". Sorry -- I took the "few" from "milliamps" and applied it to "volts" as well.

That's going to make your job tremendously difficult (and your bipolar transistors suddenly make more sense) -- not only do you need something that'll work down to the sub-volt level at all, but your switcher design needs to be able to pull lots-o-current at those levels.

You really need to specify _how_ much less than a volt -- 0.9V in vs.

0.5V is a huge difference, and if you want it down to 0.1V then you're probably in a world of hurt. 
--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

I totally missed Michael's "less than 1V" constraint.

You could fix the 16V in problem with an LDO, since efficiency doesn't matter -- but not with an internal-switch device.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

How tightly does it need to hold the voltage above input? Is that

15.0000 volts, 12-18V, 14.5 is OK but only if it's dead steady, what?

What's "a few mA"? 2? 5? 10?

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

The LT1615 probably comes close. But only close. This is one of those jobs that in all likelihood has to be done with discretes.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

You went to a lot of trouble, Tim. The least I can do is explain why the circuit has to run on a volt, so most likely a chip won't work. Vcc (the armature voltage of an antique six volt generator) isn't going to start at some higher voltage and drop to a volt, which might allow bootstrapping. When the generator first spins up, Vcc comes up to about a volt because of residual magnetism in the soft iron pole shoes (possibly even a little less than a volt). Whereupon, nothing more will happen: unless the booster produces some output, generator output will remain flat at one volt. The booster has to take that one volt and boost it enough to turn on a mosfet, and drive current in the field coils around the pole shoes. Then Vcc (the generator output) will rise. The circuit I posted only needs two thirds of a volt to run, according to the simulator. Eight transistors and about thirty passives. It'll take up some board space, as you pointed out, but those forty jelly beans are still cheaper than the chip. And I think the LT8410 requires 2.5 volts.

Reply to
Michael Robinson

Tim, my requirements are a lot more forgiving on the output side. No need for accuracy, it can float up or down a volt without any ill effects at all. The tough part is on the input. I can't use a chip that requires 2.5 volts to run. You went to a lot of trouble and the least I can do is explain why the circuit has to run on a volt. Vcc (the armature voltage of an antique six volt generator) isn't going to start at some higher voltage and drop to a volt, which might allow bootstrapping. Vcc starts at zero and comes up to about a volt because of residual magnetism in the soft iron pole shoes (possibly even a little less than a volt). Whereupon, nothing more will happen: unless the booster produces some output, generator output will remain flat at one volt. The booster has to take that one volt and boost it enough to turn on a mosfet, and get some current going in the field coils around the pole shoes. Then will Vcc (the generator output) rise. The circuit I posted only needs two thirds of a volt to run, according to the simulator.

Reply to
Michael Robinson

Sometimes the thing to do is stick a lithium battery into the circuit. A aa-sized 3-volt lithium will run some low-power circuits for decades. Or some more voltage could actually bootstrap the field.

How about a 9-volt alkaline. They have 10-year shelf lives nowadays.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators
Reply to
John Larkin

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